A novel electrochemical biosensor for detection of micrococcal nuclease in milk based on a U-shaped DNA structure

Abstract

Micrococcal nuclease (MNase) is an extracellular endo-exonuclease of Staphylococcus aureus (S. aureus) that can hydrolyze single and double-stranded DNA and RNA. The presence of MNase is used as an outstanding diagnostic biomarker for the identification of S. aureus. Herein, we designed a novel U-shaped electrochemical biosensor to sensitively detect MNase using a gold electrode, thiol-modified oligonucleotide strands and their complementary strand (CS). The principle of the sensing platform is that in the absence of MNase, a U-shaped DNA structure on the gold electrode surface prohibits [Fe(CN)6]3-/4- from reaching the electrode surface through physical inhibition and electrostatic repulsion. Following the addition of MNase, the oligonucleotide sequences are digested into the short DNA sections, which leads the redox agent access to the surface of the working electrode and a sharp current peak. This analytical method can detect MNase in a linear range of 0.00022–0.02 U/μL with the detection limit of 2.37 × 10−5 U/μL. The presented biosensor showed satisfying results for the MNase recognition in the spiked milk samples. Moreover, the biosensor exhibited a prominent electrochemical signal when exposed to MNase secreted from S. aureus in the culture medium sample. Overall, the proposed biosensor has a strong potential for highly selective and sensitive detection of MNase.