Colorimetric-Switch Sensing System Based on Cobalt, Nitrogen and Chlorine-doped Carbon Dots for Detection of Acid Phosphatase Activity

Element doping is one of the strategies for increasing the activity of enzyme-like materials. In this study, cobalt, nitrogen and chlorine-doped carbon dots (Co,N,CI-CDs) were prepared by one-step hydrothermal synthesis utilizing CoCl2, and glutamate as raw ingredients. In weakly acidic environments, Co,N,CI-CDs exhibited high peroxidase-like activity and could catalyze the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) by hydrogen peroxide into oxided TMB (oxTMB), resulting in a distinct color change. Free radical scavenging and electron spin resonance techniques were used to further investigate the catalytic reaction mechanism of Co,N.CI-CDs, and the reactive intermediates produced during the reaction were identified as hydroxyl radical. Acid phosphatase (ACP) could catalyze the hydrolysis of sodium ascorbyl phosphate to release ascorbic acid, which could reduce the blue oxTMB into colorless TMB. Based on this principle, a colorimetric-switching sensing system for detection of ACP was developed by coupling Co,N.CI-CDs and ACP. The sensing system demonstrated good linearity in ACP activity range of 0.5-20 U/L, with a detection limit of 0.17 U/L. The developed sensing system was used to detection of ACP in real serum samples with good recoveries (97.1%-105.7%) and reproducibility (RSD<5%). The sensing system developed here based on Co,N,CI-CDs had many advantages such as low detection cost, process visualization, and high sensitivity, providing reference for detection of ACP.