Optical spectroscopy and fluorescence imaging for cancer diagnostics

Abstract: This work presents optical methods for diagnosing cancer. A complementary method for diagnosing eye cancer was investigated using a technique developed within this work named transscleral optical spectroscopy (TOS). Furthermore, nano-sized crystals doped with lanthanides were exploited as probes for fluorescence imaging with direct applications to preclinical cancer research. Almost all intraocular malignancies can today be correctly diagnosed using techniques like ophthalmoscopy, ultrasonography and fluorescein angiography. Even with the rich flora of tools available, some tumors present non-typical behaviors and are difficult to diagnose. As a complementary diagnostic method, TOS was developed, which exploits the natural optical contrast in tissue for diagnosis. The method is particularly sensitive in identifying physiological changes characteristic of tumors, i.e. tissue hemoglobin (total, oxy- , and deoxy- forms), oxygen saturation, blood volume fraction, water content, melanin content and cellular structure. In a series of experiments on porcine eyes, TOS was successful in quantifying the blood and melanin content of tumor phantoms placed in the choroid. It was also showed that TOS measurements did not cause any visible damage to the sclera, resulted in a significant temperature rise, or led to an unacceptable intra ocular pressure elevation. In further experiments on enucleated human eyes with a predetermined melanoma diagnosis, TOS measurements were found to correlated well with the degree of pigmentation in the melanoma. To summarize, TOS offers a tool to probe the physiology of intraocular tumor, which can be used in a complementary diagnosis. Fluorescence imaging is a versatile tool for studying biology on the nanometer to centimeter length-scale through labeling tissue with fluorescent probes to induce the desired contrast. In this work, upconverting nanoparticles (UPNs) were evaluated as fluorescent probes for deep tissue fluorescence imaging. Efficient upconversion was achieved using a NaYF4 host co-doped with Yb3+ and Tm3+ or Er3+ ions. In comparison to traditional fluorescent probes, UPNs were found to have the follow benefits: 1) they allow autofluorescence insensitive imaging through anti-Stokes shifted 2) they show no signs of photo-damage even at high intensities. 3) for deep tissue imaging, they provide higher resolution images. 4) they emit multiple line emissions with large Stoke shifts. To summarize, UPNs hold unique optical properties which make them attractive as fluorescent probes.