Silicon optocouplers for biosensing

Here we review on the fabrication and the bioanalytical applications of a monolithic silicon optocoupler that integrates an array of silicon avalanche diodes as light sources, detectors and silicon nitride optical fibres, all intercoupled through a self-alignment technique. The optocoupler is combined with a microfluidic module that allows for simultaneous real-time sensing of multiple analytes. Detection is performed through reaction of the immobilised biomolecules with labelled counterpart molecules. The binding of these molecules within the evanescent field at the surface of the optical fibre causes absorption of the waveguided modes and reduction of the detector photocurrent. The biotin-streptavidin model assay was used for the evaluation of the analytical potentials of the device developed. A detection limit of 3.8 pM in terms of gold nanoparticle labelled streptavidin was achieved which was further improved to 20 fM by silver-plating of the immobilised gold nanoparticles. In addition, results that demonstrate the efficiency of the device for multiple protein and DNA detection are provided. The ability of the developed integrated silicon optocoupler for label-free analyte determinations is also discussed.