Ultrasensitive copper(II) detection using plasmon-enhanced and photo-brightened luminescence of cdse quantum dots

Here, we present a simple platform for the use of the enhanced emission of 16-mercaptohexadecanoic acid (16-MHA) capped CdSe quantum dots (QDs) as a probe for ultrasensitive copper(II) detection. In this study, the photoluminescence (PL) of the QDs was first enhanced by Ag nanoprisms which were self-assembled on Si surfaces and then further increased by photobrightening. Using this approach, the control and different analytes could be readily probed all on a single platform using fluorescence microscopy. The enhanced PL intensity of CdSe QDs was selectively quenched in the presence of Cu²⁺, accompanied by the emergence of a new red-shifted luminescence band. The quenching mechanism was found to be due to a cation exchange mechanism as confirmed by X-ray photoelectron spectroscopy (XPS) measurements. Herein, we have demonstrated that this simple methodology can offer a rapid and reliable detection of Cu ²⁺ with a detection limit as low as 5 nM and a dynamic range up to 100 μM in a fixed fast reaction time of 5 min. The potential applications of this technique were tested in two ways, for mixed-ion solutions and in physiological fluids, and both experiments exhibited good selectivity toward Cu²⁺.