Sensor plasmônico baseado em nanopartículas de ouro para detecção de combustível adulterado

Abstract

Plasmonic sensors based on gold nanoparticles (AuNPs) are based on the Localized Surface Plasmon Resonance (LSPR) effect which is capable of monitoring variations in the refractive index (IR) of the contact medium with the metal surface. In this sense, the objective of this work was to synthesize and characterize gold nanospheres (AuNSs) to obtain a plasmon platform. The synthesis of AuNSs was performed using the method described by Turkevich which consists of the union of a gold precursor salt with sodium citrate solution in a boiling reaction medium under reflux. AuNSs were characterized by UV-Vis spectrophotometry. In the sequence AuNSs were immobilized on glass using (3-Aminopropyl)triethoxysilane and the sensitivity of the platform to variations in refractive index was determined. Different ethanol/water blending compositions were prepared to test the plasmon response of the sensor and to obtain an analytical curve. AuNSs of different diameters, close to 20 nm and homogeneous, were obtained using different amounts of sodium citrate solution. The colloidal suspensions presented values of wavelengths at maximum absorption (λmáx) and full width at half maximum (FWHM) considered good for application in plasmonic sensors. The tests performed with the substrates revealed that, after the plasmonic substrate production, the values of FWHM and λmax showed an increase, possibly due to the decrease of the interparticle distances that occur during the immobilization of AuNSs on the glass. The substrate that presented the best sensitivity was for the sample synthesized with 2,5 mL of sodium citrate solution and 1 hour of activation time, being 198,36 nm/UIR, in which it was able to detect ethanol/water of different concentrations. Finally, due to the stability presented by in organic solvents, it is suggested that other fuels such as diesel or gasoline can be tested.