A ratiometric fluorescence probe based on carbon dots for discriminative and highly sensitive detection of acetylcholinesterase and butyrylcholinesterase in human whole blood

Abstract

A ratiometric fluorescence probe based on carbon dots (CDs) was developed for discriminative and highly sensitive detection of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activity in human whole blood. When o-phenylenediamine (OPD) was oxidized by Cu²⁺, the product 2,3-diaminophenazine (oxOPD) could effectively quench the fluorescence of CDs at 460 nm due to the inner filter effect and gave rise to a new emission peak at 570 nm. The AChE or BChE catalyzed hydrolysis reaction of acetylthiocholine or butyrylthiocholine to generate thiocholine, whose sulfhydryl group strongly captured Cu²⁺ to inhibit the oxidization of OPD, thus effectively preserving the natural fluorescence emission of CDs. The resulting fluorescence intensity ratio served as the signal output of the probe for cholinesterases (ChEs) activity sensing. The activities of AChE and BChE were determined to range from 0.2 to 14.0 U L^-1 and from 0.1 to 5.0 U L^-1, with detection limits of 0.1 U L^-1 and 0.04 U L^-1, respectively. Additionally, the IC₅₀ of tacrine and ethopropazine for the inhibition of AChE and BChE were estimated to be 29.8 nM and 132.6 nM, respectively. Moreover, the probe was successfully applied to the discriminative determination of AChE and BChE in human whole blood without any pretreatment. These results suggested that the proposed strategy provided a discriminative, sensitive and robust analytical platform for ChEs clinical diagnostics and drug screening.

Keywords: Acetylcholinesterase; Butyrylcholinesterase; Carbon dots; Discriminative detection; Ratiometric fluorescence.