Enhanced spatial resolution in optical imaging of biotissues labelled with upconversion nanoparticles using a fibre-optic probe scanning technique

The new generation of synthetic nanomaterials, upconversion nanoparticles (UCNPs), have the potential for high-contrast optical imaging of biological tissue by virtue of their unique luminescent properties which enable the autofluorescence and excitation signals to be completely suppressed and avoid biotissue absorption. The potential for deep tissue imaging, such as whole animal imaging, is demonstrated in this report on a comparative study of two epiluminescent imaging methods suitable for the localization of a UCNP-labelled pathology site buried in highly scattering biological tissue modelled by an optical tissue phantom. The lateral resolution exhibited in scanning imaging by an illumination-collection fibre-optic probe appeared to be almost 1.73 times better than that shown by the wide-field CCD commonly used in diffuse optical tomography systems. We attribute this improved lateral resolution to the enhanced angular selectivity of the illumination-collection regime and to the nonlinear dependence of the UCNP luminescence on the excitation intensity.