Reduced graphene oxide nanosheets functionalized with poly(styrene sulfonate) as a peroxidase mimetic in a colorimetric assay for ascorbic acid

The authors describe a highly sensitive colorimetric method for the determination of ascorbic acid. It is based on the finding that nanosheets of reduced graphene oxide that were functionalized with poly(styrene sulfonate) (PSS-rGO) possess peroxidase-like activity that catalyzes the oxidization of the substrate 3,3',5,5'-tetramethylbenzidine (TMB) by H2O2 to form a blue product (oxidized TMB; oxTMB) that can be quantified by photometry or visually. If ascorbic acid is present, a fraction of H2O2 will be consumed and hence less oxTMB (with an absorption peak at 652 nm) will be formed. Ascorbic acid can be quantified by photometry in the 0.8 to 60 mu M concentration range with a 0.15 mu M detection limit. The method was successfully applied to the determination of ascorbic acid in vitamin C tablets and orange juice.