Miniature integrated optical modules for chemical and biochemical sensing

An overview is given on the principal ideas, new concepts and practical issues for accomplishing complete miniature sensor modules for chemical and biochemical applications, which are at the same time small, highly sensitive and stable. The novelty of the approach is mainly based on using different types of smart planar optical transducer (SPOT) chips, which not only carry out the task of conventional integrated optical transducers, but also perform additional functions for which peripheral equipment is otherwise needed. The emphasis is on pointing out and discussing the most important aspects for refractometric modules. Different approaches and sensor types are compared with respect to fulfilling the requirements for practical applications. New results concerning the use of multilayer waveguides and the implementation of novel modules are also presented. Key issues discussed are the importance of a proper theoretical modelling of the sensor chips and the (bio-) chemical sensing layers; the availability of micro-and nanofabrication technologies suitable for realizing sensors based on a variety of substrate materials, such as glasses, polymers and semiconductors; the possibility of mass-producing low-cost SPOT chips; using standardized waveguides for the implementation of miniature integrated optical chemical benches; employing planar micro-optical elements for accomplishing illumination and detection sub-modules; the advantages of surface-emitting chip configurations with respect to miniaturization and adaptation to different applications; schemes for single-chip multicomponent analysis based on sensor-pad arrays; and the significance of using on-chip measuring variables and true differential on-chip referencing for achieving both high sensitivity and stability.