This program is aimed at the development of a deployable sensor for direct measurement of carbonate ions in saline waters with a sensitivity of 5 ?M. The sensor combines the selectivity of carbonate ionophore with the unique structure of a carbon nanotube array to achieve a large dynamic range, high specificity and sensitivity. Phase I was focused on demonstrating the proof-of-principle concept for selective and sensitive detection of carbonate ions with a sensitivity of 5 ?M in saline waters. The specific objectives of the Phase I SBIR program were: a) Demonstration of direct measurement of carbonate ion with a sensitivity of 5 ?, b) Establishing the specificity for carbonate ion detection in sea water, c) Fast response time, d) Dynamic range of 0 500 ?M for carbonate detection and e) Initiation of the circuitry and mechanical design for autonomous detection. Except for the complete dynamic range, all the other objectives of Phase I have been achieved. Phase II work will involve increasing the dynamic range in addition to design, develop and testing of a prototype sensor in conditions of relevance to NOAA applications. Also, the system will be3 designed to enable integration with existing infrastructure and communications protocols of NOAA.