Synthesis of N-acetyl-L-cysteine capped Mn:doped CdS quantum dots for quantitative detection of copper ions

In this work, a new assembled copper ions sensor based on the Mn metal-enhanced fluorescence of N-acetyl-L-cysteine protected CdS quantum dots (NAC-Mn:CdS QDs) was developed. The NAC and Mn:CdS QDs nanoparticles were assembled into NAC-Mn:CdS QDs complexes through the formation of Cd–S and Mn–S bonds. As compared to NAC capped CdS QDs, higher fluorescence quantum yields of NAC-Mn:CdS QDs was observed, which is attributed to the surface plasmon resonance of Mn metal. In addition, the fluorescence intensity of as-formed complexes weakened in the presence of copper ions. The decrease in fluorescence intensity presented a linear relationship with copper ions concentration in the range from 0.16–3.36 μM with a detection limit of 0.041 μM. The characterization of as-formed QDs was analyzed by photoluminescence (PL), ultra violet-visible (UV–vis), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and energy dispersive spectroscopy (EDS) respectively. Furthermore, the recoveries and relative standard deviations of Cu²⁺ spiked in real water samples for the intra-day and inter-day analyses were 88.20–117.90, 95.20–109.90, 0.80–5.80 and 1.20–3.20%, respectively. Such a metal-enhanced QDs fluorescence system may have promising application in chemical and biological sensors.