Micrococcal nuclease detection based on peptide-bridged energy transfer between quantum dots and dye-labeled DNA

A novel and simple method was presented for micrococcal nuclease (MNase) detection based on fluorescence resonance energy transfer (FRET) realized by electrostatic interaction. In this study, mercaptoacetic acid capped quantum dots (MAA-QDs) and ROX-modified single-stranded DNA (ROX-ssDNA) were chosen as energy donor and acceptor, respectively. At slightly basic pH, the positively charged peptide served as a bridge to bring negatively charged QDs and negatively charged ROX-ssDNA into close contact to energy transfer. When the ROX-ssDNA was cleaved into small fragments by MNase, the relatively weak electrostatic interaction between the fragmented ssDNA chains and the QDs/peptide complex should make the ROX away from the QDs/peptide complex, and thus the FRET efficiency decreased. Consequently, the fluorescence intensity of acceptor decreased and a quantification of the MNase was enabled. Under the optimal conditions, experimental results showed that the fluorescence intensity of acceptor was proportional to the logarithm of MNase concentration in a range of 4.0×10−3–8.0×10−2 U mL−1. The proposed approach offered adequate sensitivity for the detection of the MNase at 2.9×10−3 U mL−1.