Síntese e caracterização de nanopartículas anisotrópicas de Au para a construção de biossensores plasmônicos

Abstract

The present thesis had as study the synthesis and characterization of anisotropic Au nanoparticles (AuNPs) and their application as plasmonic biosensors using the localized surface plasmon resonance (LSPR), surface enhanced Raman scattering (SERS) and surface enhanced fluorescence (SEF). Three different Au nanostructures were synthetized: Nanorods (AuNRs), nanobypiramids (AuNBs) and nanobranches (AuNGs), using the seed mediated growth method. These anisotropic AuNPs were characterized with UV-Vis spectroscopy and scanning and transmission electronic microscopy. AuNRs present larger yield in your preparations and, therefore, were the nanostructures used in biosensors construction. LSPR based biosensors were prepare in two different configurations. AuNRs in suspension, S-AuNRS, and chemically adsorbed on glass slides, AuNRs-chip. The glass adsorption was done using the 3-mercaptopropyltrimethoxisilane, that was utilized as binding molecule between glass/AuNRs and between AuNRs/AuNRS, these substrates were characterized with UV-Vis spectroscopy and atomic force microscopy. The S-AuNRs and AuNRs-chip show sensitivities of 196 nm RIU-1 and 297 nm RIU-1 respectively, and figure of merit (FOM) of 2.2 RIU-1 and 3.0 RIU-1. The AuNRs, which had the adsorption process improved, obtained an increase of 18% on sensitivity and 15% on FOM related to other AuNRs in the literature. The substrates had the surface modified for biomolecule detection, like the bovine serum albumin antibody (anti-BSA), through the methodology using N’ethylcarbodiimide (EDC) and N-hidroxysuccnimide (NHS). Posteriorly, the BSA was immobilized on the surface and the anti-BSA detection was made through antigen-antibody interaction, observed by the shift of the LSPR band. This shift was similar to two configurations, although AuNRs-chip show larger values of sensitivity and FOM, indicating that the environment surrounding the AuNRs influences the detection efficiency. The anti-BSA detection through SERS and SEF techniques was realized by the extrinsic method, using a sandwich immunoassay and the two AuNRs configurations together. The reporter molecules used for SERS and SEF were Nile blue and IR-820 dyes respectively. In the presence of the analyte, the SERS biosensor presents a twice larger average signal than blank and a larger number of positive events at SERS digital mapping. The SEF biosensor present a three times bigger average signal than blank and a larger number of positive events at SEF digital mapping, indicating the anti-BSA detection through these techniques. AuNBs and AuNGs were adequate SERS substrates, showing a good intensification in Nile blue Raman signal. The biosensors constructed in this thesis are simple, fast and have good efficiency and performance on anti-BSA detection.