Raman applications in nanodiagnostics and templating

Abstract

A lot of techniques for detection of specific Nucleic acid sequences have been used for diagnosis of diseases. Some of the techniques involve labeling oligonucleotides with specific sequences with fluorescence dyes and use hybridization for detection of the required base sequences. Expensive techniques like PCR are also used to detect nucleic acids at real time. The high cost and technical skills required for PCR technique and complex chemistry involved in fluorescent labeling are the drawbacks of these processes. A novel technique involving core shell super-paramagnetic nanoparticles, oligonucleotide capture and detector probes have been devised for easy separation and detection of specific sequences of nucleotides. The detector probes hybridized to specific base sequences and labeled with Raman probes are detected by using Surface Enhanced Raman Spectroscopy which is a highly sensitive and versatile technique. The level of detection of analyte molecule can go down to ultralow concentration levels and even to single molecular level. One of the several significant usages of graphene and graphite oxide as well as carbon nanotubes is that of chemical sensors. The characteristics and concentration of defects on graphene gives rise to interesting properties which can be harnessed to make molecular and gas sensors. Raman spectroscopy studies of defects on graphite oxide on interaction with small molecules have shown that this method can be optimized and possibly can be used as sensors for small biologically relevant molecules like amino acids and glucose. vii The preparation of nanomaterials which gives optimum and quantitative SERS is a challenging area of research now. Nanostructures of various shapes, sizes and arrangements are made these days which are being tested for their efficiency in giving good SERS signals with high enhancement factors. Multifunctional silver nanorods synthesized were found to give good enhancement factor to be used in SERS studies. Also methods of encapsulation of gold nanoparticles inside organic microtubes to form nanoarrays of gold nanoparticles have been devised. This method can be used like lithography to pattern nanoparticles or form arrays at desired locations. These nanoparticle arrays are also SERS active. Therefore they can be used for trace molecules detection. Templating biomaterials for growth of nanostructures have also gained considerable interest owing to their multifunctionality. These materials being environment friendly, cost effective and being easily available are attractive materials to be used in a variety of applications from antibacterial wound dressing materials to building substrates for ultrasensitive chemical and biochemical analysis. Bacterial cellulose, naturally occurring polymers, have considerable mechanical strength and porosity to be used as an antibacterial material. Its efficiency can be further improved by incorporating silver nanoparticles which has proven antibacterial activity. Not only silver nanoparticle incorporation makes it a better antibacterial material but also these plasmonic nanoparticles can be utilized for SERS for ultra-trace analysis making these materials truly multifunctional. A simple method has been used to incorporate silver chloride and silver nanoparticles into bacterial cellulose for its use as antibacterial materials and also template for SERS. viii In this thesis, Chapter 1 contains introduction to the topics. Chapter 2 deals with Nucleic acid detection by SERS using oligonucleotide capped core shell nanoparticles. Chapter 3 deals with the Graphite oxide as molecular sensors. Chapter 4 deals with formation of nanoparticle arrays and multifunctional nanostructures for Surface Enhanced Raman Spectroscopy. Chapter 5 deals with Incorporation of silver chloride and silver nanoparticles in bacterial cellulose membranes.