Continuous Optical Monitoring of Red Blood Cells During a Photosensitization Reaction

An oxygen-enriched photosensitizer solution was created by the addition of red blood cells (RBCs) as an investigative tool for photosensitization reactions (PRs). Although the oxygen levels and reaction progress can be monitored using the optical characteristics of hemoglobin, previously this has only been done using intermittent measurements. An increase in methemoglobin concentration with irradiation time was reported. We constructed a continuous optical measurement system to study the dynamics of the PR in a photosensitizer solution containing RBCs. We also measured the relationship between hemolysis and methemoglobin production in the solution. A 664 nm wavelength continuous laser beam at 60 mW/cm² was used to drive the PR, and a broadband (475-650 nm) light beam was used to monitor the absorption spectra during the PR. The light sources were arranged perpendicularly to cross at a 1 × 10 mm cuvette. The sample in this cuvette was prepared from a low-hematocrit rabbit RBC suspension medium containing 30 μg/mL talaporfin sodium, a chlorine photosensitizer. The concentrations of oxygenated hemoglobin, deoxygenated hemoglobin, and methemoglobin were obtained using a multiple regression analysis of the measured spectra. The oxygen saturation decreased continuously during the PR. The relationship between the degree of hemolysis and produced methemoglobin concentration was confirmed. We determined the dynamics of the oxidation and oxygen desorption of hemoglobin, as well as RBC hemolysis, during the PR. Our measurement system, which uses the properties of hemoglobin contained in RBCs, might be useful for continuous monitoring of PR dynamics.