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 (center dot 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 center dot 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 center dot 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 center dot NO scavenging activity of the tested antioxidants mu mol L-1 levels. The method gave good recovery from food samples.