The goal of this project is to develop a colorimetric test strip for small sample size (5 muL) lithium measurements. This sample size can easily be obtained with capillary blood from a finger stick instead of using a phlebotomist to obtain a venipuncture. This project will make lithium determination a point of care measurement that could be performed at any location. The primary medical use of lithium is for the treatment of manic- depressive disorders and cluster headaches. Lithium is not prescribed merely by dose because toxic effects occur at serum levels that are within or close to the therapeutic range. Lithium toxicity is closely related to serum lithium concentrations so determination of the concentration of lithium ion in blood is crucial for proper patient management. Low blood lithium levels are also problematic because patient's symptoms will not be relieved. Convenient, inexpensive lithium measurements will contribute to the objective of better patient management by allowing tight control, minimizing side effects and help monitor treatment compliance. PROPOSED COMMERCIAL APPLICATIONS: Lithium blood testing must be performed when lithium is prescribed as a therapeutic agent. With approximately 2 million people in the United States undergoing lithium treatment, there is a potential annual market of $40 million for home self-testing and point-of-care testing. Point-of-care service providers include primary care, hospitals, residential care and the various legal system settings such as prisons.