Peroxidase-like activity of MoS₂ nanoflakes with different modifications and their application for H₂O₂ and glucose detection

MoS₂ nanoflakes (MoS₂ NFs) with a diameter of ∼390 nm were obtained by a facile one-pot hydrothermal method and the NFs exhibited intrinsic peroxidase-like activity. After being modified by commonly used biocompatible surfactants including polyethyleneimine (PEI), polyacrylic acid (PAA), polyvinylpyrrolidone (PVP), and cysteine (Cys), the peroxidase-like catalytic activities of MoS₂ NFs were investigated by using 3,3',5,5'-tetramethylbenzidine (TMB) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)diammonium salt (ABTS) as chromogenic substrates. Compared to the polymer modified MoS₂ NFs, Cys functionalized MoS₂ NFs exhibited a high catalytic activity toward H₂O₂ in the presence of TMB or ABTS. Zeta potential and Michaelis-Menten analyses implied that the electrostatic force induced affinity or repulsion between the MoS₂ NFs and substrates, as well as surface modifications of the MoS₂ NFs played a key role in the catalytic reactions. Notably, a new peroxidase-like catalytic reaction mechanism was proposed based on the formation of a transient state of Cys-MoS₂ NFs containing H₂O₂ and ABTS, and the catalytic reaction could occur because the Cys on the surface of the MoS₂ NFs served as an electron transfer bridge between H₂O₂ and ABTS. Based on this finding, we also established a platform for colorimetric detection of H₂O₂ and glucose using Cys-MoS₂ NFs as a peroxidase substitution. The limit of detection (LOD) was determined to be 4.103 μmol L^-1 for H₂O₂, and the linear range (LR) was from 0 to 0.3 mmol L^-1. The LOD for glucose was 33.51 μmol L^-1 and the LR was from 0.05 to 1 mmol L^-1, which is suitable for biomedical diagnosis. This work provides a new insight into the catalytic mechanism of peroxidase-like MoS₂ NFs, and paves the way for enzyme-like nanomaterials to be used for medical diagnosis.