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

Abstract

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 Förster 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 ΔI/I₀ (ΔI = 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 ΔI/I₀ 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.