Deficiency of protein C (PC), one of the human body＇s key anticoagulants, can lead to massive thrombotic complications. There is a diagnostic need to perform real-time assays, in order to quickly identify and treat this disease. An immune-optical biosensor for the diagnosing of PC deficiencies and monitoring of PC concentrations is being developed for this purpose. Monoclonal antibody against PC (anti-PC) is immobilized on the surface of a tapered quartz fiber that is enclosed in a glass tube (capacity similar to 200 mu L). Following sample injection, PC within a sample binds to the anti-PC in a highly specific reaction. The system is then probed with a fluorophore-tagged secondary antibody against PC. Excitation light is applied through the fiber, and the fluorescence intensity is correlated with the PC concentration in the sample. This study presents (1) a feasibility, direct binding assay, (2) a comparison of methods to immobilize anti-PC upon the fiber (direct immobilization vs an avidin-biotin bridge), and (3) effectiveness of an elution step to regenerate the fiber. PC-deficient patients typically have a concentration range less than 2.5 mu g/mL. It was found that the sensor could detect PC levels down to 0.1 mu g/mL in pure buffer with minimal optimization. Avidin-biotin immobilization of the primary antibody produced enhanced signals, up to 470% of the original intensities. Preliminary fiber regeneration tests achieved nearly a 50% increase in fiber lifetime with the use of a CaCl2 elution step. Ultimately, further development may lead to automation and the use of the system as a multi-blood factor analyzer.