Síntese e caracterização de nanopartículas de ouro de diferentes tamanhos para aplicação em sensores plasmônicos

Abstract

A sensor class that is currently being widely discussed in the literature are those based on surface plasmon resonance phenomenon (SPR). The PRS consists of a trapping effect of incident electromagnetic radiation, due to a resonant interaction with the electrons of the valence band metallic material under appropriate conditions. Gold nanoparticles (AuNPs) have on their surface the effect of surface plasmons and, due to their small enough dimensions, is known as localized SPR (LSPR). A striking feature of the SPR effect (and LSPR) is that the electromagnetic field coupling with the surface of the nanostructures is heavily dependent on the diameter of the same and also the refractive index of the medium around. This fact enables the creation of sensors that are based on monitoring of binding events that occur in AuNPs surface incorporated to the sensory device. Therefore, in this design was proposed the synthesis and characterization of gold nanoparticles by reduction of a gold salt by sodium citrate. It was also studied the influence of some parameters of the synthesis as reflux time during the metal reduction and concentration of sodium citrate in average diameter, size distribution as well as the concentration of nanoparticles generated. The solution synthesized in the optimal condition was used to prepare plasmonic substrates from AuNPs adsorption on glass activated with different concentrations of 3- aminopropyltriethoxysilane (APTES). The best condition for synthesis was the one which used 5.0 mL of sodium citrate solution 1% (w/v) and reflux time equal to 35 minutes. This condition was obtained greater production of AuNPs and a low distribution of diameters. The sensitivities of the produced substrates were 20.94 and 39.5 nm/UIR for substrates with APTES 1% and 2%, respectively. These values were considered low when compared with literature data and also the responses of the devices did not adjust well to a linear behavior. A sensitivity test using a wider range of refractive index may be useful to improve these drawbacks.