Photonic sensing platform based on photocorrosion of III-V semiconductor microstructures

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This program aims at exploring both electrochemical and optical properties of III-V semiconductor microstructures comprising heterostructures, quantum wells (QW) or quantum dots (QD) for detection of electrically charged biomolecules immobilized in the vicinity of the surface of such microstructures. The sensitivity of the photoluminescence (PL) effect to band bending of a semiconductor near its surface and modification of both density and nature of the surface states is a well known effect investigated for chemical and biological sensing. We have discovered recently that photocorrosion of a semiconductor heterostructure, if induced under optimized conditions determined by light excitation power, average photon fluence and etching power of a semiconductor surrounding electrolyte, could become a fingerprint of the electrochemical or biochemical reactions taking place at distances, typically, less than 40 nm from the semiconductor surface. The employment of the photocorrosion effect for monitoring surface reactions adds an attractive dimension to the PL-based detection of surface-immobilized biomolecules. We have observed a dissociation process of a stack of epitaxially-grown GaAs/AlGaAs heterojunctions, by employing PL of a GaAs layer buried by such heterostructures. The ability to resolve in situ the photocorrosion of a 1 nm thin GaAs layer has suggested that this approach could offer conditions attractive for monitoring the reactions involving low concentrations of electrically charged biomolecules. Another potential advantage of this "reverse molecular beam epitaxy" concerns in situ biofunctionalization of the photocorrosion-revealed surface of a semiconductor. This could create conditions optimized, e.g., for the grow of high-quality self-assembled monolayers (SAM) that otherwise requires the application of expensive vacuum or high-purity environment controlling equipment. The results of the photocorrosion experiment with a stack of ten (10) GaAs/AlGaAs heterojunctions have suggested that devices with even larger number of heterojunctions could be designed for biofunctionalization and sequential monitoring of biochemical reactions taking place in their vicinity. The innovative character of the photocorrosion-based diagnostics, and the potential of this approach to lead to a new class of (bio)sensors and techniques to monitor surface reactions involving electrically charged molecules, have created the base of a program described in this document. At the center of the program is the development of a quantitative (or a quasi-quantitative) picture of charged molecules interacting in a liquid environment with surfaces of different semiconductor microstructures. This will lead to the construction of a family of devices with stacks of heterostructures, QW or QD optimized for yielding a sensitive diagnostics, rapidly and at a highly attractive cost.