Exciton behavior control of high-quality CdSSe/CdS/ZnS quantum dots and its application for ultrasensitive sensing copper ions

Improving the sensitivity of the fluorescence method is crucial in biosensor fields. In this study, an ultrasensitive and excellent selectivity method was developed for the detection of trace Cu2+ ions using 3-mercaptopropionic acid capped CdSSe/CdS/ZnS quantum dots (MPA-CdSSe/CdS/ZnS QDs) as a fluorescent probe. Through energy band engineering to optimize the interior inorganic structure and passivate the surface defects, the photoluminescence quantum yield of the MPA-CdSSe/CdS/ZnS QDs in aqueous solution had as high as 70 %. The X-ray diffraction (XRD) and Transmission Electron Microscope (TEM) analysis revealed the prepared CdSSe/CdS/ZnS QDs were cubic zinc blende structure with average diameter 7.2 nm. Further, the fluorescence of the MPA-CdSSe/CdS/ZnS QDs was significantly quenched by the Cu2+ with fast response time through an efficient photo-induced electron transfer (PET) progress. By optimizing the thickness of CdS shell, the MPA-CdSSe/CdS/ZnS QDs probe with appropriate CdS shell thickness exhibited excellent linear linearity and sensitivity for the detection of Cu2+ ions with limit of detection as low as 0.05 nM. Additionally, ions interference experiments demonstrated the good selectivity of the probe towards Cu2+. Furthermore, this sensing system could also be applied to the measurement of Cu2+ ions in real water samples with satisfactory recoveries. This work provided new insights to design and synthesize high-performance QDs-based fluorescence probes with controllable exciton emission behavior for their applications in biosensor and biological fields.