Proposal of estimation method for drug concentration in blood by Raman spectroscopy of tear fluids

Drug concentrations in blood are good indexes for drug therapy. This study proposed an approach based on Raman spectroscopy of tears for a rapid and minimally invasive monitoring of the concentration. Tear fluid reflects the drug concentration in blood and its collection can be performed easily and noninvasively in comparison to blood drawing. Raman spectroscopy is a rapid and sensitive analytical technique, which is suitable for measurement of small volume samples such as human tears. As a first step, we measured the Raman spectra of 2 μL solutions of valproic acid to reveal the sensitivity toward a small amount of drug in tears. The measurement was performed with hydrophobic silicon substrates to concentrate fluid samples. The experimental result demonstrates that the method has sufficient sensitivity to monitor concentration of valproic acid in blood.