The Fabrication Of Flexible Surface Enhanced Raman Scattering Substrate And Its Applications In Environmental Monitoring

In recent years, there is an increasing demand for methods that are capable of performing fast, on-site detection and identification of various analytes on surfaces, as in homeland security and food safety screening. The development of surface contamination analysis is restricted because of lacking of powerful surface analysis method. In this work, we report a method for fabrication of a new type SERS substrate which is shape adaptable for surface contamination analysis of different roughness.Based on the traditional slime preparation, we made Poly (vinyl alcohol) (PVA) dissolved in Ag colloidal solution before mixing with borax to form the slime. Optimization of the slime SERS substrate has been conducted, different factors that may affect the performance of the slime SERS substrate have been examined, including the concentration of Ag NPs, the concentration of PVA, the condense factor of PVA-Ag NPs mixture, the v:v ratio between borax and PVA-Ag NPs mixture. We concluded that the best protocol is:A 5mM Ag colloidal suspension was first prepared and used as the solvent for dissolving 4% PVA. Then the PVA-Ag NPs mixture was concentrated at a factor of 6 and mixed with 4% borax (w/w) at 10:3ratio(v/v).Next, the analytical performance of the slime substrate has been explored by applying a Raman probe nile blue A (NBA) onto surfaces of different materials and different roughness. It was found that the LOD (limit of detection, LOD) for NBA is 0.79 pg per～3 cm2 on glass. Surfaces of different materials, including sandpapers, cotton, metal, and wood, previously contaminated with NBA were analyzed with the PVA slime SERS substrate. Limits of detection (LOD) as low as 100 ppb (0.79 ng in a total amount on an area of ～3 cm2) were achieved for all surfaces tested.Finally, based on the as prepared PVA hydrogel (slime) SERS substrate, which can conform to any surface shapes, the pesticide triazophos and the illegal additive Sudan red III (SR III) have been detected on the real world surface. Simply by applying the hydrogel SERS substrate on the surface of interest, limit of quantification for triazophos on the surface of apple, orange and cabbage was found to be below the national standard level (0.2,0.2,0.1 ppm, respectively). The time decay of SR Ⅲ on spiked kumquat was monitored with the proposed SERS hydrogel substrate and HPLC analysis was also performed to validate the SERS results. It is found that, even after nearly 1 month of storage, with a SR Ⅲ content of sub-ppb level, SR Ⅲ on fruit kumquat can still be easily detected within 2 min, including sampling time. With virtually no sample preparation requirement, the PVA hydrogel SERS substrate based portable Raman spectrometer could be used for future onsite food quality assurance applications.