Colorimetric and surface-enhanced Raman scattering method for vanillin detection based on two types of reduced silver nanoparticles

It’s the first time we found that vanillin and 3,3′,5,5′-tetramethylbenzidine (TMB) can reduce Tollens’ reagent to different types of Ag nanoparticles (Ag NPs) because of their different reducibility. Vanillin reduced the Tollens’ reagent to small size of Ag NPs (Ag45 NPs) which was colorless and has the maxmium absorption at 350 nm, while pink large Ag NPs (Ag100 NPs) with the maxmium absorption at 490 nm was reduced by TMB. Based on different types of AgNPs reduced by vanillin and TMB, dual-mode detection of vanillin by colorimetry and surface-enhanced Raman scattering (SERS) was designed. The solution changed from pink to colorless with the increasing concentration of vanillin (within 3 min). On the other hand, the reduced Ag45 NPs shows a high SERS enhancement factor, which can be applied for ultra-sensitive detection of vanillin in situ. The SERS had a low detection limit of 25.8 pM, which was 5-orders lower than the colorimetric method and most previously reported methods. Importantly, It avoids the additional procedures to prepare SERS-active substrates and can be used to discriminate vanillin from ethylvanillin, both of which are very difficult to be distinguished because of their much highly similar structure and property. Therefore, the visual, fast and high-sensitive dual-mode strategy has great potential in food safety assessment.