Biological Applications of Single Crystalline Gold Nanowire and Gold Nanoplate

Abstract

In this research, we have studied varied biological applications of single crystalline gold nanowires (Au NWs) and gold nanoplates (Au NPLs), which are synthesized via chemical vapor transport method. For clear demonstration, this thesis comprises four chapters. The first chapter contains the general introduction for various synthesis methods and applications of gold nanostructures. The second chapter demonstrates the application of Au NWs in monitoring neuronal activities. The third chapter and fourth chapter illustrate the development of surface-enhanced Raman scattering (SERS) sensors for molecular detection and malaria diagnosis employing Au particle-on-plate SERS platform. The detailed descriptions covered in chapter 2-4 are as follows. In chapter 2, we recorded neural activities of somatosensory cortex using a Au NW electrode (Au NWE) with a diameter of around 100 nm. Reduced electrode dimension and mechanically desirable characteristics enabled the Au NWE to be inserted into a live rat's brain with minimal tissue damage. In addition, excellent electric conductivity allowed in vivo extracellular recordings from single and multiple neurons. Especially, by using the Au NWE, it was possible to dominantly monitor neural activities originated from a single neuron. It is expected that the Au NWE can be used as a highly capable electrode for monitoring electrophysiological activities from a specific target cell and finding out neural circuits which require long-term recordings. In chapter 3, we utilized Au NPLs to provide ideal surfaces for SERS sensor. Avidin was sandwiched between two biotinylated nanostructures, Au NPL and Au nanoparticles (NPs), creating SERS-active sites to enhance Raman signal. We also constructed the same sandwich assays on Au film and compared the molecular detection capabilities of Au NPL-based sensor with the Au film-based one. The Au NPL-based platform showed the linear correlation between SERS signals and until 10 pM of avidins could be detected. On the other hand, Au film-based platform could not analyze the target under 1 nM. We expect that SERS sensor based on ultraclean and ultraflat Au NPLs can contribute to the development of biosensor with high sensitivity and low detection limit. In chapter 4, we have fabricated a SERS aptasensor to detect Plasmodium lactate dehydrogenase (pLDH), which is a critical biomarker for malaria. To develop a robust malaria diagnostic biosensor for malaria-endemic regions, thermally stable aptamers were used as capture probes and Au particle-on-plate SERS platform was applied as a detection method. SERS intensity of the sensor showed correlation with the concentration of the pLDH and the pLDH was successfully detected until 10 pM. It is expected that this aptamer-based SERS platform will play an important role in the fabrication of practical diagnostic tools for malaria.