Flexible and transparent Surface Enhanced Raman Scattering (SERS)-Active Ag NPs/PDMS composites for in-situ detection of food contaminants.

The fabrication of flexible and transparent Surface Enhanced Raman Scattering (SERS) substrates enabling fast, sensitive and on site detection is relevant for the practical application of SERS for real world analysis, such as food safety and organic pollutants monitoring. In this work novel Ag NPs/PDMS composites were fabricated and employed for the SERS detection of food contaminants directly on food surfaces. Ag NPs/PDMS composites were obtained by self-assembly of organic Ag nanoparticle solutions on flexible PDMS surfaces. Preliminary evaluation of the suitability of Ag NPs/PDMS probes for SERS analysis showed that composites were characterized by a SERS enhancement factor (EF) of 3.1 × 105, good stability and resistance to harsh conditions as well as good uniformity and batch to bach reproducibility. The "sticky" nature of Ag NPs/PDMS composites was exploited to "paste" them on irregular analytical surfaces, thus enabling the detection in situ of food contaminant crystal violet (CV) and pesticide thiram, respectively. Specifically, CV and thiram concentrations as low as 1 × 10-7 M and 1 × 10-5 M were measured on contaminated fish skin and orange peel, respectively. Furthermore, efficient SERS detection by micro-extraction of CV from fish skin and thiram from fruit surfaces was achieved, showing the analytical versatility of the fabricated SERS composites.