Affinity sensor for subcutaneous glucose monitoring   Continuous glucose monitoring (CGM) allows the most timely detection of abnormal glucose levels, and can be accomplished by either non-invasive or minimally invasive approaches. Minimally invasive, subcutaneously implanted devices allow direct and accurate extraction of ISF glucose levels. Existing minimally invasive systems are mostly based on electrochemical detection of enzyme-catalyzed reactions. While electrochemical methods allow sensitive glucose detection, they have some significant drawbacks. First, glucose is irreversibly consumed during detection. This might change the equilibrium concentration of glucose in tissue, and thus, the actual measured glucose level. Furthermore, the rate of glucose consumption is diffusion limited. Any changes in diffusion layers (e.g. by cell deposition, capsule formation) on the sensor surface affect the diffusion rate, and, thus, the device sensitivity. In addition, drift hydrogen peroxide production and interference from electrode-active chemicals often cause inaccuracies. As a result, electrochemical CGM sensors often exhibit large drifts and require frequent calibration (typically at least once every 12 h). This lack of reliability has been severely hindering CGM applications to practical diabetes treatment.   To overcome these limitations, alternative glucose sensing techniques have been under active investigation. In particular, methods that use non-consumptive, competitive affinity binding of glucose have shown great promise. Basing on this method, we develop a MEMS viscometric glucose sensor that consists of a polymer microcantilever coated with a permalloy thin film, which is located in a microfluidic chamber and vibrates in a remotely applied magnetic field. The sensing fluid, consisting of the polymer with specific affinity to glucose, exchanges glucose with the fluid outside the device through a semi-permeable membrane. The damping on the cantilever vibration depends on the viscosity of the sensing fluid, which in turn is determined by the interaction of glucose with Con A. Thus, the cantilever vibration can be measured to obtain the glucose concentration. The device represents a first step toward an implantable MEMS sensor that is miniaturized and affords the excellent stability offered by nonconsumptive equilibrium binding principles.