Development of microwave synthetic routes to silica and gadolinium oxide nanoparticles for potential bio-imaging applications

The main aim of this research was to develop microwave synthetic pathways to monodisperse silica nanoparticles, which have potential uses in bio-imaging. Functionalisation of these nanoparticles was also attempted, using the fluorescent dye, Rhodamine B. Microwave synthesis was also investigated as a route to metal oxide nanoparticles, specifically gadolinium oxide and doped-gadolinium oxide nanoparticles, which find uses as magnetic resonance contrast agents.

A novel method to produce silica nanoparticles using a one-pot microwave synthesis has been developed. It has been demonstrated that small monodisperse silica nanoparticles can be prepared at temperatures as low as 50°C for a reaction time of as little as 30 minutes. This has been achieved using a combination of the traditional Stöber process and the use of microwave irradiation, with tertraethoxyorthosilicate as a precursor, in ethanol, water and ammonium hydroxide. A systematic study has been carried out, varying the reaction times and temperatures to identify the optimum synthetic conditions. The temperatures used were 50, 75, 85 and 100°C and the reaction times used were 0.5, 1, 2 and 5 h. To analyse particle size (Z-average) and polydispersity, dynamic light scattering (DLS) were employed. Scanning electron microscopy was also used to image the nanoparticles. It was found that typically smaller particles, with an average size of 65 nm or lower, displayed high monodispersity, compared to larger particles.

Fluorescent doping of silica nanoparticles was also demonstrated using the dye Rhodamine B. These particles were larger in size compared to the pure silica nanoparticles analogues, but remained highly fluorescent, even two months after synthesis.

Gadolinium oxide and europium-doped gadolinium oxide nanoparticles were also prepared using a combination of microwave irradiation and polyol synthesis. Both sets of particles displayed fluorescent properties, which could make them useful in future bioimaging applications.