An improved surface enhanced Raman spectroscopic method using a paper-based grape skin-gold nanoparticles/graphene oxide substrate for detection of rhodamine 6G in water and food

Organic toxins are persistent chemicals of global concern capable of accumulating in environment and food. Surface enhanced Raman spectroscopy (SERS) is a promising technique that facilitates onsite detection of organic toxins. However, the fabrication of a SERS substrate is complicated and difficult to provide flexibility, fastness and cost-effectiveness. This study aims to develop a paper-based SERS method using grape skin-gold nanoparticles/graphene oxide (GE-AuNPs/GO) as SERS substrate and evaluate its efficiency with rhodamine 6G (Rh6G) as a model organic toxin and a real water and food contaminant. GE-AuNPs synthesized by green method using grape skin waste extract and GE-AuNPs/GO showed a surface plasmon resonance at 536 and 539 nm, particle size 18.6 and 19.5 nm, and zeta potential -44.6 and -59.7 mV, respectively. Paper-based SERS substrates were prepared by coating a hydrophobic thin-film of 30% polydimethylsiloxane solution in hexane on Whatman no. 1 filter paper, followed by drop-casting GE-AuNPs or GE-AuNPs/GO and drying. The SERS signals of Rh6G showed an enhancement factor of 5.8 × 104 for GE-AuNPs and 1.92 × 109 for GE-AuNPs/GO, implying that a combination of electromagnetic surface plasmon, charge transfer and molecular resonances may be responsible for a higher enhancement of signal by the latter. A low detection limit of 7.33 × 10-11 M in the linear range of 10-11-10-5 M was obtained for GE-AuNPs/GO, while the relative standard deviation of repeatability and reproducibility was 9.6 and 12.6%, respectively. Paper-based GE-AuNPs/GO SERS substrate was highly stable as <20% loss in efficiency was shown over a 60-day storage period. Application to real samples showed a high recovery of Rh6G from tap water (93.9-100.8%) as well as food samples such as red chilli powder (91.0-95.4%), red glutinous rice ball (96.6-98.3%) and tomato ketchup (98.9-102.3%) after QuEChERS extraction. Collectively, the developed paper-based GE-AuNPs/GO can be a potential substrate for sensitive onsite detection of rhodamine 6G by SERS method.