The research will provide basic information for the preparation of a fiber optic probe for lithium ion based on new fluorescent lithium ion carriers immobilized on fiber optic bundles by Langmuir-Blodgett (L-B) film techniques. This is a Small Business Innovation Research (SBIR) award. In Phase I four new florescent ionophores were synthesized. One of these has greater sensitivity and great Li/Na selectivity than any other fluorescent ionophore reported in the literature and is suitable for preparation of L-B films. In the current Phase II additional analogs of these ionophores which will have absorption and emission in the visible spectrum will be evaluated. Those having the best optical characteristics and specificity for lithium, when prepared as L-B films, will be used to prepare fiber optic probes. These will be evaluated as sensors for determination of lithium in blood serum.