Zhang_2024_Mikrochim.Acta_191_411

Ratiometric fluorescence and colorimetric strategies for detecting activity of butyrylcholinesterase (BChE) in human serum were developed by using g-C(3)N(4) nanosheets, silver ion (Ag(+)) and o-phenylenediamine (OPD) as chromogenic agents. The oxidation-reduction reaction of OPD and Ag(+) generates 2,3-diaminophenazine (oxOPD). Under exciation at 370 nm, g-C(3)N(4) nanosheets and oxOPD emit fluorescence at 440 nm (F(440)) and 560 nm (F(560)), respectively. Additionally, oxOPD exhibits quenching ability towards g-C(3)N(4) nanosheets via photoinduced electron transfer (PET) process. Thiocholine (TCh), as a product of BChE-catalyzed hydrolysis reaction of butylthiocholine iodide (BTCh), can coordinate with Ag(+) intensively, and consequently diminish the amount of free Ag(+) in the testing system. Less amount of free Ag(+) leads to less production of oxOPD, resulting in less fluorescence quenching towards g-C(3)N(4) nanosheets as well as less fluorescence emission of oxOPD. Therefore, by using g-C(3)N(4) nanosheets and oxOPD as fluorescence indicators, the intensity ratio of their fluorescence (F(440)/F(560)) was calculated and employed to evaluate the activity of BChE. Similarly, the color variation of oxOPD indicated by the absorbance at 420 nm (deltaA(420)) was monitored for the same purpose. These strategies were validated to be sensitive and selective for detecting BChE activity in human serum, with limits of detection (LODs) of 0.1 U L(-1) for ratiometric fluorescence mode and 0.7 U L(-1) for colorimetric mode.