Preparation of Carbon Dots with Peroxidase-like Activity and Their Application in <i>Staphylococcus aureus</i> Detection and Antimicrobial Susceptibility Test
Dan Zhao, Rong Wang, Changpeng Zhang, Xincai Xiao
Abstract
Carbon dot (CD) nanozymes with excellent biocompatibility, optical properties, and catalytic activity show great promise for microbial detection and drug sensitivity testing. This study reports the synthesis of metal-doped green-emitting CDs with good peroxidase-like activity, which were synthesized via a one-step hydrothermal route using thiourea, N-[3-(trimethoxysilyl)propyl]ethylenediamine, and catechol as the starting materials and FeCl 3 as the doping agent. In the presence of H 2 O 2, CDs catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB), producing a blue product; however, in the presence of bacteria and H 2 O 2, the bacterial catalase enzyme decomposes H 2 O 2 and inhibits the catalytic activity of CDs, preventing the color change. The bacterial catalase enzyme neutralizes H 2 O 2, which prevents the CDs from producing the color-changing reaction with TMB. Based on the CDs-TMB-H 2 O 2 cascade system of bioenzymes and nanozymes, we developed a rapid, sensitive, and direct colorimetric detection method for Staphylococcus aureus ( S. aureus ) with a detection limit of 2 × 10 3 CFU/mL and a linear range of 2 × 10 3 –2 × 10 6 CFU/mL. This visual detection method was successfully applied to the detection of S. aureus in food samples. Antibiotics have different effects on the proliferation of sensitive and resistant bacterial strains, leading to different levels of hydrolysis of H 2 O 2 in the bacterial solution and resulting in varying intensities of the solution color; therefore, we developed a simple and visual antibiotic susceptibility test. The applications of CD nanozymes provide a powerful tool for detecting pathogenic bacteria in food, clinical, and environmental samples and infections.