A recyclable graphene/Ag/TiO2 SERS substrate with high stability and reproducibility for detection of dye molecules

Few-layer chemical vapor deposition (CVD) graphene was successively wet-transferred on a magnetron sputtering Ag/TiO2 film to develop a recyclable surface-enhanced Raman scattering (SERS) substrate with high sensitivity, stability, and reproducibility owing to the passivation of graphene, the SERS function of Ag and the photocatalytic activity of TiO2. The detection limit of rhodamine 6G (R6G) for the graphene/Ag/TiO2 nanocomposite could be lowered to 10(-11) M, and its enhancement factor was 3.75 x 10(6). Moreover, a good linear response was observed between Raman intensity and R6G concentration with a fitted curve (R-2 = 0.98), demonstrating that the prepared substrate can estimate the concentration of probe molecules for practical testing applications. Importantly, the homogeneity of the substrate structure and the passivation protection of the graphene layer resulted in excellent reproducibility (relative standard deviation less than 9%) and stability (the substrate maintained good SERS activity after 30 days of exposure to air) of the SERS substrate. Besides, the photocatalytic properties of TiO2 could eliminate the Raman signal of methylene blue (MB) efficiently and make this substrate recyclable. After being reused five times, its excellent SERS performance was still retained. Thus, the successful preparation of this composite structure opens up new avenues for the construction of high-performance multilayer composite SERS substrate, which is expected to become a new type of ultra-sensitive, highly stable, and reusable analytical tool.