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| MISL's first, chemical analysis microinstrument was the surface plasmon resonance immunosensor. It was demonstrated in 1993 with the detection of avidin-biotin binding at the surface of a thin gold metal surface in a saline environment. The microinstrument was a hybrid system utilizing a four substrate stack: two micromachined silicon layers, one glass micromachined layer and a laser drilled, alumina substrate. The stack was assembled and aligned using the keying of small glass beads and etched pits in each of the four substrates. Bonding was achieved using a low temperature curing polyimide and solder sealing. The micromachined silicon layers contained a torsional, all silicon micromirror and V-grooves for optical fiber and GRIN lens, and a position sensing photodiode (PSD). The silicon micromirror was electrostatically deflected through 9-10 degrees to direct the light beam emitted from the end of a fiber through a range of angles incident onto the metal film, setting up a surface plasmon. The position and intensity of the reflected beam was recorded with the position sensing photodiode, from which a surface plasmon reflectance curve, i.e. intensity versus angle of incidence, is obtained. Covalently attaching a ligand to the metal film produces a sensor sensitive to the complexing analyte, i.e. antibody/antigen conjugates or avidin/biotin for example. Specific absorption of the analyte to the surface alters the complex dielectric of the interface and shifts the plasmon resonance angle which is quantitatively measured by the PSD. |
