Quantum dots immobilized paper for specific and sensitive quantitation of Ni(II) by headspace photochemical vapor generation: Mechanism and application for RGB detection in tea fusion with a smartphone

Abstract

To avoid the interferences of coexisting ions from sample matrixes during CdTe quantum dots (QDs) based fluorescence and colorimetric assay, an instrument-free paper-based analytical device immobilized CdTe QDs was developed for specific and sensitive quantitation of Ni(II) by headspace photochemical vapor generation (HS-PVG). In the PVG procedure, Ni(II) was converted to volatile Ni(CO)4 by reacting with formic acid under ultraviolet light irradiation, which can effectively quench the fluorescence of the CdTe QDs coated paper. The quenching mechanism was studied in depth via both experimental and theoretical investigations. The results of X-Ray diffraction, X-ray photoelectron spectroscopy, and density functional theory (DFT) show that the generated Ni(CO)4 was reacted with O2 to decompose into NiO at room temperature, which was deposited on the surface of CdTe QDs coated paper, causing its fluorescence quenching. Moreover, visual detection of Ni(II) was achieved with a smartphone by identifying the RGB value of QDs coated paper via HS-PVG procedure. A limit of detection (LOD) of 6.2 μg L−1 was required, which can match those obtained by other large-scale instruments. The concentration of Ni(II) in a series of tea infusions was accurately detected with different leaching experiments and soaking conditions.