Metal-Enhanced Fluorescence due to Salicylaldehyde-Silver Nanoparticle Interactions for Fe3+ Sensing

Abstract

Silver nanoparticles were synthesized using alkaline salicylaldehyde (SL) in the presence of silver nitrate. SL was oxidized to quinone form, while silver(I) was converted to silver (0). The solution was highly fluorescent, (quantum yield 7 %, λex 290 nm, λmax 424 nm), where silver (0) exhibited metal-enhanced fluorescence and quinone acted as the fluorophore. The fluorescence was selectively quenched with the addition of Fe3+. No other metal shows such drastic fluorescence quenching. Thus, silver-enhanced fluorescence is used to detect iron selectively and sensitively (limit of detection 2×10−9 M, linear detection ranges from 10−4 M to 8×10−9 M). The detection of iron was also done at various water of natural sources (drinking water tap water, rainwater, and Ganga River water). The iron concentration was quite similar to atomic absorption spectroscopy. The enhancement of fluorescence of the sliver atom is attributed to enhanced photonic mode density, related to the lightning rod effect. The quenching of silver-enhanced fluorescence was attributed to the destruction of the capping agent due to SL-iron complexation. The variation of distance between the fluorophore and metalized surface was anticipated for the alteration of fluorescence with and without the Fe3+ion.