Fabrication of a large-area, flexible micro-pyramid PET film SERS substrate and its application in the detection of dye in herbal tea

A simple method, based on a roll-to-roll ultraviolet micro-pyramid imprinting technique and a nanoparticle self-assembling process in aqueous solution, to fabricate a large-area, flexible surface-enhanced Raman scattering (SERS) polyethylene glycol terephthalate substrate is proposed. The SERS substrate is demonstrated to be of high sensitivity. The detection concentration of Rhodamine 6G (R6G) measured by a portable Raman spectrometer is down to 10⁻⁹ mol l⁻¹. The relative standard deviation values of different spots and different substrates are less than 13%. In addition, the feasibility for rapid detection of dye in herbal tea based on this SERS substrate and a portable Raman spectrometer is investigated. Three industrial dyes are employed to simulate the dyeing process. It is presented that R6G of $4.8\times {10}^{-7}$ g ml⁻¹, malachite green of 10⁻⁶ g ml⁻¹ and Auramine O of 10⁻⁶ g ml⁻¹ in herbal tea could be detected rapidly. The experimental results imply that this method could be potentially applied in the field of dyed herbal tea detection. (letter)