DNA controllable peroxidase-like activity of Ti3C2 nanosheets for colorimetric detection of microcystin-LR

The peroxidase-like activity of Ti 3 C 2 nanosheets (Ti 3 C 2 NSs) was evaluated by catalytic oxidation of colorless o-phenylenediamine (OPD) into orange-yellow 2,3-diaminophenazine (DAP) with the aid of H 2 O 2 . The catalytic behavior followed the typical Michaelis–Menten kinetics. Systematic studies about the catalytic activity of Ti 3 C 2 NSs including cytochrome C (Cyt C) electron transfer experiments, radical capture experiments, and fluorescence analysis were conducted, revealing that the catalytic mechanism of Ti 3 C 2 NSs was attributed to nanozyme-accelerated electron transfer between substrates and nanozyme-promoted generation of active species (superoxide anion free radical (·O 2 − ) and holes (h + )). Single-stranded DNA (ssDNA) inhibited the peroxidase-like activity of Ti 3 C 2 NSs, and the reduced catalytic activity was ascribed to DNA-hindered substrate accessibility to nanozyme surface. Based on the DNA controllable peroxidase-mimicking activity of Ti 3 C 2 NSs, taking microcystin-LR (MC-LR) aptamer as an example, a label-free colorimetric aptasensor was proposed for the sensitive detection of MC-LR. The colorimetric aptasensor showed a wide linear range (0.01–60 ng mL −1 ), low limit of detection (6.5 pg mL −1 ), and high selectivity. The practicality of the colorimetric aptasensor was demonstrated by detecting different levels of MC-LR in spiked real water samples; satisfactory recoveries (97.2–102.1%) and low relative standard deviations (1.16–3.72%) were obtained. Graphical abstract