Selective colorimetric detection of copper (II) by a protein-based nanoprobe

In this work, we report a novel protein-based nanoprobe (PNP) that can be employed for quantitative analysis of Cu²⁺ in pure water medium and real samples. Structurally, the proposed nanoprobe comprises a biofriendly protein (hen egg-white lysozyme (HEWL)) and a Cu²⁺-specific chromogenic agent, where HEWL acts as a nanocarrier encapsulating a structurally tailored rhodamine B derivate. The resulting PNP exhibits a hydrodynamic diameter of ~ 106 nm and efficiently disperses in water, enabling the detection of Cu²⁺ in pure aqueous systems without the aid of any organic co-solvents. The high sensitivity and selectivity of PNP allow the colorimetric detection of Cu²⁺ in the presence of other metal interferents with a low detection limit of 160 nM. The satisfying recovery of trace level Cu²⁺ in environmental samples demonstrate the great potential of employing PNP for the determination of Cu²⁺ in actual applications. Most importantly, the simple co-grinding method employing proteins and chromogenic agents provides a novel strategy to generate sensing systems that are useful detection of pollutants in aqueous samples.