UV-light-induced synthesis of PEI-CuNCs based on Cu2+-quenched fluorescence turn-on assay for sensitive detection of biothiols, acetylcholinesterase activity and inhibitor

Abstract

Polyethyleneimine-protected copper nanoclusters (PEI-CuNCs) were synthesized and applied to detect Cu2+, biothiols, and acetylcholinesterase (AChE). A facile UV-light-induced method was used in the synthesize process to obtain PEI-CuNCs with high stability and strong fluorescence intensity. Based on the quenching mechanism, a label-free assay for sensing Cu2+ by PEI-CuNCs was developed with the limit of detection (LOD) of 0.12 μM. Biothiols with SH functional groups could react with Cu2+ to form the RSH–Cu2+ complex, making Cu2+-triggered fluorescence quenching turned on. Two biothiols, glutathione and cysteine, were determined with LODs of 0.26 μM and 0.34 μM within linear ranges of 0.5–25 μM and 1–25 μM, respectively. AChE could hydrolyze acetylthiocholine into thiocholine (TCh), which reacted with Cu2+ to form TCh–Cu2+ complex and turned on Cu2+-quenched fluorescence. LOD of AChE was calculated to be 1.38 mU/mL within a linear range from 3 to 200 mU/mL. A typical inhibitor of AChE, tacrine, was also detected by this convenient fluorescence turn-on assay with the corresponding IC50 value (the inhibitor concentration required for 50% inhibition of the enzyme activity) of 53.4 nM. Moreover, the assay was successfully applied to the detection of biothiols and AChE activity in human serum samples. Results demonstrated the great potential of PEI-CuNCs and paved a new avenue for exploring their versatile biosensing applications.