Ultrasensitive optical sensor for hydrogen peroxide using silver nanoparticles synthesized at room temperature by GQDs

The present study describes the synthesis of silver nanoparticles capped with GQDs (Ag-GQDs) at room temperature for the first time and their application towards the optical sensing of H2O2. Unlike the previous reports, the preparation of Ag-GQDs not involves external heating because more number of hydroxyl groups present in the surface of GQDs synthesized in the present study. The GQDs are prepared from citric acid by pyrolysis at 200 degrees C. The size of the Ag-GQDs is found to be 9 +/- 1 nm. They show characteristic SPR band at 403 nm and show emission maximum at 457 nm when excited at 365 nm. The emission intensity of Ag-GQDs was drastically quenched when compared to GQDs, which show emission maximum at 451 nm at the same excitation. This is due to the masking of free functional groups responsible for emission of GQDs besides the oxidation of hydroxyl groups to aldehyde after reducing Ag+ to Ag-0. The synthesized Ag-GQDs were then successfully used for the sensitive determination of H2O2 by spectrofluorimetry. The addition of 0.1 mu M H2O2 to Ag-GQDs leads to decrease in the absorbance intensity at 403 nm besides the yellow color becomes colorless. Interestingly, even the addition of 25 nM H2O2 increases the emission intensity at 457 nm. The decrease in the absorbance and increase in the fluorescence are attributed to the leaching of Ag+ from the surface of GQDs due to the oxidation of Ag-0 to Ag+ by H2O2. Further, the practical application of the present method was demonstrated by determining H2O2 in human urine samples. (C) 2017 Elsevier B.V. All rights reserved.