Sensitive and selective detection of copper ions using low cost nitrogen doped carbon quantum dots as a fluorescent sensing plateform

Abstract

The current study reports a facile, single step microwave assisted synthesis of nitrogen, oxygen-doped carbon quantum dots (NCQDs) with high quantum yield (~36%). The synthesized NCQDs with an average size of 4 nm demonstrate many fold increase in the intensity of photoluminescence (PL) over the undoped carbon quantum dots (CQDs). UV–Vis absorption peak exhibits a red shift of 26 nm for NCQDs with respect to pristine CQDs. The spectral shift was further confirmed by density functional theory based calculations. X-ray photoelectron spectroscopy measurements reveal the graphitic nature and significantly high nitrogen doping of NCQDs (38.2%). The NCQDs exhibited excitation dependent PL behaviour in the visible region with maximum emission peak recorded at 415 nm with optimum excitation wavelength of 340 nm. The remarkably enhanced PL properties of NCQDs have been employed as fluorescent probe for sensitive and selective sensing of Cu2+ ions. The Cu2+ quenches the fluorescence intensity of NCQDs due to its high binding affinity towards N and O containing functional groups in quantum dots. The NCQDs render a simple, reliable and sensitive detection of Cu2+ ions with limit of detection as low as 1.8 µM.