Laser-based optical fiber absorbance probes for clinical analyses

Conventional bio-analytical techniques generally involve invitro measurements of chemicals in extracted samples of fluids or tissues. Unfortunately, a close correlation between a chemical's concentration in an extracted sample and its concentration in the living system is not guaranteed. Remote spectroscopic measurements are now preformed routinely. However, bulky equipment and large sample volumes generally prohibit in-vivo analysis using current technology.

Design variations of a previously developed fluoroprobe make it possible to preform in-vivo chemical absorption measurements. I have developed an absorption probe consisting of a single optical fiber encased in a blunt hypodermic needle with a highly reflective surface affixed at the end of the needle, thus forming a microabsorbance cell. The blunt needle is inserted inside a larger needle to form a cannula. By aspirating through the inner needle, biological fluid is drawn into the microabsorbance cell. The sample is irradiated with monochromatic light and, using a beam splitter, the nonabsorbed radiation is measured with a photomultiplier tube. Corrections are made for scattered radiation also.

There are numerous potential clinical applications for the absorption probe. Our attention was focused on the monitoring of bilirubin, a degradation product of the hemolysis of erythrocytes, in body fluids using the absorption probe. Quantitation of bilirubin in cerebral spinal fluid and amnionic fluid would be helpful in the diagnosis of a cerebral vascular hemorrhage and erythroblastosis fetal is, respectively. This thesis contains descriptions of the construction of the experimental prototype, optimization experiments, and in-vitro experiments to exemplify the in-vivo capabilities. Comparative analysis was conducted to confirm the values obtained by the absorption probe method. Linearity, limits of detection, and linear dynamic range are also reported.