Dual signal AA detection based on fluorescence and local surface plasmon resonance absorption technology

The core/shell Au@MnO₂ nanoparticles (Au@MnO₂ NPs) were prepared and characterized by UV-vis spectrum, transmission electron microscopy (TEM) and X-ray photoelectron spectrum (XPS). It was found that MnO₂ in the shell of Au@MnO₂ NPs could oxidize thiamine (VB₁) into blue fluorescent thiochrome (TC). The reduction of MnO₂ in the shell layer could lead to a decrease of Au@MnO₂ NPs size along with a blue shift of the localized surface plasmon resonance (LSPR) peak. Once ascorbic acid (AA) was introduced, MnO₂ in the shell was rapidly reduced to Mn²⁺ ions. Accordingly, the oxidation of VB₁ was inhibited and the fluorescence of TC was weakened. Based on these phenomena, we have established a dual signal method for AA determination with the help of UV-vis and fluorescence spectrophotometer. Under the optimum conditions, the LSPR absorption peak shift (Δλ) of Au@MnO₂ NPs and the decrease in fluorescence of TC correlated well with AA concentration ranging from 0.75 to 17.5 μM. The detection limits of LSPR absorption assay and fluorescence assay were 0.18 and 0.47 μM, respectively. More importantly, this dual-signal detection method has been used for the determination of AA in vitamin C tablets with high accuracy and precision, indicating its promising potential applications.