Growth of gold-covered oxide nanostructures for application in surface enhanced Raman scattering

Author(s)

Grazielle de Oliveira Setti

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Química
• Defense date: 2016-03-31

Examining board members

Dosil Pereira de Jesus; Ronaldo Censi Faria; Thiago Regis Longo Cesar da Paixão; Italo Odone Mazali; Jarbas José Rodrigues Rohwedder

• Advisor: Dosil Pereira de Jesus; Ednan Joanni

Abstract

The surface enhanced Raman scattering (SERS) effect has been widely studied for several reasons, including the possibility of application of Raman spectroscopy in chemical analysis involving detection of analytes at very low concentrations. In this work, zinc oxide nanostructures were grown by hydrothermal synthesis and indium tin oxide was fabricated by sputtering. Both surfaces were covered by a thin gold film using the sputtering method and applied as SERS substrates. Crystal violet was used as an analyte during the initial evaluation of the SERS substrates. These substrates showed good potential for this application, and were used for detection of a dye (crystal violet), a thiol (4-mercaptobenzoic acid, 4-MBA), and a pesticide (carbaril). The 4-MBA was detected in the range from 0.1 to 100 µmol/L and carbaril between 0.5 and 50 ppm. The results obtained with the substrates fabricated in this work were similar or even superior to the ones achieved using a commercial substrate (Klarite®). Having in mind the future application in microfluidic devices, the substrates were immersed in crystal violet and 4-MBA solutions and the evolution of the Raman signal with time was evaluated. Since the signal stabilization was not achieved even after 6h of measurements, the SERS substrates were exposed to UV radiation aiming to decrease the hydrophobicity of the substrates. They were immersed in CV and SERS spectra as a function of time were obtained. Changings in the nanostructures growth steps were made in order to decrease the density of nanostructures and verify the efficiency of the SERS substrates. The results allowed to infer that the complexity of the nanostructured surface hinder the diffusion of the analyte to the base of the nanostructures, where the signal intensification is stronger. Microfluidic devices with SERS substrates inside the microchannels were developed and evaluated. The analyte flow accelerated the adsorption equilibrium of the analyte on the nanostructures and the Raman signal stabilization was reached in approximately 30 min. Flow of 5 e 20 µL/min were used and the peak height measured after the signal stabilization were around 1.1x10^3 e 0.7x10^3 to 10 and 1 µmol/L Crystal violet solutions, respectively. The results show the potential application of the device in chemical analysis with SERS detection (AU)

• FAPESP's process: 13/25108-9 - Fabrication of nanostrucuted substrates for application in surface enhanced Raman Scattering
• Grantee: Grazielle de Oliveira Setti Gibin
• Support Opportunities: Scholarships in Brazil - Doctorate