Ultrathin-FeOOH-coated MnO2 nanozyme with enhanced catalase-like and oxidase-like activities for photoelectrochemical and colorimetric detection of organophosphorus pesticides.

Herein, we develop a dual-mode biosensor for photoelectrochemical and colorimetric detection of organophosphate pesticides (OPPs) based on ultrathin-FeOOH-coated MnO2 (MO@FHO) nanozyme. In this biosensor, OPPs can inhibit the alkaline phosphatase (ALP) activity and hinder the dephosphorylation of l-ascorbic acid-2-phosphate, preventing the decomposition of MO@FHO nanozyme and inducing both a photoelectrochemical (PEC) signal and the colorimetric change. The MO@FHO nanozyme not only possesses an enhanced catalase-like activity to degrade H2O2 for the generation of an improved cathodic photocurrent, but also exhibits an excellent oxidase-like activity to oxidize 3,3,5,5-tetramethylbenzidine with high catalytic efficiency. This biosensor displays a detection limit of 50 pmol/L for the PEC mode and a detection limit of 0.8 nmol/L for the colorimetric mode. Moreover, this biosensor exhibits excellent performance in complex biological matrices, and the smartphone-based visual sensing platform facilitates rapid and sensitive detection of OPPs, holding promising applications in food safety monitoring, and on-site detection.

Construction of a Dual-Mode Biosensor with Ferrocene as Both a Signal Enhancer and a Signal Tracer for Electrochemiluminescent and Electrochemical Enantioselective Recognition.

We demonstrate for the first time the construction of a dual-mode biosensor for electrochemiluminescent (ECL) and electrochemical chiral recognition of l- and d-isomers of amino acids, with ferrocene (Fc) as both a signal enhancer and a signal tracer. With the dissolved oxygen as a coreactant, ZnIn2S4 acts as the ECL emitter to generate a weak cathodic ECL signal. Fc can enter into the ß-cyclodextrin (ß-CD) cavity on ZnIn2S4-modified electrode as a result of host-guest interaction. Since Fc can promote H2O and O2 to produce abundant reactive oxygen species (ROS) (e.g., O2·- and ·OH), the ECL signal of ZnIn2S4 can be further amplified with Fc as a coreaction accelerator. Meanwhile, Fc molecules on the ß-CD/ZnIn2S4-modified electrode can be electrochemically oxidized to Fc+ to produce a remarkable oxidation peak current. When l-histidine (l-His) is present, the matching of the l-His configuration with the ß-CD cavity leads to the entrance of more l-His into the cavity of ß-CD than d-histidine (d-His), and the subsequent competence of l-His with Fc on the Fc/ß-CD/ZnIn2S4-modified electrode induces the decrease in both Fc peak current and ZnIn2S4-induced ECL intensity. This dual-mode biosensor can efficiently discriminate l-His from d-His, and it can sensitively monitor l-His with a detection limit of 7.60 pM for ECL mode and 3.70 pM for electrochemical mode. Moreover, this dual-mode biosensor can selectively discriminate l-His from other l- and d-isomers (e.g., threonine, phenylalanine, and glutamic acid), with potential applications in the chiral recognition of nonelectroactive chiral compounds, bioanalysis, and disease diagnosis.

Development of an exogenous coreactant-free electrochemiluminescent sensor for sensing glucose.

Covalent organic frameworks (COFs) are crystalline porous polymers with the characteristics of a large specific surface area, controllable pore structures, high stability, and low mass density. Herein, we demonstrate the development of an exogenous coreactant-free electrochemiluminescent sensor based on a hydrazone-linked COF for sensing glucose. We synthesized a TFPPy-DMeTHz-COF with the hydrazone bond as the linkage and 2,5-dimethoxyterephthalohydrazide (DMeTHz) and 1,3,6,8-tetrakis(4-formylphenyl)pyrene (TFPPy) as the monomers. The obtained TFPPy-DMeTHz-COF exhibits high electrochemiluminescence (ECL) efficiency (21.7%) without either the addition of any coreactants or the removal of dissolved O2, and the ECL signal intensity of the TFPPy-DMeTHz-COF is 6.6 and 113-fold higher than those of TFPPy and DMeTHz, respectively. The enhanced ECL emission of the TFPPy-DMeTHz-COF is induced by OH- in PBS, and the ECL signal exhibits linear dependence on the pH value in the range from 3 to 10. When glucose is present, the addition of glucose oxidase (GOx) to the O2-containing solution generates gluconic acid, and the resultant gluconic acid can induce the decrease of the pH value and the quenching of the ECL emission of the TFPPy-DMeTHz-COF. This exogenous coreactant-free electrochemiluminescent sensor exhibits good selectivity, excellent stability, and high sensitivity with a limit of detection (LOD) of 0.031 µM, and it can accurately detect glucose in human serum.