Analytical properties and sensor size effects of a micrometer-sized optical fiber glucose biosensor

A micrometer-sized fiber-optic fluorescence biosensor for glucose has been fabricated. The sensor is 100 times smaller than existing glucose optodes. It is based on the enzymatic reaction of glucose oxidase that catalyzes the oxidation of glucose to gluconic acid and hydrogen peroxide while consuming oxygen. Tris(1,10-phenanthroline)ruthenium chloride, an oxygen indicator, is used as a transducer. The ruthenium complex and glucose oxidase are incorporated into acrylamide polymer that is attached covalently to a silanized optical fiber tip surface by photocontrolled polymerization. A study of the dependence of the fluorescence intensity on sensor size shows that, under normal operating conditions, the signal decreases with the sensor diameter rather than its volume. Also, the response of micrometer-sized sensors is improved by about 20% compared to that of larger fiber-optic glucose sensors. Due to its small size and the lack of membrane support, the response time of the sensor is only 2 s. An absolute detection limit of around 1 x 10(-15) mol is achieved. The new glucose sensor is at least 25 times faster and its absolute sensitivity 5-6 orders of magnitude higher than that of current glucose optodes.