MOF-templated hollow Pd/CdS@Co3S4 nanocages with synergistic Z-scheme/Schottky effects for photoelectrochemical biosensing of chlorpyrifos featuring exceptional dynamic range

MOF-templated hollow Pd/CdS@Co3S4 nanocages with synergistic Z-scheme/Schottky effects for photoelectrochemical biosensing of chlorpyrifos featuring exceptional dynamic range | 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 MOF-templated hollow Pd/CdS@Co3S4 nanocages with synergistic Z-scheme/Schottky effects for photoelectrochemical biosensing of chlorpyrifos featuring exceptional dynamic range Shipeng Huang, Haicai Huang, Jingqiu Liu, Haoyu Duan, Xi Chen, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7047958/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 05 Sep, 2025 Read the published version in Microchimica Acta → Version 1 posted 14 You are reading this latest preprint version Abstract Conventional detection of organophosphorus pesticides (OPs) like chlorpyrifos (CPF) often faces challenges. This work presents a novel ternary synergistic PEC probe utilizing metal-organic framework (MOF)-templated Pd/CdS@Co 3 S 4 nanocages for sensing CPF. Derived from ZIF-67 via in situ sulfidation, the hollow nanocage architecture integrated CdS nanoparticles with Co 3 S 4 to form a direct Z-scheme heterojunction while decorating Pd quantum dots (QDs) created a Schottky barrier, implementing a crucial dual charge-transfer enhancement strategy. DFT simulations confirmed a 0.36 eV Fermi level difference at heterojunction interface, verifying a forced built-in electric field. The optimized Pd/CdS@Co 3 S 4 nanocomposite exhibited a remarkable ~ 5-fold photocurrent amplification over its pristine components, establishing a high-intensity signal baseline essential for accommodating wide-range concentration-dependent signal attenuation. Acetylcholinesterase (AChE)-immobilized biosensor quantified CPF via inhibition-triggered competitive electron consumption to attenuate photocurrent. The sensor demonstrated exceptional performance for CPF detection, most notably featuring a linear dynamic range spanning 4 orders of magnitude (0.1 ~ 2000 ng·mL − 1 ). Furthermore, it achieved a low detection limit (0.05 ng·mL − 1 , S/N = 3), outstanding specificity against interfering species, excellent long-term stability, and reliable accuracy in complex real samples (98.5 ~ 102.1%). This study proposes dual charge-transfer enhancement strategy and hollow architecture, addressing the broad-concentration-range in environmental pesticide detection with sensitivity and adaptability to real-world matrices. Photoelectrochemical sensor MOF-templated nanocages Z-scheme heterojunction Dual charge transfer Chlorpyrifos detection Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction As a representative organophosphorus insecticide, chlorpyrifos (CPF) maintains widespread application in contemporary agricultural practices due to its cost-effectiveness and broad-spectrum pest control capabilities[ 1 ]. Environmental monitoring data reveal that more than 90% of field-applied CPF ultimately migrates into ecosystems through spray drift and surface runoff[ 2 ]. This compound demonstrates remarkable environmental persistence, principally governed by two physicochemical characteristics: a water solubility and a soil organic carbon-water partitioning coefficient[ 3 ]. These intrinsic properties necessitate stringent surveillance of CPF residues to mitigate ecological risks and prevent human exposure through contaminated food chains. Therefore, the detection and monitoring of CPF residues are of critical significance for safeguarding human health. Current CPF detection methodologies predominantly rely on conventional analytical techniques such as high-performance liquid chromatography (HPLC) [ 4 ], gas chromatography (GC) [ 5 ], gas chromatography-tandem mass spectrometry (GC-MS/MS)[ 6 ], enzyme inhibition assays[ 7 ], and fluorescence analysis[ 8 , 9 ]. Nevertheless, these conventional techniques are hampered by notable limitations, including time-consuming sample preparation, costly instrumentation requirements, and insufficient sensitivity. Consequently, it is critically required to establish rapid, sensitive, and cost-effective analytical platforms for detecting CPF in environmental samples. Photoelectrochemical (PEC) analysis combines photoactive materials with effective sensing strategies, converting excitation signals (light) into detectable signals (photocurrent). This technique has garnered substantial attention in sensing applications due to its inherent advantages of high sensitivity, low background interference, rapid signal acquisition, and operational simplicity [ 10 – 12 ]. In PEC sensors, the sensing performance critically depends on the photoelectric conversion efficiency and electron-hole pair separation capability of the photoactive materials[ 13 ]. Despite these merits, the design of high-efficiency photosensitive materials for trace-level detection of environmental pollutants in PEC systems remains a significant challenge. Recent studies have demonstrated that rationally engineered hollow-structured metal-organic framework (MOF)-derived materials can not only preserve the inherent advantages of MOFs (e.g., large specific surface area and high porosity) but also significantly enhance photoelectric conversion efficiency and promote the separation of photogenerated carriers [ 14 , 15 ]. Especially, as a non-noble metal compound with favorable band alignment, MOF-derived Co 3 S 4 has emerged as a promising material in PEC applications[ 16 – 18 ]. Kumar et al. found that the hollow thin-shell Co 3 S 4 , obtained by in situ sulfidation of ZIF-67, enhanced light-harvesting efficiency and photocurrent response through multi-reflection effects in its internal cavities.[ 19 ]. However, its widespread application is hindered by inherent limitations such as rapid charge recombination and structural instability. To address these challenges, constructing efficient heterojunctions with compatible metal sulfides (e.g., CdS, ZnS) has been recognized as an effective strategy for improving charge separation towards high PEC performances. For instance, Huang and Mo et al. developed a multi-MOF integration (ZIF-67@ZIF-8) synthesis strategy and employed a regulated pyrolysis-sulfurization process to fabricate a concentric-layered Co 3 S 4 /NC@ZnS/NC architecture. This heterojunction exhibited superior photoelectrochemical response under visible light irradiation compared to individual Co 3 S 4 and ZnS/NC components[ 20 ]. Besides, the incorporation of noble metal quantum dots (QDs) also has been shown to significantly enhance charge separation efficiency[ 21 , 22 ]. Specifically, palladium quantum dots can serve as effective electron acceptors to trap photoelectrons and suppress electron-hole recombination[ 23 ]. Wen et al. demonstrated that Pd serves as an electron acceptor, facilitating the dissociation of photoinduced charge carriers via establishing a Schottky barrier between Pd and CdS microspheres, thereby enhancing the behavior of the photogenerated carriers[ 24 ]. Guided by this train of thought, a dual charge-transfer system was developed using ZIF-67-derived Pd/CdS@Co 3 S 4 for sensitive CPF detection, as shown in Scheme 1 . The configuration strategically incorporated AChE as biological recognition elements through covalent immobilization. The designed heterostructure exhibited exceptional electron-hole pair separation efficiency via optimized built-in electric field modulation. The precisely aligned energy bands and enhanced carrier transport properties inherent to this Z-scheme architecture facilitated generation of a stable, amplified anodic photocurrent signal. Moreover, Pd QDs functioned as efficient electron reservoirs, enhancing interfacial charge separation through Schottky barrier effects. The nanocomposite was subsequently anchored onto screen-printed electrodes (SPEs), functionalized with glutaraldehyde (GLD), and covalently conjugated with AChE via a crosslinking strategy to achieve biorecognition probe fixation. CPF detection relied on enzyme-mediated phosphorylation producing electroactive species that competed with the Pd/CdS@Co 3 S 4 system for photogenerated electrons. This electron depletion mechanism generated concentration-dependent photocurrent reduction, establishing a highly responsive biosensing platform. The linear correlation between photocurrent attenuation and CPF concentration enabled precise quantification across an extensive dynamic range. 2. Experiment section 2.1 Synthesis of nanomaterials. Synthesis of ZIF-67 derived Co 3 S 4 . The ZIF-67 precursor was synthesized according to a literature method[ 25 ]. Co 3 S 4 was subsequently synthesized from ZIF-67 via a solvothermal approach. Specifically, ZIF-67 (120 mg) along with thioacetamide (TAA, 100 mg) were separately dissolved in ethanol (30 mL each) and ultrasonically dispersed. The solutions were mixed and stirred for 30 min, then sealed in a Teflon-lined stainless steel autoclave and maintained at 160°C for 12 h under solvothermal conditions. The resultant precipitate was collected via centrifugal isolation (8000 rpm, 5 min), rinsed thrice alternately with deionized water and ethanol, followed by vacuum dehydration at 70°C to afford the final black Co 3 S 4 powder. Synthesis of CdS@Co 3 S 4 . Co 3 S 4 (90 mg), Cd(NO 3 ) 2 ·4H 2 O (32 mg), and TAA (15.6 mg) were separately dissolved in ethanol (20 mL each) and ultrasonically dispersed. The Cd(NO 3 ) 2 ·4H 2 O solution was slowly added to the Co 3 S 4 solution with stirring for 10 min. Subsequently, the TAA solution was slowly added to the mixture and stirred for 20 min. The mixture then underwent solvothermal reaction at 120°C for 10 h. The product was collected, washed thoroughly, and dried overnight under vacuum at 70°C. Synthesis of Pd/CdS@Co 3 S 4 . Pd QDs were deposited onto the surface of CdS@Co 3 S 4 using a photo-reduction method adapted from the literature[ 26 ]. Specifically, CdS@Co 3 S 4 material (100 mg) was dispersed in ethanol (30 mL). To this dispersion, 0.6 mL of a palladium acetate solution in DMF (1.67 mg/mL) was added. The mixture was stirred for 30 min in the dark, then illuminated (300 W Xe lamp) and agitated for a further 15 min to perform the photo-reduction reaction. The product was washed several times with water and ethanol, and dried in a vacuum oven. 2.2 Construction of Pd/CdS@Co 3 S 4 -based PEC biosensing platform A 10 µL aliquot of Pd/CdS@Co 3 S 4 suspension (5 mg·mL − 1 ) was deposited onto the central region of the SPE and dried at 60°C. Then, 10 µL of 5% glutaraldehyde (GLD) solution was applied and incubated at room temperature for 30 min. Next, 10 µL of AChE solution was applied and incubated at 37°C for 2 h for enzyme immobilization via amide bond formation onto the material surface. The electrode was thoroughly rinsed with 0.1 M PBS (pH 7.0) after each modification step to remove non-specifically bound components. The fabricated SPE was stored at 4°C for storage for subsequent applications. 2.3 PEC detection of CPF The CPF assay was performed by drop-casting 10 µL of CPF solutions with various concentrations onto the modified screen-printed electrode, followed by incubation at 37°C for 1 h to facilitate CPF phosphorylation with AChE. After incubation, the electrode was thoroughly rinsed with PBS buffer to eliminate unbound CPF molecules. Subsequently, 60 µL of 0.1 M phosphate buffer (pH 7.0) comprising 0.1 M ascorbic acid (AA) was applied to electrode surface. PEC measurements were conducted using a photoelectrochemical system integrated with a 1 W LED light source (emission wavelength: 465 nm) under an applied bias potential of -65 mV. All electrochemical experiments were implemented using a standard electrochemical workstation. 3. Results and discussion 3.1 Characterization The progressive morphological evolution of Pd/CdS@Co 3 S 4 was systematically investigated through scanning electron microscopy (SEM) analysis. As demonstrated in Fig. 1 A and Fig. S1 A , the ZIF-67 precursor displayed uniform rhombic dodecahedral morphology with particle diameters spanning 800 ~ 900 nm. Following sulfidation treatment, this structure underwent complete transformation into hollow Co 3 S 4 polyhedrons characterized by pronounced surface texturization and distinct edge notching (Fig. 1 B, S1B-C). Fig. S1 D further revealed the formation of an ultrathin Co 3 S 4 shell with an average thickness of precisely 35 nm. Subsequent deposition of CdS nanoparticles onto the Co 3 S 4 framework yielded well-defined CdS@Co 3 S 4 heterostructures, which successfully maintained the dodecahedral architecture while exhibiting uniform surface nanoparticle decoration (Fig. 1 C). Critically, the introduced Pd QDs were integrated without destroying the structural integrity of the CdS@Co 3 S 4 framework or inducing morphological alterations (Fig. 1 D). The detailed microstructures of as-prepared Pd/CdS@Co 3 S 4 sample were further explored by the transmission electron microscopy (TEM) and energy spectrum analysis (EDS) mapping. As shown in Fig. 1 E and Fig. S1 E , Pd/CdS@Co 3 S 4 was reconfirmed as a hollow dodecahedral spherical nanostructure with approximately 800–900 nm, consistent with previous observations. In addition, it can be seen that the Pd QDs with ~ 7 nm were uniformly attached to the outer shell layer ( Fig. S1 F) . Notably, the synthesized engineered nanocages effectively promote the charge-carrier dissociation and migration, while offering an increased surface area and enhanced exposure of active sites[ 27 ]. HRTEM (Fig. 1 F) revealed these two semiconductors with interplanar distances of 0.355 and 0.331 nm, corresponding to (111) facet of CdS and (311) facet of Co 3 S 4 , respectively[ 28 ]. TEM-EDS mapping analysis verified that the Co, Cd, S, and Pd elements were uniformly distributed in the composite material (Fig. 1 G). Besides, SEM-EDS characterization confirmed the proportional composition of Pd/CdS@Co 3 S 4 nanocomposites aligned with theoretical predictions primarily comprising Co, Cd, S, and Pd elements ( Fig. S2 ). The crystalline phases and structural evolution of the materials were examined through X-ray diffraction (XRD) analysis, as presented in Fig. 2 A. Pristine CdS exhibited three distinct diffraction peaks at 26.54°, 44.04°, and 52.16°, indexed as the (111), (220), and (311) crystallographic facets of cubic zinc blende CdS (PDF # 01-080-0019)[ 29 ]. Successful synthesis of ZIF-67 precursors was confirmed by their characteristic diffraction pattern ( Fig. S3 ). Subsequent sulfidation converted ZIF-67 into Co 3 S 4 , demonstrating four prominent peaks at 26.86°, 31.61°, 38.35°, and 55.36° indexed to the (220), (311), (400), and (440) planes of cubic Co 3 S 4 (PDF # 01-071-4923)[ 30 ]. Hydrothermal treatment with cadmium nitrate and thioacetamide yielded CdS@Co 3 S 4 composites, evidenced by the coexistence of characteristic CdS peaks superimposed on the Co 3 S 4 diffraction pattern. Notably, Pd QDs incorporation could not adjust the primary diffraction features of CdS@Co 3 S 4 without introducing new crystalline phases. The absence of discernible Pd-related diffraction signals suggests effective dispersion of Pd QDs below the XRD detection threshold, attributable to their ultralow loading concentration and atomic-scale distribution within the composite matrix[ 31 ]. The elemental composition and chemical valence state of the composites were investigated using X-ray photoelectron spectroscopy (XPS). As show in Fig. 2 B, the presence of Co, Cd, Pd and S elements across the survey XPS spectra of the hybrid material, proving the successfully synthesis of Pd/CdS@Co 3 S 4 nanocomposites. In Fig. 2 C, the high-resolved Co 2p spectrum displays two spin-orbit doublets accompanied by dual satellite signatures (Sat.). It can be seen that the binding energies observed at 778.3 eV and 782.6 eV, as well as 793.1 eV and 798.8 eV, were assigned as Co 2p 3/2 and Co 2p 1/2 orbitals. This doublet confirms the simultaneous presence of Co 2+ and Co 3+ states that was in consistent with valence of Co in the Co 3 S 4 [ 32 ]. Furthermore, Fig. 2 D reveals the high-resolved XPS spectra of Cd 2p, the strong peaks located at 405.0 eV and 411.7 eV in the Cd XPS scans could be characteristic of Cd 3d 5/2 and Cd 3d 3/2 states for divalent cadmium in CdS, respectively. The peaks at 161.4 eV and 162.7 eV were identified as the Co–S and Cd–S bond features captured by the S 2p 1/2 and S 2p 3/2 orbital signals (Fig. 2 E)[ 33 ]. Notably, the S 2p spectrum exhibits strong peaks at 169.3 eV and 170.4 eV, which could be ascribed to the formation of sulfate species originated from surface oxidation[ 34 , 35 ]. Moreover, the two characteristic peaks at 336.2 eV and 341.4 eV belong to the Pd 3d 5/2 and Pd 3d 3/2 orbitals of palladium (Fig. 2 F), respectively, suggesting Pd is primarily in the form of Pd 0 [ 36 ]. Besides, the element contents of Pd/CdS@Co 3 S 4 composite was determined in Table S1 . The separation and transport behavior of photoinduced carriers in the as-prepared samples were studied by measuring their PEC signals (Fig. 3 A). CdS@Co 3 S 4 exihibited an particularly obvious photocurrent response compared with Co 3 S 4 and CdS, suggesting the establishment of a Z-scheme junction at their interface. However, The PEC response signal of Pd/CdS@Co 3 S 4 was approximately 1.5 times higher than that of CdS @Co 3 S 4 , indicating that the Pd QDs effectively accelerated the dissociation of photoinduced charge carriers, thereby enhancing the signal response and sensitivity of the composite material. Additionally, the optimal deposition quantities of CdS and Pd QDs on ZIF-67-derived Co 3 S 4 were systematically investigated and determined ( Fig. S4 ). Subsequently, electrochemical impedance spectroscopy (EIS) was conducted on the various samples to evaluate the charge carrier transfer efficiency associated with the PEC responses. The Fig. 3 B revealed that the Pd/CdS@Co 3 S 4 exhibited a notably reduced impedance compared to CdS@Co 3 S 4 , demonstrating that the incorporation of Pd QDs significantly improved the mobility of photogenerated charge carriers, which consequently led to an enhanced PEC performance. On the other hand, the transient photocurrent responses conducted on the screen-printed electrode (SPE) modified with the as-prepared samples displayed excellent consistency with the results depicted in Fig. 3 A, as illustrated in Fig. 3 C. The optical properties of different samples were investigated through UV–Vis diffuse reflectance spectroscopy (DRS). As shown in Fig. 3 D, pristine CdS displayed a characteristic absorption edge at ~ 480 nm, consistent with its intrinsic bandgap properties. In contrast, Co 3 S 4 exhibited broad-spectrum absorption spanning ultraviolet to near-infrared regions, a feature retained in both CdS@Co 3 S 4 and Pd/CdS@Co 3 S 4 composites. Notably, the heterostructured composites demonstrated significantly enhanced light absorption capacity compared to individual Co 3 S 4 components. This optical enhancement suggests effective interfacial charge transfer between Co 3 S 4 and CdS, facilitated by heterojunction formation. The optimized light utilization in Pd/CdS@Co 3 S 4 further confirms the beneficial role of Pd ODs in promoting photon harvesting through surface plasmon resonance effects. 3.2 Mechanism of Z-scheme heterojunction in Pd/CdS@Co 3 S 4 To elucidate the electronic band configuration, energy gaps (E g ) of Co 3 S 4 and CdS were quantified via the Kubelka-Munk method based on the equation[ 37 , 38 ]: ( αℎυ ) 1/2 =A ( ℎυ - E g ). Thus, the E g values for Co 3 S 4 and CdS were evaluated at 1.5 eV and 2.3 eV from Tauc’s plot (Fig. 4 A), aligning with literature[ 39 , 40 ]. Complementary Mott-Schottky analysis explored the flat-band potentials (E fb ). As illustrated in Fig. 4 B, the E fb values for Co 3 S 4 and CdS were − 0.88 and 0.77 eV ( vs. Ag/AgCl), respectively. The characteristic positive slopes confirmed both as n-type semiconductors. For n-type materials, E fb approximates the conduction band minimum (E CB )[ 41 ]. Hence, E CB and valence band (E VB ) positions were derived using[ 42 ]: E CB ( NHE ) = E fb ( vs. Ag/AgCl ) + 0.197 , yielding the data shown in Table S2 . At interfaces formed between dissimilar semiconductors, the work function (WF) of each material dictates the relative positioning of its energy bands, and this value determines the orientation of the spontaneously formed internal electric field within the junction structure. In Fig. 4 C-D, the density functional theory (DFT) computations were conducted to calculate the WF of Co 3 S 4 (311) and CdS (111), the results were 4.84 eV and 6.35 eV. Besides, the Fermi level (E f ) and Vacuum level (E VAC ) of Co 3 S 4 and CdS were calculated to be -1.28 eV and − 1.64 eV, 3.56 eV and 4.71 eV, respectively ( Table S2 ). In the absence of light, the internal electric field generated by the interfacial potential difference at the CdS@Co 3 S 4 junction drives electron transfer from Co 3 S 4 with a higher Fermi level (-1.28 eV) to CdS with a lower Fermi level (-1.64 eV), establishing Fermi level equilibrium[ 43 ]. This caused upward band bending at the Co 3 S 4 side due to electron depletion and downward band bending at the CdS side due to electron accumulation. Under illumination, photoelectrons in the conduction band of Co 3 S 4 may migrate and recombine with photoholes in the valence band of CdS, facilitated by coulombic interactions. Consequently, the combination of Co 3 S 4 and CdS can result in a proficient Z-scheme CdS@Co 3 S 4 heterostructure. To trace the pathway of charge transfer within the Pd/CdS@Co 3 S 4 PEC sensing platform, electron spin resonance (ESR) spectroscopy targeted transient •O 2 ⁻ radical species. 5,5-Dimethyl-1-pyrroline-N-oxide (DMPO) acted as a stabilizing agent for these radicals, enabling the observation of •O 2 ⁻ in methanol-based dispersions. As depicted in Fig. 5 A, the Pd/Co 3 S 4 and Pd/CdS@Co 3 S 4 both exhibited the DMPO-•O 2 ⁻ signal peaks under visible light irradiation. One can be seen that, the peak intensity of the latter was exceeding that of the former by several folds, indicating that the encapsulation of CdS significantly enhanced the trapping of •O 2 ⁻. To explain these findings, a possible electron migration pathway was proposed. As illustrated in the Fig. 5 B, if photogenerated electrons from the CB of Co 3 S 4 migrated to the CB of CdS, subsequently captured by Pd QDs and transferred to the external circuit via the SPE, the high recombination rate of photogenerated electron-hole pairs, combined with the higher CB potential of CdS (-0.57 eV) compared to that of Co 3 S 4 , would have hindered the trapping of •O 2 ⁻. Conversely, if photogenerated electrons from the CB of CdS migrated to the VB of Co 3 S 4 , concurrently with CB-derived photoelectrons of Co 3 S 4 were captured by Pd QDs and transferred to the external circuit via the SPE, this migration pathway would have suppressed the recombination of photoinduced electron-hole pairs. Moreover, the lower potential (-0.68 eV) of this pathway would have strongly promoted the trapping of •O 2 ⁻. This electron migration behavior further confirmed the Z-scheme configuration of the CdS@Co 3 S 4 heterostructure. 3.3 Feasibility of the developed PEC sensor Electrochemical impedance spectroscopy (EIS) assessed the sensing electrode preparation, with the Nyquist plot semicircle size representing the resistance to charge transfer (Rct) at the interface. As shown in Fig. 6 A, the bare SPE (curve a) displayed the smallest Rct value. Modification with Pd/CdS@Co 3 S 4 (curve b) substantially increased the Rct due to the semiconductor characteristics. Subsequent immobilization of AChE through amide bond formation (curve c) induced a sharp Rct increase caused by steric hindrance effects. Following incubation with 10 ppb CPF for 60 min (curve d), the developed-SPE exhibited further elevated Rct. This final increase originated from the irreversible phosphorylation of AChE by chlorpyrifos, which modifies the enzyme's tertiary structure and increases electron transfer barrier. The stepwise electrode modification process was corroborated through PEC characterization. As demonstrated in Fig. 6 B, the pristine SPE showed negligible photocurrent response, while the Pd/CdS@Co 3 S 4 -modified SPE exhibited maximum photocurrent intensity due to superior photoelectric conversion capability. AChE functionalization caused significant photocurrent attenuation, consistent with EIS analysis. Subsequent incubation with 10 ppb CPF induced further photocurrent decrease. This signal suppression mechanism arises from enzyme inhibition-induced phosphorylated adduct formation, where the phosphorylation products serve as competitive electron acceptors that intercept photogenerated electrons from Pd/CdS@Co 3 S 4 , thereby impeding electron migration to the collector electrode. The proposed sensing mechanism is schematically presented in Fig. 6 C. The complementary EIS and PEC results collectively validate successful sensor fabrication. 3.4 Performance of the PEC sensor for CPF detection Prior to CPF detection, the optimization of AChE immobilization and the CPF incubation were systematically explored. As depicted in Fig. S5 , photocurrent stabilization was achieved at 2 h for AChE immobilization and 60 min for CPF incubation, establishing these durations as optimal operational parameters for the sensing platform. Under optimized conditions, the photocurrent changes of the sensing system exposed to different concentrations of CPF were recorded using an electrochemical workstation (Fig. 7 A). In the absence of CPF, a high intensity photocurrent signal was observed (curve a). However, introducing CPF caused a progressive attenuation of the photocurrent response as its concentration rose from 0.1 to 2000 ppb (curves b-j). This response resulted from the biomolecular recognition event between CPF and the sensing platform's AChE component, which led to the formation of electron-withdrawing groups on the electrode surface. As a result, the photogenerated charge carriers produced by light excitation became less accessible for capture by the electrochemical workstation, leading to a reduction in the photocurrent. Consequently, the photocurrent displayed a strong linear correlation with the logarithm of CPF concentrations across the 0.1 ppb to 2 ppm range, following the equation [I (µA) = -3.1426 lg C CPF + 22.1199, R 2 = 0.9983], as presented in Fig. 7 B. This exceptional four order of magnitude dynamic range primarily results from synergistic Z-scheme and Schottky effects in the engineered heterostructure. The dual charge transfer mechanism integrates Z scheme recombination suppression with Schottky barrier electron trapping, achieving approximately five-fold photocurrent amplification versus pristine components. This enhanced signal baseline critically enables accommodation of extensive concentration dependent attenuation, thereby facilitating ultra wide linear quantification, with the calculated LOD shown 0.05 ppb (S/N = 3). Comparable analytical capability for CPF was observed with the developed PEC sensing platform when measured against most existing methodologies summarized in Table S3 . Assessing the sensor's specificity is vital for determining its real-world utility. Consequently, relevant interfering species, including various metal ions as well as other organic pesticides such as imidacloprid (IMI), acetamiprid (ACE), carbaryl (CAR), and parathion-methyl (PM), were used to evaluate the selectivity of the PEC enzymatic sensor. As depicted in Fig. 7 C-D, compared to CPF and its mixtures, the interfering substances did not exhibit significant photocurrent responses, indicating that the developed PEC sensor possesses excellent selectivity. Furthermore, Fig. 7 E demonstrated that the photocurrent showed no significant variation during repeated illumination over 300s, with a well relative standard deviation (RSD) of 1.22%, demonstrating the exceptional robustness of the PEC sensor. Furthermore, reproducibility assessments were executed via performing PEC tests on 2 ng·mL − 1 CPF using six paralleled electrodes under identical conditions (Fig. 7 F). The results revealed that the sensor exhibited terrific reproducibility, with an RSD of 1.96%. After storage in a 4°C for 7 days, the PEC signals of 100 ng·mL − 1 of CPF remained at 97% of its first day value, confirming the storage stability of the sensor ( Fig. S6 ). Validating this engineered biosensor's performance in detecting CPF across environmental specimens, recovery studies were performed using Yangtze River water. Known concentrations of CPF (10, 50, and 100 ng·mL − 1 ) were spiked into pre-processed samples. As summarized in Table S4 , the obtained RSDs and recovery rates ranged from 5.04%~6.02% and 98.5%~102.1%, respectively. These results confirmthe reliability of the Pd/CdS@Co 3 S 4 PEC enzymatic sensor for quantifying CPF in complex environmental matrices. 4. Conclusion In summary, This study demonstrated a MOF-templated ternary hollow Pd/CdS@Co 3 S 4 nanocage photoelectrochemical biosensor that achieved ultra-broad linear detection of chlorpyrifos (0.1 ~ 2000 ng·mL − 1 ) through engineered multi-electron transfer pathways. DFT-validated interfacial charge manipulation was explored by a Fermi-level offset driving Z-scheme heterojunction formation between CdS and Co 3 S 4 , which thereby created a built-in electric field that synergized with Schottky electron trapping via Pd QDs. This dual charge-transfer strategy amplifies photocurrent ~ 5-fold versus pristine components, establishing the critical high-intensity signal baseline necessary for accommodating concentration-dependent attenuation across four orders of magnitude. Functionalized with AChE, the platform quantifies CPF via inhibition-mediated competitive electron consumption, delivering a 0.05 ng·mL − 1 detection limit alongside exceptional specificity, stability (> 97% signal retention over 7 days), and reproducibility (RSD = 1.96%). Validated in complex matrices with 98.5 ~ 102.1% recovery accuracy, this work establishes DFT-guided electronic engineering of MOF heterostructures as a promising strategy for designing next-generation environmental sensors with prominent dynamic range. Declarations Author Contribution Shipeng Huang: Writing-Original Draft, Methodology, Validation. Haicai Huang: Data Curation, Methodology. Jingqiu Liu: Data Curation, Formal analysis. Haoyu Duan: Data Curation, Formal analysis. Xi Chen: Writing - Review & Editing, Conceptualization, Validation, Funding acquisition. Houyang Chen: Writing - Review & Editing, Conceptualization, Investigation, Funding acquisition. Acknowledgement This work is supported by the Postdoctoral Program of Natural Science Foundation of Chongqing (CSTB2023NSCQ-BHX0231), the Startup Foundation of Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences. Computations were performed on Hefei advanced computing center. Electronic Supplementary Material The Electronic Supplementary Material is available free of charge. Materials and reagents, electrochemical tests, application of the PEC sensor in real sample, density functional theory (DFT) calculations, SEM images, transient photocurrent responses, stability tests, and so on. Funding Declaration This work is supported by the Postdoctoral Program of Natural Science Foundation of Chongqing (CSTB2023NSCQ-BHX0231), the Startup Foundation of Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences. Computations were performed on Hefei advanced computing center. References C.S. Pundir, A. Malik, Preety, Bio-sensing of organophosphorus pesticides: A review, Bioseors and Bioelectronics 140 (2019) 111348. M. Zhang, Z. Chen, X. Liu, C. Song, C. Zeng, T. Lv, Z. Xu, X. Chen, L. Wang, B. Liu, X. Peng, Dual-mode supramolecular fluorescent probe for rapid and on-site detection of chlorpyrifos in the environment, Journal of Hazardous Materials 452 (2023) 131177. J. Ma, P. Zhu, W. Wang, X. Zhang, P. Wang, Y. Sultan, Y. Li, W. Ding, X. Li, Environmental impacts of chlorpyrifos: Transgenerational toxic effects on aquatic organisms cannot be ignored, Science of The Total Environment 905 (2023) 167311. I. Ion, A.C. Ion, Determination of chlorpyriphos in broccoli using a voltammetric acetylcholinesterase sensor based on carbon nanostructure–chitosan composite material, Materials Science and Engineering: C 32 (2012) 1001–1004. A.R. Kulkarni, K.S. Soppimath, A.M. Dave, M.H. Mehta, T.M. Aminabhavi, Solubility study of hazardous pesticide (chlorpyrifos) by gas chromatography, Journal of Hazardous Materials 80 (2000) 9–13. D.A. Varela-Martínez, M.Á. González-Curbelo, J. González-Sálamo, J. Hernández-Borges, Analysis of multiclass pesticides in dried fruits using QuEChERS-gas chromatography tandem mass spectrometry, Food Chemistry 297 (2019) 124961. Z. Chen, L. Zhao, Z. Zhang, J. Wu, L. Zhang, X. Jing, X. Wang, Dispersive liquid‒liquid microextraction combined with enzyme-linked immunosorbent assay for the analysis of chlorpyrifos in cereal samples, Talanta 265 (2023) 124802. M. Zhang, Z. Chen, X. Liu, C. Song, C. Zeng, T. Lv, Z. Xu, X. Chen, L. Wang, B. Liu, X. Peng, Dual-mode supramolecular fluorescent probe for rapid and on-site detection of chlorpyrifos in the environment, Journal of Hazardous Materials 452 (2023) 131177. D. Zhao, R. Jiang, X. Liu, S. Alwarappan, Flexible enzyme-like platform based on a 1-D CeVO 4 /2-D rGO-MCC heterostructure as sensor for the detection of intracellular superoxide anions, Sensors and Actuators B: Chemical 400 (2024) 134863. K. Yin, J. Zhang, Y. Xue, A.-J. Wang, L.-P. Mei, P. Song, J.-J. Feng, Target-assisted self-powered photoelectrochemical sensor based on Ag 2 S/BiOCl heterojunction for ultrasensitive chlorpyrifos detection, Talanta 286 (2025) 127502. J. Qian, Y. Liu, H. Cui, F. You, H. Yang, K. Wang, J. Wei, L. Long, C. Wang, Incorporation of ZnIn 2 S 4 semiconductors with S-vacancy engineered MoS 2 nanosheets to develop sensitive photoelectrochemical aptasensor for aflatoxin B1 detection, Sensors and Actuators B: Chemical 403 (2024) 135195. L. Zhang, F.-Z. Chen, H. Sun, R. Meng, Q. Zeng, X. Wang, H. Zhou, Stimulus-Responsive Metal–Organic Framework Signal-Reporting System for Photoelectrochemical and Fluorescent Dual-Mode Detection of ATP, ACS Appl. Mater. Interfaces 14 (2022) 46103–46111. H. Shang, H. Xu, L. Jin, C. Wang, C. Chen, T. Song, Y. Du, 3D ZnIn 2 S 4 nanosheets decorated ZnCdS dodecahedral cages as multifunctional signal amplification matrix combined with electroactive/photoactive materials for dual mode electrochemical – photoelectrochemical detection of bovine hemoglobin, Biosensors and Bioelectronics 159 (2020) 112202. J. Peng, J. Yang, B. Chen, S. Zeng, D. Zheng, Y. Chen, W. Gao, Design of ultrathin nanosheet subunits ZnIn 2 S 4 hollow nanocages with enhanced photoelectric conversion for ultrasensitive photoelectrochemical sensing, Biosensors and Bioelectronics 175 (2021) 112873. M. Liu, Z. Xing, Z. Li, W. Zhou, Recent advances in core–shell metal organic frame-based photocatalysts for solar energy conversion, Coordination Chemistry Reviews 446 (2021) 214123. F. Zhang, H.-Q. Zhuang, J. Song, Y.-L. Men, Y.-X. Pan, S.-H. Yu, Coupling cobalt sulfide nanosheets with cadmium sulfide nanoparticles for highly efficient visible-light-driven photocatalysis, Applied Catalysis B: Environmental 226 (2018) 103–110. J. Qiu, W. Zheng, R. Yuan, C. Yue, D. Li, F. Liu, J. Zhu, A novel 3D nanofibrous aerogel-based MoS 2 @Co 3 S 4 heterojunction photocatalyst for water remediation and hydrogen evolution under simulated solar irradiation, Applied Catalysis B: Environmental 264 (2020) 118514. Y. Xie, L. Chen, Q. Jin, J. Yun, X. Liang, MoS 2 –Co 3 S 4 hollow polyhedrons derived from ZIF-67 towards hydrogen evolution reaction and hydrodesulfurization, International Journal of Hydrogen Energy 44 (2019) 24246–24255. P. Anil Kumar Reddy, C. Lee, S. Bae, ZIF-67 templated synthesis of sea urchin-like P–Co 3 S 4 @CdS nanocomposite for enhanced H2 production and dye oxidation under solar light: Role of P-doping on cocatalyst property of Co3S4, Composites Part B: Engineering 295 (2025) 112178. L. Huang, S. Mo, X. Zhao, J. Zhou, X. Zhou, Y. Zhang, Y. Fan, Q. Xie, B. Li, J. Li, Constructing Co and Zn atomic pairs in core-shell Co 3 S 4 /NC@ZnS/NC derived from MOF-on-MOF nanostructures for enhanced photocatalytic CO 2 reduction to C 2 H 4 , Applied Catalysis B: Environment and Energy 352 (2024) 124019. S. Liang, Y. Xia, S. Zhu, S. Zheng, Y. He, J. Bi, M. Liu, L. Wu, Au and Pt co-loaded g-C 3 N 4 nanosheets for enhanced photocatalytic hydrogen production under visible light irradiation, Applied Surface Science 358 (2015) 304–312. S.A. Rawool, M.R. Pai, A.M. Banerjee, S. Nath, R.D. Bapat, R.K. Sharma, Jagannath, B. Dutta, P.A. Hassan, A.K. Tripathi, Superior Interfacial Contact Yields Efficient Electron Transfer Rate and Enhanced Solar Photocatalytic Hydrogen Generation in M/C 3 N 4 Schottky Junctions, ACS Appl. Mater. Interfaces 15 (2023) 39926–39945. X. Zhou, X. Yu, L. Peng, J. Luo, X. Ning, X. Fan, X. Zhou, X. Zhou, Pd(II) coordination molecule modified g-C 3 N 4 for boosting photocatalytic hydrogen production, Journal of Colloid and Interface Science 671 (2024) 134–144. Z. Wen, W. Zhu, F. You, R. Yuan, L. Ding, N. Hao, J. Wei, K. Wang, Ultrasensitive photoelectrochemical aptasensor for carbendazim detection based on in-situ constructing Schottky junction via photoreducing Pd nanoparticles onto CdS microsphere, Biosensors and Bioelectronics 203 (2022) 114036. J. Tan, B. Peng, L. Tang, G. Zeng, Y. Lu, J. Wang, X. Ouyang, X. Zhu, Y. Chen, H. Feng, CuS QDs/Co 3 O 4 Polyhedra-Driven Multiple Signal Amplifications Activated h-BN Photoeletrochemical Biosensing Platform, Anal. Chem. 92 (2020) 13073–13083. X. Chen, H. Huang, Q. Wu, F. Xue, Z. Zhao, J. Liu, H. Duan, H. Chen, Triggering “signal-on” photoelectrochemical responses by heterojunction transition for selective detection of copper(II) based on Pd/MoS 2 @g-C 3 N 4 nanocomposites, Analytica Chimica Acta 1283 (2023) 341940. S. Wang, B.Y. Guan, X. Wang, X.W.D. Lou, Formation of Hierarchical Co 9 S 8 @ZnIn 2 S 4 Heterostructured Cages as an Efficient Photocatalyst for Hydrogen Evolution, J. Am. Chem. Soc. 140 (2018) 15145–15148. H. Huang, Y. Cai, Q. Xu, M. Xiong, L. Ding, X. Wang, Q. Jiang, Q. Li, X. Han, J. Hu, Y. Liu, S‐Scheme CdS/Co 3 S 4 Double‐Shelled Hollow Nanoboxes for Enhanced Photocatalytic Hydrogen Evolution, Small (2025) 2501710. F. Jiang, S. Liu, W. Li, Y. Li, S. Wang, H. Lin, Q. Liu, Y. Li, Q. Wei, A signal-on photoelectrochemical sensor based on the target-triggered double-ion exchange reaction for Hg 2+ under visible light, Sensors and Actuators B: Chemical 405 (2024) 135368. Y. Guo, J. Tang, H. Qian, Z. Wang, Y. Yamauchi, One-Pot Synthesis of Zeolitic Imidazolate Framework 67-Derived Hollow Co 3 S 4 @MoS 2 Heterostructures as Efficient Bifunctional Catalysts, Chem. Mater. 29 (2017) 5566–5573. X. Chen, W. Zhang, L. Zhang, L. Feng, J. Wen, J. Yang, C. Zhang, J. Jiang, H. Wang, An urchin-like Ag 3 PO 4 /Pd/LaPO 4 photocatalyst with Z-scheme heterojunction for enhanced hydrogen evolution, Applied Surface Science 497 (2019) 143771. L. Luo, Y. Zhou, W. Yan, G. Du, M. Fan, W. Zhao, Construction of advanced zeolitic imidazolate framework derived cobalt sulfide/MXene composites as high-performance electrodes for supercapacitors, Journal of Colloid and Interface Science 615 (2022) 282–292. B.-F. Xu, J. Zhang, A.P. Tanjung, F. Xu, A.-J. Wang, L.-P. Mei, P. Song, J.-J. Feng, MOF-derived sandwich-structured dual Z-Scheme Co 9 S 8 @ZnIn 2 S 4 /CdSe hollow nanocages heterojunction: Target-induced ultrasensitive photoelectrochemical sensing of chlorpyrifos, Biosensors and Bioelectronics 257 (2024) 116324. T.S. Priya, T.-W. Chen, S.-M. Chen, T. Kokulnathan, M. Akilarasan, W.-C. Liou, A.M. Al-Mohaimeed, M.A. Ali, M.S. Elshikh, J. Yu, In-situ growth of MOF-derived Co 3 S 4 @MoS 2 heterostructured electrocatalyst for the detection of furazolidone, Chemosphere 356 (2024) 141895. M. Tang, D. Zhang, Y. Sun, Q. Chen, Y. Chen, G. Xi, Z. Wang, X. Shao, CVD-fabricated Co 3 O 4 -Co 3 S 4 heterojunction for ultra-sensitive detection of CO in SF6 discharge decomposition products, Sensors and Actuators B: Chemical 401 (2024) 134968. L. Han, Z. Ren, P. Ou, H. Cheng, N. Rui, L. Lin, X. Liu, L. Zhuo, J. Song, J. Sun, J. Luo, H.L. Xin, Modulating Single‐Atom Palladium Sites with Copper for Enhanced Ambient Ammonia Electrosynthesis, Angew Chem Int Ed 60 (2021) 345–350. X. Ma, J. Kang, Y. Wu, C. Pang, S. Li, J. Li, Y. Xiong, J. Luo, M. Wang, Z. Xu, A bifunctional polycentric-affinity MOF/MXene heterojunction-based molecularly imprinted photoelectrochemical organophosphorus-sensing platform, Chemical Engineering Journal 469 (2023) 143888. J. Zou, J. Liu, Y. Xie, G. Peng, L. Duan, D. Hu, S. Chen, F. Qu, L. Lu, Bifunctional bismuth molybdate/biochar composite with an enhanced photo-assisted electrochemical activity: Memory effect-free Hg(II) detection and efficient photocatalytic reduction of Cr(VI), Chemical Engineering Journal 468 (2023) 143849. C. Zhou, S. Shi, Y. Wei, A. Chen, N. Tang, J. Zuo, Q. He, P. Deng, High-sensitivity electrochemical sensing platform for acetaminophen based on MnS/Co3S4 hybrids doped electrochemically reduced graphene oxide nanocomposite, Inorganic Chemistry Communications 155 (2023) 111123. L. Meng, J. Wang, Y. Zhang, B. Zhou, J. Shi, K. Xiao, Engineering MOF-derived 2D NPC-TiO 2 nanotablet/3D marigold-like ZnIn 2 S 4 /CdS nanoparticles dual Z-scheme heterojunction with excellent photoelectric performance: A novel material for sensitive and facile photoelectrochemical sensing detection of mercury ions in aqueous environments by ion-exchange sensing strategy, Sensors and Actuators B: Chemical 414 (2024) 135897. H. Wang, D. Liang, Y. Xu, X. Liang, X. Qiu, Z. Lin, A highly efficient photoelectrochemical sensor for detection of chlorpyrifos based on 2D/2D β-Bi 2 O 3 /g-C 3 N 4 heterojunctions, Environ. Sci.: Nano 8 (2021) 773–783. S. Abdpour, E. Kowsari, B. Bazri, M.R.A. Moghaddam, S.S. Tafreshi, N.H. De Leeuw, I. Simon, L. Schmolke, D. Dietrich, S. Ramakrishna, C. Janiak, Amino-functionalized MIL-101(Cr) photodegradation enhancement by sulfur-enriched copper sulfide nanoparticles: An experimental and DFT study, Journal of Molecular Liquids 319 (2020) 114341. C. Zhou, M. Zhou, K. Lu, W. Huang, C. Yu, K. Yang, Electrostatic self-assembly of MnIn 2 S 4 @BiVO 4 S-scheme heterojunction for photothermal-enhanced photocatalytic antibiotic removal with the boosted spatial charge separation, Journal of Materials Science & Technology 233 (2025) 166–178. Scheme 1 Scheme 1 is available in the Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files GraphicalAbstract.jpg ElectronicSupplementaryMaterial.doc Scheme1.png Scheme 1. Schematic diagram illustrating the working principle of the PEC biosensor for CPF detection, including fabrication of AChE-functionalized Pd/CdS@Co 3 S 4 sensing interface, synergistic charge transfer, and enzyme inhibition-based photocurrent attenuation mechanism. Cite Share Download PDF Status: Published Journal Publication published 05 Sep, 2025 Read the published version in Microchimica Acta → Version 1 posted Editorial decision: Revision requested 22 Jul, 2025 Reviews received at journal 22 Jul, 2025 Reviews received at journal 21 Jul, 2025 Reviews received at journal 16 Jul, 2025 Reviewers agreed at journal 13 Jul, 2025 Reviews received at journal 11 Jul, 2025 Reviewers agreed at journal 11 Jul, 2025 Reviewers agreed at journal 10 Jul, 2025 Reviewers agreed at journal 10 Jul, 2025 Reviewers agreed at journal 10 Jul, 2025 Reviewers invited by journal 10 Jul, 2025 Editor assigned by journal 10 Jul, 2025 Submission checks completed at journal 09 Jul, 2025 First submitted to journal 04 Jul, 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-7047958","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":484706092,"identity":"c4b715a2-1315-4c43-8ffa-259b6403bcf8","order_by":0,"name":"Shipeng Huang","email":"","orcid":"","institution":"Chongqing Institute of Green and Intelligent Technology","correspondingAuthor":false,"prefix":"","firstName":"Shipeng","middleName":"","lastName":"Huang","suffix":""},{"id":484706093,"identity":"70a3bc1e-3eac-41f7-93fc-0f041f477ea1","order_by":1,"name":"Haicai Huang","email":"","orcid":"","institution":"Chongqing Institute of Green and Intelligent Technology","correspondingAuthor":false,"prefix":"","firstName":"Haicai","middleName":"","lastName":"Huang","suffix":""},{"id":484706094,"identity":"7ed7b832-6abb-4756-be16-f5d45a84f0ce","order_by":2,"name":"Jingqiu Liu","email":"","orcid":"","institution":"Chongqing Institute of Green and Intelligent Technology","correspondingAuthor":false,"prefix":"","firstName":"Jingqiu","middleName":"","lastName":"Liu","suffix":""},{"id":484706095,"identity":"2c997123-7056-4ea0-ae10-9caa65f7b671","order_by":3,"name":"Haoyu Duan","email":"","orcid":"","institution":"Chongqing Institute of Green and Intelligent Technology","correspondingAuthor":false,"prefix":"","firstName":"Haoyu","middleName":"","lastName":"Duan","suffix":""},{"id":484706096,"identity":"c153f9c6-5a38-4c38-8313-86ea4b6c749c","order_by":4,"name":"Xi Chen","email":"","orcid":"","institution":"Chongqing Institute of Green and Intelligent Technology","correspondingAuthor":false,"prefix":"","firstName":"Xi","middleName":"","lastName":"Chen","suffix":""},{"id":484706097,"identity":"475b45c1-038c-4ec8-8dc7-a7c7d960ea93","order_by":5,"name":"Houyang Chen","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA/UlEQVRIiWNgGAWjYDACCQYGZiiT8QGDAQMPSVqYDUBaCOtB0sImASIJauGf3XzscUHF4cT+2e3XKn4U1MrYMzA//MBQcwe3JXeOpRvPOHM4ccadM2U3ewyOAx3GZizBcOwZTi0GEjlm0rxthxMbbuSk3WYwOAbyixkDY8NhPFryv4G1zAdqKYZoYf9GQEsOG1jLhhvpx5gZDGqAWnjw2yJxI81MmudMuvHGGznMkj0GB3h4DvMUSyQcw62Ff0byM2meCmvZeTfSH3748afOnr29feOHDzW4tcCAYwMDjwGQPgyJpgSCGhgY7BkY2B8A6Toi1I6CUTAKRsFIAwBtj1C4tmpNZQAAAABJRU5ErkJggg==","orcid":"","institution":"Chongqing Institute of Green and Intelligent Technology","correspondingAuthor":true,"prefix":"","firstName":"Houyang","middleName":"","lastName":"Chen","suffix":""}],"badges":[],"createdAt":"2025-07-04 15:08:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7047958/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7047958/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00604-025-07469-3","type":"published","date":"2025-09-05T15:57:13+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":86758866,"identity":"36e1d769-3b4c-4f06-83bb-4b8ec3432d91","added_by":"auto","created_at":"2025-07-15 09:53:49","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":403951,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of the fabrication procedure Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e including (A) ZIF-67 precursor, (B) sulfuration toward Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e , (C) CdS in-situ growth on Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e yielding the CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e, (D) Pd coating on CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e toward Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e ; (E) TEM images of the Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e with (F) magnified view, (G) EDS element mappings of Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7047958/v1/fc341ef29ce425f6f0362cd4.png"},{"id":86758858,"identity":"08396ac9-bc88-4a68-9287-9f83df82ec1e","added_by":"auto","created_at":"2025-07-15 09:53:48","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":73687,"visible":true,"origin":"","legend":"\u003cp\u003e(A) XRD patterns of different samples; (B) full XPS spectra of Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4 \u003c/sub\u003e; high resolution XPS spectra of (C) Co 2p, (D) Cd 3d, (E) S 2p and (F) Pd 3d.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7047958/v1/afb7f53921c3c3d2f8141383.png"},{"id":86758853,"identity":"63507979-b2a4-4668-9eb6-9092a90666cb","added_by":"auto","created_at":"2025-07-15 09:53:48","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":37080,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Transient photocurrent responses and (B) electrochemical impedance spectra of CdS, Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e, CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e and Pd /CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e in 0.10 M KCl containing 5.0 mM Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3- /4-\u003c/sup\u003e (pH 7.0). (C) Photocurrent signals on SPEs modified with different samples. (D) UV−vis diffuse reflectance spectra of different samples.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7047958/v1/612abcab24a64d81d9278649.png"},{"id":86758761,"identity":"77590fac-9ca6-4bcb-8bbd-9826a2798761","added_by":"auto","created_at":"2025-07-15 09:53:46","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":102121,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Tauc’s plots, (B) Mott-Schottky plots of Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4 \u003c/sub\u003eand CdS; (C) Calculated work functions for Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e (311) plane and (D) CdS (111) plane; (E) Schematic illustration of the charge transfer mechanism between Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4 \u003c/sub\u003eand CdS before and after contact, as well as that of CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e under light illumination (E\u003csub\u003eVAC\u003c/sub\u003e and E\u003csub\u003ef\u003c/sub\u003e stand for vacuum level and Fermi level, respectively).\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7047958/v1/581d3826aaffa57710a2fbd0.png"},{"id":86759383,"identity":"1f8a84e4-6f69-41ea-8c4b-139fc92e0b29","added_by":"auto","created_at":"2025-07-15 10:01:47","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":98578,"visible":true,"origin":"","legend":"\u003cp\u003e(A) ESR spectra of Pd/Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e and Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e, (B) Schematic diagram of possible\u003c/p\u003e\n\u003cp\u003ephotoexcited electron hole transfer pathways of Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7047958/v1/07bf34aac3f279ffc0af0a7e.png"},{"id":86758778,"identity":"64d98680-c866-4f58-a184-e98472ba7866","added_by":"auto","created_at":"2025-07-15 09:53:47","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":117711,"visible":true,"origin":"","legend":"\u003cp\u003e(A) EIS plots, and (B) timebased photocurrent responses for 3 consecutive light on-and-off cycles of bare SPE (curve a)，Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e/a (curve b)，AChE/b (curve c) and 10ppb CPF/c (curve d); (C) Schematic illustration of the possible sensing mechanism of the PEC sensor.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7047958/v1/11cc4af02ea13cb964560007.png"},{"id":86758794,"identity":"9e0de42c-e8c4-4cef-873e-8eb563711ba6","added_by":"auto","created_at":"2025-07-15 09:53:47","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":58843,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Photocurrent responses to different concentrations of CPF (0, 0.1, 1, 2, 10, 20, 100, 500, 1000, and 2000 ppb, from curve a to curve j), and (B) the corresponding calibration curve. Selectivity of the PEC enzymatic sensor toward 2 ng mL\u003csup\u003e-1\u003c/sup\u003e CPF in comparison with (C) 50-fold of diferent metal ions\u003csup\u003e \u003c/sup\u003eand mixture, (D) 25-fold of other competitive pesticides and mixture. (E) Time-dependent photocurrent stability. (F) Six-fabricated reproducibility.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-7047958/v1/b92de6107300e5d551dbba51.png"},{"id":90827927,"identity":"f8468018-3912-4fb1-90f1-42fe78b5bd5d","added_by":"auto","created_at":"2025-09-08 16:03:28","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1762299,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7047958/v1/be3a0464-fe02-4f06-8c8f-d83b0530f771.pdf"},{"id":86758852,"identity":"dbce3abe-f81f-427b-bef5-e8468abedf1d","added_by":"auto","created_at":"2025-07-15 09:53:48","extension":"jpg","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":50960,"visible":true,"origin":"","legend":"","description":"","filename":"GraphicalAbstract.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7047958/v1/cbfc03d50a93a7e5c65d0551.jpg"},{"id":86758791,"identity":"d7e40263-9620-4175-9659-4332651023ec","added_by":"auto","created_at":"2025-07-15 09:53:47","extension":"doc","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":1069697,"visible":true,"origin":"","legend":"","description":"","filename":"ElectronicSupplementaryMaterial.doc","url":"https://assets-eu.researchsquare.com/files/rs-7047958/v1/18fcf6b61e48e66f7a2b1bf0.doc"},{"id":86759385,"identity":"d4ca96ad-c7c9-4935-b560-c071ca0eab75","added_by":"auto","created_at":"2025-07-15 10:01:48","extension":"png","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":203559,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme 1\u003c/strong\u003e. Schematic diagram illustrating the working principle of the PEC biosensor for CPF detection, including fabrication of AChE-functionalized Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e sensing interface, synergistic charge transfer, and enzyme inhibition-based photocurrent attenuation mechanism.\u003c/p\u003e","description":"","filename":"Scheme1.png","url":"https://assets-eu.researchsquare.com/files/rs-7047958/v1/ae0235256e91ef51f0459da7.png"}],"financialInterests":"No competing interests reported.","formattedTitle":"MOF-templated hollow Pd/CdS@Co3S4 nanocages with synergistic Z-scheme/Schottky effects for photoelectrochemical biosensing of chlorpyrifos featuring exceptional dynamic range","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eAs a representative organophosphorus insecticide, chlorpyrifos (CPF) maintains widespread application in contemporary agricultural practices due to its cost-effectiveness and broad-spectrum pest control capabilities[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Environmental monitoring data reveal that more than 90% of field-applied CPF ultimately migrates into ecosystems through spray drift and surface runoff[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. This compound demonstrates remarkable environmental persistence, principally governed by two physicochemical characteristics: a water solubility and a soil organic carbon-water partitioning coefficient[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. These intrinsic properties necessitate stringent surveillance of CPF residues to mitigate ecological risks and prevent human exposure through contaminated food chains. Therefore, the detection and monitoring of CPF residues are of critical significance for safeguarding human health. Current CPF detection methodologies predominantly rely on conventional analytical techniques such as high-performance liquid chromatography (HPLC) [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], gas chromatography (GC) [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], gas chromatography-tandem mass spectrometry (GC-MS/MS)[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], enzyme inhibition assays[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], and fluorescence analysis[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Nevertheless, these conventional techniques are hampered by notable limitations, including time-consuming sample preparation, costly instrumentation requirements, and insufficient sensitivity. Consequently, it is critically required to establish rapid, sensitive, and cost-effective analytical platforms for detecting CPF in environmental samples.\u003c/p\u003e\u003cp\u003ePhotoelectrochemical (PEC) analysis combines photoactive materials with effective sensing strategies, converting excitation signals (light) into detectable signals (photocurrent). This technique has garnered substantial attention in sensing applications due to its inherent advantages of high sensitivity, low background interference, rapid signal acquisition, and operational simplicity [\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. In PEC sensors, the sensing performance critically depends on the photoelectric conversion efficiency and electron-hole pair separation capability of the photoactive materials[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Despite these merits, the design of high-efficiency photosensitive materials for trace-level detection of environmental pollutants in PEC systems remains a significant challenge. Recent studies have demonstrated that rationally engineered hollow-structured metal-organic framework (MOF)-derived materials can not only preserve the inherent advantages of MOFs (e.g., large specific surface area and high porosity) but also significantly enhance photoelectric conversion efficiency and promote the separation of photogenerated carriers [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Especially, as a non-noble metal compound with favorable band alignment, MOF-derived Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e has emerged as a promising material in PEC applications[\u003cspan additionalcitationids=\"CR17\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Kumar \u003cem\u003eet al.\u003c/em\u003e found that the hollow thin-shell Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e, obtained by in situ sulfidation of ZIF-67, enhanced light-harvesting efficiency and photocurrent response through multi-reflection effects in its internal cavities.[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. However, its widespread application is hindered by inherent limitations such as rapid charge recombination and structural instability. To address these challenges, constructing efficient heterojunctions with compatible metal sulfides (e.g., CdS, ZnS) has been recognized as an effective strategy for improving charge separation towards high PEC performances. For instance, Huang and Mo \u003cem\u003eet al.\u003c/em\u003e developed a multi-MOF integration (ZIF-67@ZIF-8) synthesis strategy and employed a regulated pyrolysis-sulfurization process to fabricate a concentric-layered Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e/NC@ZnS/NC architecture. This heterojunction exhibited superior photoelectrochemical response under visible light irradiation compared to individual Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e and ZnS/NC components[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Besides, the incorporation of noble metal quantum dots (QDs) also has been shown to significantly enhance charge separation efficiency[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Specifically, palladium quantum dots can serve as effective electron acceptors to trap photoelectrons and suppress electron-hole recombination[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Wen \u003cem\u003eet al.\u003c/em\u003e demonstrated that Pd serves as an electron acceptor, facilitating the dissociation of photoinduced charge carriers via establishing a Schottky barrier between Pd and CdS microspheres, thereby enhancing the behavior of the photogenerated carriers[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eGuided by this train of thought, a dual charge-transfer system was developed using ZIF-67-derived Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e for sensitive CPF detection, as shown in Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The configuration strategically incorporated AChE as biological recognition elements through covalent immobilization. The designed heterostructure exhibited exceptional electron-hole pair separation efficiency via optimized built-in electric field modulation. The precisely aligned energy bands and enhanced carrier transport properties inherent to this Z-scheme architecture facilitated generation of a stable, amplified anodic photocurrent signal. Moreover, Pd QDs functioned as efficient electron reservoirs, enhancing interfacial charge separation through Schottky barrier effects. The nanocomposite was subsequently anchored onto screen-printed electrodes (SPEs), functionalized with glutaraldehyde (GLD), and covalently conjugated with AChE via a crosslinking strategy to achieve biorecognition probe fixation. CPF detection relied on enzyme-mediated phosphorylation producing electroactive species that competed with the Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e system for photogenerated electrons. This electron depletion mechanism generated concentration-dependent photocurrent reduction, establishing a highly responsive biosensing platform. The linear correlation between photocurrent attenuation and CPF concentration enabled precise quantification across an extensive dynamic range.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"2. Experiment section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Synthesis of nanomaterials.\u003c/h2\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003cp\u003e\u003cb\u003eSynthesis of ZIF-67 derived Co\u003c/b\u003e\u003csub\u003e\u003cb\u003e3\u003c/b\u003e\u003c/sub\u003e\u003cb\u003eS\u003c/b\u003e\u003csub\u003e\u003cb\u003e4\u003c/b\u003e\u003c/sub\u003e. The ZIF-67 precursor was synthesized according to a literature method[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e was subsequently synthesized from ZIF-67 via a solvothermal approach. Specifically, ZIF-67 (120 mg) along with thioacetamide (TAA, 100 mg) were separately dissolved in ethanol (30 mL each) and ultrasonically dispersed. The solutions were mixed and stirred for 30 min, then sealed in a Teflon-lined stainless steel autoclave and maintained at 160\u0026deg;C for 12 h under solvothermal conditions. The resultant precipitate was collected via centrifugal isolation (8000 rpm, 5 min), rinsed thrice alternately with deionized water and ethanol, followed by vacuum dehydration at 70\u0026deg;C to afford the final black Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e powder.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003cp\u003e\u003cb\u003eSynthesis of CdS@Co\u003c/b\u003e\u003csub\u003e\u003cb\u003e3\u003c/b\u003e\u003c/sub\u003e\u003cb\u003eS\u003c/b\u003e\u003csub\u003e\u003cb\u003e4\u003c/b\u003e\u003c/sub\u003e. Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e (90 mg), Cd(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;4H\u003csub\u003e2\u003c/sub\u003eO (32 mg), and TAA (15.6 mg) were separately dissolved in ethanol (20 mL each) and ultrasonically dispersed. The Cd(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;4H\u003csub\u003e2\u003c/sub\u003eO solution was slowly added to the Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e solution with stirring for 10 min. Subsequently, the TAA solution was slowly added to the mixture and stirred for 20 min. The mixture then underwent solvothermal reaction at 120\u0026deg;C for 10 h. The product was collected, washed thoroughly, and dried overnight under vacuum at 70\u0026deg;C.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003cp\u003e\u003cb\u003eSynthesis of Pd/CdS@Co\u003c/b\u003e\u003csub\u003e\u003cb\u003e3\u003c/b\u003e\u003c/sub\u003e\u003cb\u003eS\u003c/b\u003e\u003csub\u003e\u003cb\u003e4\u003c/b\u003e\u003c/sub\u003e. Pd QDs were deposited onto the surface of CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e using a photo-reduction method adapted from the literature[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Specifically, CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e material (100 mg) was dispersed in ethanol (30 mL). To this dispersion, 0.6 mL of a palladium acetate solution in DMF (1.67 mg/mL) was added. The mixture was stirred for 30 min in the dark, then illuminated (300 W Xe lamp) and agitated for a further 15 min to perform the photo-reduction reaction. The product was washed several times with water and ethanol, and dried in a vacuum oven.\u003c/h2\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Construction of Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e-based PEC biosensing platform\u003c/h2\u003e\u003cp\u003eA 10 \u0026micro;L aliquot of Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e suspension (5 mg\u0026middot;mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) was deposited onto the central region of the SPE and dried at 60\u0026deg;C. Then, 10 \u0026micro;L of 5% glutaraldehyde (GLD) solution was applied and incubated at room temperature for 30 min. Next, 10 \u0026micro;L of AChE solution was applied and incubated at 37\u0026deg;C for 2 h for enzyme immobilization via amide bond formation onto the material surface. The electrode was thoroughly rinsed with 0.1 M PBS (pH 7.0) after each modification step to remove non-specifically bound components. The fabricated SPE was stored at 4\u0026deg;C for storage for subsequent applications.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e2.3 PEC detection of CPF\u003c/h2\u003e\u003cp\u003eThe CPF assay was performed by drop-casting 10 \u0026micro;L of CPF solutions with various concentrations onto the modified screen-printed electrode, followed by incubation at 37\u0026deg;C for 1 h to facilitate CPF phosphorylation with AChE. After incubation, the electrode was thoroughly rinsed with PBS buffer to eliminate unbound CPF molecules. Subsequently, 60 \u0026micro;L of 0.1 M phosphate buffer (pH 7.0) comprising 0.1 M ascorbic acid (AA) was applied to electrode surface. PEC measurements were conducted using a photoelectrochemical system integrated with a 1 W LED light source (emission wavelength: 465 nm) under an applied bias potential of -65 mV. All electrochemical experiments were implemented using a standard electrochemical workstation.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Characterization\u003c/h2\u003e\u003cp\u003eThe progressive morphological evolution of Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e was systematically investigated through scanning electron microscopy (SEM) analysis. As demonstrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA and \u003cb\u003eFig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003eA\u003c/b\u003e, the ZIF-67 precursor displayed uniform rhombic dodecahedral morphology with particle diameters spanning 800\u0026thinsp;~\u0026thinsp;900 nm. Following sulfidation treatment, this structure underwent complete transformation into hollow Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e polyhedrons characterized by pronounced surface texturization and distinct edge notching (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB, S1B-C). \u003cb\u003eFig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003eD\u003c/b\u003e further revealed the formation of an ultrathin Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e shell with an average thickness of precisely 35 nm. Subsequent deposition of CdS nanoparticles onto the Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e framework yielded well-defined CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e heterostructures, which successfully maintained the dodecahedral architecture while exhibiting uniform surface nanoparticle decoration (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eC). Critically, the introduced Pd QDs were integrated without destroying the structural integrity of the CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e framework or inducing morphological alterations (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eD).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe detailed microstructures of as-prepared Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e sample were further explored by the transmission electron microscopy (TEM) and energy spectrum analysis (EDS) mapping. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eE and \u003cb\u003eFig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003eE\u003c/b\u003e, Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e was reconfirmed as a hollow dodecahedral spherical nanostructure with approximately 800\u0026ndash;900 nm, consistent with previous observations. In addition, it can be seen that the Pd QDs with ~\u0026thinsp;7 nm were uniformly attached to the outer shell layer (\u003cb\u003eFig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003eF)\u003c/b\u003e. Notably, the synthesized engineered nanocages effectively promote the charge-carrier dissociation and migration, while offering an increased surface area and enhanced exposure of active sites[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. HRTEM (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eF) revealed these two semiconductors with interplanar distances of 0.355 and 0.331 nm, corresponding to (111) facet of CdS and (311) facet of Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e, respectively[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. TEM-EDS mapping analysis verified that the Co, Cd, S, and Pd elements were uniformly distributed in the composite material (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eG). Besides, SEM-EDS characterization confirmed the proportional composition of Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e nanocomposites aligned with theoretical predictions primarily comprising Co, Cd, S, and Pd elements (\u003cb\u003eFig. S2\u003c/b\u003e).\u003c/p\u003e\u003cp\u003eThe crystalline phases and structural evolution of the materials were examined through X-ray diffraction (XRD) analysis, as presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA. Pristine CdS exhibited three distinct diffraction peaks at 26.54\u0026deg;, 44.04\u0026deg;, and 52.16\u0026deg;, indexed as the (111), (220), and (311) crystallographic facets of cubic zinc blende CdS (PDF # 01-080-0019)[\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Successful synthesis of ZIF-67 precursors was confirmed by their characteristic diffraction pattern (\u003cb\u003eFig. S3\u003c/b\u003e). Subsequent sulfidation converted ZIF-67 into Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e, demonstrating four prominent peaks at 26.86\u0026deg;, 31.61\u0026deg;, 38.35\u0026deg;, and 55.36\u0026deg; indexed to the (220), (311), (400), and (440) planes of cubic Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e (PDF # 01-071-4923)[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Hydrothermal treatment with cadmium nitrate and thioacetamide yielded CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e composites, evidenced by the coexistence of characteristic CdS peaks superimposed on the Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e diffraction pattern. Notably, Pd QDs incorporation could not adjust the primary diffraction features of CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e without introducing new crystalline phases. The absence of discernible Pd-related diffraction signals suggests effective dispersion of Pd QDs below the XRD detection threshold, attributable to their ultralow loading concentration and atomic-scale distribution within the composite matrix[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe elemental composition and chemical valence state of the composites were investigated using X-ray photoelectron spectroscopy (XPS). As show in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB, the presence of Co, Cd, Pd and S elements across the survey XPS spectra of the hybrid material, proving the successfully synthesis of Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e nanocomposites. In Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eC, the high-resolved Co 2p spectrum displays two spin-orbit doublets accompanied by dual satellite signatures (Sat.). It can be seen that the binding energies observed at 778.3 eV and 782.6 eV, as well as 793.1 eV and 798.8 eV, were assigned as Co 2p\u003csub\u003e3/2\u003c/sub\u003e and Co 2p\u003csub\u003e1/2\u003c/sub\u003e orbitals. This doublet confirms the simultaneous presence of Co\u003csup\u003e2+\u003c/sup\u003e and Co\u003csup\u003e3+\u003c/sup\u003e states that was in consistent with valence of Co in the Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e[\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Furthermore, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eD reveals the high-resolved XPS spectra of Cd 2p, the strong peaks located at 405.0 eV and 411.7 eV in the Cd XPS scans could be characteristic of Cd 3d\u003csub\u003e5/2\u003c/sub\u003e and Cd 3d\u003csub\u003e3/2\u003c/sub\u003e states for divalent cadmium in CdS, respectively. The peaks at 161.4 eV and 162.7 eV were identified as the Co\u0026ndash;S and Cd\u0026ndash;S bond features captured by the S 2p\u003csub\u003e1/2\u003c/sub\u003e and S 2p\u003csub\u003e3/2\u003c/sub\u003e orbital signals (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eE)[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Notably, the S 2p spectrum exhibits strong peaks at 169.3 eV and 170.4 eV, which could be ascribed to the formation of sulfate species originated from surface oxidation[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Moreover, the two characteristic peaks at 336.2 eV and 341.4 eV belong to the Pd 3d\u003csub\u003e5/2\u003c/sub\u003e and Pd 3d\u003csub\u003e3/2\u003c/sub\u003e orbitals of palladium (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eF), respectively, suggesting Pd is primarily in the form of Pd\u003csup\u003e0\u003c/sup\u003e[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. Besides, the element contents of Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e composite was determined in \u003cb\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e.\u003c/p\u003e\u003cp\u003eThe separation and transport behavior of photoinduced carriers in the as-prepared samples were studied by measuring their PEC signals (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA). CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e exihibited an particularly obvious photocurrent response compared with Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e and CdS, suggesting the establishment of a Z-scheme junction at their interface. However, The PEC response signal of Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e was approximately 1.5 times higher than that of CdS @Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e, indicating that the Pd QDs effectively accelerated the dissociation of photoinduced charge carriers, thereby enhancing the signal response and sensitivity of the composite material. Additionally, the optimal deposition quantities of CdS and Pd QDs on ZIF-67-derived Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e were systematically investigated and determined (\u003cb\u003eFig. S4\u003c/b\u003e). Subsequently, electrochemical impedance spectroscopy (EIS) was conducted on the various samples to evaluate the charge carrier transfer efficiency associated with the PEC responses. The Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB revealed that the Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e exhibited a notably reduced impedance compared to CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e, demonstrating that the incorporation of Pd QDs significantly improved the mobility of photogenerated charge carriers, which consequently led to an enhanced PEC performance. On the other hand, the transient photocurrent responses conducted on the screen-printed electrode (SPE) modified with the as-prepared samples displayed excellent consistency with the results depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC.\u003c/p\u003e\u003cp\u003eThe optical properties of different samples were investigated through UV\u0026ndash;Vis diffuse reflectance spectroscopy (DRS). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eD, pristine CdS displayed a characteristic absorption edge at ~\u0026thinsp;480 nm, consistent with its intrinsic bandgap properties. In contrast, Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e exhibited broad-spectrum absorption spanning ultraviolet to near-infrared regions, a feature retained in both CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e and Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e composites. Notably, the heterostructured composites demonstrated significantly enhanced light absorption capacity compared to individual Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e components. This optical enhancement suggests effective interfacial charge transfer between Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e and CdS, facilitated by heterojunction formation. The optimized light utilization in Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e further confirms the beneficial role of Pd ODs in promoting photon harvesting through surface plasmon resonance effects.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e3.2 Mechanism of Z-scheme heterojunction in Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e\u003c/h2\u003e\u003cp\u003eTo elucidate the electronic band configuration, energy gaps (E\u003csub\u003eg\u003c/sub\u003e) of Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e and CdS were quantified via the Kubelka-Munk method based on the equation[\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]: (\u003cem\u003eαℎυ\u003c/em\u003e)\u003csup\u003e\u003cem\u003e1/2\u003c/em\u003e\u003c/sup\u003e \u003cem\u003e=A\u003c/em\u003e (\u003cem\u003eℎυ - E\u003c/em\u003e\u003csub\u003e\u003cem\u003eg\u003c/em\u003e\u003c/sub\u003e). Thus, the E\u003csub\u003eg\u003c/sub\u003e values for Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e and CdS were evaluated at 1.5 eV and 2.3 eV from Tauc\u0026rsquo;s plot (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA), aligning with literature[\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. Complementary Mott-Schottky analysis explored the flat-band potentials (E\u003csub\u003efb\u003c/sub\u003e). As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB, the E\u003csub\u003efb\u003c/sub\u003e values for Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e and CdS were \u0026minus;\u0026thinsp;0.88 and 0.77 eV (\u003cem\u003evs.\u003c/em\u003e Ag/AgCl), respectively. The characteristic positive slopes confirmed both as n-type semiconductors. For n-type materials, E\u003csub\u003efb\u003c/sub\u003e approximates the conduction band minimum (E\u003csub\u003eCB\u003c/sub\u003e)[\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. Hence, E\u003csub\u003eCB\u003c/sub\u003e and valence band (E\u003csub\u003eVB\u003c/sub\u003e) positions were derived using[\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]: \u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eCB\u003c/em\u003e\u003c/sub\u003e (\u003cem\u003eNHE\u003c/em\u003e)\u0026thinsp;\u003cem\u003e=\u0026thinsp;E\u003c/em\u003e\u003csub\u003e\u003cem\u003efb\u003c/em\u003e\u003c/sub\u003e (\u003cem\u003evs. Ag/AgCl\u003c/em\u003e)\u0026thinsp;\u003cem\u003e+\u0026thinsp;0.197\u003c/em\u003e, yielding the data shown in \u003cb\u003eTable S2\u003c/b\u003e.\u003c/p\u003e\u003cp\u003eAt interfaces formed between dissimilar semiconductors, the work function (WF) of each material dictates the relative positioning of its energy bands, and this value determines the orientation of the spontaneously formed internal electric field within the junction structure. In Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eC-D, the density functional theory (DFT) computations were conducted to calculate the WF of Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e (311) and CdS (111), the results were 4.84 eV and 6.35 eV. Besides, the Fermi level (E\u003csub\u003ef\u003c/sub\u003e) and Vacuum level (E\u003csub\u003eVAC\u003c/sub\u003e) of Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e and CdS were calculated to be -1.28 eV and \u0026minus;\u0026thinsp;1.64 eV, 3.56 eV and 4.71 eV, respectively (\u003cb\u003eTable S2\u003c/b\u003e). In the absence of light, the internal electric field generated by the interfacial potential difference at the CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e junction drives electron transfer from Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e with a higher Fermi level (-1.28 eV) to CdS with a lower Fermi level (-1.64 eV), establishing Fermi level equilibrium[\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. This caused upward band bending at the Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e side due to electron depletion and downward band bending at the CdS side due to electron accumulation. Under illumination, photoelectrons in the conduction band of Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e may migrate and recombine with photoholes in the valence band of CdS, facilitated by coulombic interactions. Consequently, the combination of Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e and CdS can result in a proficient Z-scheme CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e heterostructure.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eTo trace the pathway of charge transfer within the Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e PEC sensing platform, electron spin resonance (ESR) spectroscopy targeted transient \u0026bull;O\u003csub\u003e2\u003c/sub\u003e⁻ radical species. 5,5-Dimethyl-1-pyrroline-N-oxide (DMPO) acted as a stabilizing agent for these radicals, enabling the observation of \u0026bull;O\u003csub\u003e2\u003c/sub\u003e⁻ in methanol-based dispersions. As depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA, the Pd/Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e and Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e both exhibited the DMPO-\u0026bull;O\u003csub\u003e2\u003c/sub\u003e⁻ signal peaks under visible light irradiation. One can be seen that, the peak intensity of the latter was exceeding that of the former by several folds, indicating that the encapsulation of CdS significantly enhanced the trapping of \u0026bull;O\u003csub\u003e2\u003c/sub\u003e⁻.\u003c/p\u003e\u003cp\u003eTo explain these findings, a possible electron migration pathway was proposed. As illustrated in the Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB, if photogenerated electrons from the CB of Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e migrated to the CB of CdS, subsequently captured by Pd QDs and transferred to the external circuit via the SPE, the high recombination rate of photogenerated electron-hole pairs, combined with the higher CB potential of CdS (-0.57 eV) compared to that of Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e, would have hindered the trapping of \u0026bull;O\u003csub\u003e2\u003c/sub\u003e⁻. Conversely, if photogenerated electrons from the CB of CdS migrated to the VB of Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e, concurrently with CB-derived photoelectrons of Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e were captured by Pd QDs and transferred to the external circuit via the SPE, this migration pathway would have suppressed the recombination of photoinduced electron-hole pairs. Moreover, the lower potential (-0.68 eV) of this pathway would have strongly promoted the trapping of \u0026bull;O\u003csub\u003e2\u003c/sub\u003e⁻. This electron migration behavior further confirmed the Z-scheme configuration of the CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e heterostructure.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Feasibility of the developed PEC sensor\u003c/h2\u003e\u003cp\u003eElectrochemical impedance spectroscopy (EIS) assessed the sensing electrode preparation, with the Nyquist plot semicircle size representing the resistance to charge transfer (Rct) at the interface. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eA, the bare SPE (curve a) displayed the smallest Rct value. Modification with Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e (curve b) substantially increased the Rct due to the semiconductor characteristics. Subsequent immobilization of AChE through amide bond formation (curve c) induced a sharp Rct increase caused by steric hindrance effects. Following incubation with 10 ppb CPF for 60 min (curve d), the developed-SPE exhibited further elevated Rct. This final increase originated from the irreversible phosphorylation of AChE by chlorpyrifos, which modifies the enzyme's tertiary structure and increases electron transfer barrier.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe stepwise electrode modification process was corroborated through PEC characterization. As demonstrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eB, the pristine SPE showed negligible photocurrent response, while the Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e-modified SPE exhibited maximum photocurrent intensity due to superior photoelectric conversion capability. AChE functionalization caused significant photocurrent attenuation, consistent with EIS analysis. Subsequent incubation with 10 ppb CPF induced further photocurrent decrease. This signal suppression mechanism arises from enzyme inhibition-induced phosphorylated adduct formation, where the phosphorylation products serve as competitive electron acceptors that intercept photogenerated electrons from Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e, thereby impeding electron migration to the collector electrode. The proposed sensing mechanism is schematically presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eC. The complementary EIS and PEC results collectively validate successful sensor fabrication.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003e3.4 Performance of the PEC sensor for CPF detection\u003c/h2\u003e\u003cp\u003ePrior to CPF detection, the optimization of AChE immobilization and the CPF incubation were systematically explored. As depicted in \u003cb\u003eFig. S5\u003c/b\u003e, photocurrent stabilization was achieved at 2 h for AChE immobilization and 60 min for CPF incubation, establishing these durations as optimal operational parameters for the sensing platform. Under optimized conditions, the photocurrent changes of the sensing system exposed to different concentrations of CPF were recorded using an electrochemical workstation (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eA). In the absence of CPF, a high intensity photocurrent signal was observed (curve a). However, introducing CPF caused a progressive attenuation of the photocurrent response as its concentration rose from 0.1 to 2000 ppb (curves b-j). This response resulted from the biomolecular recognition event between CPF and the sensing platform's AChE component, which led to the formation of electron-withdrawing groups on the electrode surface. As a result, the photogenerated charge carriers produced by light excitation became less accessible for capture by the electrochemical workstation, leading to a reduction in the photocurrent. Consequently, the photocurrent displayed a strong linear correlation with the logarithm of CPF concentrations across the 0.1 ppb to 2 ppm range, following the equation [I (\u0026micro;A) = -3.1426 lg C\u003csub\u003eCPF\u003c/sub\u003e + 22.1199, R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.9983], as presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eB. This exceptional four order of magnitude dynamic range primarily results from synergistic Z-scheme and Schottky effects in the engineered heterostructure. The dual charge transfer mechanism integrates Z scheme recombination suppression with Schottky barrier electron trapping, achieving approximately five-fold photocurrent amplification versus pristine components. This enhanced signal baseline critically enables accommodation of extensive concentration dependent attenuation, thereby facilitating ultra wide linear quantification, with the calculated LOD shown 0.05 ppb (S/N\u0026thinsp;=\u0026thinsp;3). Comparable analytical capability for CPF was observed with the developed PEC sensing platform when measured against most existing methodologies summarized in \u003cb\u003eTable S3\u003c/b\u003e.\u003c/p\u003e\u003cp\u003eAssessing the sensor's specificity is vital for determining its real-world utility. Consequently, relevant interfering species, including various metal ions as well as other organic pesticides such as imidacloprid (IMI), acetamiprid (ACE), carbaryl (CAR), and parathion-methyl (PM), were used to evaluate the selectivity of the PEC enzymatic sensor. As depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eC-D, compared to CPF and its mixtures, the interfering substances did not exhibit significant photocurrent responses, indicating that the developed PEC sensor possesses excellent selectivity. Furthermore, Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eE demonstrated that the photocurrent showed no significant variation during repeated illumination over 300s, with a well relative standard deviation (RSD) of 1.22%, demonstrating the exceptional robustness of the PEC sensor. Furthermore, reproducibility assessments were executed via performing PEC tests on 2 ng\u0026middot;mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e CPF using six paralleled electrodes under identical conditions (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eF). The results revealed that the sensor exhibited terrific reproducibility, with an RSD of 1.96%. After storage in a 4\u0026deg;C for 7 days, the PEC signals of 100 ng\u0026middot;mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e of CPF remained at 97% of its first day value, confirming the storage stability of the sensor (\u003cb\u003eFig. S6\u003c/b\u003e).\u003c/p\u003e\u003cp\u003eValidating this engineered biosensor's performance in detecting CPF across environmental specimens, recovery studies were performed using Yangtze River water. Known concentrations of CPF (10, 50, and 100 ng\u0026middot;mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) were spiked into pre-processed samples. As summarized in \u003cb\u003eTable S4\u003c/b\u003e, the obtained RSDs and recovery rates ranged from 5.04%~6.02% and 98.5%~102.1%, respectively. These results confirmthe reliability of the Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e PEC enzymatic sensor for quantifying CPF in complex environmental matrices.\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn summary, This study demonstrated a MOF-templated ternary hollow Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e nanocage photoelectrochemical biosensor that achieved ultra-broad linear detection of chlorpyrifos (0.1\u0026thinsp;~\u0026thinsp;2000 ng\u0026middot;mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) through engineered multi-electron transfer pathways. DFT-validated interfacial charge manipulation was explored by a Fermi-level offset driving Z-scheme heterojunction formation between CdS and Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e, which thereby created a built-in electric field that synergized with Schottky electron trapping via Pd QDs. This dual charge-transfer strategy amplifies photocurrent\u0026thinsp;~\u0026thinsp;5-fold versus pristine components, establishing the critical high-intensity signal baseline necessary for accommodating concentration-dependent attenuation across four orders of magnitude. Functionalized with AChE, the platform quantifies CPF via inhibition-mediated competitive electron consumption, delivering a 0.05 ng\u0026middot;mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e detection limit alongside exceptional specificity, stability (\u0026gt;\u0026thinsp;97% signal retention over 7 days), and reproducibility (RSD\u0026thinsp;=\u0026thinsp;1.96%). Validated in complex matrices with 98.5\u0026thinsp;~\u0026thinsp;102.1% recovery accuracy, this work establishes DFT-guided electronic engineering of MOF heterostructures as a promising strategy for designing next-generation environmental sensors with prominent dynamic range.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eShipeng Huang: Writing-Original Draft, Methodology, Validation. Haicai Huang: Data Curation, Methodology. Jingqiu Liu: Data Curation, Formal analysis. Haoyu Duan: Data Curation, Formal analysis. Xi Chen: Writing - Review \u0026amp; Editing, Conceptualization, Validation, Funding acquisition. Houyang Chen: Writing - Review \u0026amp; Editing, Conceptualization, Investigation, Funding acquisition.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThis work is supported by the Postdoctoral Program of Natural Science Foundation of Chongqing (CSTB2023NSCQ-BHX0231), the Startup Foundation of Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences. Computations were performed on Hefei advanced computing center.\u003c/p\u003e\u003cp\u003e\u003cb\u003eElectronic Supplementary Material\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe Electronic Supplementary Material is available free of charge. Materials and reagents, electrochemical tests, application of the PEC sensor in real sample, density functional theory (DFT) calculations, SEM images, transient photocurrent responses, stability tests, and so on.\u003c/p\u003e\u003cp\u003e\u003cb\u003eFunding Declaration\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThis work is supported by the Postdoctoral Program of Natural Science Foundation of Chongqing (CSTB2023NSCQ-BHX0231), the Startup Foundation of Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences. Computations were performed on Hefei advanced computing center.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eC.S. Pundir, A. Malik, Preety, Bio-sensing of organophosphorus pesticides: A review, Bioseors and Bioelectronics 140 (2019) 111348.\u003c/li\u003e\n\u003cli\u003eM. Zhang, Z. Chen, X. Liu, C. Song, C. Zeng, T. Lv, Z. Xu, X. Chen, L. Wang, B. Liu, X. Peng, Dual-mode supramolecular fluorescent probe for rapid and on-site detection of chlorpyrifos in the environment, Journal of Hazardous Materials 452 (2023) 131177. \u003c/li\u003e\n\u003cli\u003eJ. Ma, P. Zhu, W. Wang, X. Zhang, P. Wang, Y. Sultan, Y. Li, W. Ding, X. Li, Environmental impacts of chlorpyrifos: Transgenerational toxic effects on aquatic organisms cannot be ignored, Science of The Total Environment 905 (2023) 167311. \u003c/li\u003e\n\u003cli\u003eI. Ion, A.C. Ion, Determination of chlorpyriphos in broccoli using a voltammetric acetylcholinesterase sensor based on carbon nanostructure\u0026ndash;chitosan composite material, Materials Science and Engineering: C 32 (2012) 1001\u0026ndash;1004. \u003c/li\u003e\n\u003cli\u003eA.R. Kulkarni, K.S. Soppimath, A.M. Dave, M.H. Mehta, T.M. Aminabhavi, Solubility study of hazardous pesticide (chlorpyrifos) by gas chromatography, Journal of Hazardous Materials 80 (2000) 9\u0026ndash;13.\u003c/li\u003e\n\u003cli\u003eD.A. Varela-Mart\u0026iacute;nez, M.\u0026Aacute;. Gonz\u0026aacute;lez-Curbelo, J. Gonz\u0026aacute;lez-S\u0026aacute;lamo, J. Hern\u0026aacute;ndez-Borges, Analysis of multiclass pesticides in dried fruits using QuEChERS-gas chromatography tandem mass spectrometry, Food Chemistry 297 (2019) 124961. \u003c/li\u003e\n\u003cli\u003eZ. Chen, L. Zhao, Z. Zhang, J. Wu, L. Zhang, X. Jing, X. Wang, Dispersive liquid‒liquid microextraction combined with enzyme-linked immunosorbent assay for the analysis of chlorpyrifos in cereal samples, Talanta 265 (2023) 124802. \u003c/li\u003e\n\u003cli\u003eM. Zhang, Z. Chen, X. Liu, C. Song, C. Zeng, T. Lv, Z. Xu, X. Chen, L. Wang, B. Liu, X. Peng, Dual-mode supramolecular fluorescent probe for rapid and on-site detection of chlorpyrifos in the environment, Journal of Hazardous Materials 452 (2023) 131177. \u003c/li\u003e\n\u003cli\u003eD. Zhao, R. Jiang, X. Liu, S. Alwarappan, Flexible enzyme-like platform based on a 1-D CeVO\u003csub\u003e4\u003c/sub\u003e/2-D rGO-MCC heterostructure as sensor for the detection of intracellular superoxide anions, Sensors and Actuators B: Chemical 400 (2024) 134863. \u003c/li\u003e\n\u003cli\u003eK. Yin, J. Zhang, Y. Xue, A.-J. Wang, L.-P. Mei, P. Song, J.-J. Feng, Target-assisted self-powered photoelectrochemical sensor based on Ag\u003csub\u003e2\u003c/sub\u003eS/BiOCl heterojunction for ultrasensitive chlorpyrifos detection, Talanta 286 (2025) 127502. \u003c/li\u003e\n\u003cli\u003eJ. Qian, Y. Liu, H. Cui, F. You, H. Yang, K. Wang, J. Wei, L. Long, C. Wang, Incorporation of ZnIn\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e semiconductors with S-vacancy engineered MoS\u003csub\u003e2\u003c/sub\u003e nanosheets to develop sensitive photoelectrochemical aptasensor for aflatoxin B1 detection, Sensors and Actuators B: Chemical 403 (2024) 135195.\u003c/li\u003e\n\u003cli\u003eL. Zhang, F.-Z. Chen, H. Sun, R. Meng, Q. Zeng, X. Wang, H. Zhou, Stimulus-Responsive Metal\u0026ndash;Organic Framework Signal-Reporting System for Photoelectrochemical and Fluorescent Dual-Mode Detection of ATP, ACS Appl. Mater. Interfaces 14 (2022) 46103\u0026ndash;46111.\u003c/li\u003e\n\u003cli\u003eH. Shang, H. Xu, L. Jin, C. Wang, C. Chen, T. Song, Y. Du, 3D ZnIn\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e nanosheets decorated ZnCdS dodecahedral cages as multifunctional signal amplification matrix combined with electroactive/photoactive materials for dual mode electrochemical \u0026ndash; photoelectrochemical detection of bovine hemoglobin, Biosensors and Bioelectronics 159 (2020) 112202. \u003c/li\u003e\n\u003cli\u003eJ. Peng, J. Yang, B. Chen, S. Zeng, D. Zheng, Y. Chen, W. Gao, Design of ultrathin nanosheet subunits ZnIn\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e hollow nanocages with enhanced photoelectric conversion for ultrasensitive photoelectrochemical sensing, Biosensors and Bioelectronics 175 (2021) 112873. \u003c/li\u003e\n\u003cli\u003eM. Liu, Z. Xing, Z. Li, W. Zhou, Recent advances in core\u0026ndash;shell metal organic frame-based photocatalysts for solar energy conversion, Coordination Chemistry Reviews 446 (2021) 214123.\u003c/li\u003e\n\u003cli\u003eF. Zhang, H.-Q. Zhuang, J. Song, Y.-L. Men, Y.-X. Pan, S.-H. Yu, Coupling cobalt sulfide nanosheets with cadmium sulfide nanoparticles for highly efficient visible-light-driven photocatalysis, Applied Catalysis B: Environmental 226 (2018) 103\u0026ndash;110. \u003c/li\u003e\n\u003cli\u003eJ. Qiu, W. Zheng, R. Yuan, C. Yue, D. Li, F. Liu, J. Zhu, A novel 3D nanofibrous aerogel-based MoS\u003csub\u003e2\u003c/sub\u003e@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e heterojunction photocatalyst for water remediation and hydrogen evolution under simulated solar irradiation, Applied Catalysis B: Environmental 264 (2020) 118514. \u003c/li\u003e\n\u003cli\u003eY. Xie, L. Chen, Q. Jin, J. Yun, X. Liang, MoS\u003csub\u003e2\u003c/sub\u003e\u0026ndash;Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e hollow polyhedrons derived from ZIF-67 towards hydrogen evolution reaction and hydrodesulfurization, International Journal of Hydrogen Energy 44 (2019) 24246\u0026ndash;24255.\u003c/li\u003e\n\u003cli\u003eP. Anil Kumar Reddy, C. Lee, S. Bae, ZIF-67 templated synthesis of sea urchin-like P\u0026ndash;Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e@CdS nanocomposite for enhanced H2 production and dye oxidation under solar light: Role of P-doping on cocatalyst property of Co3S4, Composites Part B: Engineering 295 (2025) 112178.\u003c/li\u003e\n\u003cli\u003eL. Huang, S. Mo, X. Zhao, J. Zhou, X. Zhou, Y. Zhang, Y. Fan, Q. Xie, B. Li, J. Li, Constructing Co and Zn atomic pairs in core-shell Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e/NC@ZnS/NC derived from MOF-on-MOF nanostructures for enhanced photocatalytic CO\u003csub\u003e2\u003c/sub\u003e reduction to C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e4\u003c/sub\u003e, Applied Catalysis B: Environment and Energy 352 (2024) 124019. \u003c/li\u003e\n\u003cli\u003eS. Liang, Y. Xia, S. Zhu, S. Zheng, Y. He, J. Bi, M. Liu, L. Wu, Au and Pt co-loaded g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets for enhanced photocatalytic hydrogen production under visible light irradiation, Applied Surface Science 358 (2015) 304\u0026ndash;312.\u003c/li\u003e\n\u003cli\u003eS.A. Rawool, M.R. Pai, A.M. Banerjee, S. Nath, R.D. Bapat, R.K. Sharma, Jagannath, B. Dutta, P.A. Hassan, A.K. Tripathi, Superior Interfacial Contact Yields Efficient Electron Transfer Rate and Enhanced Solar Photocatalytic Hydrogen Generation in M/C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e Schottky Junctions, ACS Appl. Mater. Interfaces 15 (2023) 39926\u0026ndash;39945.\u003c/li\u003e\n\u003cli\u003eX. Zhou, X. Yu, L. Peng, J. Luo, X. Ning, X. Fan, X. Zhou, X. Zhou, Pd(II) coordination molecule modified g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e for boosting photocatalytic hydrogen production, Journal of Colloid and Interface Science 671 (2024) 134\u0026ndash;144.\u003c/li\u003e\n\u003cli\u003eZ. Wen, W. Zhu, F. You, R. Yuan, L. Ding, N. Hao, J. Wei, K. Wang, Ultrasensitive photoelectrochemical aptasensor for carbendazim detection based on in-situ constructing Schottky junction via photoreducing Pd nanoparticles onto CdS microsphere, Biosensors and Bioelectronics 203 (2022) 114036.\u003c/li\u003e\n\u003cli\u003eJ. Tan, B. Peng, L. Tang, G. Zeng, Y. Lu, J. Wang, X. Ouyang, X. Zhu, Y. Chen, H. Feng, CuS QDs/Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e Polyhedra-Driven Multiple Signal Amplifications Activated h-BN Photoeletrochemical Biosensing Platform, Anal. Chem. 92 (2020) 13073\u0026ndash;13083. \u003c/li\u003e\n\u003cli\u003eX. Chen, H. Huang, Q. Wu, F. Xue, Z. Zhao, J. Liu, H. Duan, H. Chen, Triggering \u0026ldquo;signal-on\u0026rdquo; photoelectrochemical responses by heterojunction transition for selective detection of copper(II) based on Pd/MoS\u003csub\u003e2\u003c/sub\u003e@g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposites, Analytica Chimica Acta 1283 (2023) 341940.\u003c/li\u003e\n\u003cli\u003eS. Wang, B.Y. Guan, X. Wang, X.W.D. Lou, Formation of Hierarchical Co\u003csub\u003e9\u003c/sub\u003eS\u003csub\u003e8\u003c/sub\u003e@ZnIn\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e Heterostructured Cages as an Efficient Photocatalyst for Hydrogen Evolution, J. Am. Chem. Soc. 140 (2018) 15145\u0026ndash;15148.\u003c/li\u003e\n\u003cli\u003eH. Huang, Y. Cai, Q. Xu, M. Xiong, L. Ding, X. Wang, Q. Jiang, Q. Li, X. Han, J. Hu, Y. Liu, S‐Scheme CdS/Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e Double‐Shelled Hollow Nanoboxes for Enhanced Photocatalytic Hydrogen Evolution, Small (2025) 2501710.\u003c/li\u003e\n\u003cli\u003eF. Jiang, S. Liu, W. Li, Y. Li, S. Wang, H. Lin, Q. Liu, Y. Li, Q. Wei, A signal-on photoelectrochemical sensor based on the target-triggered double-ion exchange reaction for Hg\u003csup\u003e2+\u003c/sup\u003e under visible light, Sensors and Actuators B: Chemical 405 (2024) 135368. \u003c/li\u003e\n\u003cli\u003eY. Guo, J. Tang, H. Qian, Z. Wang, Y. Yamauchi, One-Pot Synthesis of Zeolitic Imidazolate Framework 67-Derived Hollow Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e@MoS\u003csub\u003e2\u003c/sub\u003e Heterostructures as Efficient Bifunctional Catalysts, Chem. Mater. 29 (2017) 5566\u0026ndash;5573. \u003c/li\u003e\n\u003cli\u003eX. Chen, W. Zhang, L. Zhang, L. Feng, J. Wen, J. Yang, C. Zhang, J. Jiang, H. Wang, An urchin-like Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e/Pd/LaPO\u003csub\u003e4\u003c/sub\u003e photocatalyst with Z-scheme heterojunction for enhanced hydrogen evolution, Applied Surface Science 497 (2019) 143771. \u003c/li\u003e\n\u003cli\u003eL. Luo, Y. Zhou, W. Yan, G. Du, M. Fan, W. Zhao, Construction of advanced zeolitic imidazolate framework derived cobalt sulfide/MXene composites as high-performance electrodes for supercapacitors, Journal of Colloid and Interface Science 615 (2022) 282\u0026ndash;292. \u003c/li\u003e\n\u003cli\u003eB.-F. Xu, J. Zhang, A.P. Tanjung, F. Xu, A.-J. Wang, L.-P. Mei, P. Song, J.-J. Feng, MOF-derived sandwich-structured dual Z-Scheme Co\u003csub\u003e9\u003c/sub\u003eS\u003csub\u003e8\u003c/sub\u003e@ZnIn\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e/CdSe hollow nanocages heterojunction: Target-induced ultrasensitive photoelectrochemical sensing of chlorpyrifos, Biosensors and Bioelectronics 257 (2024) 116324.\u003c/li\u003e\n\u003cli\u003eT.S. Priya, T.-W. Chen, S.-M. Chen, T. Kokulnathan, M. Akilarasan, W.-C. Liou, A.M. Al-Mohaimeed, M.A. Ali, M.S. Elshikh, J. Yu, In-situ growth of MOF-derived Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e@MoS\u003csub\u003e2\u003c/sub\u003e heterostructured electrocatalyst for the detection of furazolidone, Chemosphere 356 (2024) 141895.\u003c/li\u003e\n\u003cli\u003eM. Tang, D. Zhang, Y. Sun, Q. Chen, Y. Chen, G. Xi, Z. Wang, X. Shao, CVD-fabricated Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e heterojunction for ultra-sensitive detection of CO in SF6 discharge decomposition products, Sensors and Actuators B: Chemical 401 (2024) 134968.\u003c/li\u003e\n\u003cli\u003eL. Han, Z. Ren, P. Ou, H. Cheng, N. Rui, L. Lin, X. Liu, L. Zhuo, J. Song, J. Sun, J. Luo, H.L. Xin, Modulating Single‐Atom Palladium Sites with Copper for Enhanced Ambient Ammonia Electrosynthesis, Angew Chem Int Ed 60 (2021) 345\u0026ndash;350.\u003c/li\u003e\n\u003cli\u003eX. Ma, J. Kang, Y. Wu, C. Pang, S. Li, J. Li, Y. Xiong, J. Luo, M. Wang, Z. Xu, A bifunctional polycentric-affinity MOF/MXene heterojunction-based molecularly imprinted photoelectrochemical organophosphorus-sensing platform, Chemical Engineering Journal 469 (2023) 143888.\u003c/li\u003e\n\u003cli\u003eJ. Zou, J. Liu, Y. Xie, G. Peng, L. Duan, D. Hu, S. Chen, F. Qu, L. Lu, Bifunctional bismuth molybdate/biochar composite with an enhanced photo-assisted electrochemical activity: Memory effect-free Hg(II) detection and efficient photocatalytic reduction of Cr(VI), Chemical Engineering Journal 468 (2023) 143849.\u003c/li\u003e\n\u003cli\u003eC. Zhou, S. Shi, Y. Wei, A. Chen, N. Tang, J. Zuo, Q. He, P. Deng, High-sensitivity electrochemical sensing platform for acetaminophen based on MnS/Co3S4 hybrids doped electrochemically reduced graphene oxide nanocomposite, Inorganic Chemistry Communications 155 (2023) 111123.\u003c/li\u003e\n\u003cli\u003eL. Meng, J. Wang, Y. Zhang, B. Zhou, J. Shi, K. Xiao, Engineering MOF-derived 2D NPC-TiO\u003csub\u003e2\u003c/sub\u003e nanotablet/3D marigold-like ZnIn\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e/CdS nanoparticles dual Z-scheme heterojunction with excellent photoelectric performance: A novel material for sensitive and facile photoelectrochemical sensing detection of mercury ions in aqueous environments by ion-exchange sensing strategy, Sensors and Actuators B: Chemical 414 (2024) 135897. \u003c/li\u003e\n\u003cli\u003eH. Wang, D. Liang, Y. Xu, X. Liang, X. Qiu, Z. Lin, A highly efficient photoelectrochemical sensor for detection of chlorpyrifos based on 2D/2D \u0026beta;-Bi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e heterojunctions, Environ. Sci.: Nano 8 (2021) 773\u0026ndash;783.\u003c/li\u003e\n\u003cli\u003eS. Abdpour, E. Kowsari, B. Bazri, M.R.A. Moghaddam, S.S. Tafreshi, N.H. De Leeuw, I. Simon, L. Schmolke, D. Dietrich, S. Ramakrishna, C. Janiak, Amino-functionalized MIL-101(Cr) photodegradation enhancement by sulfur-enriched copper sulfide nanoparticles: An experimental and DFT study, Journal of Molecular Liquids 319 (2020) 114341. \u003c/li\u003e\n\u003cli\u003eC. Zhou, M. Zhou, K. Lu, W. Huang, C. Yu, K. Yang, Electrostatic self-assembly of MnIn\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e@BiVO\u003csub\u003e4\u003c/sub\u003e S-scheme heterojunction for photothermal-enhanced photocatalytic antibiotic removal with the boosted spatial charge separation, Journal of Materials Science \u0026amp; Technology 233 (2025) 166\u0026ndash;178.\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":"Photoelectrochemical sensor, MOF-templated nanocages, Z-scheme heterojunction, Dual charge transfer, Chlorpyrifos detection","lastPublishedDoi":"10.21203/rs.3.rs-7047958/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7047958/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eConventional detection of organophosphorus pesticides (OPs) like chlorpyrifos (CPF) often faces challenges. This work presents a novel ternary synergistic PEC probe utilizing metal-organic framework (MOF)-templated Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e nanocages for sensing CPF. Derived from ZIF-67 via in situ sulfidation, the hollow nanocage architecture integrated CdS nanoparticles with Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e to form a direct Z-scheme heterojunction while decorating Pd quantum dots (QDs) created a Schottky barrier, implementing a crucial dual charge-transfer enhancement strategy. DFT simulations confirmed a 0.36 eV Fermi level difference at heterojunction interface, verifying a forced built-in electric field. The optimized Pd/CdS@Co\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e nanocomposite exhibited a remarkable\u0026thinsp;~\u0026thinsp;5-fold photocurrent amplification over its pristine components, establishing a high-intensity signal baseline essential for accommodating wide-range concentration-dependent signal attenuation. Acetylcholinesterase (AChE)-immobilized biosensor quantified CPF via inhibition-triggered competitive electron consumption to attenuate photocurrent. The sensor demonstrated exceptional performance for CPF detection, most notably featuring a linear dynamic range spanning 4 orders of magnitude (0.1\u0026thinsp;~\u0026thinsp;2000 ng\u0026middot;mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). Furthermore, it achieved a low detection limit (0.05 ng\u0026middot;mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, S/N\u0026thinsp;=\u0026thinsp;3), outstanding specificity against interfering species, excellent long-term stability, and reliable accuracy in complex real samples (98.5\u0026thinsp;~\u0026thinsp;102.1%). This study proposes dual charge-transfer enhancement strategy and hollow architecture, addressing the broad-concentration-range in environmental pesticide detection with sensitivity and adaptability to real-world matrices.\u003c/p\u003e","manuscriptTitle":"MOF-templated hollow Pd/CdS@Co3S4 nanocages with synergistic Z-scheme/Schottky effects for photoelectrochemical biosensing of chlorpyrifos featuring exceptional dynamic range","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-15 09:53:13","doi":"10.21203/rs.3.rs-7047958/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-07-22T12:47:14+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-22T12:36:02+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-21T05:24:43+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-17T01:15:44+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"153414588266942426829096188160099070746","date":"2025-07-13T16:05:51+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-11T15:05:31+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"76243313265543867976240275713532012302","date":"2025-07-11T05:27:53+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"166900651217351356681714478575389354384","date":"2025-07-11T02:27:34+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"319034673592588534684362665569273158264","date":"2025-07-11T01:21:36+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"136232610466129960482370084712628569330","date":"2025-07-10T23:01:42+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-10T20:30:46+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-10T10:49:00+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-07-09T04:31:15+00:00","index":"","fulltext":""},{"type":"submitted","content":"Microchimica Acta","date":"2025-07-04T14:54:37+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":"aadcddf3-9deb-40a9-937d-d01368c77d9f","owner":[],"postedDate":"July 15th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-09-08T15:59:16+00:00","versionOfRecord":{"articleIdentity":"rs-7047958","link":"https://doi.org/10.1007/s00604-025-07469-3","journal":{"identity":"microchimica-acta","isVorOnly":false,"title":"Microchimica Acta"},"publishedOn":"2025-09-05 15:57:13","publishedOnDateReadable":"September 5th, 2025"},"versionCreatedAt":"2025-07-15 09:53:13","video":"","vorDoi":"10.1007/s00604-025-07469-3","vorDoiUrl":"https://doi.org/10.1007/s00604-025-07469-3","workflowStages":[]},"version":"v1","identity":"rs-7047958","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7047958","identity":"rs-7047958","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}