Dual-mode colorimetric-photothermal sensing platform of acetylcholinesterase activity based on the peroxidase-like activity of Fe-N-C nanozyme

Sensors based on colorimetry, fluorescence, and electrochemistry have been widely employed to detect acetylcholinesterase and its inhibitors, however, there are only a minority of strategies for AChE detection based on photothermal method. This work reports a versatile dual-mode colorimetric and photothermal biosensing platform for acetylcholinesterase (AChE) detection and its inhibitor (paraoxon-ethyl, a model of AChE inhibitors) monitor based on Fe-N-C/H₂O₂/3,3',5,5'-tetramethylbenzidine (TMB) system. The Fe-N-C with abundant active Fe-Nx sites shows outstanding peroxidase-mimicking activity and can be used to promote the generation of •OH by H₂O₂ to oxidize TMB. However, the introduction of mercapto molecules tending to coordinate with metal atoms result in the block of action site in Fe-N-C, thereby decrease its peroxidase-mimetic activity. The designed biosensor principle is based on the block of active sites of Fe-N-C by thiocholine (TCh, one kind of mercapto molecules) that can be produced by acetylthiocholine (ATCh) in the presence of AChE. Under optimum conditions, the limit of detection (LOD) for AChE activity is 1.9 mU mL^-1 (colorimetric) and 2.2 mU mL^-1 (photothermal), while for paraoxon-ethyl is 0.012 μg mL^-1 (colorimetric) and 0.013 μg mL^-1 (photothermal), respectively. The assay we proposed not only can be designed to monitor AChE detection and its inhibitors, but also can be easily extended for the detection of other biomolecules relate to the generation or consumption of H₂O₂.