Peroxidase-like activity and mechanism of gold nanoparticle-modified Ti 3 C 2 MXenes for the construction of H 2 O 2 and ampicillin colorimetric sensors.

Transition metal carbides modified by Au nanoparticles (Au/Ti3 C2 ) were synthesized and developed as a colorimetric sensor for the determination of H2 O2 and ampicillin. The surface electrical properties of Ti3 C2 were changed, and Au nanoparticles (AuNPs) and gold growth solution were synthesized simultaneously. Au/Ti3 C2 was obtained by seed growth method with AuNPs modified on the surface of transition metal carbides, nitrides or carbon-nitrides (Ti3 C2 MXenes). The synthesized AuNPs and Ti3 C2 had no peroxidase-like activity, but Au/Ti3 C2 had. The peroxidase catalytic mechanism was due to electron transfer. The peroxidase activity of Au/Ti3 C2 can be utilized for the determination of H2 O2 . The linear range of Au/Ti3 C2 for H2 O2 was 1-60 µM, and the detection limit was 0.12 µM (S/N = 3). A colometric sensor for ampicillin detection based on Au/Ti3 C2 was further constructed since S in ampicillin formed an Au-S bond with Au/Ti3 C2 , leading to the weakening of its peroxidase-like property. The change of peroxidase-like property attenuated oxidation of TMB, and the ampicillin content was inversely proportional to the concentration of oxidized TMB, and the blue color of solution faded, which enabled the determination of ampicillin. The linear range for ampicillin was 0.005-0.5 µg mL- 1 , and the detection limit was 1.1 ng mL- 1 (S/N = 3). The sensor was applied to the detection of ampicillin in milk and human serum.