Visual and fast detection of trace copper ions using biosensor based on FRET

The development of a simple, rapid and sensitive sensor to detect copper ion is very important for environmental detection. Here, we constructed a fluorescence biosensor based on fluorescence resonance energy transfer (FRET) between copper resistance operon coded protein C (CopC), a copper binding protein, and dansyl chloride (DNS-Cl) to selectively detect copper ion. At alkaline conditions, DNS-Cl was contently attached to CopC forming biosensor of DNS-Cl/CopC, in which fluorescence emission of CopC at 320 nm was absorbed by DNS-Cl. After binding with copper ion, the fluorescence of DNS-Cl was quenched significantly to 47%. Within the range of 0.04–11 μM (R = 0.989), the good linearity was obtained and the detection limit reached to 7 nM. More importantly, the biosensor of DNS-Cl/CopC has been successfully used to detecting of copper ion level in purified water, tap water and waste water drained from steel mill. And the results were consistent well with those obtained from the inductively coupled plasma mass spectrometry. Therefore, the established biosensor DNS-Cl/CopC is a creditable method to detect copper ion with high sensitivity and selectivity, which can be utilized as a powerful tool to monitor copper pollution in the environments.