Differential Surface Plasmon Resonance Sensor for the Detection of Chemicals and Biochemicals

Surface plasmon resonance is one the most common optical sensing techniques for the detection of chemicals and biochemicals, although still mainly confined to lab applications. Typically, these sensors are made by a thin gold layer deposited on a glass prism or on an optical fiber similar to those used in telecom applications. Key advantages of this technique are the possibility to specifically detect different chemicals through functionalization of the metal surface and the high sensitivity, although the latter may turn into a weakness in long term monitoring applications due to cross-sensitivity to parasitic effects. To overcome this limitation the paper proposes a novel sensor implementation with a cascaded double sensing area, particularly suited for long term monitoring of pollutant since one sensing area is actually used to detect the desired molecules, while the other for compensating drifts due to fluctuations, misalignments and temperature variations. The paper addresses mainly the prism-based implementation, but the proposed configuration is suited also for an all-fiber approach. Examples of practical implementation of the proposed techniques are given, evidencing an accuracy improvement of more than an order of magnitude.