Masters thesis

Fluorescent magnetic silica core-shell microspheres for use as an intracellular MRI contrast agent

Masters thesis at the Van't Hoff Laboratory for Physical and Colloid Chemistry, Utrecht University. Supervisors: dr. Ben Erné & Bob Luigjes, MSc.

In this thesis the preparation of fluorescent silica-coated magnetic nanoparticle clusters is described. First, iron oxide nanoparticles were prepared. Secondly, these nanoparticles were assembled into spherical clusters. Finally, the nanoparticle clusters were coated with a silica shell.

To synthesize monodisperse iron oxide nanocrystals a thermal decomposition of iron oleate in a high boiling solvent was performed. Since the boiling point of the solvent directly determines the particle size, 1-octadecene was used to produce nanocrystals with a diameter of 12 nm as described by Hyeon et al. [1]. Although the size polydispersity of the nanoparticles was very low (σ_d = 3.5%), the magnetic polydispersity was found to be high (σ_d,mag = 52%).

Spherical colloidal clusters of nanoparticles were prepared by controlled aggregation using solvophobic interactions as described by Zhuang et al. [2]. Interestingly, another mechanism was observed than was described by Zhuang et al., which led us to perform an alternative method which combines the work done by Graf et al. [3] and Zhuang. The prepared clusters show good non-remanent magnetic properties and an acceptable polydispersity (20–30%). In contrast to Zhuang no clear colloidal crystallinity within the clusters is observed. Moreover, a disturbing amount of single nanoparticles is observed next to the clusters. This might be caused by two effects: the use of an alternative (anti)solvent and the stability of the stabilizing polymer. In the work of Zhuang et al., ethylene glycol served as a solvent for the clusters and partly as an antisolvent for single nanoparticles. Here, the omitting of ethylene glycol might have caused the presence of more single nanoparticles. Second, the polymer PVP is thought to be slowly decomposing in water. This might have caused the clusters to become less colloidally stable resulting in more single nanoparticles and aggregation of clusters.

The coating of nanoparticle clusters with silica and the coating of fluorescent silica were performed using a modified Stöber procedure. Clusters were pretreated with PVP and coated with silica in more than one step. To incorporate a fluorescent dye in the silica, FITC dye was used, covalently bound to the coupling agent APS. Although aggregation of clusters was a problem, silica coating was successfully observed using TEM and fluorescence was observed using confocal microscopy.

1. J. Park, J. Joo, S. G. Kwon, Y. Jang, and T. Hyeon, “Synthesis of monodisperse spherical nanocrystals,” Angewandte Chemie International Edition, vol. 46, no. 25, pp. 4630–4660, 2007.
2. J. Zhuang, H. Wu, Y. Yang, and Y. C. Cao, “Controlling colloidal superparticle growth through solvophobic interactions,” Angewandte Chemie International Edition, vol. 47, no. 12, pp. 2208– 2212, 2008.
3. C. Graf, D. L. J. Vossen, A. Imhof, and A. van Blaaderen, “A general method to coat colloidal particles with silica,” Langmuir, vol. 19, no. 17, pp. 6693–6700, 2003.