N,S co-doped Co3O4 core-shell nanospheres with high peroxidase activity for the fast colorimetric detection of catechol

Nanozymes sensor array for discrimination and intelligent sensing of phenolic acids in food

Although nanozymes sensor arrays have the potential to recognize multiple target substances simultaneously, they currently rarely identify phenolic acids in food due to limited catalytic performance and complex preparation conditions of nanozymes. Here, inspired by the structure of polyphenol oxidase, we have successfully prepared a novel gallic acid-Cu (GA-Cu) nanozyme with laccase-like activity. Due to the different catalytic efficiency of GA-Cu nanozymes towards six common phenolic acids, a three-channel colorimetric sensor array was constructed using reaction kinetics as the sensing unit to achieve high-throughput detection and identification of six phenolic acids within a concentration range from 1 to 100 μM. This method avoids the creation of numerous sensing units. Notably, the successful discrimination of six phenolic acids in samples of juice, beer, and wine has been achieved by the sensor array. Finally, aided by smartphones, a portable technique has been devised for the detection of phenolic acids.

Sensing platform for the highly sensitive detection of catechol based on composite coupling with conductive Ni3(HITP)2 and nanosilvers

Catechol, which has a high toxicity and low degradability, poses significant risks to both human health and the environment. Tracking of catechol residues is essential to protect human health and to assess the safety of the environment. We constructed sensing platforms to detect catechol based on the conductive metal-organic frameworks [Ni3(HITP)2] and their nanosilver composites. The reduction process of catechol at the Ni3(HITP)2/AgNP electrode is chemically irreversible as a result of the difference in compatibility of the oxidation stability and conductivity between the Ni3(HITP)2/AgNS and Ni3(HITP)2/AgNP electrodes. The electrochemical results show that the Ni3(HITP)2/AgNS electrode presents a lower detection limit of 0.053 μM and better sensitivity, reproducibility and repeatability than the Ni3(HITP)2/AgNP electrode. The kinetic mechanism of the catechol electrooxidation at the surface of the electrode is controlled by diffusion through a 2H+/2e- process. The transfer coefficient is the key factor used to illustrate this process. During the electrochemical conversion of phenol to ketone, more than half of ΔG is used to change the activation energy. We also studied the stability, anti-interference and reproducibility of these electrode systems.

Enhanced peroxidase-like activity of 2(3), 9(10), 16(17), 23(24)-octamethoxyphthalocyanine modified CoFe LDH for a sensor array for reducing substances with catechol structure

Improving the catalytic activity of artificial nanozymes to realize the real-time detection of small molecules becomes an important task. Herein, a highly active nanozyme, 2(3), 9(10), 16(17), 23(24)-octamethoxyphthalocyanine (Pc(OH)₈) modified CoFe LDH microspheres (Pc(OH)₈-CoFe LDH) have been prepared by the two-step hydrothermal method. The 3,3',5,5'-tetramylbenzidine (TMB), a chromogenic substrate, was fast oxidized into blue oxTMB by H₂O₂ in the presence of Pc(OH)₈-CoFe LDH, indicating that Pc(OH)₈-CoFe LDH possesses high peroxidase-like activity rather than pure CoFe LDH. The enhancement peroxidase-like activity of the Pc(OH)₈-CoFe LDH is ascribed to the synergistic action between Pc(OH)₈ and CoFe LDH. Experimental results of radical scavenger and fluorescence probe verify that superoxide radical (•O₂^-) plays an important role during the catalytic reaction. Interestingly, the absorption intensity of reaction system has been enhanced largely, due to adding of the reducing substances containing catechol structure. Based on this, the three reducing substances (dopamine, procyanidin B2, catechins) containing catechol structure were distinguished from other reducing substances without catechol structure. Thus, a colorimetric array has been constructed using reaction time as the sensing element to realize the sensitive and selective recognition of catechol structures at a certain concentration.

Enhancing enzymatic activity of Mn@Co3O4 nanosheets as mimetic nanozyme for colorimetric assay of ascorbic acid

In nanozyme-based assays, increasing enzymatic activity is very desirable for enhancing sensitivity and lowering the detection limit. In this study, novel Mn doped cobalt oxide nanosheets (Mn@Co₃O₄ NSs) were synthesized by hydrothermal process. The obtained Mn@Co₃O₄ possessed enhanced dual-enzyme mimetic, oxidase and peroxidase, and can catalytically oxidize of 3, 3', 5, 5'-tetramethylbenzidine (TMB), to a blue product of oxidized TMB. The enzyme kinetics were well-described mathematically using a common Michaelis-Menten and Lineweaver Burk model. The enzyme kinetics constant (K_m) was found to be 0.15 mM, which is relatively low comparing with pure Co₃O₄ nanosheets (0.35 mM) and natural enzyme HRP (0.434 mM). Therefore, the efficient colorimetric method was achieved for determination of H₂O₂ and ascorbic acid. The limit of detection (LOD) of H₂O₂ was 8.0 μM and the linear range was 20-200 μM based on direct turn on of the peroxidase-like activity of Mn@Co₃O₄. While, for ascorbic acid detection based on turn-off approach, the linearity range for the ascorbic acid was 1-8 μM with LOD of 0.4 μM. Moreover, the colorimetric system exhibited good stability and selectivity toward the detection of ascorbic acid effectively in real samples (vitamin C tablets) with satisfactorily accuracy and precision.

An ordered one-step colorimetric sensor for the selective determination of catechol based on the polyacrylic acid-coated cerium oxide with laccase-like activity

A sensitive colorimetric sensor was constructed for an ordered and one-step determination of catechol based on PAA-CeO2 with a significant laccase-like activity.