ENZYMATIC BIOSENSORS FOR BIOCHEMICAL MONI- TORING OF THE EXTRACELLULAR MATRIX: CHARAC- TERISTICS, INTERFERENCES AND STRATEGIES FOR SAFEGUARDING ANALYTICAL PERFORMANCES

A biosensor is defined as “a self-contained analytical device that combines a biological component with a physicochemical device for the detection of an analyte of biological importance”. This specialized device is based on the recognition due to the presence of a biological element able to selectively recognize and transform the analyte under study in a detectable byproduct. Several biological elements are used in biosensing: among them nucleic acids, receptors, antibodies, whole cells and much more frequently different class of enzymes, that are specific for the studied compound and must remain stable under normal conditions of use and storage. The biosensor design is conceived dependently on the analyte, so the working electrode (WE) materials and the components layered onto the WE surface are very important. Equally important is the matrix in which the analyte is to bemeasured; this is particularly true for implantable biosensors. Actually, enzyme biosensors are particularly prone to the interferences derived from different compounds present in the sample matrix. This problem became particularly problematic in biological samples (as fluids or tissues for instance), especially when electrochemical biosensors are used. In fact, in this kind of matrix, numerous molecules as cells, proteins, and small oxidizable metabolites can interfere with the analyte detection. The biosensor performance can also be affected by other phenomena such as inflammations, neoplasias or other pathological conditions, as they can modify some chemical parameters as pH or fluids’ composition which, in fact, may interfere with the enzymaticactivity. Sample manipulations, as derivatization, concentration, extraction or pre-filtration, can be useful in order to avoid matrix interferences, although the direct usage of biosensors in a matrix is more desirable because it avoids the sample manipulations and eventual loss of analyte.