A method and apparatus for enhancing the integrity of an implantable sensor. Voids formed between an outer tubing and a sensor substrate or spacing element may be back-filled with a curable, implantable material, minimizing the extent to which unwanted fluids diffuse within the sensor. An enzyme or protein matrix pellet below the sensor window may be pre-treated with a reducing agent to enhance its bond stability, and to reduce undesired swelling that may cause the sensor window to detach or leak. The bonding between the enzyme pellet and a hydrogel layer may be reinforced by application of an intervening bonding layer of a protein material, such as human serum albumin (HSA). The size of the window may be minimized by minimizing the size of an underlying electrode, providing reduced flux and lengthening sensor. A coating may be deposited on the surface of the sensor leads, providing stiffening and lubrication.