Colorimetric determination of biothiols based on peroxidase-mimicking Ag nanoparticles decorated Ti₃C₂ nanosheets

Ag nanoparticle-decorated Ti₃C₂ nanosheets (AgNPs@Ti₃C₂ NSs) were facilely synthesized via a self-reduction approach, in which Ti₃C₂ NSs acted as both reductant and supporter. The AgNPs@Ti₃C₂ NS nanocomposite exhibited excellent peroxidase-like activity with o-phenylenediamine (OPD) and H₂O₂ as substrates. The catalytic behavior followed the typical Michaelis-Menten kinetics; Michaelis constant (K_m) and maximum initial velocity (V_max) for OPD were 0.263 mM and 43.2 × 10^-8 M^-1 s, indicating high affinity and high catalytic efficiency towards OPD. The catalytic mechanism was revealed to be an accelerated electron transfer process. Based on the inhibition effect on the peroxidase-like activity of AgNPs@Ti₃C₂ NSs, a simple, fast, and sensitive colorimetric method for detection of low-weight biothiols (cysteine (Cys), homocysteine (Hcy), and glutathione (GSH)) was developed by measuring the absorbance at 425 nm. The colorimetric method displayed wide linear range (50 nM to 50 μM for Cys, 10 nM to 250 μM for Hcy, 10 nM to 50 μM for GSH), low limit of detection (48.5 nM for Cys, 5.5 nM for Hcy, 7.0 nM for GSH), and good selectivity and short assay time (3 min). Moreover, the feasibility of this colorimetric sensor was demonstrated by accurately determining Cys in diluted human serum samples; good recovery (95.9-101.0%) and low relative standard deviations (2.8-4.9%) were obtained, showing great promise for point-of-care test in clinical samples.