Nanozymes with reductase-like activities: antioxidant properties and electrochemical behavior

Surface modification strategies and the functional mechanisms of gold nanozyme in biosensing and bioassay

Gold nanozymes (GNZs) have been widely used in biosensing and bioassay due to their interesting catalytic activities that enable the substitution of natural enzyme. This review explains different catalytic activities of GNZs that can be achieved by applying different modifications to their surface. The role of Gold nanoparticles (GNPs) in mimicking oxidoreductase, helicase, phosphatase were introduced. Moreover, the effect of surface properties and modifications on each catalytic activity was thoroughly discussed. The application of GNZs in biosensing and bioassay was classified in five categories based on the combination of the enzyme like activities and enhancing/inhibition of the catalytic activities in presence of the target analyte/s that is realized by proper surface modification engineering. These categories include catalytic activity enhancer, reversible catalytic activity inhibitor, binding selectivity enhancer, agglomeration base, and multienzyme like activity, which are explained and exemplified in this review. It also gives examples of those modifications that enable the application of GNZs for in vivo biosensing and bioassays.

Flavocytochrome b2-Mediated Electroactive Nanoparticles for Developing Amperometric L-Lactate Biosensors

L-Lactate is an indicator of food quality, so its monitoring is essential. Enzymes of L-Lactate metabolism are promising tools for this aim. We describe here some highly sensitive biosensors for L-Lactate determination which were developed using flavocytochrome b₂ (Fcb₂) as a bio-recognition element, and electroactive nanoparticles (NPs) for enzyme immobilization. The enzyme was isolated from cells of the thermotolerant yeast Ogataea polymorpha. The possibility of direct electron transfer from the reduced form of Fcb₂ to graphite electrodes has been confirmed, and the amplification of the electrochemical communication between the immobilized Fcb₂ and the electrode surface was demonstrated to be achieved using redox nanomediators, both bound and freely diffusing. The fabricated biosensors exhibited high sensitivity (up to 1436 A·M^-1·m^-2), fast responses, and low limits of detection. One of the most effective biosensors, which contained co-immobilized Fcb₂ and the hexacyanoferrate of gold, having a sensitivity of 253 A·M^-1·m^-2 without freely diffusing redox mediators, was used for L-Lactate analysis in samples of yogurts. A high correlation was observed between the values of analyte content determined using the biosensor and referenced enzymatic-chemical photometric methods. The developed biosensors based on Fcb₂-mediated electroactive nanoparticles can be promising for applications in laboratories of food control.

Reusable alcohol oxidase-nPtCu/alginate beads for highly sensitive ethanol assay in beverages

Nanozymes (NZs) are nanoparticles that mimic the catalytic properties of natural enzymes. The present work aimed to obtain effective peroxidase mimetics (PO-like NZs), to characterize their morphological properties, estimate the kinetic parameters of NZs and evaluate the prospects of their application in analysis of ethanol. Herein, we have proposed a convenient spectrophotometric method for ethanol assay using reusable alginate beads enriched with alcohol oxidase (AO) and nanoparticles of PtCu (nPtCu) as PO-like NZs, and 3,3',5,5'-tetramethylbenzidine (TMB) as a chromogen. The linear range for the proposed nPtCu-AO/alginate beads/TMB-based method is from 0.01 mM to 0.15 mM with a limit of detection of 3.3 μM ethanol. The method is used for the quantitative determination of ethanol in alcoholic beverages. The obtained results proved to be in a good correlation with the enzymatic reference method. These results highlight the potential of the nPtCu with PO-like activity in bioanalytical applications. The proposed method, being sensitive, economical and suitable for routine and micro-volume formats, can be used in clinical diagnostics for the detection of ethanol.