Fluorescent responses of CdSe and Si QDs toward Copper (II) ion and the mixed-QDs probe for Cu2+ ion sensing

•Ratiometric fluorescent sensors based on Si and CdSe QDs were fabricated.•FRET between Si and CdSe QDs was investigated.•Copper(II) ion were detected with high sensitivity and selectivity. Although copper (II) ion is essential for the human body, but an excess of Cu2+ causes damage to the human cell and is implicated in many diseases. Cu2+ is also counted among heavy metal pollutants in the environment, especially in water. Thus, a new approach towards quantifying Cu2+ ion is appealing. Here, we reported new ratiometric mixed-QDs probe for Cu2+ detection in an aqueous solution with the combined concept of ratiometric and fluorescence resonance energy transfer. This probe consists of blue Si QDs (donor) and yellow CdSe QDs (acceptor). The energy transfer from Si QDs and CdSe QDs was confirmed using the time-resolved fluorescence. The changes in the ratiometric fluorescence response of the mixed-QDs probe upon exposure to Cu2+ were studied using fluorospectrometry, while the mechanism of the Cu2+ quenching to the probe was studied using an X-ray photoelectron spectrometer. This approach provides a simple, fast, sensitive, selective, and accurate method with low detection limit (3.89 nmol L−1) with high selectivity to Cu2+ versus other biological and environmental relevant ions. Furthermore, this new mixed-QDs probe could be used as a naked-eye detection of Cu2+ for water samples and biological specimens with further development. [Display omitted]