Synthesis of highly fluorescent P,O-g-C3N4 nanodots for the label-free detection of Cu2+ and acetylcholinesterase activity

Abstract

Highly fluorescent phosphorus, oxygen-doped graphitic carbon nitride nanodots (P,O-g-C₃N₄ nanodots) were synthesized using chemical oxidation and hydrothermal etching of bulk P-g-C₃N₄ obtained via pyrolysis of phytic acid and melamine. The P,O-g-C₃N₄ nanodots emitted strong blue fluorescence with a high quantum yield of 90.2%, and displayed high resistance to photobleaching and high ionic strength. A sensitive and facile fluorescence sensing approach for Cu²⁺ was developed through fluorescence quenching based on the static fluorescence quenching and photoinduced electron transfer. Under optimal conditions, a rapid detection of Cu²⁺ could be completed in 5 min with a detection limit of 2 nM, and a linearity ranging from 0 to 1 μM. Using acetylthiocholine (ATCh) as the substrate, the fluorescence of the P,O-g-C₃N₄ nanodots–Cu²⁺ system could be sensitively turned on in the presence of acetylcholinesterase (AChE) through the reaction between Cu²⁺ and thiocholine, the hydrolysis product of ATCh by AChE. A linearity ranging from 0.01 to 3 mU mL⁻¹ could be obtained with a detection limit of 0.01 mU mL⁻¹. In addition, the proposed approach showed potential application for the detection of Cu²⁺ in natural water samples and AChE activity in human plasma.