Turn-on fluorometric assay based on functionalized gold nanoparticles for measurement of nitric oxide radical scavenging activity of phenol-, amine-, and thiol-type antioxidants.

An innovative fluorometric method has been developed to detect nitric oxide radicals (•NO) and NO-scavenging activity of antioxidants. Nitric oxide radicals were generated from the precursor sodium nitroprusside (SNP), and gold nanoparticles modified with a thiolate ligand (4-hydroxythiophenol) (AuNPs@4-HTP) was designed as the detector probe; addition of •NO to the thiophenol ring of AuNPs@4-HTP was followed by autoxidation of the NO-substituent to -NO2 which in turn interacted with the fluorophore N-(1-naphthyl)ethylenediamine (NEDa) as a Lewis acceptor-donor pair. As a result of the interaction of nitrated AuNPs@4-HTP(ox) with the amine groups of NEDa, the fluorescence of NEDa was quenched. However, antioxidants added to the probe solution scavenged •NO, thus the non-nitrated AuNPs@4-HTP could not interact with NEDa, and the fluorescence of the probe solution was recovered, with simultaneous measurement of the •NO scavenging activity of the tested antioxidants μmol L-1 levels. The method gave good recovery from food samples.