Colorimetric Detection of Ascorbic Acid Based on the Trigger of Gold Nanoparticles Aggregation by Cr(III) Reduced from Cr(VI).

Au nanoparticles (AuNPs) dispersed in water were stabilized by tripolyphosphate (P3O105-). When Cr2O72- (Cr(VI)) was present, the AuNPs did not change; when Cr3+ (Cr(III)) was present, the AuNPs would aggregate because of cooperative metal-ligand reaction. Aggregated AuNPs showed different color from the non-aggregated ones. Thus, a simple colorimetric assay was made using AuNPs-Cr(VI) to detect ascorbic acid (AA). Upon introducing AA to the AuNPs-Cr(VI) system, Cr(VI) was reduced to Cr(III), and the aggregation of AuNPs occurred. This colorimetric assay performed high selectivity and a linear concentration response in the range of 0.2 to 10 μM; its limit of detection was 0.15 μM.