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

The peroxidase-like activity of TiC nanosheets (TiC NSs) was evaluated by catalytic oxidation of colorless o-phenylenediamine (OPD) into orange-yellow 2,3-diaminophenazine (DAP) with the aid of HO. The catalytic behavior followed the typical Michaelis-Menten kinetics. Systematic studies about the catalytic activity of TiC NSs including cytochrome C (Cyt C) electron transfer experiments, radical capture experiments, and fluorescence analysis were conducted, revealing that the catalytic mechanism of TiC NSs was attributed to nanozyme-accelerated electron transfer between substrates and nanozyme-promoted generation of active species (superoxide anion free radical (·O) and holes (h)). Single-stranded DNA (ssDNA) inhibited the peroxidase-like activity of TiC 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 TiC 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), low limit of detection (6.5 pg mL), 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.