Development of an optically based porous silicon biosensor

Inexpensive biosensors designed to provide rapid multi-analyte detection are highly sought after for use in drug design and disease diagnosis. The basic design of most biosensors involves the incorporation of two components: a specific analyte recognition element and a transducer which transforms a molecular recognition event into a quantifiable signal. We have reported the discovery of a system that utilizes porous silicon (PS) as an immobilization matrix for biomolecules and as an optical interferometric transducer of molecular binding events. In addition to its unique optical and chemical properties, PS was chosen as the matrix material due to its high surface area. In comparison to flat surfaces, PS offers an immense increase in surface area, allowing for an increased amount of immobilized receptor molecules, and thereby increased sensitivity.; The sensor is based upon changes in the refractive index of the PS film. When incident white light is reflected off a PS sample, Fabry-Perot fringes in its reflectometric spectrum are observed. By introducing molecular species into the sensing matrix, changes in the refractive index were monitored. The slight increase in the overall effective refractive index of the porous matrix caused an increase in the effective optical thickness, which was directly observed in the interference pattern as a shift to longer wavelengths. Since this system is solely dependent on refractive index changes, the PS biosensor is independent of analyte distance from the surface, unlike sensors employing surface plasmon resonance (SPR).; The development of the PS biosensor involved several challenges, including the fabrication of macroporous PS, surface derivatization, and protein immobilization. The dimensions of the PS layer were tunable, displaying pore sizes ranging from micro to macropores. Surface derivatization involving a heterobifunctional silane was achieved and provided a versatile surface for protein conjugation via an amide or disulfide bond.; The reversibility, specificity, stability, and scaling of signal response to analyte mass were quantified. The sensor consisted of a protein A modified PS surface. The system was probed with various fragments of human IgG analyte. These initial studies provide promise for the PS sensor to be used to monitor affinity based interactions.