A novel sensing strategy for the detection of Staphylococcus aureus DNA by using a graphene oxide-based fluorescent probe

A novel sensing strategy for sequence-specific recognition of Staphylococcus aureus (S. aureus) DNA was designed based on the DNA hybridization between dye-labeled single-stranded DNA (ssDNA) and the complementary target DNA. Graphene oxide (GO) can adsorb FITC-labeled probes and quench the fluorescence efficiently via Forster resonance energy transfer (FRET). However, the formation of double-stranded DNA (dsDNA) will alter the conformation of ssDNA and disturb the interaction between GO and ssDNA. Thus the dsDNA-GO mixture exhibits a stronger fluorescence emission than that of the ssDNA-GO mixture, and the relative fluorescence intensity Delta I/I-0 (Delta l - I-a - I-q) is related to the concentration of ssDNA (S. aureus DNA). Here we illustrate a post-mixing strategy in which the fluorescent dye-labeled DNA was allowed to hybridize with S. aureus DNA prior to the addition of GO. In this experiment, the competition between ssDNA-GO adsorption and the dsDNA formation was avoided and the incubation time was shortened to 20 min. Under the optimum conditions, the relative fluorescence intensity Delta I/I-0 was proportional to the concentration of S. aureus DNA in the range 0.0125-3.125 nmol L-1, with a detection limit of 0.00625 nmol L-1 and good sequence selectivity.