Controlling the surface-enhanced Raman scattering performance of graphene oxide by laser irradiation

It is now recognized that graphene and its derivatives are regarded as appropriate surface-enhanced Raman scattering (SERS) substrates. Nevertheless, the reported results show considerable conflicts, and consequently, the mechanism of the SERS effect for graphene-based materials shows wide debate. In this paper, graphene oxide (GO) and laser-irradiated graphene oxide (LGO) suspensions in pure water have been produced and employed for SERS measurements. The utilization of LGO as SERS substrate has not been reported before. LGO substrates suspensions were produced using a nanosecond pulsed laser (532 nm) with constant fluence similar to 0.35 J/cm(2) at different irradiation times (0 to 180 min). R6G dye molecules were used to study and compare SERS activities of both GO and LGO. Depending on the irradiation period, the observed enhancement factor of LGO substrates is as large as 10(3), which is comparable to that of GO. However, the associated fluorescence background is significantly quenched relative to that of the GO substrate. It is found that such LGO substrates can detect R6G molecules at extremely low concentrations down to similar to 10(-9) M. The impact of the irradiation period on GO was illustrated using various spectroscopic techniques. First and second-order Raman bands of GO were utilized as markers to assess the laser impact on oxygen content as well as the reconstruction of the sp(2) domain in irradiated samples. Accordingly, the mechanisms of SERS for GO and LGO are discussed.