White Metal-Organic Framework Nanozymes with Enzyme-Mimicking Ac-tivity Specificity: Overcoming Interferences of Color and O2 in Colorimetric Test Strips

White Metal-Organic Framework Nanozymes with Enzyme-Mimicking Ac-tivity Specificity: Overcoming Interferences of Color and O2 in Colorimetric Test Strips | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article White Metal-Organic Framework Nanozymes with Enzyme-Mimicking Ac-tivity Specificity: Overcoming Interferences of Color and O2 in Colorimetric Test Strips Lei Han, Jingying Tan, Yucui Zhang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7027508/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 04 Dec, 2025 Read the published version in Communications Chemistry → Version 1 posted You are reading this latest preprint version Abstract Given the promising prospect of nanozymes in colorimetric test strips, it is essential to eliminate the interferences of their multi-activities and various colors on the test strip. Here, white Mn-based metal-organic frameworks (Mn-MOFs) with ultrathin 2D morphology (3 nm thick) were successfully synthesized by a simple ultrasonic approach. The origin of the white optical property in Mn-MOFs was systematically investigated, revealing that it stems from specific metal-ligand coordination polymerization rather than morphological features or defect states. This specific coordination suppressed visible light absorption while enhancing diffuse reflection efficiency. Mn-MOF nanozymes possessed exclusive peroxidase-mimicking activity rather than oxidase-like activity, effectively resisting O 2 interference during colorimetric assay. Moreover, these nanozymes displayed unique substrate selectivity without additional modification. Unlike other colored nanozymes, the whiteness of Mn-MOF nanozymes not only prevented their color interference to colorimetric results, but also enhanced the paper’s whiteness, boosting contrast for colorimetric detection on test strip. The constructed H 2 O 2 test strip demonstrated high sensitivity, strong anti-interference capability, excellent storage stability, broad applicability for other various analytes, and reliability for real sample assays. This study pioneers a systematic investigation into the origin of whiteness in MOF nanozymes. The coordination-defined properties enable interference-free optical design and O 2 -resistant on-site detection. Physical sciences/Chemistry/Analytical chemistry/Bioanalytical chemistry Physical sciences/Nanoscience and technology/Nanoscale materials/Two-dimensional materials Physical sciences/Chemistry/Materials chemistry/Metal–organic frameworks metal-organic framework white nanozymes interference-free color catalytic selectivity colorimetric test strip Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Introduction So far, enzyme have been widely applied as common recognition elements in analytical platforms, due to their high activity and selectivity 1 , 2 . Nevertheless, enzymes generally face some application bottlenecks, such as complex purification process, poor stability and high cost 3 – 5 . Recently, nanozymes (nanomaterials with enzyme-like activities) 6 , 7 , have emerged as a promising alternative to traditional enzymes in diagnostics, detection and sensing, owing to their high catalytic activity, easy preparation, good stability, and low cost 8 – 14 . However, compared to natural enzymes, the relatively weak reaction selectivity of nanozymes still poses significant challenges to the analytical applications 15 – 17 . For example, peroxidase-like nanozymes, one of the most common subfamily of nanozymes, are widely used in colorimetric analysis, where they catalyze the oxidation of chromogenic substrate with H 2 O 2 to produce a chromogenic product 16 , 18 , 19 . Nevertheless, many peroxidase-like nanozymes also possess oxidase-like activity, such as V 2 O 5 20 , Co 3 O 4 21 , MnO 2 22 , CeO 2 23 , CuO 24 , Co 3 V 2 O 8 25 , Pt 26 , Pd@Ir 27 , Fe/Co-based metal-organic framework (Fe/Co-MOF) 28 , Au-MOF 29 , Pt-MOF 30 , and Prussian Blue 31 . This will cause the chromogenic substrates to be directly oxidized by O 2 in the air in the absence of H 2 O 2 . Moreover, the concentration of O 2 in various real samples differs and fluctuates dynamically, which disrupts the colorimetric assay results based on peroxidase-like activity 32 . Therefore, it is crucial to explore the peroxidase-like nanozymes without oxidase-like activity for the colorimetric analytic methods. At present, known nanozymes generally lack inherent substrate specificity 33 , 34 . To achieve optimal substrate selectivity, researchers have explored several modification techniques, such as molecular imprinting 33 , 35 , and surface modification 36 . For example, Liu’s group utilized molecular imprinting technology to achieve high selectivity to chromogenic substrate 37 . However, these methods often involve the complicated operations, the reduced activity and even the structural damage of nanozymes, especially MOF-based nanozymes 35 . Considering that some MOFs can selectively adsorb certain molecules, MOF nanozymes are anticipated to achieve substrate selectivity without the need for additional modification. Nonetheless, known MOFs are rarely involved in the selectivity of catalytic activity, especially enzyme-like activity 38 . Thus, it is of great significance to discover MOF nanozymes with inherent substrate selectivity to address the poor selectivity of nanozymes. Nanozymes have found widespread applications in the diverse colorimetric platforms, including solution assays, test strips, and microfluidic chips 39 , 40 . In particular, the powerful combination of nanozymes with colorimetric test strips has significantly reduced detection costs while improving storage, stability and portability, making their widespread adoption more feasible 18 , 41 . On nanozyme-based colorimetric test strips, nanozymes catalyze the chromogenic reaction to produce a visible color result 16 , 18 . Unfortunately, known nanozymes generally have various colors, such as yellow (V 2 O 5 42 , CeO 2 43 and Ce-based metal-organic frameworks (Ce-MOF) 44 , black (Co 3 O 4 45 and Fe 3 O 4 46,47 ), brown (CuO 48 , MnO 2 49 , Pd 29 ), red (Au) 50 , pink (Co-MOF) 29 , blue (Prussian Blue) 27 and orange (Fe-MOF) 51 . Although the abundant and uniform distribution of nanozymes on white paper can promote activity and amplify signal, the diversity of colors can interfere the judgement of the chromogenic results on white paper. Therefore, it is fascinating to study how to avoid the color interference of nanozymes and even enhance the whiteness of paper. This inspired us to excavate white nanozymes and explore their applications on test strips. Here, we facilely synthesized the white ultra-thin Mn-MOF nanosheets (NSs) by a simple ultrasonic method (Fig. 1 a). In sharp contrast, the traditional hydrothermal method can only produce micron-sized chunks, which come with significant safety risks and the need for high-seal equipment. Remarkably, Mn-MOF NSs exhibit excellent whiteness, the origin of which has been systematically investigated. Notably, Mn-MOF NSs not only exhibited enzyme-like activity but also demonstrated two levels of catalytic specificity: (1) Reaction selectivity: It possessed peroxidase-like activity but not oxidase-like activity, thereby preventing the interference of O 2 during detection (Fig. 1 b). (2) Substrate selectivity: It also exhibited inherent substrate specificity without further modification, as it could specifically oxidize substrate 3,3’,5,5'-tetramethylbenzidine (TMB) while other substrates remained unaffected (Fig. 1 c). Furthermore, we found an ideal application for these white nanozymes—white nanozyme test strips. Excitingly, unlike other colored nanozymes, the whiteness of Mn-MOF nanozymes not only avoided color interference from the nanozymes, but also strengthened the whiteness of paper, highlighting color changes on the test strip and thus improving sensitivity. Further, the constructed H 2 O 2 test strip showed high sensitivity, strong anti-interference capability in aerobic environment, and excellent store stability (Fig. 1 c). To demonstrate its versatility, we further extended the use of nanozymes for detecting glucose and sarcosine. This study is anticipated to stimulate further exploration of the unique whiteness and catalytic properties of MOF nanozymes for advanced colorimetric detection applications. Results Synthesis and characterization of Mn-MOF nanozymes In view of the fact that the most of MOF nanozymes were synthesized by hydrothermal approach, which requires high temperature, high pressure and sealed equipment, we tried to synthesize Mn-MOF by facile ultrasonic method (Fig. 1 a). MnCl 2 and terephthalic acid (TPA) were rapidly added into the solution containing dimethyl formamide (DMF) and triethylamine (TEA). After ultrasonic processing, a uniform white solution was produced, and white Mn-MOF precipitates were obtained by centrifugation and vacuum drying (Fig. 2 a). Significantly, white Mn-MOF had no absorption peak within 300–900 nm (Fig. 2 a), which will facilitate the chromogenic assay results. The morphology of white products was observed by transmission electron microscopy (TEM). They exhibited two-dimension (2D) nanosheet structure with smooth edges (Fig. 2 b, c). More detailed information about morphology and size of Mn-MOF was researched by atomic force microscope (AFM). Mn-MOF nanosheets displayed a smooth surface with an average thickness of 3 nm (Fig. 2 d, e), confirming the ultra-thin 2D structure. X-ray diffractometer (XRD) pattern of Mn-MOF (Fig. 2 f) was consistent with the previously reported monoclinic crystalline framework, Mn 4 (TPA) 4 (H 2 O) 8 52 , and the well-resolved peaks indicated high crystallinity. To better demonstrate the advantages of the ultrasonic synthesis method, we adopted the traditional hydrothermal method at 150°C to prepare Mn-MOF 52 , which resulted in micron-sized, solid, irregular chunks (Supplementary Fig. 1a, b). This comparison highlights the advantage of our synthesis approach, which not only eliminates the need for high-temperature heating and sealed equipment, but also successfully produces ultra-thin 2D nanostructured morphology. Chemical composition (Mn, O, and C) and uniform distribution of Mn-MOF are affirmed by energy dispersive X-ray (EDX) spectroscopy (Fig. 2 g). The Fourier transform infrared (FT-IR) spectra (Fig. 2 h) reflected that the characteristic beaks of Mn-MOF were different with ligand TPA. The peaks of TPA at 2822, 1691 and 526 cm - 1 conformed to ν (OH), ν (C = O) and δ (C = O) of the nonionized carboxyl groups. As for Mn-MOF, the above peaks disappeared, while new peaks were generated at 1578 and 1386 cm - 1 , which were correspond to asymmetric and symmetrirc stretching vibrations of –COO. These results demonstrated the deprotonation of acidic carboxyl, attributing to the complexation of manganese ions and carboxyl groups. Moreover, the appearance of characteristic peak at 752 cm -1 indicated that the 1,4-substituent bond core of TPA turned into the ring-out-of-plane vibration, indicating the effective coordination between the manganese ions and TPA. To further determine the surface elements and the oxidation state of manganese, X-ray photoelectron spectroscopy (XPS) was conducted. The XPS survey spectra of Mn-MOF (Supplementary Fig. 2a) suggest the existences of Mn, C, and O elements. The Mn 2p XPS spectrum of Mn-MOF also displayed evident peaks at 642.2 and 653.4 eV (Fig. 2 i), coinciding with Mn2p 3/2 of Mn 2+ in Mn‒O bonds, different from the peaks of MnO 5 3 . The oxidation states of manganese can be identified by the spin-orbit peak splitting of Mn 3s 5 4 . As shown in Fig. 2 j, the peak splitting value of Mn 3s was measured to be 6.0 eV, confirming the presence of Mn²⁺. Meanwhile, the fitting characteristic peaks of O 1s at 531.6 and 533.1eV (Fig. 2 k) corresponded to the Mn-carbonate/C = O and C-O bonds. Particularly, the peak of O 1s at 531.6 eV was not characteristic of metal oxides. Moreover, the C 1s spectrum of Mn-MOF could be deconvoluted into three peaks at 284.8, 286.3 and 288.5 eV (Supplementary Fig. 2b), which were typical values of C-C/C = C, C-O and O = C-O, respectively 4 9 , indicating the existence of TPA. These above results indicated white 2D ultra-thin Mn-MOF nanosheets were successfully synthesized by facile ultrasonic approach. The mesoporous properties of Mn-MOF nanozymes were studied by nitrogen adsorption/desorption isotherm (BET). The isotherm shows IV type and H 3 -type hysteresis loop (P P 0 -1 > 0.4) (Fig. 2 l), indicating that Mn-MOF had mesoporous properties. The BET specific surface area of Mn-MOF was 6.5109 m 2 g - 1 . In addition, the pore size distribution was analyzed by Barrett-Joyner-Halenda method in the desorption part and the average pore size was 14.8 nm. The high specific surface area will be conducive to catalysis of Mn-MOF. Origin of whiteness in Mn-MOF The synthesized Mn-MOF exhibited white coloration, which holds significant importance for white test strip substrates. Therefore, this stimulates us to systematically investigated the origin of this whiteness and quantitatively evaluated its degree. Typically, whiteness arises from three primary mechanisms: (1) nanostructure-induced scattering effects, (2) defect-state luminescence, or (3) intrinsic metal/ligand characteristics 55 – 58 . The hydrothermally synthesized bulk Mn-MOF showed no apparent nanostructures (Fig. 3 a, b), yet remained white (Fig. 3 c). Moreover, both bulk Mn-MOF and ultrasonically synthesized Mn-MOF NSs maintained their white color after grinding (Fig. 3 c), eliminating nanostructure scattering as the origin. Further, the surface roughness of Mn-MOF nanosheets was measured by AFM. The arithmetic average roughness ( R a ) and root mean square roughness ( R q ) were determined to be 1.83 nm and 3.71 nm, respectively, both significantly below 10 nm. This result excludes surface roughness-enhanced scattering as the origin of whiteness. (Fig. 3 d) 58 . Furthermore, visual inspection confirmed the absence of metallic luster, ruling out specular reflection. Additionally, fluorescence spectra revealed no detectable emission peaks within 300–800 nm under 253 nm excitation (the maximum absorption wavelength), which rules out defect-state luminescence as a possible cause of the white coloration. (Fig. 3 e) 57 , 59 . These above results strongly suggested metal/ligand characteristics as the whiteness origin. To investigate the metal ion dependence, we substituted Mn 2+ with Fe 3+ and Co 2+ while keeping all other synthesis conditions unchanged. As shown in Fig. 3 f, the resulting MOFs exhibited pink and black colors, respectively. Ligand substitution of TPA with 2-aminoterephthalic acid (ATPA) or trimesic acid (TMA) produced pink and beige Mn-MOFs (Fig. 3 f). Whiteness thus depends critically on both metal ion and ligand selection, where white coloration achieved exclusively through Mn 2+ -TPA coordination. Subsequently, quantitative colorimetric evaluation was performed on these materials (Fig. 3 g). Among all MOF samples, only the Mn-TPA MOF demonstrated a luminance value ( L* ) exceeding 90 (93.09) and a whiteness index ( WI ) above 90 (93.78), showing a clear distinction in the colorimetric results. In addition, this also confirmed that neither solvent/crystallization water nor synthesis methods contributed to the whiteness. According to international standards, WI > 90 qualifies as high whiteness. Compared to standard white TiO 2 55 , the total color difference ( ΔE ) was < 1 (Fig. 3 g and Supplementary Table 1), indistinguishable to the naked eye, confirming superior whiteness. UV-Vis diffuse reflectance spectroscopy (DRS) of Mn-TPA MOF nanozymes showed about 90% reflectance within 450–800 nm (Fig. 3 h), indicating no visible light absorption 60 . Moreover, The calculated bandgap of 4.02 eV (Fig. 3 i) exceeded the 3.1 eV threshold for visible light absorption 55 . Taken together, the whiteness of Mn-MOF originates from specific metal-ligand combinations rather than nanostructures or defects, exhibiting no visible light absorption and producing high diffuse reflectance that generates its white appearance. Peroxidase-like activity and reaction specificity of Mn-MOF nanozymes To verify the peroxidase-like activity of Mn-MOF, chromogenic substrate TMB and H 2 O 2 were added into Mn-MOF-catalyzed reaction solution in air. The characteristic absorbance peaks of TMB oxide (TMB* + ) at 652 nm could be observed in TMB-H 2 O 2 -MOF system, while no obvious absorbance peaks appeared in the absence of Mn-MOF or H 2 O 2 (Fig. 4 a, b). The above results suggest Mn-MOF possess inherent peroxidase-like activity but no oxidase-like activity. In addition, neither Mn 2+ nor TPA had peroxidase-mimicking activity (Supplementary Fig. 3), indicating the peroxidase-like activity produced after the formation of the framework structure. To further prove that Mn-MOF nanozymes have no oxidase-like activity, nanozymes-catalyzed reaction system was conducted in different concentrations of O 2 . Apparently, TMB could not be oxidized in the air- and even O 2 -saturated solutions without H 2 O 2 (Fig. 4 c). In contrast, there was a high absorption peak of TMB* + in N 2 -saturated solution containing H 2 O 2 (Fig. 4 c), which was as high as that in air-saturated solution containing H 2 O 2 (Fig. 4 b). These results demonstrated the excellent reaction specificity of Mn-MOF nanozymes, i.e., single peroxidase-like activity without oxidase-like activity. Therefore, H 2 O 2 is necessary for Mn-MOF-catalyzed reaction, and O 2 cannot disturb it. Like natural peroxidase, the peroxidase-mimicking activity of Mn-MOF exhibited Mn-MOF concentration-, pH- and temperature-dependences (Fig. 4 d–f). The absorption peak at 652 nm increased with the concentrations of Mn-MOF nanozymes (Fig. 4 d and Supplementary Fig. 4 ), confirming its peroxidase-like activity. Mn-MOF nanozymes exhibited strong activity under weakly acidic condition, and reached highest activity at pH 4.0 (Fig. 4 e). The activity of Mn-MOF showed noticeable rise from 4°C to 25°C, and remained stable in a wide temperature range (25–40°C) (Fig. 4 f). Considering the activity of Mn-MOF at 25°C was similar with those at higher temperatures (Fig. 4 f), the subsequent experiments were conducted at 25°C. In addition, Mn-MOF possessed good thermal stability, and remained over 90% of original activity at even 90°C (Fig. 4 g). Moreover, Mn-MOF nanozymes still exhibited almost unchanged peroxidase-like activity and good dispersibility after the storage for 6 months at room temperature (Supplementary Fig. 5 ), showing high storage stability. Steady-State kinetics mechanism of Mn-MOF nanozymes The steady-state kinetics of Mn-MOF nanozymes were studied by varying the concentrations of TMB and H 2 O 2 , respectively (Supplementary Fig. 6). The experimental data conformed to the Michaelis-Menten equation. Moreover, as an important parameter for evaluating enzyme kinetics, the value of K m is inversely correlated with the affinity of substrates with enzyme. The K m value of Mn-MOF nanozymes for TMB (0.31 m m) was similar and lower than those of natural enzymes and some other nanozymes, and the K m value of Mn-MOF nanozymes for H 2 O 2 (0.063 m m) were 1–4 order of magnitudes lower than those of natural enzymes and some other nanozymes (Supplementary Table 2) 6 , 17 , 61 – 66 , which indicated the good affinity of Mn-MOF nanozymes with the both substrates. In order to investigate the catalytic kinetics mechanism of Mn-MOF nanozymes, the Lineweaver-Burk plots were drawn (Fig. 5 a, b). The parallel double reciprocal plots demonstrated the Ping-Pong reaction mechanism. In other words, H 2 O 2 and TMB reacted with Mn-MOF one by one. After the first product H 2 O were released, TMB reacted with Mn-MOF to produce TMB* + (Fig. 5 c). So, the catalysis may not be derived from the generation of hydroxyl radicals (·OH). To certify the above inference, terephthalic acid (TA) was chosen as probe to track hydroxyl radicals (·OH). As shown in Fig. 5 d, the presence of Mn-MOF and H 2 O 2 cannot affect the generation of the fluorescence product of TA, indicating that there is no formation of ·OH during the catalytic reaction. This was different with some enzymes and nanozymes, such as peroxidase 6 , Ni-MOF nanozymes 64 , Fe-MOF nanozymes 67 , 68 , Fe 3 O 4 nanozymes 69 . This will provide the possibility for substrate selectivity of Mn-MOF nanozymes. Discovering intrinsic substrate specificity of Mn-MOF nanozymes As mentioned above, Mn-MOF nanozymes can catalyze the oxidation of TMB. So, other common substrates including 2, 2'-azino-bis (3-ethylbenzo-thiazoline-6-sulfonic acid) diammonium salt (ABTS), o -Phenylenediamine (OPD), and diaminobenzidine (DAB) were used to replace TMB (Fig. 6 a). Surprisingly, Mn-MOF nanozymes could not catalyze the oxidation of ABTS, OPD and DAB in the presence of H 2 O 2 (Fig. 6 b and Supplementary Fig. 7), indicating that the peroxidase-like activity of Mn-MOF nanozymes possess excellent substrate selectivity to TMB. In addition, Mn-MOF also could not catalyze the oxidation of other three substrate (ABTS, OPD, and DAB) without H 2 O 2 in air and O 2 atmospheres (Supplementary Fig. 8), demonstrating Mn-MOF nanozymes really do not have oxidase-mimicking activity. To further confirm the substrate selectivity, the linear relationship between the activity unit (U) and the concentration of Mn-MOF nanozymes was investigated (Fig. 6 c). The slopes of the fitted lines represented the specific activity of Mn-MOF nanozymes for different substrates, indicating good substrate selectivity of Mn-MOF to TMB. Taken together, Mn-MOF nanozymes showed rare substrate selectivity, which is different and superior to other nanozymes and enzymes 16 , 17 , 33 , 69 . Many POD-like nanozymes work by reactive oxygen species (ROS) as intermediates, and the oxidation of organic compounds by ROS usually lacks substrate selectivity 68 , 69 . In this work, we found that total ROS did not form during the catalytic process, by using 2’,7’-dichlorofluorescin diacetate (DCFH-DA) as the fluorescent probe of broad-spectrum ROS (Fig. 6 d). This provides the possibility for the substrate selectivity. To explore the reasons for the substrate specificity, the peroxidase-like activities of the precursors (MnCl 2 and TPA) of Mn-MOF nanozymes were researched. The precursors cannot catalyze the oxidation of TMB, but peroxidase-mimicking activity arose after the formation of frame structure (Fig. 6 e and Supplementary Fig. 3). Subsequently, MOFs based on TPA and other metal ions (Ni-MOF and Fe-MOF) were also synthesized, and their peroxidase-like activities for different substrates were investigated. Ni-MOF could not catalyze the oxidation of TMB, ABTS, OPD, and DAB, meaning that Ni-MOF had no peroxidase-mimicking activity (Fig. 6 f and Supplementary Fig. 9). In contrast, Fe-MOF could rapidly catalyze the oxidation of the above four substrates, indicating Fe-MOF had excellent peroxidase-mimicking activity but no substrate selectivity (Fig. 6 f and Supplementary Fig. 10). The above results reveal that the frame structure and the metal ions of MOF nanozymes were the prerequisites to its peroxidase-mimicking activity. Keeping test strip from interferences of O 2 and color by Mn-MOF nanozymes Nowadays, nanozymes-based test strip has shown great application potential for the rapid visual detection platform, due to the portability, low cost, high stability and easy large-scale production 16 , 18 , 19 . Here, considering the white color and the single activity of Mn-MOF nanozymes, we employed Mn-MOF nanozymes for the fabrication of test strip with TMB as chromogenic substrate, on the expectation that the two outstanding features would endow test strip some unique advantages (Fig. 7 a). As a proof-of-concept, H 2 O 2 test strip was constructed by deposition of Mn-MOF nanozymes on the paper (Fig. 7 b, c). To prove the feasibility of the fabricated test strip, the H 2 O 2 assay was performed in various atmospheres. As expected, the colorimetric result was not affected by the concentration of O 2 (Fig. 7 d), because of single peroxidase-like activity of Mn-MOF nanozymes without oxidase-like activity. Since the catalytic reaction can't take place without H 2 O 2 , the reaction can be started only by adding H 2 O 2 , which prevents premature reactions in the air, and hence improves the reliability of the detection results. More interestingly, commercial white papers are usually not very white, but Mn-MOF nanozymes showed whitening effect to the papers (Fig. 7 e). This is crucial for enhancing sensitivity of the colorimetric result of test strip. To further confirm the superiority of white nanozymes to test strip, various colors of nanozymes in the same concentration were used to fabricate the nanozymes-based test strip. As shown in Fig. 7 f, colored nanozymes masked the whiteness of paper and chromogenic reaction. In a sharp contrast, the blueness of chromogenic reaction on the paper modified by Mn-MOF nanozymes could be readily observed after the addition of H 2 O 2 . These above results demonstrate that white nanozymes with activity specificity was indeed an ideal choice for the colorimetric test strip based on nanozymes. After the condition optimization (Supplementary Fig. 11), test strip was fabricated for the detection of H 2 O 2 , where colorless TMB could be oxidized into blue TMB* + by H 2 O 2 under the catalysis of Mn-MOF nanozymes. As shown in Fig. 7 g, blueness of paper deepened with the increase of H 2 O 2 concentration, indicating the constructed test strip can realize the fast qualitative assay of H 2 O 2 by naked eye. Further, the corresponding RGB values were collected by smartphone for the quantitative analysis of H 2 O 2 . With the increase of concentration of H 2 O 2 , the value of ΔB/(R + G + B) continuously increased and showed a good linear relationship within the range of 5–400 µ m . The regression equation was y = 0.00044731x + 0.000048 (R 2 = 0.995). The limit of detection (LOD) was calculated to be 0.43 µ m (S/N = 3), which was lower than some other methods including spectrophotometry and even electrochemical sensor (Supplementary Table 3) 70 – 73 , confirming the excellent sensitivity. In addition, test strip based on Mn-MOF nanozymes showed the high storage stability, and there is not obvious change in the chromogenic response after the storage for 6 months at 4°C (Fig. 7 h). So far, known nanozymes generally various colors, which seriously disturbs colorimetric analysis results of test strip, as proven by Fig. 7 f. In this work, the white nanozymes did not disturb the colorimetric results of test strip, and highlighted the blue color of TMB* + , which resulted in high sensitivity of test strip. What's more, Mn-MOF nanozymes had no oxidase-mimicking activity, and thus the proposed assay strategy could not be influenced by the varying concentration of O 2 in atmosphere and solution (Fig. 4 c, 7 d), enhancing the reliability and avoiding false positive results for test strip. In addition, Mn-MOF nanozymes also possessed the superior stability to natural peroxidases. Taken together, Mn-MOF is an ideal enzyme substitute on test strip, and test strip based on Mn-MOF nanozymes would have broad application prospects. Universality of test strip based on Mn-MOF nanozymes To prove the universality of Mn-MOF nanozymes-based test strip, glucose test strip was constructed by dropping glucose oxidase (GOx) onto Mn-MOF nanozymes-based test strip (Fig. 8 a). In the GOx-nanozyme cascade catalytic system, glucose gave rise to the generation of H 2 O 2 , and then the chromogenic reaction. As the concentration of glucose gradually increased, the blue color on the paper gradually deepened, and the corresponding ΔB/(R + G + B) value gradually increased (Fig. 8 c). Then, the calibration curve was plotted, and the regression equation was y = 0.00065347x + 0.000653 (R 2 = 0.998) within the linear range of 5–600 µ m . This method showed high sensitivity, and LOD (0.49 µ m ) was an order of magnitude lower than other colorimetric and electrochemical methods (Supplementary Table 4) 74 – 78 . In addition, we researched the selectivity of this system for other monosaccharides or disaccharides (sucrose, mannose, arabinose, galactose, and lactose). Only glucose showed a significant response, proving good selectivity of this system (Fig. 8 d). Subsequently, sarcosine test strip was also established by dropping sarcosine oxidase (SOx) onto the Mn-MOF nanozymes-modified paper (Fig. 8 b). As the concentration of sarcosine gradually increased, the blue color on the paper gradually deepened, and the corresponding ΔB/(R + G + B) value gradually increased with a good linear correlation within 5–300 µ m (Fig. 8 e). The linear regression equation was fitted (y = 0.00060184x – 0.0000225, R 2 = 0.998), and LOD was calculated to be 0.27 µ m , which was lower than previous methods (Supplementary Table 5) 79 – 83 . These results suggested the versatility of Mn-MOF nanozymes-based test strip. Moreover, the sensitivity of test strip could be really improved by the whitening effect and the activity specificity of Mn-MOF nanozymes. Various assay applications in real samples To estimate the applicability and reliability of the constructed test strip, the detection of H 2 O 2 , glucose and sarcosine in various real samples were conducted by three kinds of test strips. For H 2 O 2 detection, two water-soak foodstuffs (sea cucumber and jellyfish) were used as real samples (Table 1 ). The concentrations of H 2 O 2 were calculated according to the working curve (Fig. 7 g). The standard addition method was applied, and the recoveries of H 2 O 2 were within 99.7–100.9%, suggesting good accuracy and reliability. The relative standard deviation (RSD) was within 3.75%, showing high reproducibility and precision. Table 1 The determination of H 2 O 2 , glucose and sarcosine in real samples Analyte Sample Spiked (µ m ) Found a (µ m ) Recovery (%) RSD a (%, n = 5) H 2 O 2 Sea cucumber 0 5.60 ± 0.21 – 3.75 10 15.57 ± 0.15 99.7 0.96 150 156.43 ± 2.23 100.6 1.43 jellyfish 0 12.80 ± 0.18 – 1.41 10 22.89 ± 0.20 100.9 0.87 150 162.74 ± 2.04 100.0 1.25 Glucose apple 0 25.22 ± 0.19 – 0.75 10 35.29 ± 0.25 100.7 0.71 300 324.13 ± 2.43 99.6 0.74 grape 0 30.15 ± 1.52 – 5.04 10 40.04 ± 0.17 98.9 0.42 300 332.27 ± 2.25 100.7 0.68 Sarcosine beef 0 20.27 ± 0.24 – 1.18 10 30.59 ± 0.12 103.2 0.39 150 170.05 ± 3.03 99.9 1.78 chicken 0 9.03 ± 0.19 – 2.10 10 18.94 ± 0.27 99.1 1.43 150 159.25 ± 2.34 100.1 1.47 a For each sample, experiment was repeated five times and ‘±’ represents standard deviation ( n = 5). For the glucose detection in real samples, two fruits (apple and grape) were used as real samples (Table 1 ). After adding a known amount of glucose into the pretreated fruit juices, the recoveries of glucose were calculated to be from 98.9–100.7%. RSD was within 5.04% ( n = 5). The results suggested the fabricated glucose test strip had a good accuracy and reproducibility. For the detection in real samples, the reliability of proposed sarcosine test strip was also be verified by measuring sarcosine in two meat samples (beef and chicken). The recoveries ranged from 99.1–103.2%, and RSD was within 2.10% ( n = 5) (Table 1 ), indicating good reliability for the real samples assay. Discussion In this work, a white Mn-MOF nanozymes with good activity specificity was successfully synthesized by a simple ultrasound approach. Through comprehensive studies, we conclusively determined that the white optical property of Mn-MOFs originates exclusively from the specific coordination polymerization between Mn²⁺ and TPA ligands, independent of morphological characteristics, defect states, solvent effects, or specular reflection. The unique Mn-TPA combination exhibits negligible visible light absorption and generates high diffuse reflectance, resulting in its white appearance. Noticeably, Mn-MOF demonstrated two types of catalytic specificity. (1) Reaction specificity: it possessed single peroxidase-mimicking activity without oxidase-like activity, thus avoiding O 2 interference during the detection. (2) Substrate specificity: it specifically catalyzed the oxidation of TMB rather than other substrates (ABTS, OPD and DAB). These characteristics were innate, and do not need any additional functional modification. Significantly, white Mn-MOF nanozymes exhibited great superiority in colorimetric test strip for the apparatus-free visual detection of H 2 O 2 . Compared with other colors of nanozymes, the white Mn-MOF nanozymes avoided the interference to the judgment of the chromogenic results by the naked eye and the color extractor. Moreover, the whiteness of Mn-MOF strengthened the whiteness of paper, making the blue color of TMB* + readily distinguishable, resulting in ultra-high sensitivity. On the basis of H 2 O 2 test strip, a series of test strips were successfully developed for the detection of glucose and sarcosine, demonstrating excellent universality of Mn-MOF-based test strips. These test strips also showed high store stability for at least six months, and good reliability for real samples assay. In summary, this work establishes a fundamental paradigm for understanding the origin of whiteness in MOF-based nanozymes through systematic optical and structural characterization. By elucidating the critical role of metal-ligand coordination in governing light absorption and scattering properties, we provide a design framework for developing white nanozymes with tailored optical behaviors. These findings directly address the long-overlooked challenge of color interference in nanozyme applications. As for the analysis technology, this work not only provides an ideal biomimetic recognition element (white nanozyme with single activity), but also presents an ideal vehicle (test strip) that can perfectly exploit the advantages of white nanozyme. We expect that this study would inspire the exploration of more and more white nanozymes with high activity specificity for various colorimetric assay methods (not limited to test strip), eliminating the interference of O 2 and color of nanozymes. Looking forward, the marriage of tunable MOF optics with enzymatic specificity opens transformative possibilities. These potential nanozymes could revolutionize low-cost, portable monitoring platforms. Methods Synthesis of Mn-MOF nanozymes Mn-MOF were synthesized by ultrasound approach. Firstly, TPA (0.75 mmol) were dissolved into the mixed solution containing DMF (32 mL), ethanol (2 mL), and water (2 mL). Then, MnCl 2 ·4H 2 O (0.375 mmol) was added and dissolved into the above solution. Subsequently, TEA (0.8 mL) was quickly injected into the above solution, and then stirred for 5 min to obtain a white suspension. Then, the mixed solution was continuously sonicated at 40 kHz for 8 h, and the white product was obtained after centrifugation (4000 rpm), washing with ethanol, and drying in vacuum. Origin of whiteness in Mn-MOF As for surface roughness, 3D topographic image of Mn-MOF was acquired, and then surface roughness parameters ( R a and R q ) were measured by AFM assay (Bruker, USA). To eliminate the possibility of defect-state luminescence, the fluorescence spectrum of Mn-MOF was recorded by fluorescence spectrophotometer (Hitachi F-7000) with excitation at 253 nm (slit width: 10 nm) and emission scanned from 275–800 nm (slit width: 10 nm). To compare colorimetric parameters of different materials, their L *, a *, b *, WI , and Δ E values were conducted by a colorimeter LS171 (Linshang, China).The UV–Vis DRS of Mn-MOF powder was conducted on a spectrometer 3600-plus (Shimadzu, Japan) using diffuse reflection accessory adapted for powder samples. Then, these reflectance values were converted to Tauc plot, and the bandgap energy was assessed by Tauc plot, according to the Kubelka-Munk function. 84 Peroxidase-like activity assay of Mn-MOF nanozymes Typically, the peroxidase-like activity of Mn-MOF was assessed by the characteristic absorbance of TMB* + (TMB oxide) at 652 nm ( ε 652 nm = 39000 m − 1 cm − 1 ). H 2 O 2 (1 m m ) and TMB (0.5 m m ), and Mn-MOF (0.5 µg mL − 1 ) were reacted in the acetate buffer (0.1 m , pH 4.0) at 25°C for 30 min. Subsequently, the absorption spectra and the time-dependent absorbance at 652 nm were recorded. The effect of pH and temperature on peroxidase-like activity of Mn-MOF nanozymes was researched by the typical activity assay method, except for changing pH (pH 2.0–10.0) or temperature (4–50°C). The thermal stability of Mn-MOF was analyzed by repeating the above experimental steps after incubating Mn-MOF at different temperatures (4–50°C) for an hour. The thermal stability of Mn-MOF nanozymes were measured by the typical activity assay after Mn-MOF nanozymes were incubated at different various temperatures (4–90°C) for an hour. Each experiment was repeated at least three times. Steady-state kinetics assay The steady-state kinetic analysis on the peroxidase like activity of Mn-MOF nanozymes was performed by changing the concentration (0.05–1.2 m m ) of TMB under fixed H 2 O 2 concentration (1 m m ) or varying the concentration (0.05–2 m m ) of H 2 O 2 at the constant TMB concentration (0.5 m m ). To obtain Michaelis constant ( K m ), the activity data was fitted by the Michaelis-Menten equation: ν = V max × [S]/( K m + [S]), where ν is the initial velocity, V max represents the maximum reaction velocity, and [S] represents the substrate concentration. In order to explore the kinetic mechanism, the peroxidase like activities was measured in the presence of the different concentrations of H 2 O 2 (0.3, 0.6, 1 m m ) or TMB (0.3, 0.5, 0.7 m m ). The activity data were plotted based on the Lineweaver-Burk double reciprocal curve. Chemical ROS assay In order to explore whether ROS were generated during the catalytic process, TA and DCFH-DA were used as fluorescent probes. Hydroxyl radicals (·OH) were detected by TA, where reaction product, 2-hydroxy terephthalic acid, has an emission peak at 425 nm. H 2 O 2 (1 m m ) and TA (0.5 m m ) were reacted with or without Mn-MOF (50 µg mL − 1 ) in acetate buffer (0.1 m , pH 4.0) for 30 minutes at 25°C. Subsequently, the fluorescence emission of the reaction solution was detected at 425 nm. Total ROS were detected by DCFH, where the reaction product has an emission peak at 524 nm. Firstly, DCFH-DA (1 m m in MeOH, 1 mL) was hydrolyzed in NaOH aqueous solution (0.01 N, 4 mL) for 30 minutes to obtain the unstable DCFH. Then, the above solution was neutralized with phosphate solution (25 m m , 20 mL). Mn-MOF (10 mg mL − 1 , 20 µL), and 180 µL of fresh DCFH solution (40 µ m ) were mixed, and the fluorescence intensity at 524 nm was measured over time. Construction of different test strips based on Mn-MOF nanozymes For the typical construction of test strip for H 2 O 2 assay, 5 µL of Mn-MOF (10 mg mL − 1 ) and 10 µL of the acetate buffer solution (0.1 m , pH 4.0) containing TMB (0.5 m m ) were successively dropped onto the filter paper (6 mm diameter), and air-dried to obtain the H 2 O 2 test strip. For the construction of test strip for glucose and sarcosine, the procedure is the same as that of H 2 O 2 test strip, except for adding enzymes (GOx or SOx, 20 µg mL − 1 ) into the acetate buffer solution (0.1 m , pH 4.0) containing TMB (0.5 m m ). Detection of H 2 O 2 , glucose and sarcosine by different test strips For H 2 O 2 detection, the different concentrations of H 2 O 2 solutions (5 µL) were gently dropped onto the surface of test strip. After standing at 25°C for 10 min, the RGB values of test strip were collected by Color Picker APP in smartphone for further quantitative analysis. For detection of glucose and sarcosine, the different concentrations of glucose and sarcosine solutions (5 µL) were dropped onto the surface of corresponding test strip. After standing at 25°C for 30 min, the RGB values of test strip were collected for further quantitative analysis. The experiments were repeated three times, and LOD was calculated by the equation LOD = (3σ/s), where σ is the standard deviation of blank signals and s is the slope of the calibration curve. Detection in various real samples To demonstrate the applicability of the constructed test strip, various actual samples (including sea cucumber and jellyfish for H 2 O 2 detection, apple and grape for glucose detection, and chicken and beef for sarcosine detection) were employed. For the pretreatment of actual samples, soak solutions of water-soaked foodstuffs (cucumber and jellyfish) were centrifuged for 15 minutes. Real glucose solutions were extracted by the homogenate of fruits (apple and grape), and the filtration with a 0.22 filter. The real sarcosine solutions were extracted by ultrasonication of meats (chicken and beef, 5 g) in acetate buffer (pH 4.0, 10 mL) for 30 min. The above obtained solutions were detected by the corresponding test strips. Reporting summary Further information on research design is available in the Nature Portfolio Reporting Summary linked to this article. Declarations Data availability All the data that support the findings of this study are available within the article and Supplementary Information file, or from the corresponding authors upon request. Acknowledgements This work was financially supported by the National Natural Science Foundation of China (22376111), Shandong Provincial Natural Science Foundation (ZR2024YQ026) for Excellent Young Scholars, Taishan Scholar Foundation of Shandong Province (tsqn202408237), Youth Innovation Team Project for Talent Introduction and Cultivation in Universities of Shandong Province (096-1622002), Research Foundation for Distinguished Scholars of Qingdao Agricultural University (663-1117015). We are grateful to staff from the Instrumental Analysis Center of Qingdao Agricultural University for providing valuable assistance with the testing instruments. Author contributions L.H. conceived the study. J.T. and Y.Z. performed the experiments, and visualized the results. All authors analyzed the results. L.H. wrote and revised the manuscript with input from all the other coauthors. Competing interests The authors declare no competing interests. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7027508","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":482962610,"identity":"029256d0-afaa-4dd5-aa6c-7668cb1cff52","order_by":0,"name":"Lei Han","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAxklEQVRIiWNgGAWjYBACAwYGxgMMBjYQHg+RWhiAWtJI1sJwmAQt5uxnDxz4UHBetn9GAuODt20M8uaEtFj25CUcnGFw23jGjQRmw7ltDIY7Gwg57ECOwWEeg9uJDTcS2KR52xgSDA4Q0nL+jcHhPwbnEuffSGD/TZyWG0BbgHYlbgDawkykljcGB3sMko03nnnYLDnnnIThBsIOyzF88OOPney848kHP7wps5EnaAsMMDaAEAODBJHqIVpGwSgYBaNgFOAAAFMWRmJXyQtxAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0003-1955-0718","institution":"Qingdao Agricultural University","correspondingAuthor":true,"prefix":"","firstName":"Lei","middleName":"","lastName":"Han","suffix":""},{"id":482962611,"identity":"1c7f7d7c-0860-4204-8f73-73d63aab772a","order_by":1,"name":"Jingying Tan","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Jingying","middleName":"","lastName":"Tan","suffix":""},{"id":482962612,"identity":"128d777f-05c4-42fd-901e-f862e8ae2ab1","order_by":2,"name":"Yucui Zhang","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Yucui","middleName":"","lastName":"Zhang","suffix":""}],"badges":[],"createdAt":"2025-07-02 09:13:04","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7027508/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7027508/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s42004-025-01772-z","type":"published","date":"2025-12-04T05:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":86517274,"identity":"6613599e-9a97-47ee-bdd9-838bba2041f8","added_by":"auto","created_at":"2025-07-11 14:23:22","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":450711,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDesign of white Mn-MOF nanozymes with single peroxidase-like activity for test strip.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e Schematic preparation of Mn-MOF nanozymes. \u003cstrong\u003eb\u003c/strong\u003e Single peroxidase-like activity of Mn-MOF nanozymes unaffected by O\u003csub\u003e2\u003c/sub\u003e. \u003cstrong\u003ec\u003c/strong\u003e Colorimetric test strip based on Mn-MOF nanozymes.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7027508/v1/c296519e8fe49806bb9bc539.png"},{"id":86517190,"identity":"1c1408a7-3426-4fe2-a48e-f212008fc040","added_by":"auto","created_at":"2025-07-11 14:23:19","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1200401,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCharacterization of Mn-MOF nanozymes.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e UV-vis spectrum and photograph of Mn-MOF suspension (1 mg mL\u003csup\u003e-1\u003c/sup\u003e). \u003cstrong\u003eb,c\u003c/strong\u003e TEM images of Mn-MOF. \u003cstrong\u003ed,e\u003c/strong\u003e AFM image (d) and (e) corresponding height profile (e) of Mn-MOF. \u003cstrong\u003ef\u003c/strong\u003e XRD pattern of Mn-MOF and simulated Mn-TPA MOF. \u003cstrong\u003eg\u003c/strong\u003e SEM image and EDX elemental mapping images of Mn-MOF. \u003cstrong\u003eh\u003c/strong\u003e FT-IR spectra of Mn-MOF and TPA. \u003cstrong\u003ei-k\u003c/strong\u003e High-resolution XPS patterns for (\u003cstrong\u003ei\u003c/strong\u003e) Mn 2p, (\u003cstrong\u003ej\u003c/strong\u003e) Mn 3s and (\u003cstrong\u003ek\u003c/strong\u003e) O 1s of Mn-MOF. \u003cstrong\u003el\u003c/strong\u003e Nitrogen absorption/desorption isotherm of Mn-MOF.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7027508/v1/21ed22d42acacc82315775f8.png"},{"id":86517194,"identity":"bb311fff-0bb4-4ee0-ae50-1d39206c5fa6","added_by":"auto","created_at":"2025-07-11 14:23:19","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":2118101,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eOrigin study of whiteness of Mn-MOF. a, b\u003c/strong\u003e SEM images of hydrothermally synthesized bulk Mn-MOF. (b) Enlarged view the pane-marked areas of (a). \u003cstrong\u003ec\u003c/strong\u003e Photographs of Mn-MOF NSs and bulk Mn-MOF before and after mechanical grinding. \u003cstrong\u003ed\u003c/strong\u003e AFM topographic image of MOF NSs for surface roughness assay. \u003cstrong\u003ee\u003c/strong\u003e Fluorescence spectrum of Mn-MOF NSs under 253 nm excitation. \u003cstrong\u003ef\u003c/strong\u003e Photographs of various MOF prepared from different metal ions (Mn\u003csup\u003e2+\u003c/sup\u003e, Fe\u003csup\u003e3+\u003c/sup\u003e, Co\u003csup\u003e2+\u003c/sup\u003e) and ligands (TPA, ATPA and TMA) under identical conditions. \u003cstrong\u003eg \u003c/strong\u003eRadar chart comparing whiteness parameters (\u003cem\u003eL\u003c/em\u003e*, \u003cem\u003ea\u003c/em\u003e*, \u003cem\u003eb\u003c/em\u003e*, \u003cem\u003eWI\u003c/em\u003e, and Δ\u003cem\u003eE\u003c/em\u003e) of various MOFs. \u003cstrong\u003eh \u003c/strong\u003eUV-Vis DRS of MOF NSs. \u003cstrong\u003ei\u003c/strong\u003e Tauc\u003cstrong\u003e \u003c/strong\u003eplot derived from DRS data for direct bandgap estimation.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-7027508/v1/236ee4029dbace9187c3b2e6.png"},{"id":86518388,"identity":"f9e78ad7-2943-46e6-958e-04c5a235d673","added_by":"auto","created_at":"2025-07-11 14:31:19","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1106331,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePeroxidase-like activity of Mn-MOF nanozymes.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e Schematic of the catalytic activity of Mn-MOF nanozymes. \u003cstrong\u003eb\u003c/strong\u003e Typical UV-vis absorption spectra of catalytic oxidation of TMB by Mn-MOF nanozymes (50 μg mL\u003csup\u003e-1\u003c/sup\u003e) in the acetate buffer (pH 4.0, 0.1 m) in air. \u003cstrong\u003ec\u003c/strong\u003e Typical absorption spectra of TMB oxidation catalyzed by Mn-MOF nanozymes (50 μg mL\u003csup\u003e-1\u003c/sup\u003e) in different atmospheres. \u003cstrong\u003ed\u003c/strong\u003e Absorption spectra of TMB oxidation by H2O2 under the catalysis of different concentrations of Mn-MOF nanozymes. \u003cstrong\u003ee,f\u003c/strong\u003e The influences of (e) pH and (f) temperature on the peroxidase-like activity of Mn-MOF nanozymes. (\u003cstrong\u003eg\u003c/strong\u003e) The thermal stability of Mn-MOF nanozymes.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7027508/v1/45530ea78883fa4f7b8c3e26.png"},{"id":86517186,"identity":"322ae562-544f-4d36-9f1c-4e2c61c4231f","added_by":"auto","created_at":"2025-07-11 14:23:18","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":237714,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSteady-state kinetics of Mn-MOF nanozymes.\u003c/strong\u003e \u003cstrong\u003ea,b\u003c/strong\u003e The Lineweaver-Burk plots for various concentrations of (a) H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (0.3, 0.6 and 1 mm) and (b) TMB (0.3, 0.5 and 0.7 mm). \u003cstrong\u003ec\u003c/strong\u003e Schematic diagram of Ping-Pong catalytic mechanism. \u003cstrong\u003ed\u003c/strong\u003e Fluorescence (FL) spectra of different reaction solutions containing TA.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-7027508/v1/a2b50c39721987d5c9849434.png"},{"id":86517237,"identity":"99494285-9b7c-424e-9bf1-0b99858ebb07","added_by":"auto","created_at":"2025-07-11 14:23:21","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":322912,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSubstrate Specificity of peroxidase-like activity.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e Schematic illustration of the substrate selectivity of Mn-MOF nanozymes. \u003cstrong\u003eb\u003c/strong\u003e Peroxidase-like activity of Mn-MOF nanozymes to various substrate. \u003cstrong\u003ec\u003c/strong\u003e Activity units of different concentrations of Mn-MOF nanozymes for various substrates. \u003cstrong\u003ed\u003c/strong\u003e Fluorescence spectra of reaction solutions containing Mn-MOF nanozymes, H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, and fluorescent probe DCFH-DA. \u003cstrong\u003ee\u003c/strong\u003e Absorption spectra of catalytic oxidation of TMB by Mn-MOF nanozymes and controls in the presence of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e. \u003cstrong\u003ef\u003c/strong\u003e Peroxidase-like activity of various MOF nanozymes towards different substrates.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-7027508/v1/a0b9c6b15ee4cbb98a4ef92c.png"},{"id":86517224,"identity":"8b2dd33c-56b8-44bd-8604-88eb41067d61","added_by":"auto","created_at":"2025-07-11 14:23:20","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":1044581,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eColorimetric H\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e detection by test strip based on Mn-MOF nanozymes.\u003c/strong\u003e \u003cstrong\u003ea \u003c/strong\u003eSchematic of the proposed test strip. \u003cstrong\u003eb,c \u003c/strong\u003eSEM images (b) before and (c) after the deposition of Mn-MOF nanozymes on paper. \u003cstrong\u003ed\u003c/strong\u003e Chromogenic response for H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e on paper based on Mn-MOF nanozymes in different atmospheres (air, O\u003csub\u003e2\u003c/sub\u003e, and N\u003csub\u003e2\u003c/sub\u003e). \u003cstrong\u003ee\u003c/strong\u003e Grayscale intensity of paper before and after the deposition of Mn-MOF nanozymes. \u003cstrong\u003ef\u003c/strong\u003e Photographs and ΔB/(R+G+B) values of test strip modified by Mn-MOF and other colored nanozymes. \u003cstrong\u003eg\u003c/strong\u003e Photographs of test strip for the detection of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e and corresponding working curve of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e. \u003cstrong\u003eh\u003c/strong\u003e Chromogenic response of test strip after storage for 6 months.\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-7027508/v1/39b274b5397c9a6a604493ba.png"},{"id":86517227,"identity":"6bb76ea7-11ea-4964-a5e5-1fd3781bdb29","added_by":"auto","created_at":"2025-07-11 14:23:20","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":743841,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eUniversality of test strip based on Mn-MOF nanozymes.\u003c/strong\u003e \u003cstrong\u003ea,b\u003c/strong\u003e Schematic illustration of (a) glucose test strip, and (b) sarcosine test strip. \u003cstrong\u003ec\u003c/strong\u003e Photographs showing the response of glucose test strip to varying concentrations of glucose, and corresponding working curve for glucose\u003csub\u003e \u003c/sub\u003edetection. \u003cstrong\u003ed\u003c/strong\u003e Selectivity assay of glucose test strip. \u003cstrong\u003ee\u003c/strong\u003e Photographs of sarcosine test strip for different concentrations of sarcosine, and corresponding working curve for sarcosine detection.\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-7027508/v1/d2e1b259acd6039ef2f66998.png"},{"id":97505280,"identity":"9cfa1cf9-c25d-459f-87f5-789d69d38f99","added_by":"auto","created_at":"2025-12-05 08:07:17","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":8729852,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7027508/v1/9a387e3c-5886-4e13-802f-ac4dae3f1072.pdf"},{"id":86517225,"identity":"fe044608-432e-4a5b-8ed2-3e8c71ff303f","added_by":"auto","created_at":"2025-07-11 14:23:20","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1371754,"visible":true,"origin":"","legend":"SUPPLEMENTAL MATERIAL","description":"","filename":"SupplementaryInformationNatureCC.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7027508/v1/45ca6d69be1a3e4e0be9002b.pdf"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"White Metal-Organic Framework Nanozymes with Enzyme-Mimicking Ac-tivity Specificity: Overcoming Interferences of Color and O2 in Colorimetric Test Strips","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSo far, enzyme have been widely applied as common recognition elements in analytical platforms, due to their high activity and selectivity\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. Nevertheless, enzymes generally face some application bottlenecks, such as complex purification process, poor stability and high cost\u003csup\u003e\u003cspan additionalcitationids=\"CR4\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. Recently, nanozymes (nanomaterials with enzyme-like activities)\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e, have emerged as a promising alternative to traditional enzymes in diagnostics, detection and sensing, owing to their high catalytic activity, easy preparation, good stability, and low cost\u003csup\u003e\u003cspan additionalcitationids=\"CR9 CR10 CR11 CR12 CR13\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. However, compared to natural enzymes, the relatively weak reaction selectivity of nanozymes still poses significant challenges to the analytical applications\u003csup\u003e\u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. For example, peroxidase-like nanozymes, one of the most common subfamily of nanozymes, are widely used in colorimetric analysis, where they catalyze the oxidation of chromogenic substrate with H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e to produce a chromogenic product\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. Nevertheless, many peroxidase-like nanozymes also possess oxidase-like activity, such as V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e\u003csup\u003e20\u003c/sup\u003e, Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e21\u003c/sup\u003e, MnO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e22\u003c/sup\u003e, CeO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e23\u003c/sup\u003e, CuO\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e, Co\u003csub\u003e3\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e\u003csup\u003e25\u003c/sup\u003e, Pt\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e, Pd@Ir\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e, Fe/Co-based metal-organic framework (Fe/Co-MOF)\u003csup\u003e28\u003c/sup\u003e, Au-MOF\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e, Pt-MOF\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e, and Prussian Blue\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. This will cause the chromogenic substrates to be directly oxidized by O\u003csub\u003e2\u003c/sub\u003e in the air in the absence of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e. Moreover, the concentration of O\u003csub\u003e2\u003c/sub\u003e in various real samples differs and fluctuates dynamically, which disrupts the colorimetric assay results based on peroxidase-like activity\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e. Therefore, it is crucial to explore the peroxidase-like nanozymes without oxidase-like activity for the colorimetric analytic methods.\u003c/p\u003e \u003cp\u003eAt present, known nanozymes generally lack inherent substrate specificity\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e,\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e. To achieve optimal substrate selectivity, researchers have explored several modification techniques, such as molecular imprinting\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e,\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e, and surface modification\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e. For example, Liu\u0026rsquo;s group utilized molecular imprinting technology to achieve high selectivity to chromogenic substrate\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e. However, these methods often involve the complicated operations, the reduced activity and even the structural damage of nanozymes, especially MOF-based nanozymes\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e. Considering that some MOFs can selectively adsorb certain molecules, MOF nanozymes are anticipated to achieve substrate selectivity without the need for additional modification. Nonetheless, known MOFs are rarely involved in the selectivity of catalytic activity, especially enzyme-like activity\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e. Thus, it is of great significance to discover MOF nanozymes with inherent substrate selectivity to address the poor selectivity of nanozymes.\u003c/p\u003e \u003cp\u003eNanozymes have found widespread applications in the diverse colorimetric platforms, including solution assays, test strips, and microfluidic chips\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e,\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e. In particular, the powerful combination of nanozymes with colorimetric test strips has significantly reduced detection costs while improving storage, stability and portability, making their widespread adoption more feasible\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e. On nanozyme-based colorimetric test strips, nanozymes catalyze the chromogenic reaction to produce a visible color result\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. Unfortunately, known nanozymes generally have various colors, such as yellow (V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e\u003csup\u003e42\u003c/sup\u003e, CeO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e43\u003c/sup\u003e and Ce-based metal-organic frameworks (Ce-MOF)\u003csup\u003e\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e, black (Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e45\u003c/sup\u003e and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e46,47\u003c/sup\u003e), brown (CuO\u003csup\u003e\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u003c/sup\u003e, MnO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e49\u003c/sup\u003e, Pd\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e), red (Au)\u003csup\u003e\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e, pink (Co-MOF)\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e, blue (Prussian Blue)\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e and orange (Fe-MOF)\u003csup\u003e\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e. Although the abundant and uniform distribution of nanozymes on white paper can promote activity and amplify signal, the diversity of colors can interfere the judgement of the chromogenic results on white paper. Therefore, it is fascinating to study how to avoid the color interference of nanozymes and even enhance the whiteness of paper. This inspired us to excavate white nanozymes and explore their applications on test strips.\u003c/p\u003e \u003cp\u003eHere, we facilely synthesized the white ultra-thin Mn-MOF nanosheets (NSs) by a simple ultrasonic method (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). In sharp contrast, the traditional hydrothermal method can only produce micron-sized chunks, which come with significant safety risks and the need for high-seal equipment. Remarkably, Mn-MOF NSs exhibit excellent whiteness, the origin of which has been systematically investigated. Notably, Mn-MOF NSs not only exhibited enzyme-like activity but also demonstrated two levels of catalytic specificity: (1) Reaction selectivity: It possessed peroxidase-like activity but not oxidase-like activity, thereby preventing the interference of O\u003csub\u003e2\u003c/sub\u003e during detection (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). (2) Substrate selectivity: It also exhibited inherent substrate specificity without further modification, as it could specifically oxidize substrate 3,3\u0026rsquo;,5,5'-tetramethylbenzidine (TMB) while other substrates remained unaffected (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). Furthermore, we found an ideal application for these white nanozymes\u0026mdash;white nanozyme test strips. Excitingly, unlike other colored nanozymes, the whiteness of Mn-MOF nanozymes not only avoided color interference from the nanozymes, but also strengthened the whiteness of paper, highlighting color changes on the test strip and thus improving sensitivity. Further, the constructed H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e test strip showed high sensitivity, strong anti-interference capability in aerobic environment, and excellent store stability (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). To demonstrate its versatility, we further extended the use of nanozymes for detecting glucose and sarcosine. This study is anticipated to stimulate further exploration of the unique whiteness and catalytic properties of MOF nanozymes for advanced colorimetric detection applications.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e \u003cb\u003eSynthesis and characterization of Mn-MOF nanozymes\u003c/b\u003e \u003c/p\u003e \u003cp\u003eIn view of the fact that the most of MOF nanozymes were synthesized by hydrothermal approach, which requires high temperature, high pressure and sealed equipment, we tried to synthesize Mn-MOF by facile ultrasonic method (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). MnCl\u003csub\u003e2\u003c/sub\u003e and terephthalic acid (TPA) were rapidly added into the solution containing dimethyl formamide (DMF) and triethylamine (TEA). After ultrasonic processing, a uniform white solution was produced, and white Mn-MOF precipitates were obtained by centrifugation and vacuum drying (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). Significantly, white Mn-MOF had no absorption peak within 300\u0026ndash;900 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea), which will facilitate the chromogenic assay results.\u003c/p\u003e \u003cp\u003eThe morphology of white products was observed by transmission electron microscopy (TEM). They exhibited two-dimension (2D) nanosheet structure with smooth edges (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, c). More detailed information about morphology and size of Mn-MOF was researched by atomic force microscope (AFM). Mn-MOF nanosheets displayed a smooth surface with an average thickness of 3 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed, e), confirming the ultra-thin 2D structure. X-ray diffractometer (XRD) pattern of Mn-MOF (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef) was consistent with the previously reported monoclinic crystalline framework, Mn\u003csub\u003e4\u003c/sub\u003e(TPA)\u003csub\u003e4\u003c/sub\u003e(H\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e8\u003c/sub\u003e \u003csup\u003e52\u003c/sup\u003e, and the well-resolved peaks indicated high crystallinity. To better demonstrate the advantages of the ultrasonic synthesis method, we adopted the traditional hydrothermal method at 150\u0026deg;C to prepare Mn-MOF\u003csup\u003e\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e, which resulted in micron-sized, solid, irregular chunks (Supplementary Fig.\u0026nbsp;1a, b). This comparison highlights the advantage of our synthesis approach, which not only eliminates the need for high-temperature heating and sealed equipment, but also successfully produces ultra-thin 2D nanostructured morphology.\u003c/p\u003e \u003cp\u003eChemical composition (Mn, O, and C) and uniform distribution of Mn-MOF are affirmed by energy dispersive X-ray (EDX) spectroscopy (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg). The Fourier transform infrared (FT-IR) spectra (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eh) reflected that the characteristic beaks of Mn-MOF were different with ligand TPA. The peaks of TPA at 2822, 1691 and 526 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e conformed to \u003cem\u003eν\u003c/em\u003e(OH), \u003cem\u003eν\u003c/em\u003e(C\u0026thinsp;=\u0026thinsp;O) and \u003cem\u003eδ\u003c/em\u003e(C\u0026thinsp;=\u0026thinsp;O) of the nonionized carboxyl groups. As for Mn-MOF, the above peaks disappeared, while new peaks were generated at 1578 and 1386 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e, which were correspond to asymmetric and symmetrirc stretching vibrations of \u0026ndash;COO. These results demonstrated the deprotonation of acidic carboxyl, attributing to the complexation of manganese ions and carboxyl groups. Moreover, the appearance of characteristic peak at 752 cm\u003csup\u003e-1\u003c/sup\u003e indicated that the 1,4-substituent bond core of TPA turned into the ring-out-of-plane vibration, indicating the effective coordination between the manganese ions and TPA. To further determine the surface elements and the oxidation state of manganese, X-ray photoelectron spectroscopy (XPS) was conducted. The XPS survey spectra of Mn-MOF (Supplementary Fig.\u0026nbsp;2a) suggest the existences of Mn, C, and O elements. The Mn 2p XPS spectrum of Mn-MOF also displayed evident peaks at 642.2 and 653.4 eV (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ei), coinciding with Mn2p\u003csub\u003e3/2\u003c/sub\u003e of Mn\u003csup\u003e2+\u003c/sup\u003e in Mn‒O bonds, different from the peaks of MnO\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e3\u003c/sup\u003e. The oxidation states of manganese can be identified by the spin-orbit peak splitting of Mn 3s \u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e4\u003c/sup\u003e. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ej, the peak splitting value of Mn 3s was measured to be 6.0 eV, confirming the presence of Mn\u0026sup2;⁺. Meanwhile, the fitting characteristic peaks of O 1s at 531.6 and 533.1eV (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ek) corresponded to the Mn-carbonate/C\u0026thinsp;=\u0026thinsp;O and C-O bonds. Particularly, the peak of O 1s at 531.6 eV was not characteristic of metal oxides. Moreover, the C 1s spectrum of Mn-MOF could be deconvoluted into three peaks at 284.8, 286.3 and 288.5 eV (Supplementary Fig.\u0026nbsp;2b), which were typical values of C-C/C\u0026thinsp;=\u0026thinsp;C, C-O and O\u0026thinsp;=\u0026thinsp;C-O, respectively\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e9\u003c/sup\u003e, indicating the existence of TPA. These above results indicated white 2D ultra-thin Mn-MOF nanosheets were successfully synthesized by facile ultrasonic approach.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe mesoporous properties of Mn-MOF nanozymes were studied by nitrogen adsorption/desorption isotherm (BET). The isotherm shows IV type and H\u003csub\u003e3\u003c/sub\u003e-type hysteresis loop (P P\u003csub\u003e0\u003c/sub\u003e\u003csup\u003e-1\u003c/sup\u003e \u0026gt; 0.4) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003el), indicating that Mn-MOF had mesoporous properties. The BET specific surface area of Mn-MOF was 6.5109 m\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e g\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. In addition, the pore size distribution was analyzed by Barrett-Joyner-Halenda method in the desorption part and the average pore size was 14.8 nm. The high specific surface area will be conducive to catalysis of Mn-MOF.\u003c/p\u003e \u003cp\u003e \u003cb\u003eOrigin of whiteness in Mn-MOF\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe synthesized Mn-MOF exhibited white coloration, which holds significant importance for white test strip substrates. Therefore, this stimulates us to systematically investigated the origin of this whiteness and quantitatively evaluated its degree. Typically, whiteness arises from three primary mechanisms: (1) nanostructure-induced scattering effects, (2) defect-state luminescence, or (3) intrinsic metal/ligand characteristics\u003csup\u003e\u003cspan additionalcitationids=\"CR56 CR57\" citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e\u003c/sup\u003e. The hydrothermally synthesized bulk Mn-MOF showed no apparent nanostructures (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, b), yet remained white (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). Moreover, both bulk Mn-MOF and ultrasonically synthesized Mn-MOF NSs maintained their white color after grinding (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec), eliminating nanostructure scattering as the origin. Further, the surface roughness of Mn-MOF nanosheets was measured by AFM. The arithmetic average roughness (\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003ea\u003c/em\u003e\u003c/sub\u003e) and root mean square roughness (\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003eq\u003c/em\u003e\u003c/sub\u003e) were determined to be 1.83 nm and 3.71 nm, respectively, both significantly below 10 nm. This result excludes surface roughness-enhanced scattering as the origin of whiteness. (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed)\u003csup\u003e\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e\u003c/sup\u003e. Furthermore, visual inspection confirmed the absence of metallic luster, ruling out specular reflection. Additionally, fluorescence spectra revealed no detectable emission peaks within 300\u0026ndash;800 nm under 253 nm excitation (the maximum absorption wavelength), which rules out defect-state luminescence as a possible cause of the white coloration. (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee) \u003csup\u003e\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e,\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThese above results strongly suggested metal/ligand characteristics as the whiteness origin. To investigate the metal ion dependence, we substituted Mn\u003csup\u003e2+\u003c/sup\u003e with Fe\u003csup\u003e3+\u003c/sup\u003e and Co\u003csup\u003e2+\u003c/sup\u003e while keeping all other synthesis conditions unchanged. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef, the resulting MOFs exhibited pink and black colors, respectively. Ligand substitution of TPA with 2-aminoterephthalic acid (ATPA) or trimesic acid (TMA) produced pink and beige Mn-MOFs (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef). Whiteness thus depends critically on both metal ion and ligand selection, where white coloration achieved exclusively through Mn\u003csup\u003e2+\u003c/sup\u003e-TPA coordination.\u003c/p\u003e \u003cp\u003eSubsequently, quantitative colorimetric evaluation was performed on these materials (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg). Among all MOF samples, only the Mn-TPA MOF demonstrated a luminance value (\u003cem\u003eL*\u003c/em\u003e) exceeding 90 (93.09) and a whiteness index (\u003cem\u003eWI\u003c/em\u003e) above 90 (93.78), showing a clear distinction in the colorimetric results. In addition, this also confirmed that neither solvent/crystallization water nor synthesis methods contributed to the whiteness. According to international standards, \u003cem\u003eWI\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;90 qualifies as high whiteness. Compared to standard white TiO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e55\u003c/sup\u003e, the total color difference (\u003cem\u003eΔE\u003c/em\u003e) was \u0026lt;\u0026thinsp;1 (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg and Supplementary Table\u0026nbsp;1), indistinguishable to the naked eye, confirming superior whiteness. UV-Vis diffuse reflectance spectroscopy (DRS) of Mn-TPA MOF nanozymes showed about 90% reflectance within 450\u0026ndash;800 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eh), indicating no visible light absorption\u003csup\u003e\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e\u003c/sup\u003e. Moreover, The calculated bandgap of 4.02 eV (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ei) exceeded the 3.1 eV threshold for visible light absorption\u003csup\u003e\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e\u003c/sup\u003e. Taken together, the whiteness of Mn-MOF originates from specific metal-ligand combinations rather than nanostructures or defects, exhibiting no visible light absorption and producing high diffuse reflectance that generates its white appearance.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003ePeroxidase-like activity and reaction specificity of Mn-MOF nanozymes\u003c/b\u003e \u003c/p\u003e \u003cp\u003eTo verify the peroxidase-like activity of Mn-MOF, chromogenic substrate TMB and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e were added into Mn-MOF-catalyzed reaction solution in air. The characteristic absorbance peaks of TMB oxide (TMB*\u003csup\u003e+\u003c/sup\u003e) at 652 nm could be observed in TMB-H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e-MOF system, while no obvious absorbance peaks appeared in the absence of Mn-MOF or H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, b). The above results suggest Mn-MOF possess inherent peroxidase-like activity but no oxidase-like activity. In addition, neither Mn\u003csup\u003e2+\u003c/sup\u003e nor TPA had peroxidase-mimicking activity (Supplementary Fig.\u0026nbsp;3), indicating the peroxidase-like activity produced after the formation of the framework structure.\u003c/p\u003e \u003cp\u003eTo further prove that Mn-MOF nanozymes have no oxidase-like activity, nanozymes-catalyzed reaction system was conducted in different concentrations of O\u003csub\u003e2\u003c/sub\u003e. Apparently, TMB could not be oxidized in the air- and even O\u003csub\u003e2\u003c/sub\u003e-saturated solutions without H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec). In contrast, there was a high absorption peak of TMB*\u003csup\u003e+\u003c/sup\u003e in N\u003csub\u003e2\u003c/sub\u003e-saturated solution containing H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec), which was as high as that in air-saturated solution containing H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). These results demonstrated the excellent reaction specificity of Mn-MOF nanozymes, i.e., single peroxidase-like activity without oxidase-like activity. Therefore, H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e is necessary for Mn-MOF-catalyzed reaction, and O\u003csub\u003e2\u003c/sub\u003e cannot disturb it.\u003c/p\u003e \u003cp\u003eLike natural peroxidase, the peroxidase-mimicking activity of Mn-MOF exhibited Mn-MOF concentration-, pH- and temperature-dependences (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed\u0026ndash;f). The absorption peak at 652 nm increased with the concentrations of Mn-MOF nanozymes (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed and Supplementary Fig.\u0026nbsp;4 ), confirming its peroxidase-like activity. Mn-MOF nanozymes exhibited strong activity under weakly acidic condition, and reached highest activity at pH 4.0 (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee). The activity of Mn-MOF showed noticeable rise from 4\u0026deg;C to 25\u0026deg;C, and remained stable in a wide temperature range (25\u0026ndash;40\u0026deg;C) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef). Considering the activity of Mn-MOF at 25\u0026deg;C was similar with those at higher temperatures (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef), the subsequent experiments were conducted at 25\u0026deg;C. In addition, Mn-MOF possessed good thermal stability, and remained over 90% of original activity at even 90\u0026deg;C (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eg). Moreover, Mn-MOF nanozymes still exhibited almost unchanged peroxidase-like activity and good dispersibility after the storage for 6 months at room temperature (Supplementary Fig.\u0026nbsp;5 ), showing high storage stability.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eSteady-State kinetics mechanism of Mn-MOF nanozymes\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe steady-state kinetics of Mn-MOF nanozymes were studied by varying the concentrations of TMB and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, respectively (Supplementary Fig.\u0026nbsp;6). The experimental data conformed to the Michaelis-Menten equation. Moreover, as an important parameter for evaluating enzyme kinetics, the value of \u003cem\u003eK\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e is inversely correlated with the affinity of substrates with enzyme. The \u003cem\u003eK\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e value of Mn-MOF nanozymes for TMB (0.31 m\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em)\u003c/span\u003e was similar and lower than those of natural enzymes and some other nanozymes, and the \u003cem\u003eK\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e value of Mn-MOF nanozymes for H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (0.063 m\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em)\u003c/span\u003e were 1\u0026ndash;4 order of magnitudes lower than those of natural enzymes and some other nanozymes (Supplementary Table\u0026nbsp;2) \u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan additionalcitationids=\"CR62 CR63 CR64 CR65\" citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e\u003c/sup\u003e, which indicated the good affinity of Mn-MOF nanozymes with the both substrates.\u003c/p\u003e \u003cp\u003eIn order to investigate the catalytic kinetics mechanism of Mn-MOF nanozymes, the Lineweaver-Burk plots were drawn (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea, b). The parallel double reciprocal plots demonstrated the Ping-Pong reaction mechanism. In other words, H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e and TMB reacted with Mn-MOF one by one. After the first product H\u003csub\u003e2\u003c/sub\u003eO were released, TMB reacted with Mn-MOF to produce TMB*\u003csup\u003e+\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec). So, the catalysis may not be derived from the generation of hydroxyl radicals (\u0026middot;OH). To certify the above inference, terephthalic acid (TA) was chosen as probe to track hydroxyl radicals (\u0026middot;OH). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed, the presence of Mn-MOF and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e cannot affect the generation of the fluorescence product of TA, indicating that there is no formation of \u0026middot;OH during the catalytic reaction. This was different with some enzymes and nanozymes, such as peroxidase\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e, Ni-MOF nanozymes\u003csup\u003e\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e\u003c/sup\u003e, Fe-MOF nanozymes\u003csup\u003e\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e,\u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e\u003c/sup\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanozymes\u003csup\u003e\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e\u003c/sup\u003e. This will provide the possibility for substrate selectivity of Mn-MOF nanozymes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eDiscovering intrinsic substrate specificity of Mn-MOF nanozymes\u003c/b\u003e \u003c/p\u003e \u003cp\u003eAs mentioned above, Mn-MOF nanozymes can catalyze the oxidation of TMB. So, other common substrates including 2, 2'-azino-bis (3-ethylbenzo-thiazoline-6-sulfonic acid) diammonium salt (ABTS), \u003cem\u003eo\u003c/em\u003e-Phenylenediamine (OPD), and diaminobenzidine (DAB) were used to replace TMB (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea). Surprisingly, Mn-MOF nanozymes could not catalyze the oxidation of ABTS, OPD and DAB in the presence of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb and Supplementary Fig.\u0026nbsp;7), indicating that the peroxidase-like activity of Mn-MOF nanozymes possess excellent substrate selectivity to TMB. In addition, Mn-MOF also could not catalyze the oxidation of other three substrate (ABTS, OPD, and DAB) without H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e in air and O\u003csub\u003e2\u003c/sub\u003e atmospheres (Supplementary Fig.\u0026nbsp;8), demonstrating Mn-MOF nanozymes really do not have oxidase-mimicking activity. To further confirm the substrate selectivity, the linear relationship between the activity unit (U) and the concentration of Mn-MOF nanozymes was investigated (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec). The slopes of the fitted lines represented the specific activity of Mn-MOF nanozymes for different substrates, indicating good substrate selectivity of Mn-MOF to TMB. Taken together, Mn-MOF nanozymes showed rare substrate selectivity, which is different and superior to other nanozymes and enzymes\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e,\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eMany POD-like nanozymes work by reactive oxygen species (ROS) as intermediates, and the oxidation of organic compounds by ROS usually lacks substrate selectivity\u003csup\u003e\u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e,\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e\u003c/sup\u003e. In this work, we found that total ROS did not form during the catalytic process, by using 2\u0026rsquo;,7\u0026rsquo;-dichlorofluorescin diacetate (DCFH-DA) as the fluorescent probe of broad-spectrum ROS (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed). This provides the possibility for the substrate selectivity.\u003c/p\u003e \u003cp\u003eTo explore the reasons for the substrate specificity, the peroxidase-like activities of the precursors (MnCl\u003csub\u003e2\u003c/sub\u003e and TPA) of Mn-MOF nanozymes were researched. The precursors cannot catalyze the oxidation of TMB, but peroxidase-mimicking activity arose after the formation of frame structure (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ee and Supplementary Fig.\u0026nbsp;3). Subsequently, MOFs based on TPA and other metal ions (Ni-MOF and Fe-MOF) were also synthesized, and their peroxidase-like activities for different substrates were investigated. Ni-MOF could not catalyze the oxidation of TMB, ABTS, OPD, and DAB, meaning that Ni-MOF had no peroxidase-mimicking activity (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ef and Supplementary Fig.\u0026nbsp;9). In contrast, Fe-MOF could rapidly catalyze the oxidation of the above four substrates, indicating Fe-MOF had excellent peroxidase-mimicking activity but no substrate selectivity (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ef and Supplementary Fig.\u0026nbsp;10). The above results reveal that the frame structure and the metal ions of MOF nanozymes were the prerequisites to its peroxidase-mimicking activity.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eKeeping test strip from interferences of O\u003c/b\u003e \u003csub\u003e \u003cb\u003e2\u003c/b\u003e \u003c/sub\u003e \u003cb\u003eand color by Mn-MOF nanozymes\u003c/b\u003e\u003c/p\u003e \u003cp\u003eNowadays, nanozymes-based test strip has shown great application potential for the rapid visual detection platform, due to the portability, low cost, high stability and easy large-scale production\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. Here, considering the white color and the single activity of Mn-MOF nanozymes, we employed Mn-MOF nanozymes for the fabrication of test strip with TMB as chromogenic substrate, on the expectation that the two outstanding features would endow test strip some unique advantages (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea). As a proof-of-concept, H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e test strip was constructed by deposition of Mn-MOF nanozymes on the paper (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb, c). To prove the feasibility of the fabricated test strip, the H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e assay was performed in various atmospheres. As expected, the colorimetric result was not affected by the concentration of O\u003csub\u003e2\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ed), because of single peroxidase-like activity of Mn-MOF nanozymes without oxidase-like activity. Since the catalytic reaction can't take place without H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, the reaction can be started only by adding H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, which prevents premature reactions in the air, and hence improves the reliability of the detection results.\u003c/p\u003e \u003cp\u003eMore interestingly, commercial white papers are usually not very white, but Mn-MOF nanozymes showed whitening effect to the papers (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ee). This is crucial for enhancing sensitivity of the colorimetric result of test strip. To further confirm the superiority of white nanozymes to test strip, various colors of nanozymes in the same concentration were used to fabricate the nanozymes-based test strip. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ef, colored nanozymes masked the whiteness of paper and chromogenic reaction. In a sharp contrast, the blueness of chromogenic reaction on the paper modified by Mn-MOF nanozymes could be readily observed after the addition of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e. These above results demonstrate that white nanozymes with activity specificity was indeed an ideal choice for the colorimetric test strip based on nanozymes.\u003c/p\u003e \u003cp\u003eAfter the condition optimization (Supplementary Fig.\u0026nbsp;11), test strip was fabricated for the detection of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, where colorless TMB could be oxidized into blue TMB*\u003csup\u003e+\u003c/sup\u003e by H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e under the catalysis of Mn-MOF nanozymes. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eg, blueness of paper deepened with the increase of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentration, indicating the constructed test strip can realize the fast qualitative assay of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e by naked eye. Further, the corresponding RGB values were collected by smartphone for the quantitative analysis of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e. With the increase of concentration of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, the value of ΔB/(R\u0026thinsp;+\u0026thinsp;G\u0026thinsp;+\u0026thinsp;B) continuously increased and showed a good linear relationship within the range of 5\u0026ndash;400 \u0026micro;\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e. The regression equation was y\u0026thinsp;=\u0026thinsp;0.00044731x\u0026thinsp;+\u0026thinsp;0.000048 (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.995). The limit of detection (LOD) was calculated to be 0.43 \u0026micro;\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e (S/N\u0026thinsp;=\u0026thinsp;3), which was lower than some other methods including spectrophotometry and even electrochemical sensor (Supplementary Table\u0026nbsp;3)\u003csup\u003e\u003cspan additionalcitationids=\"CR71 CR72\" citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e73\u003c/span\u003e\u003c/sup\u003e, confirming the excellent sensitivity. In addition, test strip based on Mn-MOF nanozymes showed the high storage stability, and there is not obvious change in the chromogenic response after the storage for 6 months at 4\u0026deg;C (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eh).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSo far, known nanozymes generally various colors, which seriously disturbs colorimetric analysis results of test strip, as proven by Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ef. In this work, the white nanozymes did not disturb the colorimetric results of test strip, and highlighted the blue color of TMB*\u003csup\u003e+\u003c/sup\u003e, which resulted in high sensitivity of test strip. What's more, Mn-MOF nanozymes had no oxidase-mimicking activity, and thus the proposed assay strategy could not be influenced by the varying concentration of O\u003csub\u003e2\u003c/sub\u003e in atmosphere and solution (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec, \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ed), enhancing the reliability and avoiding false positive results for test strip. In addition, Mn-MOF nanozymes also possessed the superior stability to natural peroxidases. Taken together, Mn-MOF is an ideal enzyme substitute on test strip, and test strip based on Mn-MOF nanozymes would have broad application prospects.\u003c/p\u003e \u003cp\u003e \u003cb\u003eUniversality of test strip based on Mn-MOF nanozymes\u003c/b\u003e \u003c/p\u003e \u003cp\u003eTo prove the universality of Mn-MOF nanozymes-based test strip, glucose test strip was constructed by dropping glucose oxidase (GOx) onto Mn-MOF nanozymes-based test strip (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ea). In the GOx-nanozyme cascade catalytic system, glucose gave rise to the generation of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, and then the chromogenic reaction. As the concentration of glucose gradually increased, the blue color on the paper gradually deepened, and the corresponding ΔB/(R\u0026thinsp;+\u0026thinsp;G\u0026thinsp;+\u0026thinsp;B) value gradually increased (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ec). Then, the calibration curve was plotted, and the regression equation was y\u0026thinsp;=\u0026thinsp;0.00065347x\u0026thinsp;+\u0026thinsp;0.000653 (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.998) within the linear range of 5\u0026ndash;600 \u0026micro;\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e. This method showed high sensitivity, and LOD (0.49 \u0026micro;\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e) was an order of magnitude lower than other colorimetric and electrochemical methods (Supplementary Table\u0026nbsp;4) \u003csup\u003e\u003cspan additionalcitationids=\"CR75 CR76 CR77\" citationid=\"CR74\" class=\"CitationRef\"\u003e74\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e78\u003c/span\u003e\u003c/sup\u003e. In addition, we researched the selectivity of this system for other monosaccharides or disaccharides (sucrose, mannose, arabinose, galactose, and lactose). Only glucose showed a significant response, proving good selectivity of this system (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ed).\u003c/p\u003e \u003cp\u003eSubsequently, sarcosine test strip was also established by dropping sarcosine oxidase (SOx) onto the Mn-MOF nanozymes-modified paper (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eb). As the concentration of sarcosine gradually increased, the blue color on the paper gradually deepened, and the corresponding ΔB/(R\u0026thinsp;+\u0026thinsp;G\u0026thinsp;+\u0026thinsp;B) value gradually increased with a good linear correlation within 5\u0026ndash;300 \u0026micro;\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ee). The linear regression equation was fitted (y\u0026thinsp;=\u0026thinsp;0.00060184x \u0026ndash; 0.0000225, R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.998), and LOD was calculated to be 0.27 \u0026micro;\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e, which was lower than previous methods (Supplementary Table\u0026nbsp;5) \u003csup\u003e\u003cspan additionalcitationids=\"CR80 CR81 CR82\" citationid=\"CR79\" class=\"CitationRef\"\u003e79\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR83\" class=\"CitationRef\"\u003e83\u003c/span\u003e\u003c/sup\u003e. These results suggested the versatility of Mn-MOF nanozymes-based test strip. Moreover, the sensitivity of test strip could be really improved by the whitening effect and the activity specificity of Mn-MOF nanozymes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eVarious assay applications in real samples\u003c/b\u003e \u003c/p\u003e \u003cp\u003eTo estimate the applicability and reliability of the constructed test strip, the detection of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, glucose and sarcosine in various real samples were conducted by three kinds of test strips. For H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e detection, two water-soak foodstuffs (sea cucumber and jellyfish) were used as real samples (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The concentrations of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e were calculated according to the working curve (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eg). The standard addition method was applied, and the recoveries of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003ewere within 99.7\u0026ndash;100.9%, suggesting good accuracy and reliability. The relative standard deviation (RSD) was within 3.75%, showing high reproducibility and precision.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe determination of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, glucose and sarcosine in real samples\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAnalyte\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSpiked\u003c/p\u003e \u003cp\u003e(\u0026micro;\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFound\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e(\u0026micro;\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRecovery\u003c/p\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eRSD\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e(%, \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;5)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"5\" rowspan=\"6\"\u003e \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eSea cucumber\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e5.60\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e3.75\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e15.57\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e99.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.96\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e150\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e156.43\u0026thinsp;\u0026plusmn;\u0026thinsp;2.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e100.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.43\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003ejellyfish\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e12.80\u0026thinsp;\u0026plusmn;\u0026thinsp;0.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.41\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e22.89\u0026thinsp;\u0026plusmn;\u0026thinsp;0.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e100.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.87\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e150\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e162.74\u0026thinsp;\u0026plusmn;\u0026thinsp;2.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e100.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.25\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"5\" rowspan=\"6\"\u003e \u003cp\u003eGlucose\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eapple\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e25.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.75\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e35.29\u0026thinsp;\u0026plusmn;\u0026thinsp;0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e100.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.71\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e300\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e324.13\u0026thinsp;\u0026plusmn;\u0026thinsp;2.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e99.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.74\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003egrape\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e30.15\u0026thinsp;\u0026plusmn;\u0026thinsp;1.52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e5.04\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e40.04\u0026thinsp;\u0026plusmn;\u0026thinsp;0.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e98.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.42\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e300\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e332.27\u0026thinsp;\u0026plusmn;\u0026thinsp;2.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e100.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.68\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"5\" rowspan=\"6\"\u003e \u003cp\u003eSarcosine\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003ebeef\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e20.27\u0026thinsp;\u0026plusmn;\u0026thinsp;0.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.18\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e30.59\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e103.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.39\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e150\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e170.05\u0026thinsp;\u0026plusmn;\u0026thinsp;3.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e99.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.78\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003echicken\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e9.03\u0026thinsp;\u0026plusmn;\u0026thinsp;0.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e18.94\u0026thinsp;\u0026plusmn;\u0026thinsp;0.27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e99.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.43\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e150\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e159.25\u0026thinsp;\u0026plusmn;\u0026thinsp;2.34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e100.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.47\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003csup\u003ea\u003c/sup\u003e For each sample, experiment was repeated five times and \u0026lsquo;\u0026plusmn;\u0026rsquo; represents standard deviation (\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;5).\u003c/p\u003e \u003cp\u003eFor the glucose detection in real samples, two fruits (apple and grape) were used as real samples (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). After adding a known amount of glucose into the pretreated fruit juices, the recoveries of glucose were calculated to be from 98.9\u0026ndash;100.7%. RSD was within 5.04% (\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;5). The results suggested the fabricated glucose test strip had a good accuracy and reproducibility.\u003c/p\u003e \u003cp\u003eFor the detection in real samples, the reliability of proposed sarcosine test strip was also be verified by measuring sarcosine in two meat samples (beef and chicken). The recoveries ranged from 99.1\u0026ndash;103.2%, and RSD was within 2.10% (\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;5) (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), indicating good reliability for the real samples assay.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this work, a white Mn-MOF nanozymes with good activity specificity was successfully synthesized by a simple ultrasound approach. Through comprehensive studies, we conclusively determined that the white optical property of Mn-MOFs originates exclusively from the specific coordination polymerization between Mn²⁺ and TPA ligands, independent of morphological characteristics, defect states, solvent effects, or specular reflection. The unique Mn-TPA combination exhibits negligible visible light absorption and generates high diffuse reflectance, resulting in its white appearance.\u003c/p\u003e \u003cp\u003eNoticeably, Mn-MOF demonstrated two types of catalytic specificity. (1) Reaction specificity: it possessed single peroxidase-mimicking activity without oxidase-like activity, thus avoiding O\u003csub\u003e2\u003c/sub\u003e interference during the detection. (2) Substrate specificity: it specifically catalyzed the oxidation of TMB rather than other substrates (ABTS, OPD and DAB). These characteristics were innate, and do not need any additional functional modification.\u003c/p\u003e \u003cp\u003eSignificantly, white Mn-MOF nanozymes exhibited great superiority in colorimetric test strip for the apparatus-free visual detection of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e. Compared with other colors of nanozymes, the white Mn-MOF nanozymes avoided the interference to the judgment of the chromogenic results by the naked eye and the color extractor. Moreover, the whiteness of Mn-MOF strengthened the whiteness of paper, making the blue color of TMB*\u003csup\u003e+\u003c/sup\u003e readily distinguishable, resulting in ultra-high sensitivity. On the basis of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e test strip, a series of test strips were successfully developed for the detection of glucose and sarcosine, demonstrating excellent universality of Mn-MOF-based test strips. These test strips also showed high store stability for at least six months, and good reliability for real samples assay.\u003c/p\u003e \u003cp\u003eIn summary, this work establishes a fundamental paradigm for understanding the origin of whiteness in MOF-based nanozymes through systematic optical and structural characterization. By elucidating the critical role of metal-ligand coordination in governing light absorption and scattering properties, we provide a design framework for developing white nanozymes with tailored optical behaviors. These findings directly address the long-overlooked challenge of color interference in nanozyme applications. As for the analysis technology, this work not only provides an ideal biomimetic recognition element (white nanozyme with single activity), but also presents an ideal vehicle (test strip) that can perfectly exploit the advantages of white nanozyme. We expect that this study would inspire the exploration of more and more white nanozymes with high activity specificity for various colorimetric assay methods (not limited to test strip), eliminating the interference of O\u003csub\u003e2\u003c/sub\u003e and color of nanozymes. Looking forward, the marriage of tunable MOF optics with enzymatic specificity opens transformative possibilities. These potential nanozymes could revolutionize low-cost, portable monitoring platforms.\u003c/p\u003e "},{"header":"Methods","content":"\u003cp\u003e \u003cb\u003eSynthesis of Mn-MOF nanozymes\u003c/b\u003e \u003c/p\u003e\u003cp\u003eMn-MOF were synthesized by ultrasound approach. Firstly, TPA (0.75 mmol) were dissolved into the mixed solution containing DMF (32 mL), ethanol (2 mL), and water (2 mL). Then, MnCl\u003csub\u003e2\u003c/sub\u003e·4H\u003csub\u003e2\u003c/sub\u003eO (0.375 mmol) was added and dissolved into the above solution. Subsequently, TEA (0.8 mL) was quickly injected into the above solution, and then stirred for 5 min to obtain a white suspension. Then, the mixed solution was continuously sonicated at 40 kHz for 8 h, and the white product was obtained after centrifugation (4000 rpm), washing with ethanol, and drying in vacuum.\u003c/p\u003e\u003cp\u003e \u003cb\u003eOrigin of whiteness in Mn-MOF\u003c/b\u003e \u003c/p\u003e\u003cp\u003eAs for surface roughness, 3D topographic image of Mn-MOF was acquired, and then surface roughness parameters (\u003cem\u003eR\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e and \u003cem\u003eR\u003c/em\u003e\u003csub\u003eq\u003c/sub\u003e) were measured by AFM assay (Bruker, USA). To eliminate the possibility of defect-state luminescence, the fluorescence spectrum of Mn-MOF was recorded by fluorescence spectrophotometer (Hitachi F-7000) with excitation at 253 nm (slit width: 10 nm) and emission scanned from 275–800 nm (slit width: 10 nm). To compare colorimetric parameters of different materials, their \u003cem\u003eL\u003c/em\u003e*, \u003cem\u003ea\u003c/em\u003e*, \u003cem\u003eb\u003c/em\u003e*, \u003cem\u003eWI\u003c/em\u003e, and Δ\u003cem\u003eE\u003c/em\u003e values were conducted by a colorimeter LS171 (Linshang, China).The UV–Vis DRS of Mn-MOF powder was conducted on a spectrometer 3600-plus (Shimadzu, Japan) using diffuse reflection accessory adapted for powder samples. Then, these reflectance values were converted to Tauc plot, and the bandgap energy was assessed by Tauc plot, according to the Kubelka-Munk function.\u003csup\u003e\u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e84\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\u003cp\u003e \u003cb\u003ePeroxidase-like activity assay of Mn-MOF nanozymes\u003c/b\u003e \u003c/p\u003e\u003cp\u003eTypically, the peroxidase-like activity of Mn-MOF was assessed by the characteristic absorbance of TMB*\u003csup\u003e+\u003c/sup\u003e(TMB oxide) at 652 nm (\u003cem\u003eε\u003c/em\u003e\u003csub\u003e652 nm\u003c/sub\u003e = 39000 m\u003csup\u003e− 1\u003c/sup\u003e cm\u003csup\u003e− 1\u003c/sup\u003e). H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (1 m\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e) and TMB (0.5 m\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e), and Mn-MOF (0.5 µg mL\u003csup\u003e− 1\u003c/sup\u003e) were reacted in the acetate buffer (0.1 \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e, pH 4.0) at 25°C for 30 min. Subsequently, the absorption spectra and the time-dependent absorbance at 652 nm were recorded.\u003c/p\u003e\u003cp\u003eThe effect of pH and temperature on peroxidase-like activity of Mn-MOF nanozymes was researched by the typical activity assay method, except for changing pH (pH 2.0–10.0) or temperature (4–50°C). The thermal stability of Mn-MOF was analyzed by repeating the above experimental steps after incubating Mn-MOF at different temperatures (4–50°C) for an hour. The thermal stability of Mn-MOF nanozymes were measured by the typical activity assay after Mn-MOF nanozymes were incubated at different various temperatures (4–90°C) for an hour. Each experiment was repeated at least three times.\u003c/p\u003e\u003cp\u003e \u003cb\u003eSteady-state kinetics assay\u003c/b\u003e \u003c/p\u003e\u003cp\u003eThe steady-state kinetic analysis on the peroxidase like activity of Mn-MOF nanozymes was performed by changing the concentration (0.05–1.2 m\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e) of TMB under fixed H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentration (1 m\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e) or varying the concentration (0.05–2 m\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e) of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e at the constant TMB concentration (0.5 m\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e). To obtain Michaelis constant (\u003cem\u003eK\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e), the activity data was fitted by the Michaelis-Menten equation: \u003cem\u003eν\u003c/em\u003e = \u003cem\u003eV\u003c/em\u003e\u003csub\u003emax\u003c/sub\u003e × [S]/(\u003cem\u003eK\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e + [S]), where ν is the initial velocity, \u003cem\u003eV\u003c/em\u003e\u003csub\u003emax\u003c/sub\u003e represents the maximum reaction velocity, and [S] represents the substrate concentration.\u003c/p\u003e\u003cp\u003eIn order to explore the kinetic mechanism, the peroxidase like activities was measured in the presence of the different concentrations of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (0.3, 0.6, 1 m\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e) or TMB (0.3, 0.5, 0.7 m\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e). The activity data were plotted based on the Lineweaver-Burk double reciprocal curve.\u003c/p\u003e\u003cp\u003e \u003cb\u003eChemical ROS assay\u003c/b\u003e \u003c/p\u003e\u003cp\u003eIn order to explore whether ROS were generated during the catalytic process, TA and DCFH-DA were used as fluorescent probes. Hydroxyl radicals (·OH) were detected by TA, where reaction product, 2-hydroxy terephthalic acid, has an emission peak at 425 nm. H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (1 m\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e) and TA (0.5 m\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e) were reacted with or without Mn-MOF (50 µg mL\u003csup\u003e− 1\u003c/sup\u003e) in acetate buffer (0.1 \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e, pH 4.0) for 30 minutes at 25°C. Subsequently, the fluorescence emission of the reaction solution was detected at 425 nm.\u003c/p\u003e\u003cp\u003eTotal ROS were detected by DCFH, where the reaction product has an emission peak at 524 nm. Firstly, DCFH-DA (1 m\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e in MeOH, 1 mL) was hydrolyzed in NaOH aqueous solution (0.01 N, 4 mL) for 30 minutes to obtain the unstable DCFH. Then, the above solution was neutralized with phosphate solution (25 m\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e, 20 mL). Mn-MOF (10 mg mL\u003csup\u003e− 1\u003c/sup\u003e, 20 µL), and 180 µL of fresh DCFH solution (40 µ\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e) were mixed, and the fluorescence intensity at 524 nm was measured over time.\u003c/p\u003e\u003cp\u003e \u003cb\u003eConstruction of different test strips based on Mn-MOF nanozymes\u003c/b\u003e \u003c/p\u003e\u003cp\u003eFor the typical construction of test strip for H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e assay, 5 µL of Mn-MOF (10 mg mL\u003csup\u003e− 1\u003c/sup\u003e) and 10 µL of the acetate buffer solution (0.1 \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e, pH 4.0) containing TMB (0.5 m\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e) were successively dropped onto the filter paper (6 mm diameter), and air-dried to obtain the H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e test strip.\u003c/p\u003e\u003cp\u003eFor the construction of test strip for glucose and sarcosine, the procedure is the same as that of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e test strip, except for adding enzymes (GOx or SOx, 20 µg mL\u003csup\u003e− 1\u003c/sup\u003e) into the acetate buffer solution (0.1 \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e, pH 4.0) containing TMB (0.5 m\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003em\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e \u003cb\u003eDetection of H\u003c/b\u003e \u003csub\u003e \u003cb\u003e2\u003c/b\u003e \u003c/sub\u003e \u003cb\u003eO\u003c/b\u003e \u003csub\u003e \u003cb\u003e2\u003c/b\u003e \u003c/sub\u003e, \u003cb\u003eglucose and sarcosine by different test strips\u003c/b\u003e\u003c/p\u003e\u003cp\u003eFor H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e detection, the different concentrations of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e solutions (5 µL) were gently dropped onto the surface of test strip. After standing at 25°C for 10 min, the RGB values of test strip were collected by Color Picker APP in smartphone for further quantitative analysis. For detection of glucose and sarcosine, the different concentrations of glucose and sarcosine solutions (5 µL) were dropped onto the surface of corresponding test strip. After standing at 25°C for 30 min, the RGB values of test strip were collected for further quantitative analysis. The experiments were repeated three times, and LOD was calculated by the equation LOD = (3σ/s), where σ is the standard deviation of blank signals and s is the slope of the calibration curve.\u003c/p\u003e\u003cp\u003e \u003cb\u003eDetection in various real samples\u003c/b\u003e \u003c/p\u003e\u003cp\u003eTo demonstrate the applicability of the constructed test strip, various actual samples (including sea cucumber and jellyfish for H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e detection, apple and grape for glucose detection, and chicken and beef for sarcosine detection) were employed. For the pretreatment of actual samples, soak solutions of water-soaked foodstuffs (cucumber and jellyfish) were centrifuged for 15 minutes. Real glucose solutions were extracted by the homogenate of fruits (apple and grape), and the filtration with a 0.22 filter. The real sarcosine solutions were extracted by ultrasonication of meats (chicken and beef, 5 g) in acetate buffer (pH 4.0, 10 mL) for 30 min. The above obtained solutions were detected by the corresponding test strips.\u003c/p\u003e\u003cp\u003e \u003cb\u003eReporting summary\u003c/b\u003e \u003c/p\u003e\u003cp\u003eFurther information on research design is available in the Nature Portfolio Reporting Summary linked to this article.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll the data that support the findings of this study are available within the article and Supplementary Information file, or from the corresponding authors upon request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was financially supported by the National Natural Science Foundation of China (22376111), Shandong Provincial Natural Science Foundation (ZR2024YQ026) for Excellent Young Scholars, Taishan Scholar Foundation of Shandong Province (tsqn202408237), Youth Innovation Team Project for Talent Introduction and Cultivation in Universities of Shandong Province (096-1622002), Research Foundation for Distinguished Scholars of Qingdao Agricultural University (663-1117015). We are grateful to staff from the Instrumental Analysis Center of Qingdao Agricultural University for providing valuable assistance with the testing instruments.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eL.H. conceived the study. J.T. and Y.Z.\u0026nbsp;performed the experiments, and\u0026nbsp;visualized the\u0026nbsp;results. All authors\u0026nbsp;analyzed the results. L.H. wrote and revised the manuscript with input from all the other coauthors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInclusion \u0026amp; ethics declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study did not involve human participants or animals, and thus ethical approval was not required. No inclusion or diversity considerations apply to this theoretical study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAdditional information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSupplementary information\u0026nbsp;\u003c/strong\u003eThe online version contains supplementary material available at\u003c/p\u003e\n\u003cp\u003ehttps://doi.org/10.1038/....\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eEast-Seletsky, A.\u003cem\u003e et al.\u003c/em\u003e Two distinct RNase activities of CRISPR-C2c2 enable guide-RNA processing and RNA detection. \u003cem\u003eNature\u003c/em\u003e \u003cstrong\u003e538\u003c/strong\u003e, 270-273 (2016).\u003c/li\u003e\n\u003cli\u003eHuang, Y., Ren, J. \u0026amp; Qu, X. Nanozymes: Classification, Catalytic Mechanisms, Activity Regulation, and Applications. \u003cem\u003eChem. 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Preparation and visible-light photocatalytic activity of ag-loaded TiO\u003csub\u003e2\u003c/sub\u003e@Y\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e hollow microspheres with double-shell structure. \u003cem\u003ePowder Technol.\u003c/em\u003e\u003cstrong\u003e377\u003c/strong\u003e, 621-631 (2021).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"metal-organic framework, white nanozymes, interference-free color, catalytic selectivity, colorimetric test strip","lastPublishedDoi":"10.21203/rs.3.rs-7027508/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7027508/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eGiven the promising prospect of nanozymes in colorimetric test strips, it is essential to eliminate the interferences of their multi-activities and various colors on the test strip. Here, white Mn-based metal-organic frameworks (Mn-MOFs) with ultrathin 2D morphology (3 nm thick) were successfully synthesized by a simple ultrasonic approach. The origin of the white optical property in Mn-MOFs was systematically investigated, revealing that it stems from specific metal-ligand coordination polymerization rather than morphological features or defect states. This specific coordination suppressed visible light absorption while enhancing diffuse reflection efficiency. Mn-MOF nanozymes possessed exclusive peroxidase-mimicking activity rather than oxidase-like activity, effectively resisting O\u003csub\u003e2\u003c/sub\u003e interference during colorimetric assay. Moreover, these nanozymes displayed unique substrate selectivity without additional modification. Unlike other colored nanozymes, the whiteness of Mn-MOF nanozymes not only prevented their color interference to colorimetric results, but also enhanced the paper\u0026rsquo;s whiteness, boosting contrast for colorimetric detection on test strip. The constructed H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e test strip demonstrated high sensitivity, strong anti-interference capability, excellent storage stability, broad applicability for other various analytes, and reliability for real sample assays. This study pioneers a systematic investigation into the origin of whiteness in MOF nanozymes. The coordination-defined properties enable interference-free optical design and O\u003csub\u003e2\u003c/sub\u003e-resistant on-site detection.\u003c/p\u003e","manuscriptTitle":"White Metal-Organic Framework Nanozymes with Enzyme-Mimicking Ac-tivity Specificity: Overcoming Interferences of Color and O2 in Colorimetric Test Strips","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-11 14:23:10","doi":"10.21203/rs.3.rs-7027508/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"communications-chemistry","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"commschem","sideBox":"Learn more about [Communications Chemistry](http://www.nature.com/commschem/)","snPcode":"","submissionUrl":"","title":"Communications Chemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Communications Series","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"6efc31e6-3a23-45cc-a5d5-7534fe725cd7","owner":[],"postedDate":"July 11th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":51281552,"name":"Physical sciences/Chemistry/Analytical chemistry/Bioanalytical chemistry"},{"id":51281553,"name":"Physical sciences/Nanoscience and technology/Nanoscale materials/Two-dimensional materials"},{"id":51281554,"name":"Physical sciences/Chemistry/Materials chemistry/Metal\u0026#x2013;organic frameworks"}],"tags":[],"updatedAt":"2025-12-05T08:07:07+00:00","versionOfRecord":{"articleIdentity":"rs-7027508","link":"https://doi.org/10.1038/s42004-025-01772-z","journal":{"identity":"communications-chemistry","isVorOnly":false,"title":"Communications Chemistry"},"publishedOn":"2025-12-04 05:00:00","publishedOnDateReadable":"December 4th, 2025"},"versionCreatedAt":"2025-07-11 14:23:10","video":"","vorDoi":"10.1038/s42004-025-01772-z","vorDoiUrl":"https://doi.org/10.1038/s42004-025-01772-z","workflowStages":[]},"version":"v1","identity":"rs-7027508","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7027508","identity":"rs-7027508","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}