Synthesis and characterisation of hollow monodisperse silica-titania nanostructures for potential use in targeted delivery of drugs/vaccines/genes
In recent years, there has been a continuous growth in pharmaceutical formulations based on nanoparticle technology. Although a large number of nanocarriers have been studied, most of them are limited by their ability to carry sufficiently viable therapeutic loads, toxicity, and target specific delivery etc. There is, therefore, an urgent need to develop novel, smart nanocarriers which avoid the above limitations. Hollow nanoparticles with their hollow cavity and favourable surface modification, offer a great deal of promise in drug delivery applications. However, a good understanding and thorough characterisation of these nanoparticulate systems is crucial. In this thesis, (solid) silica nanoparticles, silica-titania core-shell nanoparticles (STCSNP) and silica-titania hollow nanoparticles (STHNP) were synthesized using literature procedures. A series of analytical techniques were used to characterize the three different nanoparticles, including dynamic light scattering, scanning transmission electron microscopy, nitrogen physisorption, energy dispersive X-ray spectroscopy and X-ray diffraction technique. Furthermore, the stabilization and purification of these nanoparticle dispersions were carried out using two different procedures (dialysis and centrifugation). Dialysis was found to be the more sophisticated procedure for the purification of these nanoparticle dispersions, i.e. without inducing aggregation. This thesis also demonstrates the versatility of solvent relaxation NMR to study silica-titania hollow nanoparticles (STHNP), along with the bare silica nanoparticles and silica-titania core-shell nanoparticles (STCSNP). The possibility of conducting porosity measurements on complex structures like mesoporous hollow nanoparticles by NMR spectroscopy was explored. NMR spectroscopy was sensitive to both the inner and outer surfaces of the hollow nanoparticles, with some sensitivity to STHNP, as well as from the transition metal (titania) present. Two relaxation rates for water were observed at low concentrations for the hollow nanoparticles, which disappeared at higher particle concentration. However, only single exponential decay curves were observed for the solid nanoparticles (silica nanoparticles and core-shell nanoparticles) as expected. Polymers are common excipients in pharmaceutical formulations, especially in nanoparticulate systems for establishing steric stability. Relaxation NMR experiments along with light scattering, revealed interactions between polymer at titania and silica-titania mixed interfaces. In this study, poly(vinyl pyrrolidone) (PVP) was used to investigate the polymer-particle interaction using solvent relaxation NMR spectroscopy. PVP was observed to adsorb on the silica nanoparticle surfaces however, only poor adsorption was observed on the pure titania (core-shell nanoparticles) and silica-titania mixed surfaces.
QD Chemistry, RS Pharmacy and materia medica
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