Cu nanoclusters-based ratiometric fluorescence probe for ratiometric and visualization detection of copper ions

• We developed a ratiometric fluorescence probe for ratiometric and visualization detection of copper ions.
• Copper nanoclusters was conjugated to silica coated CdSe quantum dots to design a ratiometric fluorescence probe.
• Highly sensitive and visualized detection of Cu2+ was achieved.
• This method provided a built-in correction for environmental interference.

Copper is a highly toxic environmental pollutant with bioaccumulative properties. Therefore, sensitive detection of Cu2+ is very important to prevent over-ingestion, and visual detection is preferred for practical applications. In this work, we developed a simple and environmental friendly approach to synthesize hyperbranched polyethyleneimine-protected copper nanoclusters (hPEI-Cu NCs) with great stability against extreme pH, high ionic strength, thiols etching and light illumination, which were then conjugated to the surface of silica coated CdSe quantum dots (QDs) to design a ratiometric fluorescence probe. In the presence of different amounts of Cu2+ ions, the fluorescence of Cu NCs can be drastically quenched, while the emission from QDs stayed constant to serve as a reference signal and the color of the probe changed from yellow-green to red, resulting in ratiometric and visualization detection of Cu2+ ion with high accuracy. The detection limit for Cu2+ was estimated to be 8.9 nM, much lower than the allowable level of Cu2+ in drinking water (∼20 μM) set by U.S. Environmental Protection Agency. Additionally, this probe can be also applied for the determination of Cu2+ ion in complex real water samples.

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