Production of three dimensional porous sers substrates using silver nanoparticles-decorated expanded graphite

Surface enhanced Raman spectroscopy (SERS) is a promising technique for single molecule detection, food safety, medical diagnostics and bio-sensing applications. However, relatively poor stability of the present substrates, high production costs due to need of sophisticated equipments, and repeatability problems limit the use of SERS as a routine analysis technique. Three dimensional (3D) porous platforms that contain metal nanostructures are highly promising for SERS applications due to fast penetration of solvent into the substrate and enabling to adsorb more metal nanoparticles and analyte molecules because of their high specific surface area. However, it is a prerequisite to develop these platforms with a low cost. In this thesis study, 3D porous substrates were prepared from expanded graphite (EG) which was decorated by silver nanoparticles (AgNPs), and their SERS-activity was investigated. EG is a relatively low cost material with a highly porous structure, high specific surface area and reactivity, which allow adsorption of large amount of nanoparticles and analyte molecules. Accordingly, spherical AgNPs in the size range of 20-100 nm were successfully synthesized by chemical reduction of AgNO3 in solution phase method and uniformly mixed with EG. The obtained EG/AgNPs nanocomposite powders were compacted in the form of a pellet and their SERS activity was tested using R6G dye. R6G solutions with different concentrations 10-3 – 10-12 M were dropped onto the substrates and the solvent penetrated into the substrate within a few minutes, enabling to perform SERS analyses immediately. The detection limit of EG for R6G was determined as 10-7 M, while the detection limit was lowered to 10-11 M when EG was decorated with AgNPs which were synthesized using ascorbic acid as a reducing agent.