| The field of biosensor development has gained interest due to the increasing demand for fast and reliable identification of pathogenic species, pollutants and biowarfare agents. Porous silicon (PSi) is an ideal substrate material for biosensors since it has a large internal surface area (sensitivity) and is compatible with silicon technology (integration capabilities). Since the surface is sensitive to charged molecules it can be used to detect biorecognition events involving charged biomolecules (such as DNA). In this work the electrical sensing properties of PSi were used to fabricate and characterize a sensor composed of macroporous silicon (pore diameter 1--2 mum) and two coplanar contacts on the back. With this novel approach the surface is exposed only to the molecule without any interaction with foreign materials. Real time measurements of capacitance and conductance were performed to detect different molecules. To understand the principle of detection and develop a model, the device was first demonstrated as a chemical sensor. The findings were then extended to detect a biological event using synthetic Deoxyribonucleic Acid (DNA) as a model molecule. The sensor characterization included selectivity, sensitivity, and the influence of the pore diameter and depth. The results demonstrate a reproducible and selective response to solvents and label free DNA binding in real time. The performance of the device is strongly influenced by the surface area, DNA concentration and pore morphology. Although single devices were used this work, PSi sensors can be fabricated in an array format and eventually integrated into a single device including instrumentation, addressing logic and display. |
