Deciphering the Mechanisms of Photo-Enhanced Catalytic Activities in Plasmonic Pd-Au Heteromeric Nanozymes for Colorimetric Analysis.

The growing demand for highly active nanozymes in various fields has led to the development of several strategies to enhance their activity. Plasmonic enhancement, a strategy used in heterogenous catalysis, represents a promising strategy to boost the activity of nanozymes. Herein, Pd-Au heteromeric nanoparticles (Pd-Au dimers) with well-defined heterointerfaces have been explored as plasmonic nanozymes. As a model system, the Pd-Au dimers with integrated peroxidase (POD)-like activity and plasmonic activity are used to investigate the effect of plasmons on enhancing the activity of nanozymes under visible light irradiation. Mechanistic studies revealed that the generation of hot electron-hole pairs plays a dominant role in plasmonic effect, and it greatly enhances the decomposition of H2 O2 to the reactive oxygen species (ROS) intermediates (•OH, •O2 - and 1 O2 ), leading to elevated POD-like activity of the Pd-Au dimers. Finally, the Pd-Au dimers are applied in the plasmon-enhanced colorimetric method for the detection of alkaline phosphatase, exhibiting broad linear range and low detection limit. This study not only provides a straightforward approach for regulating nanozyme activity through plasmonic heterostructures but also sheds light on the mechanism of plasmon-enhanced catalysis of nanozymes.

Amperometric biosensors based on alcohol oxidase and peroxidase-like nanozymes for ethanol determination.

The aim of the current research is to design alcohol oxidase-based amperometric biosensors (ABSs) using hybrid metallic nanoparticles as artificial peroxidases (PO) or PO-like nanozymes (NZs). A lot of metallic PO-like NZs were synthesized and tested with respect to their ability to substitute natural PO in solution and on amperometric electrode. The most effective PO mimetics were coupled with alcohol oxidase (AOX) on graphite electrodes (GEs) and characterized. Two types of modified GEs, namely, the AOX/nAuCePt/GE and the AOX/nFePtAu/GE show the highest sensitivities to ethanol (2600 A⋅M-1⋅m-2 and 1250 A⋅M-1⋅m-2, respectively), low limits of detection (1.5 µM and 2.2 µM), broad linear ranges (5 - 100 µM and 12 - 120 µM), as well as satisfactory storage stabilities. The most sensitive bioelectrode AOX/nAuCePt/GE was used as ABS for ethanol determination in real samples. The practical feasibility of the constructed ABS was demonstrated by determination of ethanol in beverages, human blood and saliva.

The Peroxidase-like Nanocomposites as Hydrogen Peroxide-Sensitive Elements in Cholesterol Oxidase-Based Biosensors for Cholesterol Assay.

Catalytically active nanomaterials, in particular, nanozymes, are promising candidates for applications in biosensors due to their excellent catalytic activity, stability and cost-effective preparation. Nanozymes with peroxidase-like activities are prospective candidates for applications in biosensors. The purpose of the current work is to develop cholesterol oxidase-based amperometric bionanosensors using novel nanocomposites as peroxidase (HRP) mimetics. To select the most electroactive chemosensor on hydrogen peroxide, a wide range of nanomaterials were synthesized and characterized using cyclic voltammetry (CV) and chronoamperometry. Pt NPs were deposited on the surface of a glassy carbon electrode (GCE) in order to improve the conductivity and sensitivity of the nanocomposites. The most HRP-like active bi-metallic CuFe nanoparticles (nCuFe) were placed on a previously nano-platinized electrode, followed by conjugation of cholesterol oxidase (ChOx) in a cross-linking film formed by cysteamine and glutaraldehyde. The constructed nanostructured bioelectrode ChOx/nCuFe/nPt/GCE was characterized by CV and chronoamperometry in the presence of cholesterol. The bionanosensor (ChOx/nCuFe/nPt/GCE) shows a high sensitivity (3960 A·M-1·m-2) for cholesterol, a wide linear range (2-50 µM) and good storage stability at a low working potential (-0.25 V vs. Ag/AgCl/3 M KCl). The constructed bionanosensor was tested on a real serum sample. A detailed comparative analysis of the bioanalytical characteristics of the developed cholesterol bionanosensor and the known analogs is presented.

N-doped MoS2-nanoflowers as peroxidase-like nanozymes for total antioxidant capacity assay.

Total Antioxidant Capacity (TAC) Assay plays an important role in evaluating the quality of antioxidant food and monitoring the oxidative stress level of human body. It is mainly achieved by measuring the contents of antioxidants such as AA, L-Cys and GSH, while TAC can be detected by using peroxidase-like activity of artificial nanoenzyme materials. In this work, the N-Doped, defect-rich N-MoS2NFs nano-materials were used to build the nano enzyme, which has strong stability and high peroxidase-like activity. H2O2 was detected because it can be catalyzed to generate the intermediate ·OH and make TMB appears blue. However, when H2O2, AA, L-Cys and GSH coexist in solution, due to the oxidation resistance of AA, L-Cys and GSH, they can competitively react with ·OH in solution or reduce TMB in oxidation state (oxTMB), which reduces the characteristic absorption of oxTMB, indirectly achieves the purpose of detecting AA, L-Cys and GSH, and finally realizes the determination of TAC, even in actual serum and saliva samples. At the same time, the N-MoS2 NFs/NH2-MIL-53(Al)+OPD system is further constructed. Based on the fluorescence resonance energy transfer (FRET) between NH2-MIL-53(Al) and oxidized OPD (oxOPD), the purpose of detecting TAC by fluorescence method was realized.

Fe-Coordinated Carbon Nanozyme Dots as Peroxidase-Like Nanozymes and Magnetic Resonance Imaging Contrast Agents.

The catalytic activities of currently developed peroxidase-mimic nanozymes are generally limited. Therefore, further efforts are still needed to improve the catalytic performance of peroxidase nanozymes. Herein, we synthesized Fe-coordinated carbon nanozyme dots (Fe-CDs) that can serve as both efficient peroxidase nanozymes and T2-magnetic resonance imaging (MRI) contrast agents. The intrinsic peroxidase-like activity of the Fe-CDs was explored by catalytic oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) with hydrogen peroxide (H2O2). The product showed better performance over natural horseradish peroxidase (HRP) and other mimetic peroxidases. Quantification of glucose and ascorbic acid detection showed that this nanozyme could be used to detect a minimum limit as low as 5 µM glucose. Moreover, the colorimetric detection technique was used to detect serum glucose in mice, and the detection result was comparable with autobiochemistry analyzer results using a glucose assay kit. Furthermore, the Fe-CDs showed good magnetism properties and provided promising MR imaging of tumors with excellent biocompatibility.