Selective and sensitive detection of acetylcholinesterase activity using denatured protein-protected gold nanoclusters as a label-free probe.

Based on the fluorescence quenching of novel denatured protein-protected gold nanoclusters, a label-free detection method of acetylcholinesterase (AChE) activity has been developed. Using denatured bovine serum albumin (dBSA), in which 35 cysteine residues can interact polyvalently with Au nanoclusters (AuNCs) as a stabilizing agent, water-soluble and stable fluorescent gold nanoclusters were synthesized. The fluorescence of the AuNCs was quenched by thiocholine that was produced from the AChE hydrolysis of S-acetylthiocholine iodide (ACTI) to detect the AChE activity. The linear range of the method was 0.005-0.15 U mL(-1). The limit of detection (LOD) was 0.02 mU mL(-1). Other enzymes and metal ions, i.e., GPT, γ-GT, GOx, K(+), Ca(2+) and Na(+), showed minimal interference. Using the fluorescence probe, satisfactory results for the detection of the AChE activity in human serum were obtained.