Leaching of AuNPs from the surface of GO: Sensitive turn on fluorescence detection of toxic preservative.

Development of a novel colorimetric and turn-on fluorescent sensor for potassium metabisulphite (KMS) using graphene oxide stabilized gold nanoparticles (GO-AuNPs) was described. The red color GO-AuNPs was changed to violet while adding 250 × 10 ^-5  M KMS whereas the absorbance band at 523 nm was decreased. The observed changes were ascribed to the leaching of AuNPs from GO. The emission maximum was observed at 448 nm for GO while exciting at 335 nm. However, the GO emission was "turn-off" after the formation of AuNPs on GO surface due to masking of oxygen functional groups responsible for emission. Interestingly, the emission of GO-AuNPs becomes "turn-on" after the addition of 75 × 10 ^-6  M KMS. Further addition of KMS from 150 to 1125 × 10 ^-6  M, the emission intensity of GO-AuNPs linearly increases with the correlation coefficient of 0.9980 and the limit of detection was found to be 9.4 µM L ^-1 /1.2 mg L ^-1 (S/N = 3).
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