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/Ti 3 C 2 ) were synthesized and developed as a colorimetric sensor for the determination of H 2 O 2 and ampicillin. The surface electrical properties of Ti 3 C 2 were changed, and Au nanoparticles (AuNPs) and gold growth solution were synthesized simultaneously. Au/Ti 3 C 2 was obtained by seed growth method with AuNPs modified on the surface of transition metal carbides, nitrides or carbon-nitrides (Ti 3 C 2 MXenes). The synthesized AuNPs and Ti 3 C 2 had no peroxidase-like activity, but Au/Ti 3 C 2 had. The peroxidase catalytic mechanism was due to electron transfer. The peroxidase activity of Au/Ti 3 C 2 can be utilized for the determination of H 2 O 2 . The linear range of Au/Ti 3 C 2 for H 2 O 2 was 1-60 µM, and the detection limit was 0.12 µM (S/N = 3). A colometric sensor for ampicillin detection based on Au/Ti 3 C 2 was further constructed since S in ampicillin formed an Au-S bond with Au/Ti 3 C 2 , 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.