Polyethylenimine-protected green-emission copper nanoclusters as highly effective fluorescent and colorimetric nanoprobe for selective cobalt ions and temperature sensing.

Excessive uptake of Co is harmful to one's physical health and should not be ignored. Herein, a polyethylenimine (PEI) protected hydrophilic copper nanoclusters (PEI-CuNCs) with strong green fluorescence emission around 510 nm was apace synthesized employing a one-pot method without hyperthermia. Interestingly, the as-prepared water-soluble PEI-CuNCs can be specifically quenched by Co at pH 6.0, with a wide detection range (0-500 μM) and a sensitive detection limit of 14.9 nM, which was lower than the maximum level in the body. Besides, the colorimetric detection of Co could be additionally realized based upon the typical yellow color of PEI-CuNCs changed to baby-pink color of the PEI-Co complex. Furthermore, the PEI-CuNCs was employed in fabrication portable test strip for visual detection of Co by capturing the change in fluorescence color, which can be ascribed to the coordination interaction between Co and amine groups in PEI, and also the aggregated quenching of large PEI-CuNCs-Co particles formation. Moreover, the PEI-CuNCs displayed excellent reversible thermo-responsive within a temperature range of 20-65 °C. It is worth mentioning that the PEI-CuNCs exhibited low bio-toxicity and excellent cell permeability when selectively detecting Co in living cells by fluorescence microscopy imaging. Armed with these engaging properties, the sensing system paved a new avenue for the effective development of a convenient fluorescence colorimetry sensor for general assessment of potential risks and specific assessment of human security.