Electrochemically generated green-fluorescent N-doped carbon quantum dots for facile monitoring alkaline phosphatase activity based on the Fe3+-mediating ON-OFF-ON-OFF fluorescence principle

Herein, green-fluorescent N-doped carbon quantum dots (N-CQDs) with quantum yield of 30.6% were prepared via a simple bottom-up electrochemical (EC) method using the mixtures of pyrocatechol and ethylenediamine as both precursors and electrolytes. The ON-OFF fluorescence (FL) principle that the FL intensity of the N-CQDs was quenched in the presence of Fe3+ was further extended to the ON-OFF-ON and ON-OFF-ON-OFF ones for pyrophosphate anions (PPi) and alkaline phosphatase (ALP) detection, respectively, based on the specific competitive interaction of N-CQDs with Fe3+ and PPi and the hydrolysis of PPi in the presence ALP. Under the optimized conditions, limit of detection (LOD) of 1.2 mM and 0.5 mM were achieved for assays of Fe3+ and PPi, respectively. Meanwhile, measurable evaluation of ALP activity was reached in a wide range from 5 to 360 U/L with a LOD of 1.1 U/L. The as-proposed sensors showed many advantages including label free, rapid, simple, low-cost, high sensitive, which has great promising application potential in vivo and in vitro clinical diagnosis and will promote the application of EC derived carbon nanomaterials. (C) 2017 Elsevier Ltd. All rights reserved.