Co, N co-doped porous carbon-based nanozyme as an oxidase mimic for fluorescence and colorimetric biosensing of butyrylcholinesterase activity.

A Co, N co-doped porous carbon-based nanozyme (Co-N-C nanozyme) has been fabricated. Taking advantages of the excellent oxidase catalytic activity and significant stability of Co-N-C nanozyme, we propose a fluorescence and colorimetric system based on Co-N-C nanozyme and red-emitting carbon quantum dots (RCDs) for butyrylcholinesterase (BChE) sensing. As the chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) was catalyzed and oxidized by Co-N-C nanozyme, the generated oxTMB had a new absorption peak at 652 nm, which resulted in the significant quenching of the fluorescence of the carbon quantum dots at 610 nm. Under the catalysis of BChE, thiocholine was generated from the hydrolysis of S-butyrylthiocholine iodide (BTCh), and the as-generated thiocholine effectively inhibited the oxidation of TMB catalyzed by Co-N-C nanozyme, leading to a decrease of the absorption of oxTMB at 652 nm and effective fluorescence recovery of RCDs. By measuring the absorbance of produced oxTMB at 652 nm and the fluorescence of RCDs at 610 nm, the fluorescence and colorimetric system both exhibited an outstanding linear response to the activity of BChE in the range 0.5 to 40 U L-1, with a detection limit of 0.16 U L-1 and 0.21 U L-1, respectively. Furthermore, this established dual-channel biosensing strategy has been successfully applied to the determination of BChE in human serum samples. The present work has effectively expanded the development and application of nanozyme in biosensing.