Fluorometric sensing of pH values using green-emitting black phosphorus quantum dots
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A fluorometric method is described for “turn-on” sensing of pH values via black phosphorus quantum dots (BPQD). Water-stable BPQD were synthesized by a liquid exfoliation method and characterized by TEM, FT-IR, XPS, and absorption and fluorescence spectra. The nanoparticles of BPQD have a uniform distribution with an average size of 5.2 nm. They exhibit bright green fluorescence, with excitation/emission maxima at 420/515 nm. The fluorescence of the BPQD is likely to arise from the quasi-molecular fluorophores of polycyclic aromatic compounds carrying P-P, P-O-P, and PxOy functions on its surface. The protonation and deprotonation of hydroxyl groups of BPQD causes a different degree of quenching of the BPQD. At pH values below 4.0, protons bind to BPQD to form non-fluorescent ground state complexes. At pH values above 4.0, the hydroxyl groups become deprotonated, and this induces the recovery of fluorescence. The sensor has a linear response in the pH range of 1.0–9.0. It was successfully applied to the determination of the pH values in human urine and serum samples.
KeywordsBlack phosphorus quantum dots pH sensor Green fluorescence Water-stability Liquid exfoliation Protonation Deprotonation Fluorometry Human urine Human serum
This work was financially supported by the Natural Science Foundation of China (91543206), the Natural Science Foundation (ZR2014BQ017, ZR2015BM024, and 2013SJGZ07) and the Tai-Shan Scholar Research Fund of Shandong Province and research foundation of Liaocheng University.
Compliance with ethical standards
The authors declare that they have no competing interests.
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