Quantum Semiconductor Biosensors
Currently available viral diagnostics methods are relatively slow, expensive and restricted to a single viral pathogen or family. Ideally, it would be useful to identify rapidly and simultaneously a broad spectrum of viruses. This research aims at developing a quantum semiconductor-based biosensor for the rapid detection and typing of human viral pathogens. One axis of the research concerns so-called epitaxial quantum dot biosensor (eQD), while the second axis is defined by a monolithically integrated quantum well surface plasmon resonance (QW-SPR) biosensor.
To overcome some of the key technological problems and limitations related to the application of colloidal QDs for biodetection, we have proposed a device based on an array of epitaxial QDs (eQD) that has been grown directly on semiconductor substrate by thin film deposition technology. The idea of an eQD biosensor is summarized in Figure. 1. A wafer with eQD’s emitting at a specific wavelength is functionalized with biotinylated antibodies of different analytes, or DNA-based bait molecules. Upon excitation, each eQD, which typically is 20 – 40 nm in diameter at its base, will emit photoluminescence (PL) radiation in a rapidly expanding cone. This radiation is expected to be modified in the presence of nano-objects, such as trapped viruses immobilized above.
Figure 1. A schematic architecture of the eQD biosensor. Detection of the eQD photoluminescence is used to monitor the surface state of the biosensor.
We have carried out research aimed at bio-functionalization of the surface of GaAs – the material of choice for capping InAs eQD’s. The goal is to provide conditions suitable for direct trapping of different viral pathogens on the GaAs surface. We have studied passivation of (001) GaAs with various thiols and we determined conditions for the deposition of biotin and successful immobilization of avidin. Our ab-initio calculations of thiol-GaAs interactions have indicated that the thiol-GaAs binding energy exceeds 44 kcal, which supports our observations concerning the stability of various biomolecules immobilized on thiolated surfaces of GaAs. The important conclusion of this part of the research was that the strong binding energy of thiol-GaAs, places this material system at par with a well known thiol-Au system, and validates the potential of GaAs as an attractive material for binding different bio-moieties.
Another approach for biosensing investigated in our group is based on the surface plasmon resonance (SPR) effect. We have invented a new quantum semiconductor microstructure that allows a significant increase in the propagation length of SPs propagating above semiconductor surface. The core of the invention is a dielectric adaptive layer of SiO2 that separates the Au grating from the semiconductor (GaAs) substrate comprising a quantum well (QW) buried below the surface. The proposed solution offers the possibility of constructing a monolithically integrated (ultra-small) SPR biosensing device.
Figure 2. Cross-section of a novel microstructure that allows designing a highly integrated (monolithically) self-emitting SPR biosensor device.
The optical methods of interrogating both eQD and QW-SPR biosensor surface as well as the compact biosensor microstructure have the potential to offer attractive solution for micro-total analysis systems (µTAS) at the point-of-care for rapid identification of numerous pathogens in parallel.
- D. Lepage and J.J. Dubowski, “Surface plasmon assisted photoluminescence in GaAs–AlGaAs quantum well microstructures”, Appl. Phys. Lett. 91, 163106 (2007).
- O. Voznyy and J.J. Dubowski, “Structure, bonding nature and binding energy of alkanethiolate on As-rich GaAs (001) surface: a density functional theory study”, J. Phys. Chem. B110, 23619 (2006).
- X. Ding, Kh. Moumanis, J.J. Dubowski, E. Frost and E. Escher, ”Immobilization of avidin on (001) GaAs”, Appl. Phys. A83, 357 (2006).