Boronic acid-based sugar sensing by surface-enhanced Raman spectroscopy

Abstract

Boronic acid-based sugar sensing on gold nanosurfaces have been investigated by surface-enhanced Raman spectroscopy (SERS). SERS is a sensitive molecular sensing technique where highly selective and quantitative identification of analytes are possible via vibrational fingerprints. Nowadays, SERS has a wide range of applications in biological and chemical detection. Sensitive glucose detection is one of the challenging problems in the diagnosis and treatment of diabetes and obesity. Both accurate quantification of the entire class of sugars and individual components as glucose have been regarded important for medical applications. A variety of phenylboronic acids have been used for highly selective sugar detection where the cis-diol configuration of sugars can be recognized in the dehydration reaction with phenylboronic acids. Despite the significance of the binding of vicinal glycols with boronic acid on silver surfaces, no detailed and careful study on gold surfaces has yet been reported by Raman spectroscopy. Considering that phenylboronic acids adsorbed on silver surfaces have been reported to quantify the monosaccharides concentration, it would be worthy to investigate the efficient saccharide sensing by using gold surfaces including monosaccharides and disaccharides. Gold nanosurfaces have a wide range of potential applications such as chemical sensing and biological labeling due to the stability, biocompatibility, and consistent and easy sample preparations. Two gold surfaces including gold colloidal nanoparticles and aminopropylsilane (APS) gold surfaces were synthesized, and surface adsorption of mercaptophenylboronic acid derivatives and chemical sensing of sugars were performed. Gold colloidal nanoparticles were synthesized by reducing the gold ions with citrate ions, and APS gold surfaces were prepared by immersing pre-treated APS glass slides on gold colloidal nanoparticles. ii In this thesis work, I investigated the preparation of efficient gold substrates for sugar detection by SERS. We used mercaptophenylboronic acid (MPBA) derivatives which demonstrate distinguishable Raman peaks when they bind on the metal surface via mercapto group. By using MPBA molecules with mercapto group at two different positions (4-MPBA vs. 3-MPBA), I investigated sugar detection by SERS on sugar molecules including D-glucose, D-fructose, and D-sucrose.