Surface-enhanced raman detection of glucose on several novel substrates for biosensing applications

The small normal Raman cross-section of glucose is considered to be a major challenge for its detection by Surface Enhanced Raman Spectroscopy (SERS) for medical applications. These applications include blood glucose level monitoring of diabetic patients and evaluation of patients with other medical conditions, since glucose is a marker for many human diseases. This dissertation focuses on Surface-Enhanced Raman Scattering primarily for the detection of glucose. Some experiments also are carried out for the detection of the corresponding enzyme glucose oxidase that is used in electrochemical glucose sensors and in biofuel cells. This project explores the possibility of utilizing Surface Enhanced Raman Spectroscopy (SERS) with a variety of substrates (e.g., commercial gold substrates, nanocrystalline silver and gold nanoparticles, which are chemically assembled by citrate reduction on graphene-like sheets, silver nanoparticles on a commercial graphite sheet, and on electrochemically deposited polypyrrole conducting polymer) for glucose, rhodamine 6G (R6G) dye and glucose oxidase detection. These newly fabricated substrates can also be used for biosensing applications. The results of our study demonstrate that SERS is capable of detecting the molecules with high enhancement factor. This work reports the use of commercial multilayer graphene sheets as substrates on which gold nanoparticles are chemically assembled by citrate reduction. The results show that these substrates are capable of providing SERS enhancement factors of up to 1010 with a detection limit to 10-8 M in aqueous solutions of glucose. The SERS performance on graphene substrates are many orders of magnitude higher compared with results on gold-coated chemically etched Klarite® commercial silicon substrates. Also, drop-coated Ag on Toray® graphite microfiber sheets with partition layers exhibit the best results; they yield an excellent enhancement for R6G and glucose detection limit to 10-16 M and 10-12 M of the dye and glucose molecules, ...