Microfluidics Integrated Porous Silicon Biosensor for Protein Detection

Porous silicon (PSi) is an attractive nanomaterial for the design of optical biosensors, due to its low cost and simple fabrication, large internal surface, versatile surface chemistry, and tunable optical properties. Specifically interferometric-based PSi biosensors, in which detection of the target is carried out by monitoring changes in the PSi reflectivity spectrum, enable a direct and label-free target detection, with a simple experimental set up. These have been utilized for monitoring various targets, such as small molecules, DNA, proteins and whole cells. Despite these significant advantages, the application of these PSi-based biosensors for clinical diagnostics has been limited due to their insufficient sensitivity, usually in the micromolar range. Our work aims to develop simple strategies for enhancing the sensitivity of PSi-based biosensors for protein targets, while still detecting the analyte in a direct and label-free manner. As a model platform, the simplest PSi structure, an oxidized PSi thin film, is conjugated with aptamers as capture probes, specifically binding target proteins. Two approaches for enhancing the biosensor`s sensitivity are demonstrated. In the first, integration of the PSi biosensor with a simple polydimethylsiloxane (PDMS) microfluidic device results in a >20-fold sensitivity enhancement, compared to a traditional flow-cell experimental set up. In the second, the electrokinetic isotachophoresis (ITP) technique for on-chip pre-concentration of a target protein on the PSi biosensor is applied. With ITP, a highly concentrated target zone is delivered to the sensing area, resulting in up to 1000-fold enhancement in sensitivity. With both methods, a nanomolar detection limit is achieved.