The invention consists of a sensor with multiple indicating (sensing) electrodes covered with a selectively permeable membrane for monitoring fluid concentrations in a biological environment. The indicating electrodes respond to changes in certain analytes, such as glucose, through an enzyme-mediated reaction. The currents generated from the enzyme-mediated reactions are transmitted through radio signals to an external receiver where the information is processed and recorded. Through the use of various biomaterials and biochemicals associated with the sensor, the monitoring accuracy is improved and the overall viability is prolonged. The process of foreign body fibrosis (formation of a scar capsule around the implanted sensor) eventually limits the functional life of the device. We teach methods of delivery of certain biochemicals that can increase the functional life of the sensor by inhibiting the formation of the foreign body capsule or by stimulating the growth of capillaries into the capsule.