This content is excerpted from Sensor Technology Alert and Newsletter, a sensor intelligence service published by the Technical Insights unit of Frost & Sullivan.
Many current devices for a continuous monitoring of blood glucose levels are based on direct analysis of blood withdrawn from the tip of a finger. This is disliked by many patients since the finger sticks are painful. Therefore, the goal of more advanced glucose sensing approaches is to minimize the pain associated with monitoring blood glucose levels. Among the different types of emerging glucose sensing methods, a promising one is the implantable enzymatic sensor, which can be implanted in the subcutaneous tissue using a specialized tool designed to minimize tissue damage. The tip of the sensor is made of a membrane selectively permeable to glucose. Once the glucose passes through the membrane, it is oxidized by the enzyme glucose oxidase. Reduced glucose oxidase can then be oxidized by reacting with molecular oxygen, forming hydrogen peroxide as a by-product. At the electrode surface, hydrogen peroxide is oxidized into water, generating a current, which can be measured and correlated to the glucose concentration outside the membrane.
Lately, a group of researchers from Key Laboratory of Chemical Biology and Traditional Chinese Medicine Research (Ministry of Education of China), College of Chemistry and Chemical Engineering, Hunan Normal University, together with researchers from College of Chemistry and Molecular Sciences, Wuhan University, have constructed a novel glucose biosensor based on the electrochemical detection of enzymatically generated hydrogen peroxide.
This sensor was obtained by the effective immobilization of glucose oxidase (GOD) via glutaraldehyde cross-linking with a poly(thionine) (PTH)-modified gold (Au) electrode, followed by coating with a Nafion outer layer in order to realize high selectivity. The researchers found that the PTH film provided a good matrix to immobilize more GOD, and that the performance of the sensor modified by PTH film was better than that of the one without PTH film. At an optimal potential of 0.7 V versus the potassium chloride (KCl)-saturated calomel electrode (SCE), the responses of the glucose biosensors were linear with glucose concentration from 0.005 to approximately 5 mmol L-1. The biosensor has high sensitivity, short response time, good anti-interferent ability, and exhibits good storage stability.
Research and development has tended to focus on needle-type glucose sensors (enzyme electrodes) implanted in the subcutaneous tissue. Although problems of calibration and drift have delayed clinical applications of this type of sensor (and the issue of biocompatibility has tended to impede the realization of practical continuous implantable glucose sensors) several new approaches are expected to help accelerate development of in vivo glucose sensors, such as totally implanted sensors with more robust artificial glucose receptors.