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 GeO 2 @Fe 3 O 4 /Au NPs nanocomposite to detect AA. GeO 2 @Fe 3 O 4 /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 − 10 0 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.