A polyoxometalate-based heterojunction nanozyme with peroxidase-mimic catalytic activity for sensitive biomolecule detection

Abstract

Nanozymes are a class of nanomaterials that can specifically mimic the structures and catalytic activities as well as overcome limitations of natural enzymes and have hence been considered as a competitive alternative to natural enzymes. At present, plenty of nanozymes, especially those with peroxidase (POD)-like catalytic activity, have been extensively explored for biosensing. In this work, we proposed polyoxometalate-based heterojunction GdP₅W₃₀O₁₁₀@WS₂ nanoclusters (NCs) to exert intrinsic POD-like catalytic activity even under harsh catalytic conditions. Detailedly, GdP₅W₃₀O₁₁₀@WS₂ NCs possessing conducive POD-like catalytic activity can oxidize chromogenic substrates into colored substances in the presence of H₂O₂. On the strength of the POD-like catalytic activity of GdP₅W₃₀O₁₁₀@WS₂ NCs, a reliable analytical platform is then constructed after the optimization of catalytic conditions for the detection of H₂O₂, glutathione (GSH) and glucose via a simple TMB colorimetric strategy. This work advances the utilization of versatile polyoxometalate-based nanomaterials for biosensing, dramatically broadening the potential applications of other nanozyme-based biosensors.

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Introduction

Biomolecules play crucial roles in diverse physiological and pathological processes, and their levels in the human body can serve as important indicators for monitoring physical status.^1,2 Therefore, highly selective and sensitive quantitative detection of biomolecules not only helps to reveal their functions in various physiological processes but also is a prerequisite and basis for monitoring the physical status of the human body.^3,4 Of note, benefiting from the specificity of active enzymes to substrates, enzymatic methods can achieve rapid and accurate biomolecule detection, which is one of the most mature and commonly applied typical strategies.^5,6 Natural enzymes are a class of proteins possessing high substrate specificity and efficacious catalytic activity and are implicated in almost all biocatalytic reactions in organisms.^7,8 However, their practical applications are severely limited by intrinsic shortcomings such as high cost, susceptibility to environmental factors, and difficult purification.^9,10 To overcome these drawbacks, it is of great importance to develop novel artificial enzyme mimics that have remarkable enzyme-like activities by facile synthesis. Since the first demonstration of the peroxidase (POD)-like property of Fe₃O₄ nanoparticles by Gao in 2007, many nanomaterials with multiple enzymatic catalytic activities, namely nanozymes, have been considered as strong substitutes for nature enzymes and have been widely used in biological, medical and industrial catalysis fields.¹¹ So far, a surge of artificial nanozymes with POD-like catalytic activity, such as precious metals, metal oxides, transition metal dichalcogenides (TMDCs), carbon-based nanomaterials, single-atom nanozymes and metal–organic frameworks (MOFs), have been extensively utilized for biosensing.^12–18 However, their enzymatic catalytic efficiency is still far less than that of natural enzymes. Thus, investigations on nanozymes with efficient catalytic activity, minimal cytotoxicity and high affinity to substrates are still imperative and pivotal.

In recent years, emerging kinds of metal-based nanomaterials with shifting or mixed redox states have been found to exert intrinsic POD-like catalytic activity.^19,20 However, the insufficient enzymatic performance of these nanomaterials is inadequate for their applications in the fields of biosensing. Since most of the reactions take place on the surface of nanozymes, we speculate that surface modification or increasing the specific surface area of nanozymes enables higher catalytic activity for a more sensitive enzymatic reaction.²¹ Interestingly, constructing a heterojunction structure can also further enhance the enzymatic activity of these nanozymes via accelerating the electron transfer on the heterogeneous interface and reducing the required energy for the binding between nanozymes and H₂O₂.^22–24 Based on the aforementioned findings, we assume that polyoxometalate-based heterojunctions can act as prospective POD-like nanozymes for biosensing.

Herein, polyoxometalate-based heterostructure GdP₅W₃₀O₁₁₀@WS₂ NCs were constructed (Scheme 1A). Benefiting from the specific heterostructure and high specific surface area inherited from WS₂ nanosheets, the prepared GdP₅W₃₀O₁₁₀@WS₂ exhibited a remarkable POD-like catalytic performance and superior tolerance to stringent conditions. Furthermore, GdP₅W₃₀O₁₁₀@WS₂ was implicated in a facile colorimetric platform to realize the quantitative detection of H₂O₂, glutathione (GSH) and glucose. The excellent analytical performance manifested that our work opens up broad prospects for the elaborate design and development of polyoxometalate-based nanozymes and dramatically expands the potential application of nanozyme-based biosensors.

Scheme 1 (A) Schematic illustration of the general synthetic procedures of the GdP₅W₃₀O₁₁₀@WS₂ nanozymes; (B) Mechanism description of GdP₅W₃₀O₁₁₀@WS₂ nanozymes with peroxidase-like activity for the colorimetric detection of biomolecules, including H₂O₂, GSH and glucose.

Experimental section

Chemicals

Sodium tungstate dihydrate (Na₂WO₄·2H₂O), bovine serum albumin (BSA), 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS) were obtained from Aladdin Industrial Corporation (Shanghai, China). Gadolinium(III) chloride hexahydrate (GdCl₃·6H₂O) and tungsten sulfide (WS₂, 99.8%) were purchased from Alfa Aesar Reagent Company (Shanghai, China). Sodium acetate (NaAc), acetic acid (HAc), citric acid monohydrate, disodium hydrogen phosphate anhydrous (Na₂HPO₄), methanol (CH₃OH, 99.5%) and sulfuric acid (H₂SO₄, 95–98%) were bought from Chron Chemicals Co., Ltd (Shanghai, China). Polyethylene glycol 400 (PEG-400) was supplied by Kermel (Tianjin, China). Ethanol, hydrogen peroxide (H₂O₂, 30%) and phosphoric acid (H₃PO₄, 85%) were purchased from Jinshan Chemical Reagent Co., Ltd (Chengdu, China). Potassium acetate (CH₃COOK) and potassium chloride (KCl) were from Tianjin Zhiyuan Chemical Reagent Co., Ltd (Tianjin, China). 3,3′,5,5′-Tetramethylbenzidine (TMB) was obtained from Adamas Reagent Co., Ltd. Acetic acid buffer (HAc–NaAc, 0.2 M) and Na₂HPO₄–citric acid buffer (0.2 M) solutions were prepared in the laboratory. All reagents and solvents were of commercially analytical grade and used as received without any previous purification.

Preparation of GdP₅W₃₀O₁₁₀ nanoclusters

The GdP₅W₃₀O₁₁₀ nanoclusters were synthesized by a two-step hydrothermal approach according to a previously reported procedure with an adjusted dose.²⁵ In a typical synthetic procedure, 16.5 g Na₂WO₄·2H₂O was first completely dissolved in 15 mL ultrapure water with ultrasound assistance and then 85% H₃PO₄ (13.25 mL) was slowly added into the solution. Afterwards, the above mixture was placed into a sample preparation bomb and was heated up to 120 °C for 12 h. After the bomb was spontaneously cooled down to room temperature, ultrapure water (7.5 mL) and KCl (5 g) were added into the reaction system and some white precipitate was immediately formed. Then, the precipitate was filtered and washed with potassium acetate solution (2 M) and methanol. When the precipitate naturally dried, it was dissolved in 15 mL hot ultrapure water (around 65 °C) and the intermediate product K_l2.5Na_l.5[NaP₅W₃₀O₁₁₀]·15H₂O was subsequently formed by cooling and recrystallization.

Then, K_l2.5Na_l.5[NaP₅W₃₀O₁₁₀]·15H₂O (1 g) was dissolved in 12 mL ultrapure water and heated to 65 °C. Afterwards, GdCl₃·6H₂O aqueous solution (0.08 mmol mL⁻¹, 3 mL) was dropwise added into the above solution under heating with magnetic stirring. After reaction, the mixture was poured into a sample preparation bomb and heated at 160 °C for 12 h. After the bomb was spontaneously cooled down to room temperature, KCl (4 g) was introduced into the reaction system and the precipitate was immediately formed. Then, the precipitate was filtered and washed with potassium acetate solution (2 M) and methanol. Finally, the as-synthesized GdP₅W₃₀O₁₁₀ nanoclusters were air-dried and ready for use.

Surface functionalization of GdP₅W₃₀O₁₁₀ nanoclusters with BSA

In brief, 400 mg BSA and 0.118 g GdP₅W₃₀O₁₁₀ nanoclusters were dispersed into 20 mL ultrapure water and the mixture was stirred for 6 h. The carboxy-functionalized GdP₅W₃₀O₁₁₀ nanoclusters (GdP₅W₃₀O₁₁₀-BSA) were kept at room temperature for later use.

Preparation of WS₂ nanosheets

The WS₂ nanosheets were synthesized by ultrasound-assisted liquid exfoliation using H₂SO₄ as an intercalation agent by referring to a previous report.²⁶ First, commercial WS₂ powder was ground in a ball miller for 6 h. Next, the preconditioned WS₂ (60 mg) was dispersed into 60 mL concentrated sulfuric acid (H₂SO₄, 95–98%) and the reaction mixture was kept at 90 °C in an oil bath for 24 h under stirring. Afterwards, the H₂SO₄-intercalated WS₂ was centrifugally collected at 6000 rpm (10 min) and washed with ultrapure water to remove supernatant H₂SO₄, repeating four times. Then, the purified H₂SO₄-intercalated WS₂ was re-dispersed into ultrapure water (about 30 mL) and was ultrasonically peeled off in an ice-cold water bath for 2 h. Finally, the layered WS₂ nanosheets were harvested by centrifugation (12 000 rpm, 20 min).

Surface functionalization of WS₂ nanosheets with PEG-400

To synthesize amino-functionalized WS₂ nanosheets, PEG-400 ethanol solution (50 mg mL⁻¹, 1 mL) was added into layered WS₂ solution (1 mg mL⁻¹, 10 mL), and the mixture was stirred for 12 h at room temperature. Then, the WS₂-PEG was obtained by centrifugation (6000 rpm, 10 min) and washed with ultrapure water to remove residual PEG-400.

Preparation of GdP₅W₃₀O₁₁₀@WS₂

In a typical preparation process, 5 mg 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (EDC) was first introduced into WS₂-PEG aqueous solution (1 mg mL⁻¹, 10 mL) and some white floccules formed immediately. Then, 5 mg N-hydroxysuccinimide (NHS) was added and the mixture was set under magnetic stirring until the white floccules disappeared. Afterwards, GdP₅W₃₀O₁₁₀-BSA (2 mL) was added into the above solution, followed by stirring at room temperature for 12 h. Finally, the as-prepared GdP₅W₃₀O₁₁₀@WS₂ was collected by centrifugation (6000 rpm, 10 min) and washed with ultrapure water.

Peroxidase-like catalytic activity of GdP₅W₃₀O₁₁₀@WS₂

Peroxidase-like catalytic activity assay. The representative colorimetric analysis assay using 3,3′,5,5′-tetramethylbenzidine (TMB), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and o-phenylenediamine (OPD) as peroxidase colorimetric substrates in the presence of H₂O₂ was performed to preliminarily evaluate the peroxidase-like catalytic activity of GdP₅W₃₀O₁₁₀@WS₂. The hydroxyl radical (˙OH) that was generated by a Fenton-like reaction between H₂O₂ and W⁵⁺ of GdP₅W₃₀O₁₁₀@WS₂ can oxidize colorimetric substrates into colored substances with their respective characteristic peaks. Therefore, the peroxidase-like catalytic activity of GdP₅W₃₀O₁₁₀@WS₂ can be readily determined via monitoring the absorption intensity at characteristic peaks of the reaction system. In general, GdP₅W₃₀O₁₁₀@WS₂ (final concentration 100 μg mL⁻¹) and colorimetric substrates (TMB, ABTS or OPD, final concentration 0.5 mM) were first added into Na₂HPO₄–citric acid buffer (0.2 M). Subsequently, H₂O₂ (final concentration 50 mM) was introduced into the reacting system to launch the chromogenic reaction. After 30 min incubation, the supernatant was collected by centrifugation (6000 rpm, 10 min) and the absorbance spectrum was recorded with UV-vis spectroscopy (UV-6100, MAPADA).

H₂O₂ and GSH detection by GdP₅W₃₀O₁₁₀@WS₂

Briefly, GdP₅W₃₀O₁₁₀@WS₂ (final concentration 100 μg mL⁻¹), TMB ethanol solution (final concentration 0.5 mM) as well as varied concentrations of H₂O₂ (0–50 mM) or different concentrations of GSH (0–25 μM) with 50 mM H₂O₂ were mixed into Hac–NaAc buffer (0.2 M, pH 3.0) and the solution was incubated for 30 min at 50 °C in the dark. Finally, the UV-vis spectrum was recorded by UV-vis spectroscopy.

Glucose detection by GdP₅W₃₀O₁₁₀@WS₂

In detail, GOx (final concentration 1 mg mL⁻¹) and various concentrations of glucose aqueous solution (0–1.0 mM) were first mixed together and incubated at 37 °C for 1 h. Afterwards, GdP₅W₃₀O₁₁₀@WS₂ (final concentration 100 μg mL⁻¹) and TMB ethanol solution (final concentration 0.5 mM) were then introduced and the UV-vis spectrum was recorded after 30 min reaction at 50 °C.

Results and discussion

Preparation and characterization of GdP₅W₃₀O₁₁₀@WS₂

The concise fabrication process of the heterostructure GdP₅W₃₀O₁₁₀@WS₂ NCs is illustrated in Scheme 1A. Here, the easy-to-obtain heterostructure GdP₅W₃₀O₁₁₀@WS₂ NCs were synthesized according to the previously reported strategies by a facile amidation reaction activated by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (EDC)/N-hydroxysuccinimide (NHS) (Scheme 1A).²⁷ As visualized by the transmission electron microscopy (TEM) image and the average hydrodynamic diameter recorded by dynamic light scattering (DLS) measurement, the as-synthesized GdP₅W₃₀O₁₁₀@WS₂ NCs showed a uniform and well-dispersed nanostructure and the size of GdP₅W₃₀O₁₁₀@WS₂ NCs was approximately 60 nm (Fig. 1A and B). Additionally, as presented in Fig. 1C, the changes of zeta potential for the samples could verify the successful surface loading of GdP₅W₃₀O₁₁₀ nanoclusters onto WS₂ nanosheets.²⁷ Furthermore, the Fourier transform infrared (FTIR) spectra and Raman spectra of the different components also affirmed that the as-prepared GdP₅W₃₀O₁₁₀@WS₂ NCs had specific absorption peaks corresponding to GdP₅W₃₀O₁₁₀ nanoclusters and WS₂ nanosheets (Fig. 1D and E), which is consistent with previously reported work. The strong characteristic peaks at 1164, 1170, 917 and 780 cm⁻¹ in GdP₅W₃₀O₁₁₀ nanoclusters are assigned to the stretching vibration of the P–O band, W–O asymmetric vibration and W–O–W asymmetric vibration, respectively. In addition, the chemical composition of GdP₅W₃₀O₁₁₀@WS₂ NCs was further verified by UV-vis absorption spectra, indicating the successful fabrication (Fig. 1F). Taken together, the heterojunction GdP₅W₃₀O₁₁₀@WS₂ NCs were successfully fabricated as designed and have the potential for subsequent application in sensitive biomolecule detection.

Fig. 1 Preparation and characterization of GdP₅W₃₀O₁₁₀@WS₂ nanoclusters. (A) TEM image of GdP₅W₃₀O₁₁₀@WS₂ nanoclusters. (B) Hydrodynamic size distribution of GdP₅W₃₀O₁₁₀@WS₂ nanoclusters measured by dynamic light scattering (DLS). (C) Zeta potential of GdP₅W₃₀O₁₁₀@WS₂ and its components. (D) FT-IR spectra and (E) Raman spectra of GdP₅W₃₀O₁₁₀, WS₂ and GdP₅W₃₀O₁₁₀@WS₂ nanoclusters. (F) UV-vis-NIR adsorption spectra of GdP₅W₃₀O₁₁₀, WS₂ and GdP₅W₃₀O₁₁₀@WS₂ aqueous solutions (100 μg mL⁻¹).

Peroxidase-like catalytic activity of GdP₅W₃₀O₁₁₀@WS₂

Peroxidases are a class of enzymes that can catalyze the production of reactive oxygen species (ROS) by applying peroxides (e.g., H₂O₂) as substrates, and have been widely used in biological catalysis, biosensing, disease treatment and regulating physiological activities.^28,29 Until now, a large number of nanomaterials have been shown to possess intrinsic POD-like catalytic activity, the most representative one of which is metal-based nanomaterials with mixed redox states. Inspired by the recent advances, the heterojunction GdP₅W₃₀O₁₁₀@WS₂ NCs with mixed redox states thus exhibit great potential to exert considerable peroxidase-like catalytic activity. We next investigated the POD-like catalytic activity of GdP₅W₃₀O₁₁₀@WS₂ NCs in the presence of H₂O₂ through the oxidation of a series of colorimetric substrates (e.g., 3,3′,5,5′-tetramethylbenzidine (TMB), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and o-phenylenediamine (OPD)). As shown in Fig. 2A, due to the intrinsic peroxidase-like catalytic activity of GdP₅W₃₀O₁₁₀@WS₂ NCs, H₂O₂ could be catalyzed into hydroxyl radicals (˙OH) and the reaction solution turned into the corresponding color of the oxidized colorimetric substrates (blue for oxTMB, green for oxABTS, yellow for oxOPD). As indicated in Fig. 2B, no significant characteristic absorbance and color change of TMB alone or TMB + GdP₅W₃₀O₁₁₀@WS₂ could be found. Meanwhile, the distinct characteristic absorption peaks were observed in the mixture of GdP₅W₃₀O₁₁₀@WS₂ NCs, H₂O₂ and TMB (green curve), reflecting the efficacious peroxidase-like catalytic activity. Analogously, the maximum absorption peaks of oxABTS and oxOPD in the ABTS/OPD + H₂O₂ + GdP₅W₃₀O₁₁₀@WS₂ group also implied that GdP₅W₃₀O₁₁₀@WS₂ NCs exhibited a superior peroxidase-like catalytic performance. Consequently, the prominent peroxidase-like catalytic activity of GdP₅W₃₀O₁₁₀@WS₂ NCs ensures their further controllable utilization for further application.

Fig. 2 (A) Schematic illustration of the mechanism for the peroxidase-like activity evaluation of GdP₅W₃₀O₁₁₀@WS₂ applying TMB, OPD and ABTS as substrates. UV-vis-NIR adsorption spectra of the catalyzed oxidation of (B) TMB, (C) ABTS and (D) OPD after 15 min of incubation with PBS, GdP₅W₃₀O₁₁₀@WS₂, H₂O₂ and H₂O₂ + GdP₅W₃₀O₁₁₀@WS₂ at pH 4.0.

Similar to natural enzymes, the catalytic activity of nanozymes is also largely influenced by catalytic conditions, such as concentration, pH and temperature.³⁰ In order to enable GdP₅W₃₀O₁₁₀@WS₂ to realize a maximal catalytic performance, we subsequently explored the optimal catalytic conditions in the classical TMB colorimetric system. As indicated in Fig. 3A and E, along with the increasing concentration of GdP₅W₃₀O₁₁₀@WS₂, the characteristic absorbance of oxTMB at 652 nm gradually increased, which is mainly attributed to the concentration-dependent peroxidase-like catalytic performance of GdP₅W₃₀O₁₁₀@WS₂. Meanwhile, GdP₅W₃₀O₁₁₀@WS₂ exhibited a stable peroxidase-like catalytic activity under acidic experimental conditions (pH at 3.0) and higher temperature than most natural enzymes (Fig. 3B, C, F and G). Besides, as shown in Fig. 3D and H, maximum catalytic activity was reached with 0.5 mM TMB.

Fig. 3 The optimization of (A) concentration, (B) pH, (C) temperature and (D) TMB concentration for the peroxidase-like activity of GdP₅W₃₀O₁₁₀@WS₂, GdP₅W₃₀O₁₁₀ and WS₂ calculated from the corresponding absorbance values (E–H). The maximum point in every curve was set as 100%. Error bars represent the standard error derived from three independent measurements.

Biomolecule detection by GdP₅W₃₀O₁₁₀@WS₂

Inspired by the outstanding peroxidase-like catalytic activity of GdP₅W₃₀O₁₁₀@WS₂, a GdP₅W₃₀O₁₁₀@WS₂-based analytical platform was established for biomolecule detection, including H₂O₂, GSH and glucose detection.

During the peroxidase-like catalytic process of GdP₅W₃₀O₁₁₀@WS₂, the absorbance intensity of oxidized substrates could vary according to the experimental conditions, thereby offering reliable evidence for quantifying biomolecules related to H₂O₂. In detail, ˙OH was generated under the POD-like catalytic action of GdP₅W₃₀O₁₁₀@WS₂ in the presence of H₂O₂. Subsequently, the formed ˙OH would catalyze the oxidation of TMB into oxTMB, which can be easily quantified by monitoring the characteristic absorbance intensity at 652 nm. Conceivably, a higher level of H₂O₂ would lead to higher absorbance intensity (Fig. 4A). For H₂O₂ detection, the characteristic absorbance intensity at 652 nm gradually increased with the increasing addition of H₂O₂ on a low concentration scale. As demonstrated in Fig. 4B and C, H₂O₂ concentration was linearly positively related to the absorbance intensity within the range from 0 to 50 μM.

Fig. 4 GdP₅W₃₀O₁₁₀@WS₂ nanoclusters-based sensing platform for H₂O₂ and GSH detection. (A) Mechanism description of GdP₅W₃₀O₁₁₀@WS₂ nanozymes with peroxidase-like activity for H₂O₂ and GSH detection. (B) UV-vis-NIR adsorption spectra of GdP₅W₃₀O₁₁₀@WS₂ (100 μg mL⁻¹) incubated with TMB (0.5 mM) in the presence of different concentration of H₂O₂ at pH 4.0. (C) The linear calibration plot for H₂O₂ detection. (D) UV-vis-NIR adsorption spectra of GdP₅W₃₀O₁₁₀@WS₂ (100 μg mL⁻¹) incubated with TMB (0.5 mM) and H₂O₂ (50 mM) in the presence of different concentrations of GSH at pH 4.0. (E) The linear calibration plot for GSH detection.

As one of the most representative endogenous antioxidants in cells, GSH plays a vital part in modulating the balance between free radicals and the antioxidant defense system.^31–34 The disorders of GSH homeostasis are closely associated with such diseases as cancer, aging, neurodegenerative diseases and inflammations.³³ Therefore, investigations on convenient and rational methods for GSH detection have aroused widespread concern in biochemical analysis and clinical diagnosis. As a radical scavenger, GSH can quench ˙OH released by the POD-like catalytic reaction of GdP₅W₃₀O₁₁₀@WS₂ with H₂O₂, giving rise to inhibition of the TMB oxidation process. As shown in Fig. 4A, the generation of ˙OH from H₂O₂ catalyzed by GdP₅W₃₀O₁₁₀@WS₂ could gradually oxidize the substrate TMB into oxTMB. After the introduction of GSH, the released ˙OH was depleted and weaker absorbance intensity at 652 nm could be detected. According to the considerable scavenging effect of GSH on ˙OH, a reliable analytical platform was then constructed for GSH detection. As shown in Fig. 4D, with the increasing concentration of GSH, the absorbance signal at 652 nm responded with a descending trend. Meanwhile, there was a satisfactory linear correlation between the absorbance intensity and GSH concentration ranging from 0 to 25 μM.

Glucose is the impetus of cell metabolism and is a universally available energy source for ATP production.³³ In the presence of glucose oxidase (GOx), glucose can be effectively translated into gluconic acid and H₂O₂. In this regard, assisted by GOx-triggered oxidation, the generated H₂O₂ can act as a mediate substrate for glucose detection. After linear fitting, it was found that the GdP₅W₃₀O₁₁₀@WS₂-based analytical platform was able to detect glucose in a range from 0.1 to 1 mM (Fig. 5).

Fig. 5 GdP₅W₃₀O₁₁₀@WS₂ nanoclusters-based sensing platform for glucose detection. (A) Mechanism description of GdP₅W₃₀O₁₁₀@WS₂ nanozymes with peroxidase-like activity for glucose detection. (B) UV-vis-NIR adsorption spectra of GdP₅W₃₀O₁₁₀@WS₂ (100 μg mL⁻¹) incubated with TMB (0.5 mM) and GOx (1 mg mL⁻¹) in the presence of different concentrations of glucose at pH 4.0. (C) The linear calibration plot for glucose detection.

These content results indicated the potential application value of the proposed GdP₅W₃₀O₁₁₀@WS₂-based analytical platform for biomolecule detection.

Conclusion

In conclusion, heterojunction GdP₅W₃₀O₁₁₀@WS₂ possessing intrinsic POD-like activity was prepared by a simple approach. As proved by our primary experiments, the proposed heterojunction GdP₅W₃₀O₁₁₀@WS₂ can generally oxidize several colorimetric substrates such as TMB, ABTS, and OPD in the presence of H₂O₂. Meanwhile, assisted by the excellent POD-like catalytic activity, the fabricated GdP₅W₃₀O₁₁₀@WS₂ was introduced as a probe for the sensitive detection of H₂O₂, GSH and glucose. All of the above favorable results highlighted that this work provided more possibilities for the construction of multifunctional polyoxometalate-based nanomaterials for biosensing, greatly expanding the potential value of other nanozyme-based biosensors.

Author contributions

Guobo Du and Mingzhu Lv contributed equally to this work. Yuan Yong and Guobo Du conceived and supervised this project. Mingzhu Lv, Chenghui Liu, Jiajie Liu, Zhu Yang, Huan Wang and Qiqi Xu performed the experiments and analysed the data. Yuan Yong, Guobo Du and Mingzhu Lv revised the paper. All authors have reviewed and approved the final version of this manuscript.

Conflicts of interest

The authors declare no conflict of interest.

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (31901005 and 52273304), the Natural Science Foundation of Sichuan Province (2022NSFSC0796), the Southwest Minzu University Talent Supporting Funds (RQD2021008), Scientific research and development funds of Affiliated Hospital of North Sichuan Medical College (2021ZD013), Nanchong City-School Cooperative Scientific Research Funds (20SXZRKX0006), Young Elite Scientists Sponsorship Program by CAST (YESS) (2022-2024QNRC001), the Open Project of Central Nervous System Drug Key Laboratory of Sichuan Province (230011–01SZ) and the Fundamental Research Funds for the Central Universities, Southwest Minzu University (2021NYYXS30).

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Footnote

† These authors contributed equally.

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