Luminescence Spectroscopy For Biomedical Applications

This work presents optical methods utilizing visible light for characterization of biological tissue during diagnostics and treatment processes. The main aim has been to improve the therapeutic outcome of treatment modalities in in vivo studies. An optical probe instrument based on fluorescence/reflectance spectroscopy was developed for noninvasive monitoring of photosensitizer
concentration in the course of a photodynamic therapy (PDT) procedure. Furthermore, upconverting nanoparticles were exploited as probes for fluorescent imaging with direct applications in preclinical research. Photodynamic therapy (PDT) is a minimally invasive treatment modality that uses light, a photosensitizing drug and oxygen to ablate malignant tumours and other diseased tissues. PDT has been investigated for treating malignancies in numerous organs and has become a promising modality for some types of malignancies including some skin tumours and prostate cancers. PDT is, however, a highly complex treatment modality with many parameters influencing the treatment outcome. Improvements in dosimetry for PDT are ongoing, with the
goal to better correlate the clinical outcome to what is planned prior to the treatment of PDT. Accurate dosimetry and treatment planning require knowledge of tissue optical properties and an accurate model for the light propagation in the tissue. In the present work, we present a technique, to combine fluorescence and reflectance spectroscopy to yield improvements in the accuracy of
the treatment planning. These improvements are further facilitated by multivariate analysis of the recorded data. Extracting the intrinsic fluorescence as well as optical properties of the tissue is demonstrated. This technique does not require a priori knowledge of the optical properties of the sample. The application of luminescence spectroscopy as an effective tool that allows detailed
observations of tissues to be made via labelling with exogenous probes, is growing remarkably in popularity. Lanthanide doped upconverting nanoparticles (UCNPs) have recently been developed as light-triggered luminescent probes in various biomedical applications. UCNPs have the ability to convert near-infrared (NIR) radiation with low photon energy into visible radiations with
higher energy per photon via a non-linear optical process. In this work, the non-linear dependency on the excitation intensity was compensated to improve the accuracy of measurements of the quantum efficiencies of UCNPs. Recently, UCNPs have evolved as an alternative fluorescent label to traditional fluorophores for imaging both in vitro and in vivo. Their great potential stems from
their properties which include high penetration depth into the tissue, low background signal and photostability. The aim of this work was also to optimize the excitation wavelength to achieve significant signal gain in deep tissues.