ZnO microsphere decorated with Au nanoparticles for SERS detection and removal of trace 2-Mercaptobenzothiazole in environmental water

ZnO microsphere decorated with Au nanoparticles for SERS detection and removal of trace 2-Mercaptobenzothiazole in environmental water | 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 Research Article ZnO microsphere decorated with Au nanoparticles for SERS detection and removal of trace 2-Mercaptobenzothiazole in environmental water Jiangli Shi, Boran Zhang, Li Zhang, Xinling Liu, Yiping Wu, Ying Wen, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7281108/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 13 Oct, 2025 Read the published version in Microchimica Acta → Version 1 posted 11 You are reading this latest preprint version Abstract The toxic effects, including allergenicity, mutagenicity, and potential carcinogenicity of 2-mercaptobenzothiazole (MBT), have raised serious environmental and health concerns. In this work, we proposed the synthesis of ZnO microspheres with different morphologies (spherical and flower-like) decorated with Au nanoparticles (hereafter referred to as S-ZnO-Au MPs and F-ZnO-Au MPs, respectively) as ultrasensitive SERS-active substrates for the trace-level detection of MBT in aquatic environments. Spherical and flower-like ZnO microspheres were synthesized via a hydrothermal method, followed by the in-situ reduction of chloroauric acid to deposit Au nanoparticles onto the ZnO surface. Comparative analysis revealed that the S-ZnO-Au MPs exhibited superior SERS performance, with high enhancement factor of 5.5×10 7 . Taking advantage of the synergistic effects of chemical enhancement from ZnO semiconductor and electromagnetic enhancement from AuNPs, the S-ZnO-Au MPs-based SERS assay for MBT demonstrates high sensitivity and the limit of detection 1.42×10 −10 mol/L is reached, along with a wide linear dynamic detection range of 10 −8 ~10 −4 mol/L, with correlation coeffcients (R 2 ) of 0.9901. The developed ZnO-Au MPs structure exhibit significant potential as a multifunctional SERS substrate, enabling both the sensitive detection and subsequent photocatalytic degradation of MBT in aquatic environments. ZnO microsphere Au nanoparticles 2-mercaptobenzothiazole SERS trace detection photocatalytic degradation Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1. Introduction 2-Mercaptobenzothiazole (MBT, C7H5NS2) has attracted significant attention due to its extensive industrial applications and potential ecological risks. MBT is a stable heterocyclic structure composed of a benzene ring and a thiazole ring, with a mercapto group (-SH) that provides excellent antioxidant and coordination properties. However, these same properties contribute to its persistent accumulation in aquatic environments. Previous studies have demonstrated that MBT exhibits acute toxicity toward aquatic organisms, adversely affecting the growth and reproduction of fish and, in severe cases, leading to mortality [1] . Furthermore, through biomagnification in the food chain, MBT poses a serious threat to human health and has been classified as a Group 2A carcinogen by regulatory authorities [2] . To effectively mitigate the potential hazards of MBT to the environment and human health, the development and implementation of efficient detection and removal methods are crucial. Current analytical techniques for MBT detection include high-performance liquid chromatography (HPLC) [3,4] , electrochemical analysis [5] , and ultraviolet-visible spectrophotometry [6,7] . For instance, Rennie [3] developed HPLC method for detection of MBT in river water, achieving limit of detection (LOD) 4.8 nmol/L. Xiong’s group [7] reported a colorimetric sensor integrating photoinduced Au nanoparticles formation inhibition with salt-assisted liquid–liquid microextraction, realizing MBT detection with the LOD of 0.024 μmol/L. While these conventional techniques offer high selectivity and sensitivity, they often suffer from drawbacks such as complex sample preparation procedures and high operational costs. Therefore, novel analytical platforms characterized by simplified protocols, cost-effectiveness, and enhanced detection capabilities are urgently required. Surface-enhanced Raman scattering (SERS) technology, leveraging the synergistic effects of localized electromagnetic field enhancement and chemical enhancement, enables high sensitivity and rapid non-destructive analysis [8,9] . It has been widely applied in surface science [10] , biomedicine [11] and environmental pollutant monitoring [12] . Generally, noble metal nanoparticles (Au, Ag) are widely used as SERS-active substrates because of their unique localized surface plasmonic resonance (LSPR) effect with laser excitation, which supports the intense electromagnetic field around the metal surface [13,14] . However, the high value of precursor materials and the poor stability of metal nanostructures against pH, temperature, light, and oxygens largely hinder the application in real samples. In this sense, as an ideal alternatives for plasmonic metal SERS substrates, semiconductor materials (e.g., ZnO, TiO 2 , MoS 2 ) have become hotspot SERS substrate, because they are considerably cheaper, easy to fabricate, chemically more stable, tunable band structures, excellent photostability, and biocompatibility [15–17] . Nevertheless, the potential in applications is hardly fulfilled for pure semiconductor SERS substrates, because the limited enhancement capabilities are mainly from chemical enhancement, in other words, the enhancement signal is almost exclusively from charge transfer resonance between analytes and semiconductors. In addition, only few model analytes that chemically adsorb on the surface of semiconductors could be permitted signal enhancement, which also restricts the real application for semiconductor SERS substrates. In recent studies, it has been reported that semiconductors-metal hybrid substrates such as Ag-TiO 2 [18] , Ag-ZnO [19] have highly sensitive SERS response due to the noble metal/semiconductor nanocomposites can generate an charge transfer effect at the interface of metal/semiconductor except electromagnetic effect on metal. Such composite architectures effectively lower material costs while significantly improving stability compared to pure metal nanostructures. Especially, ZnO, as an ideal candidate for semiconductor SERS substrates, exhibits excellent photostability, biocompatibility, and superior SERS activity compared to other semiconductor nanomaterials [20,21] . Its abundant raw materials and low preparation cost make it suitable for large-scale production and practical applications [22] . Therefore, ZnO can be served as an ideal supporting for the uniform loading of metal nanoparticles and ultimately improve the sensitivity and stability of SERS signals. For example, Chen and coworkers [23] fabricated a ZnO/Ag composite substrate by growing Ag nanoparticles on ZnO nanorods, enabling the detection and photocatalytic degradation of Rhodamine B with a LOD of 1 × 10⁻¹¹ mol/L. Yang’s group [24] developed ZnO/Au-based SERS platform for detecting nicotine, and the LOD is obtained of 8.9 × 10 - 12 mol/L. However, highly sensitive and stable ZnO-based hybrid substrates is urgently needed to explore for measurement of MBT in water environment. In this work, we propose a novel strategy for detection of MBT in water environments by preparing ZnO-Au composites with different morphologies (Scheme 1). Flower-like (F-ZnO) and spherical (S-ZnO) ZnO microspheres were first synthesized via a hydrothermal method, followed by in situ reduction to coat Au nanoparticles (Au NPs), termed F/S-ZnO-Au MPs. Compared to F-ZnO-Au MPs, S-ZnO-Au MPs exhibit advantages in sensitivity, uniformity, reproducibility, and stability as active SERS substrates. Finally, S-ZnO-Au MPs were used for SERS detecting MBT in environmental water. Leveraging the excellent photocatalytic properties of ZnO, the efficient catalytic degradation of MBT by ZnO-Au MPs under xenon lamp irradiation after detection was studied, realizing an integrated “detection-remediation” function. This enhances the practical application potential of the material in real-world samples. 2. Experimental section 2.1 Reagents Chloroauric acid (HAuCl 4 ·4H₂O), zinc nitrate hexahydrate (Zn(NO 3 ) 2 ·6H 2 O), MgSO 4 , and n-butanol (C 4 H 10 O) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Sodium dodecyl sulfate (C 12 H 25 SO 4 Na, SDS), NaCl, KCl, CaCO 3 , zinc acetate dihydrate (Zn(Ac) 2 ·2H 2 O), 2-Mercaptobenzothiazole (MBT), humic acid, 2-Mercaptobenzimidazole (MBI), and Benzothiazole (BT) were obtained from Adamas (China). Trisodium citrate dihydrate (Na 3 C 6 H 5 O 7 ·2H 2 O) and 4-mercaptopyridine (C 5 H 5 NS, 4-MPy) were procured from Sigma-Aldrich (USA). Urea (NH 2 CONH 2 ) was purchased from General Reagent Company. All chemicals and reagents were of analytical grade. Ultrapure water (18.2 MΩ·cm) was used for all experiments. Lake water was collected from XueSi Lake in campus of Shanghai Normal University, which is connected from the Caohejing River outside the campus. Sea water was obtained from the East China Sea. Tap water was collected in lab. Glassware was soaked in aqua regia, boiled, and thoroughly rinsed with ultrapure water. 2.2 Experimental Instruments Ultraviolet-visible (UV-Vis) spectra were collected using a UV-Vis spectrophotometer (SHIMADZU, UV-1800, Japan). X-ray photoelectron spectroscopy (XPS, Shimadzu Kratos, Japan) and X-ray diffraction (XRD, RIGAKU, Japan) were employed to determine the crystal structure and chemical composition of ZnO-Au MPs. Fluorescence spectra was collected by fluorescence spectrophotometer (Varian, Cary Eclipse). The morphology of the materials was observed using a scanning electron microscope (SEM, Gemini SEM 300, Carl Zeiss, Germany) at an accelerating voltage of 40 kV and transmission electron microscopy (TEM, JEOL, JEM-2100EXII, Japan) operating at 200 kV. Raman signals were acquired using a Dilor confocal laser Raman system (SuperLabRamII, France) with an excitation wavelength of 633 nm, laser power of 7 mW, and acquisition time of 8 s with 3 accumulations. On-site Raman detection was performed using a portable Raman spectrometer (Zolix, Beijing, China) with an excitation wavelength of 785 nm, laser power of 150 mW, and an acquisition time of 8 s per spectrum, with 3 accumulations. 2.3 Preparation of ZnO microsphere The synthesis of F-ZnO microsphere follows previous report [ 22 ] . 0.25 g of SDS was dissolved in 10 mL of n-butanol, followed by the addition of 30 mL of deionized water. The mixture was stirred until a clear solution was formed, which is referred to as solution A. Simultaneously, Solution B was prepared by dissolving 5 mmol Zn(CH₃COO)₂·2H₂O and 40 mmol urea in 50 mL deionized water under 30 min stirring. Solution A was then added dropwise to solution B and the mixture was continuously stirred at room temperature for 2 hours. The resulting mixture was transferred into a Teflon-lined stainless steel autoclave and maintained at 100°C for 12 hours. After cooling the autoclave to room temperature, the white precipitate was collected by centrifugation and washed with ethanol and distilled water. The obtained solid was dried overnight at 60°C and subsequently calcined at 500°C for 2 hours in air to yield the final F-ZnO MPs. According to the previous report [ 25 ] , S-ZnO was synthesized. In brief, 1.12 g of Zn(NO 3 ) 2 , 0.45 g of urea, and 0.11 g of trisodium citrate dihydrate were dissolved in 75 mL of deionized water. The mixture was stirred for 20 minutes to ensure complete dissolution, after which it was transferred to a Teflon-lined stainless steel autoclave and heated at 120°C for 6 h. The resulting precipitate was washed with ethanol and deionized water, respectively. Finally, the collected solid was annealed at 350°C for 45 min for obtaining the final S-ZnO microsphere. 2.4 Preparation of ZnO-Au MPs Approximately 0.0150 g of prepared F/S-ZnO microspheres was dissolved in 25 mL of ultrapure water, and the solution was heated to a gentle boil while stirring. Under continuous stirring, 1 mL of 10 − 3 mol/L HAuCl 4 solution and 1.5 mL of 1% trisodium citrate solution were added. The mixture was stirred for 30 min until the solution turned deep purple, indicating the successful preparation of ZnO-Au MPs with different morphologies. 2.5 SERS Measurement The probe molecule 4-MPy, which is used to characterize the SERS active of this complex material, was mixed with the F/S-ZnO-Au MPs suspension in a 1:1 volume ratio for SERS test. Raman signals were acquired by using a 633 laser with a power of 7 mW, an acquisition time of 8 s, and 3 accumulations. Different concentrations of MBT solution were prepared with stepwise dilution. Following the same procedure as the 4-MPy test, MBT solution mixed with F/S-ZnO-Au MPs suspension in a 1:1 volume ratio for Raman signal collecting, by using the portable Raman with 785 nm laser, 150 mW laser power, and a collection time of 8 s, with 3 accumulations. For real sample detection, different amounts of MBT were added to actual water samples to simulate real-world conditions. Before mixed with substrate material, the MBT-spiked samples were filtered with 0.45 µm filter membrane. Then, the lake water samples were thoroughly mixed with F/S-ZnO-Au MPs for subsequent SERS measurements, and the process of Raman signal collected is the same with the pure MBT test. Different reference species might co-existing in lake water (concluding K + , Ca 2+ , CO 3 2− , NO 3 − , NaCl, MgSO 4 , humic acid, BT and MBI) were used to study the anti-interference capability of this proposed SERS assay system. The process of the Raman test is the same as the detection of MBT. 3. Results and Discussion 3.1 Characterization of F/S-ZnO-Au MPs ZnO microspheres with flower-like and sphere shapes were first synthesized by using hydrothermal method, followed Au NPs were grown on the surface of ZnO by in-situ reduction, obtaining the complex materials F/S-ZnO-Au MPs. The process of the synthesis as shown in Scheme1. For determining the optical properties, UV-Vis spectra test was first carried out and the results were shown in Fig. 1A. For the pure micrometer-sized ZnO particles, a distinct characteristic absorption peak is observed around 370 nm in the UV region, which is attributed to intrinsic band gap absorptionof ZnO due to the electronic transitions from the valence to the conduction band, confirming the successful synthesis of ZnO MPs [26] . Up on the in-situ reduction and incorporation of Au NPs on the ZnO surface, a prominent absorption band emerges at 533 nm, corresponding to the characteristic surface plasmon resonance absorption peak of Au NPs [15] . Additionally, a slight blue shift in the ZnO absorption peak was observed following Au modification, indicating charge transfer from the Au to the ZnO MPs [27] . These spectral changes collectively confirm the successful formation of Au-decorated ZnO MPs. In addition, the size of Au NPs was evaluated at about 43.6 nm (Supporting information), which is in the optimal size range that AuNPs possess the better SERS performance [28] . Figure 1B and C are the scanning electron microscopic (SEM) images of F-ZnO MPs and S-ZnO MPs, respectively, and their magnification images. Figure 1B shows that the F-ZnO MPs present obvious flower-like shape with a size of 10 µm which is formed by the interlacing of sheet-like structures. In contrast, the S-ZnO MPs shown in Fig. 1C exhibit a relatively smooth surface with a similar diameter of about 10 µm. As shown in Fig. 2, the morphology and the size of ZnO happen slight changes after modifying Au NPs. This could be the function of solvent that used in the process of in-suit reduce preparation of Au NPs. The EDX images demonstrate that Au NPs were successfully coated on the surface of ZnO, and this result is in accordance with UV-Vis spectra in Fig. 1A. Figure S1 shows the powder X-ray diffraction (XRD) pattern of the prepared materials. Diffraction peaks corresponding to pure F-ZnO and S-ZnO are observed. These diffraction peaks can be indexed to the (100), (002), (101), (102), (110), (103), and (112) crystal planes of hexagonal wurtzite structured ZnO (JCPDS # 36-1451). The absence of any impurity-related peaks indicates that the precursors were fully converted into phase-pure ZnO. After decoration of Au NPs on ZnO, the intensity of ZnO diffraction peaks is decreased and characteristic peaks emerge at 38.3° and 44.42° (2θ). These new diffraction features correspond to the (111) and (200) crystallographic planes of metallic Au (JCPDS 04-0784), respectively. The XRD results indicate that Au NPs have successfully grown on the ZnO microspheres. Using S-ZnO-Au MPs as an example, we further confirmed the chemical composition and valence states of the elements in the material through X-ray photoelectron spectroscopy (XPS). In the XPS survey spectrum of ZnO (Figure S2a), C, O, and Zn elements was observed, and in the XPS survey spectrum of ZnO-Au MPs (Figure S2d), the Au element was detected. In the high-resolution XPS spectra of ZnO and ZnO-Au (Figures S2b, e), the binding energies for Zn 2p 1/2 and Zn 2p 3/2 were identified at 1040 eV and 1017 eV, respectively. These values correspond to the characteristic peaks of ZnO [29] , and it has slight change after modification of Au for the binding energy of Zn 2p. Figure S2c displays the deconvoluted O 1s spectrum, which exhibits three characteristic peaks at 526.3 eV, 528.1 eV, and 529.7 eV. These binding energies are slightly lower than typical values, likely due to electron transfer between ZnO and Au, which increases the electron density around the oxygen atoms and consequently reduces the binding energy. In Figure S2f, the binding energies of Au 4f 7/2 and Au 4f 5/2 were observed at 84.6 eV and 87.8 eV, respectively. Compared to the Au 4f 7/2 of metallic Au (83.9 eV) [30] , Au 4f 7/2 (84.6 eV) in ZnO-Au shifts to a high binding energy by 0.7 eV, indicating that Au loses some electrons, which could be the reason that the electrons transfer from Au NPs to ZnO, which is in agreement with that UV-Vis spectra test. Additionally, the peak at 79.3 eV may also result from interfacial charge transfer, leading to a shift in the binding energy of Au. 3.2 SERS performance of ZnO-Au MPs To enhance the SERS activity of ZnO-Au MPs, the amount of reducing agent and the boiling time during the in-suit coating of Au NPs were optimized. 4-MPy was used as the probe molecule to respond the variation of SERS activity. As shown in Figures S3, for both F-ZnO-Au MPs and S-ZnO-Au MPs, the strongest SERS signal of 4-MPy was achieved when 1.5 mL of reducing agent was used and the solution was boiled for 30 min. The SERS activity of the complex materials initially increased and then decreased with increasing the amount of the reducing agent and the boiling time. At an optimal amount of reducing agent, Au NPs formed on the surface of F/S-ZnO MPs with appropriate size and distribution, generating a high density of “hot spots” that significantly enhanced the SERS effect. However, excessive reducing agent led to the formation of oversized or aggregated Au NPs, reducing the number of “hot spots”, thereby diminishing the SERS activity. Similarly, prolonged boiling time caused the agglomeration of Au NPs, adversely affecting the SERS performance. Three distinct laser excitation wavelengths (532, 633, and 785 nm) were employed to acquire the SERS spectra of 4-MPy on the prepared substrates. As illustrated in Figure S4, the 785 nm laser excitation demonstrated optimal SERS performance. Higher Au concentrations exhibit enhanced LSPR responses in the near-infrared region. Consequently, the 785 nm laser excitation likely maximizes the coupling efficiency with Au LSPR modes, thereby yielding superior SERS enhancement. 4-MPy at a concentration of 1×10 − 6 mol/L was employed as the Raman probe molecule to validate the SERS effect of ZnO-Au MPs. Pure ZnO MPs and Au NPs as the SERS substrates were used as control groups. From the result of SERS response that is depicted in Fig. 3, it can be observed that the SERS intensity of 4-MPy on ZnO-Au MPs is significantly higher than that on pure ZnO MPs and Au NPs for both F-ZnO-Au MPs and S-ZnO-Au MPs. The enhanced SERS performance of ZnO-Au MPs could be the result of the synergistic effects of optimized plasmonic resonance and charge transfer. The uniform surface curvature of spherical ZnO MPs facilitates the homogeneous decoration of Au NPs, resulting in uniformly dense nanogaps that generate strong LSPR coupling effects. In contrast, the flower-like ZnO MPs contain abundant voids, which provids ample space and promotes rapid diffusion of reactant molecules, also tends to induce aggregation of Au NPs, thereby compromising SERS activity. As evidenced by the SEM images in Fig. 2, Au NPs exhibit significant aggregation on F-ZnO MPs. When Au NPs undergo extensive aggregation, the number of “hot spot” regions is markedly reduced, leading to a noticeable weakening of the SERS effect. The sensitivity of the two composite substrates was evaluated using 4-MPy as the probe molecule. Compared to F-ZnO-Au MPs, S-ZnO-Au MPs demonstrates superior SERS signal enhancement across all tested concentrations of 4-MPy (Fig. 3C and Figure S5). Figure S5 illustrates that the Raman intensity decline with the decrease of the concentration of 4-MPy. Even the concentration is 1×10 − 8 mol/L, the characteristic peak is clearly observed. The enhancement factor (EF) of 5.5×10 7 that S-ZnO-Au MPs for 4-MPy was calculated according to the following formula (Eq. (1)): EF = (C Raman I SERS ) / (C SERS I Raman ) (1) Where C Raman is the concentration of 4-MPy could generate normal Raman signal and C SERS is the concentration of 4-MPy on S-ZnO-Au MPs. I SERS and I Raman are the SERS intensity of 4-MPy on S-ZnO-Au MPs and the normal Raman intensity of 4-MPy at 1105 cm − 1 , respectively. Raman spectrum of 4-MPy and SERS spectrum of 4-MPy on S-ZnO-Au MPs are shown in Figure S6. The detailed calculation process is in supporting information. High EF indicates the excellent SERS sensitivity of S-ZnO-Au MPs. Figure 3D illustrates the schematic representation of 4-MPy molecules adsorbed on the S-ZnO-Au MPs substrate. The 4-MPy molecules interact with the ZnO-Au MPs substrate via the -SH group, forming S-Au or S-Ti bonds that serve as electron transfer channels between the substrate and the molecules. This interaction facilitates changes in molecular polarizability, thereby enhancing the Raman signal. The uniformity, stability, and batch-to-batch reproducibility of the substrate material directly influence the accuracy of quantitative analysis. Therefore, these properties were investigated for S-ZnO-Au MPs. 20 points on the surface of S-ZnO-Au MPs containing 4-MPy molecules were randomly selected for SERS detection. The result shows that the relative standard deviation (RSD) calculated based on the Raman intensity at 1105 cm⁻¹ is 5.04% (Figure S7A, B), indicating excellent detection uniformity. The Raman intensity of 4-MPy on S-ZnO-Au MPs from the same preparation batch decreased by 15.04% after 100 days of storage (Figure S7C, D), confirming the substrate's robust stability under ambient conditions over this period. Finally, the reproducibility of S-ZnO-Au MPs was examined. Three batches of substrates were selected, and three points on each batch were tested. The Raman intensity exhibits slight variation, with RSD of 4.90% (Figure S7E, F), demonstrating excellent preparation reproducibility. S-ZnO-Au MPs exhibit high uniformity, long-term stability, and excellent batch-to-batch reproducibility, making it a reliable substrate for precise quantitative SERS analysis. These properties ensure consistent and accurate performance in practical applications. 3.3 SERS Enhancement Mechanism of ZnO-Au MPs In this work, 4-MPy was employed as the probe molecule to investigate the SERS effect of the substrate. Under 785 nm (1.57 eV) laser excitation, the electromagnetic field produced by LSPR on the surface of Au plays a main role in the enhancement of Raman. Besides, the chemical enhancement main from electron transfer is not to be neglected. Based on the UV–Vis absorption spectra and the Tauc equation (the detail is in Supporting Information), the Tauc plots (Fig. 4A) were obtained, from which the band gap energies of F-ZnO MPs and S-ZnO MPs were calculated to be 3.14 eV and 3.10 eV, respectively. Compared to F-ZnO, S-ZnO exhibits a narrower bandgap, which facilitates the separation of electron-hole pairs and promotes electron transfer. Mott–Schottky plot (Fig. 4B) confirms the n-type semiconducting nature of S-ZnO MPs, as evidenced by the positive slope of the linear region. Based on the extracted flat-band potential and bandgap energy, the conduction band (E CB ) and valence band (E VB ) potentials are estimated to be − 3.783 eV and − 6.883 eV relative to the vacuum level, respectively (the detail calculation is in supporting information). Figure 4C presents the UV-Vis spectra of 4-MPy on different substrates. After mixing with 4-MPy and Au NPs, a distinct blue shift in the absorption peak of ZnO around 370 nm is observed. According to the literature [27] , it could be inferred that Au NPs act as electron donor in this hybrid system, transferring electrons to conduction band of ZnO. Simultaneously, the UV absorption peak of 4-MPy at 220 nm also exhibits a blue shift. When 4-MPy is adsorbed on the surface of ZnO or ZnO-Au, the intramolecular π-π* transition may be constrained due to coordination effects (e.g., formation of Zn-S bonds), leading to the blue shift of the absorption peak. This indicates the presence of charge transfer between the substrate and the probe molecule. Photoluminescence (PL) spectroscopy was employed to determine the recombination ratio of photoexcited electron-hole pairs (Fig. 4D). Compared to pure S-ZnO, the fluorescence intensity decreases after introduction of 4-MPy molecules, suggesting electron transfer from S-ZnO to 4-MPy, which reduces the electron-hole recombination efficiency within S-ZnO, manifesting as a decrease in fluorescence intensity. After the introduction of Au NPs, the fluorescence intensity of S-ZnO further decreases, indicating that ZnO-Au complex structure is more advantage to this electron transfer process. Figure 4E shows the solid-state Raman spectrum of 4-MPy and its SERS spectra on Au NPs and F/S-ZnO-Au MPs substrates. According to the literature [31, 32] , the peaks at 1031, 1219, and 1602 cm − 1 are assigned to the symmetric vibration of a 1 mode. The peaks at 1064 cm − 1 and 1320 cm − 1 are attributed to the nonsymmetric b 2 mode (the detail band assignments of 4-MPy are listed in supporting information Table S1). The a 1 mode is mainly attributed to SPR contribution and the b 2 mode’s intensity originates from the CT contribution. To quantify the CT contribution to SERS, the peaks at 1031 cm − 1 (a 1 ) and 1064 cm − 1 (b 2 ) are selected to calculate the degree of CT (ρ CT ), according the following formula [33] (Eq. (2)): ρ CT = \(\:\:\frac{{\text{I}}_{\text{1064}}\text{/}{\text{I}}_{\text{1031}}}{\text{1}\text{+}{\text{I}}_{\text{1064}}\text{/}{\text{I}}_{\text{1031}}}\) (2) The ρ CT of F-ZnO-Au MPs and S-ZnO-Au MPs are calculated as 30.44% and 35.59%, respectively. This result demonstrates that all 4-MPy/ZnO-Au MPs systems present a remarkable 𝜌 CT value, and the value for S-ZnO-Au MPs is higher than that for F-ZnO-Au MPs, meaning a more significant contribution of CT enhancement in S-ZnO-Au MPs system. It worth note that, the Raman signal of 4-MPy on Au is weak and the degree of peak shift (compare the peak of solid 4-MPy) is small. The ρ CT value of 4-MPy/Au is 24.60%, suggesting that ZnO has a large contribution to CT effect and subsequently enhance the Raman intensity. In summary, ZnO, a typical n-type semiconductor, more electrons congregate the surface. The electrons congregated at the surface of ZnO will be injected into the Fermi level of the Au when Au is in contact with it. This will induce that the Fermi level of the Au will be elevated until the charges at the junction of gold and ZnO are balanced, which augments the CT from the Au to the 4-MPy molecules in the S-ZnO-Au MPs-4-MPy system. Meanwhile, a Schottky junction is formed on the interface of Au and ZnO (Fig. 4F). ZnO, in the S-ZnO-Au MPs assembly, also plays a role in transmitting the electrons by its conduction band. Under 785 nm laser excitation, the LSPR of Au generates electromagnetic enhancement. The laser energy facilitates the transfer of electrons from the Fermi level of Au to the conduction band of ZnO and then transmit to the lowest unoccupied molecular orbital (LUMO) level of 4-MPy. This process may require additional energy that supplied by hot electrons or tunneling effects [34, 35] . Additionally, charge transfer may occur from the highest occupied molecular orbital (HOMO) level of 4-MPy to the valence band of ZnO. This promotes charge separation and changes in molecular polarizability, thereby enhancing the Raman signals. 3.4 Measurement of MBT To evaluate the practical application capability of S-ZnO-Au MPs, the environmental pollutant molecule MBT was detected by using portable Raman spectrometer. Figure S8 shows the Raman spectrum of MBT and its SERS spectrum on S-ZnO-Au MPs. The SERS enhancement effect of S-ZnO-Au MPs for MBT is significant, and the assignments of the relevant peaks are listed in Table S2 [36] . Figure 5A is SERS spectra of MBT with different concentrations. It can be observed that the SERS signal intensity gradually diminishes as the concentration of MBT decreases. The characteristic Raman peaks remain observable even when the MBT concentration is as low as 10 − 8 mol/L, which demonstrates the significant detection sensitivity of S-ZnO-Au MPs. To investigate the correlation between MBT signal intensity and concentration, the Raman peak intensity at 1249 cm − 1 was plotted against MBT concentration within the range from 1.0×10 − 8 to 1.0×10 − 4 mol/L, as shown in Fig. 5B. The linear fitting yielded the equation: I = 7971.59 log C + 69578.68 (R 2 = 0.9901) Where I is the SERS intensity peaked at 1249 cm⁻¹ and C is the concentration of MBT. The LOD of this presented SERS system for MBT is 1.42×10 − 10 mol/L, which is concluded according to IUPAC method [37] (process of the calculation is in supporting information). These results indicate this semiconductor-based SERS substrate can be applied to highly sensitive and quantitative detection of MBT. 3.5 Application in real samples The feasibility of the S-ZnO-Au MPs composite in real samples measurement is further assessed through detection of MBT in seawater, lake water and tap water, respectively. Figure 6 present the quantitative spiked detection of MBT in these samples. Among these, the highest sensitivity was achieved for MBT detection in lake water, with a LOD as low as 1.0×10 − 10 mol/L. The lowest sensitivity was observed in seawater, likely due to the high concentration of electrolytes in seawater. These ions may reduce the adsorption capacity of MBT molecules on the substrate surface through electrostatic shielding effects. Additionally, the high salt content may induce aggregation or surface passivation of Au nanoparticles, compromising the stability and enhancement efficiency of the SERS substrate. Tap water, with its lower electrolyte concentration compared to seawater, still contains trace disinfectants and dissolved inorganic salts. These components may partially occupy the active sites of the nanomaterials or compete with MBT for adsorption, resulting in lower sensitivity than in lake water. In contrast, lake water, as a natural freshwater system, exhibits the lowest electrolyte concentration. Organic impurities may enhance the enrichment of MBT on the nanomaterial surface through hydrophobic interactions, thereby improving the efficiency of interactions between the substrate and MBT. Moreover, the matrix complexity of lake water is relatively low, making it more controllable for experimental analysis. For demonstrating the reliability of this S-ZnO-Au MPs based SERS assay, different concentrations MBT was spiked in lake water obtaining the spiked real sample (5.0, 0.5, 0.05 µmol/L) to measure the recovery. The result shown in Table 1, the recoveries ranged from 100% ~110% with an acceptable RSD (n = 3). The against-interference of this S-ZnO-Au MPs-based SERS platform is investigated by addition of different possible coexisting substances in lake water, including high concentrations (10 − 5 mol/L) of various salt ions, salt compounds, humic acid, as well as structurally similar compounds such as benzothiazole (BT) and 2-mercaptobenzimidazole (MBI). The lake water samples containing above species were measured using this prepared SERS sensor, and the result is shown in Fig. 7. As exhibit in SERS spectra (Fig. 7A), the characteristic peak of MBT can’t be observed from samples containing interference materials, indicating excellent selectivity for MBT detection, as evidenced by the histogram drawn by characteristic Raman peak observed at 1249 cm⁻¹ (Fig. 7B). Table 1 Detection recovery of MBT in lake water by S-ZnO-Au based SERS. Samples Spiked MBT (µmol/L) Found by SERS (µmol/L) Recovery ± RSD (%) No.1 5.00 5.44 108.8 ± 0.05 No.2 0.50 0.51 101.0 ± 0.03 No.3 0.05 0.05 109.3 ± 0.08 3.6 Photocatalytic Degradation To investigate the capacity of photocatalytic degradation of this semiconductor- metal composite material, the photocatalytic degradation experiment of MBT was conducted under Xenon lamp irradiation. After undergoing the illumination, the UV-Vis and Raman characteristic signal of MBT were collected and their intensity decrease (Fig. 8). When the illumination time is 50 min, the 98% degradation efficiency is achieved, indicating the excellent performance in photocatalytic degradation. It worth noted, from the signals of low concentrations MBT, it can be seen that the Raman method is more sensitive than UV-Vis for detecting the residue of MBT. The proposed degradation mechanism is deduced as follows: Under light irradiation, ZnO-Au absorbs energy, inducing electron transitions and generating electron-hole pairs. These electron-hole pairs interact with adsorbed H 2 O and O 2 on the surface, producing highly reactive hydroxyl radicals (·OH) and superoxide radicals (O 2 ⁻·). These radicals oxidize the MBT molecules adsorbed on the material surface, thereby achieving catalytic degradation. Conclusion Two distinct morphologies of S/F-ZnO-Au MPs semiconductor-noble metal composite materials were successfully synthesized by using hydrothermal and in-suit reduction method. The physicochemical properties of the composite materials were characterized using various techniques. S-ZnO-Au MPs exhibit superior SERS activity compared to F-ZnO-Au MPs due to its smooth spherical surface structure, which enables the ordered arrangement of Au NPs, preventing inefficient aggregation. Investigation of the enhancement mechanisms revealed that the synergistic effects of electromagnetic field enhancement and chemical enhancement significantly improved the SERS detection sensitivity with EF of 5.5×10 7 . On this basis, the S-ZnO-Au MPs-based SERS detection strategy was applied to detection of MBT in environmental water, achieving a LOD of 1.42×10 − 10 mol/L. Additionally, ZnO-Au exhibited excellent photocatalytic degradation performance for MBT, achieving approximately 98% degradation efficiency within 50 minutes. Combined with the portable Raman spectrometer, the semiconductor-noble metal composite SERS substrates developed in this work hold great potential for the on-site rapid detection and photocatalytic degradation of harmful substances in aquatic environments. Declarations Credit authorship contribution statement Jiangli Shi : Visualization, Validation, Methodology, Investigation, Formal analysis, Data curation. Boran Zhang : Writing–review & editing, Visualization, Validation, Methodology, Investigation. Li Zhang : Methodology, Investigation, Formal analysis. Xinling Liu : Methodology, Investigation. Yiping Wu : Investigation. Ying Wen : Investigation. Haifeng Yang : Writing – review & editing, Supervision,Funding acquisition. Xiaoyu Guo : Writing – review & editing, Supervision. Acknowledgements This work was partly supported by the National Natural Science Foundation of China (No. 22374100); Shanghai Engineering Research Center of Green Energy Chemical Engineering (18DZ2254200); International Joint laboratory on Resource Chemistry (IJLRC); Shanghai Key Laboratory of Rare Earth Functional Materials, Shanghai Municipal Education. Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References Li, D.; Fan, Z. 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Supplementary Files supportinginformation.docx GraphicalAbstract.jpg GA Scheme1.jpg Scheme 1 The preparation of F-ZnO-Au MPs and S-ZnO-Au MPs and their application in SERS detection of MBT Cite Share Download PDF Status: Published Journal Publication published 13 Oct, 2025 Read the published version in Microchimica Acta → Version 1 posted Editorial decision: Revision requested 27 Aug, 2025 Reviews received at journal 27 Aug, 2025 Reviews received at journal 25 Aug, 2025 Reviews received at journal 25 Aug, 2025 Reviewers agreed at journal 12 Aug, 2025 Reviewers agreed at journal 11 Aug, 2025 Reviewers agreed at journal 10 Aug, 2025 Reviewers invited by journal 10 Aug, 2025 Editor assigned by journal 07 Aug, 2025 Submission checks completed at journal 06 Aug, 2025 First submitted to journal 02 Aug, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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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-7281108","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":499446841,"identity":"2c0f38b0-4977-49ab-a7b9-6a21cd070730","order_by":0,"name":"Jiangli Shi","email":"","orcid":"","institution":"Ministry of Education, Shanghai Normal University","correspondingAuthor":false,"prefix":"","firstName":"Jiangli","middleName":"","lastName":"Shi","suffix":""},{"id":499446842,"identity":"7891cc54-f644-49fb-ae09-642d58e1d697","order_by":1,"name":"Boran Zhang","email":"","orcid":"","institution":"Ministry of Education, Shanghai Normal University","correspondingAuthor":false,"prefix":"","firstName":"Boran","middleName":"","lastName":"Zhang","suffix":""},{"id":499446843,"identity":"2c54b9db-46b5-4a18-b1ef-e818fcbe1564","order_by":2,"name":"Li Zhang","email":"","orcid":"","institution":"Ministry of Education, Shanghai Normal University","correspondingAuthor":false,"prefix":"","firstName":"Li","middleName":"","lastName":"Zhang","suffix":""},{"id":499446844,"identity":"c268c951-fed3-425c-9e25-5e9870b1eda2","order_by":3,"name":"Xinling Liu","email":"","orcid":"","institution":"Ministry of Education, Shanghai Normal University","correspondingAuthor":false,"prefix":"","firstName":"Xinling","middleName":"","lastName":"Liu","suffix":""},{"id":499446845,"identity":"0cfd032e-6d91-4eb3-8766-f8d2da9543e3","order_by":4,"name":"Yiping Wu","email":"","orcid":"","institution":"Ministry of Education, Shanghai Normal University","correspondingAuthor":false,"prefix":"","firstName":"Yiping","middleName":"","lastName":"Wu","suffix":""},{"id":499446846,"identity":"e10063c4-74b5-4238-b3e0-6387102c1fdf","order_by":5,"name":"Ying Wen","email":"","orcid":"","institution":"Ministry of Education, Shanghai Normal University","correspondingAuthor":false,"prefix":"","firstName":"Ying","middleName":"","lastName":"Wen","suffix":""},{"id":499446847,"identity":"b46dfae8-5f93-47ca-8285-e8cdcc2df6b6","order_by":6,"name":"Haifeng Yang","email":"","orcid":"","institution":"Ministry of Education, Shanghai Normal University","correspondingAuthor":false,"prefix":"","firstName":"Haifeng","middleName":"","lastName":"Yang","suffix":""},{"id":499446848,"identity":"eb554223-0aa3-4a55-8e8e-6fc1f6a9cca1","order_by":7,"name":"Xiaoyu Guo","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA30lEQVRIiWNgGAWjYHACxgcJBjZyDBJgDjNRWpgNPhSkGZOkhU1yxofDiQ1Ea5GPyDGQ5jFgTp8/u/eYBEOFdWID+9kDeLUYnjljYMxjwJa74c65NAmGM+mJDTx5Cfi1tPcYJPMY8ORukMgxk2BsA7mQxwC/lmYeg8M8BhLp8jNAWv4RoUWevcewcYaBQQLDDZCWBiK0GPAcK2b4YJBguOFGjrFFwrF04zaeHAK2zEje/iPhz395oMMMb3yosZbtZz9DwJYDHEgKEoCYDa96kC0N7A8IqRkFo2AUjIKRDgAnU0JM9bFqQgAAAABJRU5ErkJggg==","orcid":"","institution":"Ministry of Education, Shanghai Normal University","correspondingAuthor":true,"prefix":"","firstName":"Xiaoyu","middleName":"","lastName":"Guo","suffix":""}],"badges":[],"createdAt":"2025-08-03 03:53:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7281108/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7281108/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00604-025-07592-1","type":"published","date":"2025-10-13T15:58:30+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":89101570,"identity":"8555486c-c1cb-4635-a5d7-07faaa927c21","added_by":"auto","created_at":"2025-08-14 16:21:10","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":113114,"visible":true,"origin":"","legend":"\u003cp\u003e(A) UV-Vis spectra of (a) S-ZnO MPs, (b) S-ZnO-Au MPs, (c) F-ZnO MPs, (d) F-ZnO-Au MPs; SEM images of (B) F-ZnO MPs and (C) S-ZnO MPs with different magnifications\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7281108/v1/ae3662a54f9fbc3736446e83.jpg"},{"id":89102646,"identity":"5060fadf-8d43-4ef9-9d0a-b3810c374b79","added_by":"auto","created_at":"2025-08-14 16:29:10","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":214418,"visible":true,"origin":"","legend":"\u003cp\u003eSEM and EDX images of (A) F-ZnO-Au MPs, (B) S-ZnO-Au MPs. (a, b are the SEM images; c-f are the EDX images)\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7281108/v1/d4569a610966051344d201ce.jpg"},{"id":89101573,"identity":"26ed2c6c-2c99-46a7-91d4-0ff922fae3ea","added_by":"auto","created_at":"2025-08-14 16:21:10","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":92745,"visible":true,"origin":"","legend":"\u003cp\u003eSERS spectra of 4-MPy (1×10\u003csup\u003e-6\u003c/sup\u003e mol/L) on different substrates (A) F-ZnO-Au MPs and (B) S-ZnO-Au MPs and their control groups; (C)The comparison of the Raman intensity at 1105 cm\u003csup\u003e-1\u003c/sup\u003e of 4-MPy with different concentrations on F-ZnO-Au MPs and S-ZnO-Au MPs; (D) The scheme of 4-MPy on the surface of S-ZnO-Au MPs\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7281108/v1/bc3d26808985662683060fdd.jpg"},{"id":89101574,"identity":"e1995982-bd5f-465e-81a0-a6b0636d13c7","added_by":"auto","created_at":"2025-08-14 16:21:10","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":99813,"visible":true,"origin":"","legend":"\u003cp\u003e(A) The Tauc plot of F-ZnO and S-ZnO; (B) The Mott-Schottky plot of S-ZnO; (C) UV-Vis spectra of ZnO, 4-MPy and the mixture of 4-MPy with different substrates; (D) Photoluminescence spectra of ZnO, ZnO-Au and ZnO-Au-4-MPy; (E) From bottom to top is Raman spectrum of 4-MPy (solid) and SERS spectra of 4-MPy on Au and F-ZnO-Au MPs, S-ZnO-Au MPs; (F) Scheme of electron transfer path\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7281108/v1/bcd5d649f83569477d1f34eb.jpg"},{"id":89102973,"identity":"b345b9de-e211-480c-82d7-553886e05213","added_by":"auto","created_at":"2025-08-14 16:37:10","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":69977,"visible":true,"origin":"","legend":"\u003cp\u003e(A) SERS spectra of MBT with different concentrations (1×10\u003csup\u003e-8\u003c/sup\u003e ~1×10\u003csup\u003e-4\u003c/sup\u003e mol/L) on S-ZnO-Au MPs. (B) The concentration linear relationship of MBT ranging from 10\u003csup\u003e−8\u003c/sup\u003e to 10\u003csup\u003e−4\u003c/sup\u003e mol/L (R\u003csup\u003e2\u003c/sup\u003e = 0.9901). Each point is the mean of three replicate sample measurements. Error bars indicate standard deviation\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7281108/v1/a17cbb2a5de1935b55f2b1eb.jpg"},{"id":89101580,"identity":"f1c4f18f-6015-41d1-b02c-7521ece63cfa","added_by":"auto","created_at":"2025-08-14 16:21:10","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":107940,"visible":true,"origin":"","legend":"\u003cp\u003eSERS spectra of different concentrations MBT in (A) sea water, (B) lake water, (C) tap water\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7281108/v1/df3f58c23e35ecdec06c016b.jpg"},{"id":89101578,"identity":"b12de58c-8209-4cf5-adc0-e597dc1744a1","added_by":"auto","created_at":"2025-08-14 16:21:10","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":75100,"visible":true,"origin":"","legend":"\u003cp\u003e(A) SERS spectra of MBT (1×10\u003csup\u003e-6\u003c/sup\u003e mol/L) and other coexisting substances (1×10\u003csup\u003e-5\u003c/sup\u003e mol/L) on S-ZnO-Au MPs, the species from bottom to top are: Ca\u003csup\u003e2+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e, CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e, NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e, NaCl, MgSO\u003csub\u003e4\u003c/sub\u003e, HA, BT, MBI, and MBT; (B) The histogram of Raman intensity at 1249 cm\u003csup\u003e-1\u003c/sup\u003e versus species\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7281108/v1/8081f69ecd4be57d7bf9ca94.jpg"},{"id":89101579,"identity":"02e6a099-a1b5-4513-8c21-7729f9e0ce87","added_by":"auto","created_at":"2025-08-14 16:21:10","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":80200,"visible":true,"origin":"","legend":"\u003cp\u003e(A) UV-Vis spectrum of pure MBT; (B) The UV-Vis signals change with the photocatalytic degradation time; (C) The Raman signals change with the photocatalytic degradation time; (D) The dependence relation between the Raman intensity at 1249 cm\u003csup\u003e-1\u003c/sup\u003e and the photocatalytic degradation time\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7281108/v1/e767266acc657f2aafa277d5.jpg"},{"id":93956089,"identity":"945244c0-7034-4c96-a2a6-011b5f4d5873","added_by":"auto","created_at":"2025-10-20 16:10:21","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1822904,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7281108/v1/25389223-ae99-41a9-a7a8-dafa59319d0c.pdf"},{"id":89102974,"identity":"7a20fb55-4d57-47c7-9f86-1e2e617b7e43","added_by":"auto","created_at":"2025-08-14 16:37:10","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1661382,"visible":true,"origin":"","legend":"","description":"","filename":"supportinginformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-7281108/v1/540d622b468ef23f932eaaaa.docx"},{"id":89101571,"identity":"2009b426-2356-4fd5-a878-d8fc87707b90","added_by":"auto","created_at":"2025-08-14 16:21:10","extension":"jpg","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":66748,"visible":true,"origin":"","legend":"\u003cp\u003eGA\u003c/p\u003e","description":"","filename":"GraphicalAbstract.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7281108/v1/b6ed72690e01662177c17965.jpg"},{"id":89101572,"identity":"0a33992a-a498-4f6e-93f8-5548298bef5c","added_by":"auto","created_at":"2025-08-14 16:21:10","extension":"jpg","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":71762,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme 1\u003c/strong\u003e The preparation of F-ZnO-Au MPs and S-ZnO-Au MPs and their application in SERS detection of MBT\u003c/p\u003e","description":"","filename":"Scheme1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7281108/v1/3c4c991e47bc59e3ae30352c.jpg"}],"financialInterests":"No competing interests reported.","formattedTitle":"ZnO microsphere decorated with Au nanoparticles for SERS detection and removal of trace 2-Mercaptobenzothiazole in environmental water","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003e2-Mercaptobenzothiazole\u0026nbsp;(MBT, C7H5NS2) has attracted significant attention due to its extensive industrial applications and potential ecological risks. MBT is a stable heterocyclic structure composed of a benzene ring and a thiazole ring, with a mercapto group (-SH) that provides excellent antioxidant and coordination properties. However, these same properties contribute to its persistent accumulation in aquatic environments. Previous studies have demonstrated that MBT exhibits acute toxicity toward aquatic organisms, adversely affecting the growth and reproduction of fish and, in severe cases, leading to mortality\u003csup\u003e[1]\u003c/sup\u003e. Furthermore, through biomagnification in the food chain, MBT poses a serious threat to human health and has been classified as a Group 2A carcinogen by regulatory authorities \u003csup\u003e[2]\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eTo effectively mitigate the potential hazards of MBT to the environment and human health, the development and implementation of efficient detection and removal methods are crucial. Current analytical techniques for MBT detection include high-performance liquid chromatography\u003csup\u003e\u0026nbsp;\u003c/sup\u003e(HPLC)\u0026nbsp;\u003csup\u003e[3,4]\u003c/sup\u003e, electrochemical analysis \u003csup\u003e[5]\u003c/sup\u003e, and ultraviolet-visible spectrophotometry\u003csup\u003e\u0026nbsp;[6,7]\u003c/sup\u003e. For instance, Rennie \u003csup\u003e[3]\u003c/sup\u003e developed HPLC method for detection of MBT in river water, achieving limit of detection (LOD) 4.8 nmol/L. Xiong\u0026rsquo;s group\u003csup\u003e[7]\u003c/sup\u003e reported a colorimetric sensor integrating photoinduced Au nanoparticles formation inhibition with salt-assisted liquid\u0026ndash;liquid microextraction, realizing MBT detection with the LOD of 0.024 \u0026mu;mol/L. While these conventional techniques offer high selectivity and sensitivity, they often suffer from drawbacks such as complex sample preparation procedures and high operational costs.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eTherefore,\u0026nbsp;novel analytical platforms characterized by simplified protocols, cost-effectiveness, and enhanced detection capabilities are urgently required. \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eSurface-enhanced Raman scattering (SERS) technology, leveraging the synergistic effects of localized electromagnetic field enhancement and chemical enhancement, enables high sensitivity and rapid non-destructive analysis \u003csup\u003e[8,9]\u003c/sup\u003e. It has been widely applied in surface science \u003csup\u003e[10]\u003c/sup\u003e, biomedicine \u003csup\u003e[11]\u003c/sup\u003e and environmental pollutant monitoring \u003csup\u003e[12]\u003c/sup\u003e. Generally, noble metal nanoparticles (Au, Ag) are widely used as SERS-active substrates because of their unique localized surface plasmonic resonance (LSPR) effect with laser excitation, which supports the intense electromagnetic field around the metal surface\u003csup\u003e[13,14]\u003c/sup\u003e. However, the high value of precursor materials and the poor stability of metal nanostructures against pH, temperature, light, and oxygens largely hinder the application in real samples. In this sense, as an ideal alternatives for plasmonic metal SERS substrates, semiconductor materials (e.g., ZnO, TiO\u003csub\u003e2\u003c/sub\u003e, MoS\u003csub\u003e2\u003c/sub\u003e) have become hotspot SERS substrate, because they are considerably cheaper, easy to fabricate, chemically more stable, tunable band structures, excellent photostability, and biocompatibility\u003csup\u003e[15\u0026ndash;17]\u003c/sup\u003e. Nevertheless, the potential in applications is hardly fulfilled for pure semiconductor SERS substrates, because the limited enhancement capabilities are mainly from chemical enhancement, in other words, the enhancement signal is almost exclusively from charge transfer resonance between analytes and semiconductors. In addition, only few model analytes that chemically adsorb on the surface of semiconductors could be permitted signal enhancement, which also restricts the real application for semiconductor SERS substrates.\u003c/p\u003e\n\u003cp\u003eIn recent studies, it has been reported that semiconductors-metal hybrid substrates such as Ag-TiO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e[18]\u003c/sup\u003e, Ag-ZnO\u003csup\u003e[19]\u0026nbsp;\u003c/sup\u003ehave highly sensitive SERS response due to the noble metal/semiconductor nanocomposites can generate an charge transfer effect at the interface of metal/semiconductor except electromagnetic effect on metal. Such composite architectures effectively lower material costs while significantly improving stability compared to pure metal nanostructures. Especially, ZnO, as an ideal candidate for semiconductor SERS substrates, exhibits excellent photostability, biocompatibility, and superior SERS activity compared to other semiconductor nanomaterials \u003csup\u003e[20,21]\u003c/sup\u003e. Its abundant raw materials and low preparation cost make it suitable for large-scale production and practical applications\u003csup\u003e[22]\u003c/sup\u003e. Therefore, ZnO can be served as an ideal supporting for the uniform loading of metal nanoparticles and ultimately improve the sensitivity and stability of SERS signals. For example, Chen and coworkers \u003csup\u003e[23]\u003c/sup\u003e fabricated a ZnO/Ag composite substrate by growing Ag nanoparticles on ZnO nanorods, enabling the detection and photocatalytic degradation of Rhodamine B with a LOD of 1 \u0026times; 10⁻\u0026sup1;\u0026sup1; mol/L. Yang\u0026rsquo;s group \u003csup\u003e[24]\u003c/sup\u003e developed ZnO/Au-based SERS platform for detecting nicotine, and the LOD is obtained of 8.9 \u003cem\u003e\u0026times;\u0026nbsp;\u003c/em\u003e10\u003cem\u003e\u003csup\u003e-\u003c/sup\u003e\u003c/em\u003e\u003csup\u003e12\u003c/sup\u003e mol/L. However, highly sensitive and stable ZnO-based hybrid substrates is urgently needed to explore for measurement of MBT in water environment.\u003c/p\u003e\n\u003cp\u003eIn this work, we propose a novel strategy for detection of MBT in water environments by preparing ZnO-Au composites with different morphologies (Scheme 1). Flower-like (F-ZnO) and spherical (S-ZnO) ZnO microspheres were first synthesized via a hydrothermal method, followed by in situ reduction to coat Au nanoparticles (Au NPs), termed F/S-ZnO-Au MPs. Compared to F-ZnO-Au MPs, S-ZnO-Au MPs exhibit advantages in sensitivity, uniformity, reproducibility, and stability as active SERS substrates. Finally, S-ZnO-Au MPs were used for SERS detecting MBT in environmental water. Leveraging the excellent photocatalytic properties of ZnO, the efficient catalytic degradation of MBT by ZnO-Au MPs under xenon lamp irradiation after detection was studied, realizing an integrated \u0026ldquo;detection-remediation\u0026rdquo; function. This enhances the practical application potential of the material in real-world samples. \u0026nbsp;\u003c/p\u003e"},{"header":"2. Experimental section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Reagents\u003c/h2\u003e\u003cp\u003eChloroauric acid (HAuCl\u003csub\u003e4\u003c/sub\u003e\u0026middot;4H₂O), zinc nitrate hexahydrate (Zn(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO), MgSO\u003csub\u003e4\u003c/sub\u003e, and n-butanol (C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e10\u003c/sub\u003eO) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Sodium dodecyl sulfate (C\u003csub\u003e12\u003c/sub\u003eH\u003csub\u003e25\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003eNa, SDS), NaCl, KCl, CaCO\u003csub\u003e3\u003c/sub\u003e, zinc acetate dihydrate (Zn(Ac)\u003csub\u003e2\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO), 2-Mercaptobenzothiazole (MBT), humic acid, 2-Mercaptobenzimidazole (MBI), and Benzothiazole (BT) were obtained from Adamas (China). Trisodium citrate dihydrate (Na\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e5\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO) and 4-mercaptopyridine (C\u003csub\u003e5\u003c/sub\u003eH\u003csub\u003e5\u003c/sub\u003eNS, 4-MPy) were procured from Sigma-Aldrich (USA). Urea (NH\u003csub\u003e2\u003c/sub\u003eCONH\u003csub\u003e2\u003c/sub\u003e) was purchased from General Reagent Company. All chemicals and reagents were of analytical grade. Ultrapure water (18.2 MΩ\u0026middot;cm) was used for all experiments. Lake water was collected from XueSi Lake in campus of Shanghai Normal University, which is connected from the Caohejing River outside the campus. Sea water was obtained from the East China Sea. Tap water was collected in lab. Glassware was soaked in aqua regia, boiled, and thoroughly rinsed with ultrapure water.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Experimental Instruments\u003c/h2\u003e\u003cp\u003eUltraviolet-visible (UV-Vis) spectra were collected using a UV-Vis spectrophotometer (SHIMADZU, UV-1800, Japan). X-ray photoelectron spectroscopy (XPS, Shimadzu Kratos, Japan) and X-ray diffraction (XRD, RIGAKU, Japan) were employed to determine the crystal structure and chemical composition of ZnO-Au MPs. Fluorescence spectra was collected by fluorescence spectrophotometer (Varian, Cary Eclipse). The morphology of the materials was observed using a scanning electron microscope (SEM, Gemini SEM 300, Carl Zeiss, Germany) at an accelerating voltage of 40 kV and transmission electron microscopy (TEM, JEOL, JEM-2100EXII, Japan) operating at 200 kV. Raman signals were acquired using a Dilor confocal laser Raman system (SuperLabRamII, France) with an excitation wavelength of 633 nm, laser power of 7 mW, and acquisition time of 8 s with 3 accumulations. On-site Raman detection was performed using a portable Raman spectrometer (Zolix, Beijing, China) with an excitation wavelength of 785 nm, laser power of 150 mW, and an acquisition time of 8 s per spectrum, with 3 accumulations.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Preparation of ZnO microsphere\u003c/h2\u003e\u003cp\u003eThe synthesis of F-ZnO microsphere follows previous report\u003csup\u003e[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]\u003c/sup\u003e. 0.25 g of SDS was dissolved in 10 mL of n-butanol, followed by the addition of 30 mL of deionized water. The mixture was stirred until a clear solution was formed, which is referred to as solution A. Simultaneously, Solution B was prepared by dissolving 5 mmol Zn(CH₃COO)₂\u0026middot;2H₂O and 40 mmol urea in 50 mL deionized water under 30 min stirring. Solution A was then added dropwise to solution B and the mixture was continuously stirred at room temperature for 2 hours. The resulting mixture was transferred into a Teflon-lined stainless steel autoclave and maintained at 100\u0026deg;C for 12 hours. After cooling the autoclave to room temperature, the white precipitate was collected by centrifugation and washed with ethanol and distilled water. The obtained solid was dried overnight at 60\u0026deg;C and subsequently calcined at 500\u0026deg;C for 2 hours in air to yield the final F-ZnO MPs.\u003c/p\u003e\u003cp\u003eAccording to the previous report\u003csup\u003e[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/sup\u003e, S-ZnO was synthesized. In brief, 1.12 g of Zn(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e, 0.45 g of urea, and 0.11 g of trisodium citrate dihydrate were dissolved in 75 mL of deionized water. The mixture was stirred for 20 minutes to ensure complete dissolution, after which it was transferred to a Teflon-lined stainless steel autoclave and heated at 120\u0026deg;C for 6 h. The resulting precipitate was washed with ethanol and deionized water, respectively. Finally, the collected solid was annealed at 350\u0026deg;C for 45 min for obtaining the final S-ZnO microsphere.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4 Preparation of ZnO-Au MPs\u003c/h2\u003e\u003cp\u003eApproximately 0.0150 g of prepared F/S-ZnO microspheres was dissolved in 25 mL of ultrapure water, and the solution was heated to a gentle boil while stirring. Under continuous stirring, 1 mL of 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e mol/L HAuCl\u003csub\u003e4\u003c/sub\u003e solution and 1.5 mL of 1% trisodium citrate solution were added. The mixture was stirred for 30 min until the solution turned deep purple, indicating the successful preparation of ZnO-Au MPs with different morphologies.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.5 SERS Measurement\u003c/h2\u003e\u003cp\u003eThe probe molecule 4-MPy, which is used to characterize the SERS active of this complex material, was mixed with the F/S-ZnO-Au MPs suspension in a 1:1 volume ratio for SERS test. Raman signals were acquired by using a 633 laser with a power of 7 mW, an acquisition time of 8 s, and 3 accumulations.\u003c/p\u003e\u003cp\u003eDifferent concentrations of MBT solution were prepared with stepwise dilution. Following the same procedure as the 4-MPy test, MBT solution mixed with F/S-ZnO-Au MPs suspension in a 1:1 volume ratio for Raman signal collecting, by using the portable Raman with 785 nm laser, 150 mW laser power, and a collection time of 8 s, with 3 accumulations.\u003c/p\u003e\u003cp\u003eFor real sample detection, different amounts of MBT were added to actual water samples to simulate real-world conditions. Before mixed with substrate material, the MBT-spiked samples were filtered with 0.45 \u0026micro;m filter membrane. Then, the lake water samples were thoroughly mixed with F/S-ZnO-Au MPs for subsequent SERS measurements, and the process of Raman signal collected is the same with the pure MBT test.\u003c/p\u003e\u003cp\u003eDifferent reference species might co-existing in lake water (concluding K\u003csup\u003e+\u003c/sup\u003e, Ca\u003csup\u003e2+\u003c/sup\u003e, CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e, NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e, NaCl, MgSO\u003csub\u003e4\u003c/sub\u003e, humic acid, BT and MBI) were used to study the anti-interference capability of this proposed SERS assay system. The process of the Raman test is the same as the detection of MBT.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec9\"\u003e\n \u003ch2\u003e3.1 Characterization of F/S-ZnO-Au MPs\u003c/h2\u003e\n \u003cp\u003eZnO microspheres with flower-like and sphere shapes were first synthesized by using hydrothermal method, followed Au NPs were grown on the surface of ZnO by in-situ reduction, obtaining the complex materials F/S-ZnO-Au MPs. The process of the synthesis as shown in Scheme1. For determining the optical properties, UV-Vis spectra test was first carried out and the results were shown in Fig. 1A. For the pure micrometer-sized ZnO particles, a distinct characteristic absorption peak is observed around 370 nm in the UV region, which is attributed to intrinsic band gap absorptionof ZnO due to the electronic transitions from the valence to the conduction band, confirming the successful synthesis of ZnO MPs \u003csup\u003e[26]\u003c/sup\u003e. Up on the in-situ reduction and incorporation of Au NPs on the ZnO surface, a prominent absorption band emerges at 533 nm, corresponding to the characteristic surface plasmon resonance absorption peak of Au NPs\u003csup\u003e[15]\u003c/sup\u003e. Additionally, a slight blue shift in the ZnO absorption peak was observed following Au modification, indicating charge transfer from the Au to the ZnO MPs \u003csup\u003e[27]\u003c/sup\u003e. These spectral changes collectively confirm the successful formation of Au-decorated ZnO MPs. In addition, the size of Au NPs was evaluated at about 43.6 nm (Supporting information), which is in the optimal size range that AuNPs possess the better SERS performance \u003csup\u003e[28]\u003c/sup\u003e.\u003c/p\u003e\n \u003cp\u003eFigure 1B and C are the scanning electron microscopic (SEM) images of F-ZnO MPs and S-ZnO MPs, respectively, and their magnification images. Figure\u0026nbsp;1B shows that the F-ZnO MPs present obvious flower-like shape with a size of 10 \u0026micro;m which is formed by the interlacing of sheet-like structures. In contrast, the S-ZnO MPs shown in Fig.\u0026nbsp;1C exhibit a relatively smooth surface with a similar diameter of about 10 \u0026micro;m.\u003c/p\u003e\n \u003cp\u003eAs shown in Fig.\u0026nbsp;2, the morphology and the size of ZnO happen slight changes after modifying Au NPs. This could be the function of solvent that used in the process of in-suit reduce preparation of Au NPs. The EDX images demonstrate that Au NPs were successfully coated on the surface of ZnO, and this result is in accordance with UV-Vis spectra in Fig.\u0026nbsp;1A.\u003c/p\u003e\n \u003cp\u003eFigure S1 shows the powder X-ray diffraction (XRD) pattern of the prepared materials. Diffraction peaks corresponding to pure F-ZnO and S-ZnO are observed. These diffraction peaks can be indexed to the (100), (002), (101), (102), (110), (103), and (112) crystal planes of hexagonal wurtzite structured ZnO (JCPDS # 36-1451). The absence of any impurity-related peaks indicates that the precursors were fully converted into phase-pure ZnO. After decoration of Au NPs on ZnO, the intensity of ZnO diffraction peaks is decreased and characteristic peaks emerge at 38.3\u0026deg; and 44.42\u0026deg; (2\u0026theta;). These new diffraction features correspond to the (111) and (200) crystallographic planes of metallic Au (JCPDS 04-0784), respectively. The XRD results indicate that Au NPs have successfully grown on the ZnO microspheres.\u003c/p\u003e\n \u003cp\u003eUsing S-ZnO-Au MPs as an example, we further confirmed the chemical composition and valence states of the elements in the material through X-ray photoelectron spectroscopy (XPS). In the XPS survey spectrum of ZnO (Figure S2a), C, O, and Zn elements was observed, and in the XPS survey spectrum of ZnO-Au MPs (Figure S2d), the Au element was detected. In the high-resolution XPS spectra of ZnO and ZnO-Au (Figures S2b, e), the binding energies for Zn 2p\u003csub\u003e1/2\u003c/sub\u003e and Zn 2p\u003csub\u003e3/2\u003c/sub\u003e were identified at 1040 eV and 1017 eV, respectively. These values correspond to the characteristic peaks of ZnO\u003csup\u003e[29]\u003c/sup\u003e, and it has slight change after modification of Au for the binding energy of Zn 2p. Figure S2c displays the deconvoluted O 1s spectrum, which exhibits three characteristic peaks at 526.3 eV, 528.1 eV, and 529.7 eV. These binding energies are slightly lower than typical values, likely due to electron transfer between ZnO and Au, which increases the electron density around the oxygen atoms and consequently reduces the binding energy. In Figure S2f, the binding energies of Au 4f\u003csub\u003e7/2\u003c/sub\u003e and Au 4f\u003csub\u003e5/2\u003c/sub\u003e were observed at 84.6 eV and 87.8 eV, respectively. Compared to the Au 4f\u003csub\u003e7/2\u003c/sub\u003e of metallic Au (83.9 eV) \u003csup\u003e[30]\u003c/sup\u003e, Au 4f\u003csub\u003e7/2\u003c/sub\u003e (84.6 eV) in ZnO-Au shifts to a high binding energy by 0.7 eV, indicating that Au loses some electrons, which could be the reason that the electrons transfer from Au NPs to ZnO, which is in agreement with that UV-Vis spectra test. Additionally, the peak at 79.3 eV may also result from interfacial charge transfer, leading to a shift in the binding energy of Au.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\"\u003e\n \u003ch2\u003e3.2 SERS performance of ZnO-Au MPs\u003c/h2\u003e\n \u003cp\u003eTo enhance the SERS activity of ZnO-Au MPs, the amount of reducing agent and the boiling time during the in-suit coating of Au NPs were optimized. 4-MPy was used as the probe molecule to respond the variation of SERS activity. As shown in Figures S3, for both F-ZnO-Au MPs and S-ZnO-Au MPs, the strongest SERS signal of 4-MPy was achieved when 1.5 mL of reducing agent was used and the solution was boiled for 30 min. The SERS activity of the complex materials initially increased and then decreased with increasing the amount of the reducing agent and the boiling time. At an optimal amount of reducing agent, Au NPs formed on the surface of F/S-ZnO MPs with appropriate size and distribution, generating a high density of \u0026ldquo;hot spots\u0026rdquo; that significantly enhanced the SERS effect. However, excessive reducing agent led to the formation of oversized or aggregated Au NPs, reducing the number of \u0026ldquo;hot spots\u0026rdquo;, thereby diminishing the SERS activity. Similarly, prolonged boiling time caused the agglomeration of Au NPs, adversely affecting the SERS performance.\u003c/p\u003e\n \u003cp\u003eThree distinct laser excitation wavelengths (532, 633, and 785 nm) were employed to acquire the SERS spectra of 4-MPy on the prepared substrates. As illustrated in Figure S4, the 785 nm laser excitation demonstrated optimal SERS performance. Higher Au concentrations exhibit enhanced LSPR responses in the near-infrared region. Consequently, the 785 nm laser excitation likely maximizes the coupling efficiency with Au LSPR modes, thereby yielding superior SERS enhancement.\u003c/p\u003e\n \u003cp\u003e4-MPy at a concentration of 1\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e mol/L was employed as the Raman probe molecule to validate the SERS effect of ZnO-Au MPs. Pure ZnO MPs and Au NPs as the SERS substrates were used as control groups. From the result of SERS response that is depicted in Fig. 3, it can be observed that the SERS intensity of 4-MPy on ZnO-Au MPs is significantly higher than that on pure ZnO MPs and Au NPs for both F-ZnO-Au MPs and S-ZnO-Au MPs. The enhanced SERS performance of ZnO-Au MPs could be the result of the synergistic effects of optimized plasmonic resonance and charge transfer.\u003c/p\u003e\n \u003cp\u003eThe uniform surface curvature of spherical ZnO MPs facilitates the homogeneous decoration of Au NPs, resulting in uniformly dense nanogaps that generate strong LSPR coupling effects. In contrast, the flower-like ZnO MPs contain abundant voids, which provids ample space and promotes rapid diffusion of reactant molecules, also tends to induce aggregation of Au NPs, thereby compromising SERS activity. As evidenced by the SEM images in Fig.\u0026nbsp;2, Au NPs exhibit significant aggregation on F-ZnO MPs. When Au NPs undergo extensive aggregation, the number of \u0026ldquo;hot spot\u0026rdquo; regions is markedly reduced, leading to a noticeable weakening of the SERS effect.\u003c/p\u003e\n \u003cp\u003eThe sensitivity of the two composite substrates was evaluated using 4-MPy as the probe molecule. Compared to F-ZnO-Au MPs, S-ZnO-Au MPs demonstrates superior SERS signal enhancement across all tested concentrations of 4-MPy (Fig.\u0026nbsp;3C and Figure S5). Figure S5 illustrates that the Raman intensity decline with the decrease of the concentration of 4-MPy. Even the concentration is 1\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;8\u003c/sup\u003e mol/L, the characteristic peak is clearly observed. The enhancement factor (EF) of 5.5\u0026times;10\u003csup\u003e7\u003c/sup\u003e that S-ZnO-Au MPs for 4-MPy was calculated according to the following formula (Eq. (1)):\u003c/p\u003e\n \u003cp\u003e\u003cem\u003eEF = (C\u003c/em\u003e\u003csub\u003e\u003cem\u003eRaman\u003c/em\u003e\u003c/sub\u003e \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003eSERS\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e) / (C\u003c/em\u003e\u003csub\u003e\u003cem\u003eSERS\u003c/em\u003e\u003c/sub\u003e \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003eRaman\u003c/em\u003e\u003c/sub\u003e \u003cem\u003e)\u003c/em\u003e (1)\u003c/p\u003e\n \u003cp\u003eWhere \u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003eRaman\u003c/em\u003e\u003c/sub\u003e is the concentration of 4-MPy could generate normal Raman signal and \u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003eSERS\u003c/em\u003e\u003c/sub\u003e is the concentration of 4-MPy on S-ZnO-Au MPs. \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003eSERS\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003eRaman\u003c/em\u003e\u003c/sub\u003e are the SERS intensity of 4-MPy on S-ZnO-Au MPs and the normal Raman intensity of 4-MPy at 1105 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively. Raman spectrum of 4-MPy and SERS spectrum of 4-MPy on S-ZnO-Au MPs are shown in Figure S6. The detailed calculation process is in supporting information. High EF indicates the excellent SERS sensitivity of S-ZnO-Au MPs. Figure\u0026nbsp;3D illustrates the schematic representation of 4-MPy molecules adsorbed on the S-ZnO-Au MPs substrate. The 4-MPy molecules interact with the ZnO-Au MPs substrate via the -SH group, forming S-Au or S-Ti bonds that serve as electron transfer channels between the substrate and the molecules. This interaction facilitates changes in molecular polarizability, thereby enhancing the Raman signal.\u003c/p\u003e\n \u003cp\u003eThe uniformity, stability, and batch-to-batch reproducibility of the substrate material directly influence the accuracy of quantitative analysis. Therefore, these properties were investigated for S-ZnO-Au MPs. 20 points on the surface of S-ZnO-Au MPs containing 4-MPy molecules were randomly selected for SERS detection. The result shows that the relative standard deviation (RSD) calculated based on the Raman intensity at 1105 cm⁻\u0026sup1; is 5.04% (Figure S7A, B), indicating excellent detection uniformity. The Raman intensity of 4-MPy on S-ZnO-Au MPs from the same preparation batch decreased by 15.04% after 100 days of storage (Figure S7C, D), confirming the substrate\u0026apos;s robust stability under ambient conditions over this period. Finally, the reproducibility of S-ZnO-Au MPs was examined. Three batches of substrates were selected, and three points on each batch were tested. The Raman intensity exhibits slight variation, with RSD of 4.90% (Figure S7E, F), demonstrating excellent preparation reproducibility. S-ZnO-Au MPs exhibit high uniformity, long-term stability, and excellent batch-to-batch reproducibility, making it a reliable substrate for precise quantitative SERS analysis. These properties ensure consistent and accurate performance in practical applications.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\"\u003e\n \u003ch2\u003e3.3 SERS Enhancement Mechanism of ZnO-Au MPs\u003c/h2\u003e\n \u003cp\u003eIn this work, 4-MPy was employed as the probe molecule to investigate the SERS effect of the substrate. Under 785 nm (1.57 eV) laser excitation, the electromagnetic field produced by LSPR on the surface of Au plays a main role in the enhancement of Raman. Besides, the chemical enhancement main from electron transfer is not to be neglected.\u003c/p\u003e\n \u003cp\u003eBased on the UV\u0026ndash;Vis absorption spectra and the Tauc equation (the detail is in Supporting Information), the Tauc plots (Fig.\u0026nbsp;4A) were obtained, from which the band gap energies of F-ZnO MPs and S-ZnO MPs were calculated to be 3.14 eV and 3.10 eV, respectively. Compared to F-ZnO, S-ZnO exhibits a narrower bandgap, which facilitates the separation of electron-hole pairs and promotes electron transfer. Mott\u0026ndash;Schottky plot (Fig.\u0026nbsp;4B) confirms the n-type semiconducting nature of S-ZnO MPs, as evidenced by the positive slope of the linear region. Based on the extracted flat-band potential and bandgap energy, the conduction band (E\u003csub\u003eCB\u003c/sub\u003e) and valence band (E\u003csub\u003eVB\u003c/sub\u003e) potentials are estimated to be \u0026minus;\u0026thinsp;3.783 eV and \u0026minus;\u0026thinsp;6.883 eV relative to the vacuum level, respectively (the detail calculation is in supporting information).\u003c/p\u003e\n \u003cp\u003eFigure 4C presents the UV-Vis spectra of 4-MPy on different substrates. After mixing with 4-MPy and Au NPs, a distinct blue shift in the absorption peak of ZnO around 370 nm is observed. According to the literature \u003csup\u003e[27]\u003c/sup\u003e, it could be inferred that Au NPs act as electron donor in this hybrid system, transferring electrons to conduction band of ZnO. Simultaneously, the UV absorption peak of 4-MPy at 220 nm also exhibits a blue shift. When 4-MPy is adsorbed on the surface of ZnO or ZnO-Au, the intramolecular \u0026pi;-\u0026pi;* transition may be constrained due to coordination effects (e.g., formation of Zn-S bonds), leading to the blue shift of the absorption peak. This indicates the presence of charge transfer between the substrate and the probe molecule. Photoluminescence (PL) spectroscopy was employed to determine the recombination ratio of photoexcited electron-hole pairs (Fig. 4D). Compared to pure S-ZnO, the fluorescence intensity decreases after introduction of 4-MPy molecules, suggesting electron transfer from S-ZnO to 4-MPy, which reduces the electron-hole recombination efficiency within S-ZnO, manifesting as a decrease in fluorescence intensity. After the introduction of Au NPs, the fluorescence intensity of S-ZnO further decreases, indicating that ZnO-Au complex structure is more advantage to this electron transfer process. Figure 4E shows the solid-state Raman spectrum of 4-MPy and its SERS spectra on Au NPs and F/S-ZnO-Au MPs substrates. According to the literature \u003csup\u003e[31, 32]\u003c/sup\u003e, the peaks at 1031, 1219, and 1602 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are assigned to the symmetric vibration of a\u003csub\u003e1\u003c/sub\u003e mode. The peaks at 1064 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1320 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are attributed to the nonsymmetric b\u003csub\u003e2\u003c/sub\u003e mode (the detail band assignments of 4-MPy are listed in supporting information Table S1). The a\u003csub\u003e1\u003c/sub\u003e mode is mainly attributed to SPR contribution and the b\u003csub\u003e2\u003c/sub\u003e mode\u0026rsquo;s intensity originates from the CT contribution. To quantify the CT contribution to SERS, the peaks at 1031 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (a\u003csub\u003e1\u003c/sub\u003e) and 1064 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (b\u003csub\u003e2\u003c/sub\u003e) are selected to calculate the degree of CT (\u0026rho;\u003csub\u003eCT\u003c/sub\u003e), according the following formula \u003csup\u003e[33]\u003c/sup\u003e (Eq. (2)):\u003c/p\u003e\n \u003cp\u003e\u003cem\u003e\u0026rho;\u003c/em\u003e\u003csub\u003e\u003cem\u003eCT\u003c/em\u003e\u003c/sub\u003e \u003cem\u003e=\u003c/em\u003e\\(\\:\\:\\frac{{\\text{I}}_{\\text{1064}}\\text{/}{\\text{I}}_{\\text{1031}}}{\\text{1}\\text{+}{\\text{I}}_{\\text{1064}}\\text{/}{\\text{I}}_{\\text{1031}}}\\) (2)\u003c/p\u003e\n \u003cp\u003eThe \u0026rho;\u003csub\u003eCT\u003c/sub\u003e of F-ZnO-Au MPs and S-ZnO-Au MPs are calculated as 30.44% and 35.59%, respectively. This result demonstrates that all 4-MPy/ZnO-Au MPs systems present a remarkable 𝜌\u003csub\u003eCT\u003c/sub\u003e value, and the value for S-ZnO-Au MPs is higher than that for F-ZnO-Au MPs, meaning a more significant contribution of CT enhancement in S-ZnO-Au MPs system. It worth note that, the Raman signal of 4-MPy on Au is weak and the degree of peak shift (compare the peak of solid 4-MPy) is small. The \u0026rho;\u003csub\u003eCT\u003c/sub\u003e value of 4-MPy/Au is 24.60%, suggesting that ZnO has a large contribution to CT effect and subsequently enhance the Raman intensity.\u003c/p\u003e\n \u003cp\u003eIn summary, ZnO, a typical n-type semiconductor, more electrons congregate the surface. The electrons congregated at the surface of ZnO will be injected into the Fermi level of the Au when Au is in contact with it. This will induce that the Fermi level of the Au will be elevated until the charges at the junction of gold and ZnO are balanced, which augments the CT from the Au to the 4-MPy molecules in the S-ZnO-Au MPs-4-MPy system. Meanwhile, a Schottky junction is formed on the interface of Au and ZnO (Fig.\u0026nbsp;4F). ZnO, in the S-ZnO-Au MPs assembly, also plays a role in transmitting the electrons by its conduction band. Under 785 nm laser excitation, the LSPR of Au generates electromagnetic enhancement. The laser energy facilitates the transfer of electrons from the Fermi level of Au to the conduction band of ZnO and then transmit to the lowest unoccupied molecular orbital (LUMO) level of 4-MPy. This process may require additional energy that supplied by hot electrons or tunneling effects\u003csup\u003e[34, 35]\u003c/sup\u003e. Additionally, charge transfer may occur from the highest occupied molecular orbital (HOMO) level of 4-MPy to the valence band of ZnO. This promotes charge separation and changes in molecular polarizability, thereby enhancing the Raman signals.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\"\u003e\n \u003ch2\u003e3.4 Measurement of MBT\u003c/h2\u003e\n \u003cp\u003eTo evaluate the practical application capability of S-ZnO-Au MPs, the environmental pollutant molecule MBT was detected by using portable Raman spectrometer. Figure S8 shows the Raman spectrum of MBT and its SERS spectrum on S-ZnO-Au MPs. The SERS enhancement effect of S-ZnO-Au MPs for MBT is significant, and the assignments of the relevant peaks are listed in Table S2\u003csup\u003e[36]\u003c/sup\u003e. Figure\u0026nbsp;5A is SERS spectra of MBT with different concentrations. It can be observed that the SERS signal intensity gradually diminishes as the concentration of MBT decreases. The characteristic Raman peaks remain observable even when the MBT concentration is as low as 10\u003csup\u003e\u0026minus;\u0026thinsp;8\u003c/sup\u003e mol/L, which demonstrates the significant detection sensitivity of S-ZnO-Au MPs. To investigate the correlation between MBT signal intensity and concentration, the Raman peak intensity at 1249 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was plotted against MBT concentration within the range from 1.0\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;8\u003c/sup\u003e to 1.0\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e mol/L, as shown in Fig. 5B. The linear fitting yielded the equation:\u003c/p\u003e\n \u003cp\u003e\u003cem\u003eI\u003c/em\u003e\u0026thinsp;=\u0026thinsp;7971.59 log\u003cem\u003eC\u003c/em\u003e\u0026thinsp;+\u0026thinsp;69578.68 (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.9901)\u003c/p\u003e\n \u003cp\u003eWhere \u003cem\u003eI\u003c/em\u003e is the SERS intensity peaked at 1249 cm⁻\u0026sup1; and \u003cem\u003eC\u003c/em\u003e is the concentration of MBT. The LOD of this presented SERS system for MBT is 1.42\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;10\u003c/sup\u003e mol/L, which is concluded according to IUPAC method \u003csup\u003e[37]\u003c/sup\u003e (process of the calculation is in supporting information). These results indicate this semiconductor-based SERS substrate can be applied to highly sensitive and quantitative detection of MBT.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\"\u003e\n \u003ch2\u003e3.5 Application in real samples\u003c/h2\u003e\n \u003cp\u003eThe feasibility of the S-ZnO-Au MPs composite in real samples measurement is further assessed through detection of MBT in seawater, lake water and tap water, respectively. Figure\u0026nbsp;6 present the quantitative spiked detection of MBT in these samples. Among these, the highest sensitivity was achieved for MBT detection in lake water, with a LOD as low as 1.0\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;10\u003c/sup\u003e mol/L. The lowest sensitivity was observed in seawater, likely due to the high concentration of electrolytes in seawater. These ions may reduce the adsorption capacity of MBT molecules on the substrate surface through electrostatic shielding effects. Additionally, the high salt content may induce aggregation or surface passivation of Au nanoparticles, compromising the stability and enhancement efficiency of the SERS substrate. Tap water, with its lower electrolyte concentration compared to seawater, still contains trace disinfectants and dissolved inorganic salts. These components may partially occupy the active sites of the nanomaterials or compete with MBT for adsorption, resulting in lower sensitivity than in lake water. In contrast, lake water, as a natural freshwater system, exhibits the lowest electrolyte concentration. Organic impurities may enhance the enrichment of MBT on the nanomaterial surface through hydrophobic interactions, thereby improving the efficiency of interactions between the substrate and MBT. Moreover, the matrix complexity of lake water is relatively low, making it more controllable for experimental analysis.\u003c/p\u003e\n \u003cp\u003eFor demonstrating the reliability of this S-ZnO-Au MPs based SERS assay, different concentrations MBT was spiked in lake water obtaining the spiked real sample (5.0, 0.5, 0.05 \u0026micro;mol/L) to measure the recovery. The result shown in Table\u0026nbsp;1, the recoveries ranged from 100% ~110% with an acceptable RSD (n\u0026thinsp;=\u0026thinsp;3).\u003c/p\u003e\n \u003cp\u003eThe against-interference of this S-ZnO-Au MPs-based SERS platform is investigated by addition of different possible coexisting substances in lake water, including high concentrations (10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e mol/L) of various salt ions, salt compounds, humic acid, as well as structurally similar compounds such as benzothiazole (BT) and 2-mercaptobenzimidazole (MBI). The lake water samples containing above species were measured using this prepared SERS sensor, and the result is shown in Fig. 7. As exhibit in SERS spectra (Fig. 7A), the characteristic peak of MBT can\u0026rsquo;t be observed from samples containing interference materials, indicating excellent selectivity for MBT detection, as evidenced by the histogram drawn by characteristic Raman peak observed at 1249 cm⁻\u0026sup1; (Fig. 7B).\u003c/p\u003e\n \u003cdiv\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 1\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eDetection recovery of MBT in lake water by S-ZnO-Au based SERS.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSamples\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSpiked MBT\u003c/p\u003e\n \u003cp\u003e(\u0026micro;mol/L)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFound by SERS (\u0026micro;mol/L)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eRecovery\u0026thinsp;\u0026plusmn;\u0026thinsp;RSD (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNo.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e108.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNo.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e101.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNo.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e109.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\"\u003e\n \u003ch2\u003e3.6 Photocatalytic Degradation\u003c/h2\u003e\n \u003cp\u003eTo investigate the capacity of photocatalytic degradation of this semiconductor- metal composite material, the photocatalytic degradation experiment of MBT was conducted under Xenon lamp irradiation. After undergoing the illumination, the UV-Vis and Raman characteristic signal of MBT were collected and their intensity decrease (Fig.\u0026nbsp;8). When the illumination time is 50 min, the 98% degradation efficiency is achieved, indicating the excellent performance in photocatalytic degradation. It worth noted, from the signals of low concentrations MBT, it can be seen that the Raman method is more sensitive than UV-Vis for detecting the residue of MBT. The proposed degradation mechanism is deduced as follows: Under light irradiation, ZnO-Au absorbs energy, inducing electron transitions and generating electron-hole pairs. These electron-hole pairs interact with adsorbed H\u003csub\u003e2\u003c/sub\u003eO and O\u003csub\u003e2\u003c/sub\u003e on the surface, producing highly reactive hydroxyl radicals (\u0026middot;OH) and superoxide radicals (O\u003csub\u003e2\u003c/sub\u003e⁻\u0026middot;). These radicals oxidize the MBT molecules adsorbed on the material surface, thereby achieving catalytic degradation.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eTwo distinct morphologies of S/F-ZnO-Au MPs semiconductor-noble metal composite materials were successfully synthesized by using hydrothermal and in-suit reduction method. The physicochemical properties of the composite materials were characterized using various techniques. S-ZnO-Au MPs exhibit superior SERS activity compared to F-ZnO-Au MPs due to its smooth spherical surface structure, which enables the ordered arrangement of Au NPs, preventing inefficient aggregation. Investigation of the enhancement mechanisms revealed that the synergistic effects of electromagnetic field enhancement and chemical enhancement significantly improved the SERS detection sensitivity with EF of 5.5\u0026times;10\u003csup\u003e7\u003c/sup\u003e. On this basis, the S-ZnO-Au MPs-based SERS detection strategy was applied to detection of MBT in environmental water, achieving a LOD of 1.42\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;10\u003c/sup\u003e mol/L. Additionally, ZnO-Au exhibited excellent photocatalytic degradation performance for MBT, achieving approximately 98% degradation efficiency within 50 minutes. Combined with the portable Raman spectrometer, the semiconductor-noble metal composite SERS substrates developed in this work hold great potential for the on-site rapid detection and photocatalytic degradation of harmful substances in aquatic environments.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCredit authorship contribution statement\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eJiangli Shi\u003c/strong\u003e: Visualization, Validation, Methodology, Investigation, Formal analysis, Data curation. \u003cstrong\u003eBoran Zhang\u003c/strong\u003e: Writing–review \u0026amp; editing, Visualization, Validation, Methodology, Investigation. \u003cstrong\u003eLi Zhang\u003c/strong\u003e: Methodology, Investigation, Formal analysis. \u003cstrong\u003eXinling Liu\u003c/strong\u003e: Methodology, Investigation. \u003cstrong\u003eYiping Wu\u003c/strong\u003e: Investigation. \u003cstrong\u003eYing Wen\u003c/strong\u003e: Investigation. \u003cstrong\u003eHaifeng Yang\u003c/strong\u003e: Writing – review \u0026amp; editing, Supervision,Funding acquisition.\u003cstrong\u003e\u0026nbsp;Xiaoyu Guo\u003c/strong\u003e: Writing – review \u0026amp; editing, Supervision.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was partly supported by the\u0026nbsp;National Natural Science Foundation of China (No. 22374100); Shanghai Engineering Research Center of Green Energy Chemical Engineering (18DZ2254200); International Joint laboratory on Resource Chemistry (IJLRC); Shanghai Key Laboratory of Rare Earth Functional Materials, Shanghai Municipal Education.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of competing interest\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eLi, D.; Fan, Z. 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Chem.\u003c/em\u003e \u003cstrong\u003e2023\u003c/strong\u003e, \u003cem\u003e95\u003c/em\u003e, 7933\u0026ndash;7940, doi:10.1021/acs.analchem.3c00466.\u003c/li\u003e\n\u003cli\u003eZhu, A.; Wang, T.; Jiang, Y.; Hu, S.; Tang, W.; Liu, X.; Guo, X.; Ying, Y.; Wu, Y.; Wen, Y.; et al. SERS Determination of Dopamine Using Metal\u0026ndash;Organic Frameworks Decorated with Ag/Au Noble Metal Nanoparticle Composite after Azo Derivatization with p-Aminothiophenol. \u003cem\u003eMicrochim Acta\u003c/em\u003e \u003cstrong\u003e2022\u003c/strong\u003e, \u003cem\u003e189\u003c/em\u003e, doi:10.1007/s00604- 022-05292-8.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Scheme 1","content":"\u003cp\u003eScheme 1 is available in the Supplementary Files section.\u003c/p\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":"microchimica-acta","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"miac","sideBox":"Learn more about [Microchimica Acta](https://link.springer.com/journal/604)","snPcode":"604","submissionUrl":"https://submission.springernature.com/new-submission/604/3","title":"Microchimica Acta","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"ZnO microsphere, Au nanoparticles, 2-mercaptobenzothiazole, SERS, trace detection, photocatalytic degradation","lastPublishedDoi":"10.21203/rs.3.rs-7281108/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7281108/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe toxic effects, including allergenicity, mutagenicity, and potential carcinogenicity of 2-mercaptobenzothiazole (MBT), have raised serious environmental and health concerns. In this work, we proposed the synthesis of ZnO microspheres with different morphologies (spherical and flower-like) decorated with Au nanoparticles (hereafter referred to as S-ZnO-Au MPs and F-ZnO-Au MPs, respectively) as ultrasensitive SERS-active substrates for the trace-level detection of MBT in aquatic environments. Spherical and flower-like ZnO microspheres were synthesized via a hydrothermal method, followed by the in-situ reduction of chloroauric acid to deposit Au nanoparticles onto the ZnO surface. Comparative analysis revealed that the S-ZnO-Au MPs exhibited superior SERS performance, with high enhancement factor of 5.5×10\u003csup\u003e7\u003c/sup\u003e. Taking advantage of the synergistic effects of chemical enhancement from ZnO semiconductor and electromagnetic enhancement from AuNPs, the S-ZnO-Au MPs-based SERS assay for MBT demonstrates high sensitivity and the limit of detection 1.42×10\u003csup\u003e−10\u003c/sup\u003e mol/L is reached, along with a wide linear dynamic detection range of 10\u003csup\u003e−8 \u003c/sup\u003e~10\u003csup\u003e−4\u003c/sup\u003e mol/L, with correlation coeffcients (R\u003csup\u003e2\u003c/sup\u003e) of 0.9901. The developed ZnO-Au MPs structure exhibit significant potential as a multifunctional SERS substrate, enabling both the sensitive detection and subsequent photocatalytic degradation of MBT in aquatic environments.\u003c/p\u003e","manuscriptTitle":"ZnO microsphere decorated with Au nanoparticles for SERS detection and removal of trace 2-Mercaptobenzothiazole in environmental water","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-14 16:21:05","doi":"10.21203/rs.3.rs-7281108/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-08-27T21:32:29+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-27T14:44:33+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-25T07:08:27+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-25T06:05:48+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"293204603759503939698705316310929227029","date":"2025-08-12T13:58:56+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"33163880364322087929594160980370459370","date":"2025-08-11T06:37:38+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"74843709851752000440664017846936312481","date":"2025-08-11T02:18:04+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-08-10T10:25:41+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-08-07T20:12:25+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-08-06T08:50:58+00:00","index":"","fulltext":""},{"type":"submitted","content":"Microchimica Acta","date":"2025-08-03T03:46:56+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"microchimica-acta","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"miac","sideBox":"Learn more about [Microchimica Acta](https://link.springer.com/journal/604)","snPcode":"604","submissionUrl":"https://submission.springernature.com/new-submission/604/3","title":"Microchimica Acta","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"71e38bbb-ce1f-4e09-a158-f9ffce24c15e","owner":[],"postedDate":"August 14th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-10-20T16:04:49+00:00","versionOfRecord":{"articleIdentity":"rs-7281108","link":"https://doi.org/10.1007/s00604-025-07592-1","journal":{"identity":"microchimica-acta","isVorOnly":false,"title":"Microchimica Acta"},"publishedOn":"2025-10-13 15:58:30","publishedOnDateReadable":"October 13th, 2025"},"versionCreatedAt":"2025-08-14 16:21:05","video":"","vorDoi":"10.1007/s00604-025-07592-1","vorDoiUrl":"https://doi.org/10.1007/s00604-025-07592-1","workflowStages":[]},"version":"v1","identity":"rs-7281108","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7281108","identity":"rs-7281108","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}