Smartphone readable colorimetry and surface-enhanced raman scattering (SERS) dual-mode sensing platform for ascorbic acid detection based on GeO2 composite nanozymes

Ascorbic acid (AA) is an essential micronutrient, which is widely used as an additive in beverages and medicines to improve food quality and human health. Herein, we developed a smartphone readable colorimetry and Surface-enhanced Raman scattering (SERS) dual-mode platform based on GeO2 @Fe3O4/Au NPs nanocomposite to detect AA. GeO2 @Fe3O4/Au NPs have excellent peroxidase-like activity and can oxidize colorless 3,3′,5,5′-tetramethylbenzidine into blue 3,3′,5,5′-tetramethylbenzidine oxide. AA can inhibit the oxidation of 3,3′,5,5′-tetramethylbenzidine, which lead to fading. Based on the above principles, we developed an innovation for micro-detection of AA using oxidized 3,3′,5,5′-tetramethylbenzidine as probe molecule, combined with smartphone readable colorimetry and SERS dual-mode detection. Under optimum conditions, the detection range of AA is 0.5 μmol/L − 340 μmol/L and 10−9 μmol/L − 100 mol/L, the detection limit is 0.6689 μmol/L and 6.162 × 10−13 mol/L, respectively. The method was successfully used for AA in fruits, vitamin C beverages and vitamin C tablets, and the results are consistent with the prescribed values.