Optical trapping is an effective non-invasive technique for manipulating particles, measuring particle interactions and directed assembly of microstructures. Most commonly, optical trapping utilizes a particle/solvent system where the refractive index of the particle material is higher than the refractive index of the solvent. If the refractive indexes are equivalent, optical trapping is not possible. However, the refractive index difference requirement limits the particle/solvent systems that can be investigated. One common particle material used in optical trapping is silica. Silica particles are readily available in various monodisperse particle sizes, compatible with a wide range of solvent systems and well suited for surface chemistry modification. One way to use silica particle systems and ensure the necessary refractive index difference is to coat the silica with layers of titania. Bare silica particles and silica particles with varying thicknesses of titania are investigated to determine the effect the titania layers have on interactions between particles, the effective refractive index of the core/shell particles and the strength of the optical trapping force. Silica particles with both a titania layer and an outer silica layer are also considered to investigate particles with higher effective refractive index while maintaining a silica surface in order to minimize particle aggregation.