Thio amino acids-modified manganese doped ZnS quantum dot probes for the photoluminescent sensing of hazardous nitro aromatics

Abstract

Abstract A simple, cost effective and rapid fluorescent method for the detection of most hazardous nitro aromatic compound, picric acid using the sulfur containing amino acids functionalized ZnS-Mn2+ Quantum dots (QDs) has been developed. The sulfur containing amino acids such as L-Cysteine and L-Methionine with the –SH and –SCH3 group respectively were introduced on the QDs for the surface functionalization and stabilization. The optical properties and structural features of the as-prepared QDs have been characterized by absorption spectra, fluorescence spectra, TCSPC lifetime studies, X-Ray diffraction, FT- IR spectral studies, DLS and Zeta potential. The amino group present in L-Cysteine and L-Methionine at the surface of the ZnS-Mn2+ QDs will bind the picric acid through the strong acid-base pairing interaction and the fluorescent quenching is mainly due to the electron transfer from the QDs to the picrate anions. The sensing ability of the synthesized QDs was confirmed by UV–visible absorption and fluorescence spectroscopic studies. The XRD studies and the FT-IR spectra also confirm the formation of picrate anion on the surface of QDs which is responsible for the sensing action. Under the optimal conditions, the response of the L-Cysteine/L-Methionine capped QDs was linearly proportional to the concentration of picric acid ranging from 0 to 2.2X10−7 M with detection limit 2.7X10-8 M and 3.2X10-8 M respectively. The developed sensing system can detect picric acid as low as 10-12 M using both the amino acids functionalized QDs.