A rapid, sensitive and selective colorimetric method for detection of ascorbic acid

In this work, we report a colorimetric method for detection of ascorbic acid based on growth of silver nanoparticles by a simple and green photo-catalytic route. This route contains two steps, photo-synthesis of silver nanoclusters (NCs) with papain under UV irradiation, and catalytic growth of silver nanoparticles (NPs) in the presence of ascorbic acid. The produced silver NCs at the first step is excellent catalyzer that could quickly catalyze the growth of silver NPs by Ag⁺ and ascorbic acid in 1 min at room temperature. And thus, in the second step, the color of the mixture changed from colorless to yellow and a strong absorption band near 420 nm could be found in their absorption spectra owing to localized surface plasmon resonance (LSPR) of produced silver NPs. We found that the absorbance changes at 420 nm have a good relationship with ascorbic acid concentration, and established a spectrophotometric method for the sensing of ascorbic acid in the range from 0.25 to 50.0 μM, with a limit of detection (LOD) as low as 79.2 nM. We also established a colorimetric assay of ascorbic acid by analyzing the yellow value (Y%) of the silver NPs photographs using cyan, magenta and yellow (CMY) color mode. The lowest detection concentration of ascorbic acid for colorimetric assay by the photographs could be estimated to ∼1 μM. Moreover, the method for ascorbic acid detection also has high selectivity. Potential interferes, such as glucose, dopamine, uric acid and cysteine will not affect the detection of ascorbic acid.