The development of a chip-based sensor array composed of individually addressable polystyrene-poly(ethylene glycol) and agarose microspheres has been demonstrated. The microspheres are selectively arranged in micromachined cavities localized on silicon wafers. These cavities are created with an anisotropic etch and serve as miniaturized reaction vessels and analysis chambers. A single drop of fluid provides sufficient analysis media to complete approximately 100 assays in these microetch pits. The cavities possess pyramidal pit shapes with trans-wafer openings that allows for both fluid flow through the microreactors/analysis chambers and optical access to the chemically sensitive microspheres. Identification and quantitation of analytes occurs via colorimetric and fluorescence changes to receptor and indicator molecules that are covalently attached to termination sites on the polymeric microspheres. Spectral data are extracted from the array efficiently using a charge-coupled device allowing for the near-real-time digital analysis of complex fluids. The power and utility of this new microbead array detection methodology is demonstrated here for the analysis of complex fluids containing a variety of important classes of analytes including acids, bases, metal cations, metabolic cofactors, and antibody reagents.

No abstract

This letter deals with resonant photorefractive devices fabricated from multiquantum wells of GaAs/Al0.3Ga0.7As and operated in a quantum-confined Stark effect geometry. Details of the processing are presented. Epitaxial lift-off was used to remove the active device from the substrate. Low-temperature Al0.3Ga.07As was used as an insulator to form metal-insulator-semiconductor structures on both sides of the multiquantum wells. Proton implant damage was used to improve the fringe visibility. Photorefractive wave mixing with a diffraction efficiency of ∼0.03% was demonstrated. The incorporation of a nitride layer between the top electrode and the low-temperature AlGaAs increased the efficiency to 0.5%. The improvement is attributed to a reduction in the conduction of carriers across the low-temperature layer into the electrode.

Hysteresis predicted in I-V curve of heterojunction resonant tunneling diodes simulated by a self consistent quantum method

We report the observation of a new room-temperature storage phenomenon based on quantum interference. Multiple, stable current-voltage curves extending continuously through zero bias have been observed in GaAs/AlAs double barrier quantum well diodes containing n−-n+-n− spacer layers. Once placed on a particular branch, the devices retain memory of the branch they lie on, even when held at zero bias for extended periods of time. The devices can be repetitively switched between the different branches of the current-voltage characteristics. The experimental observations are consistent with the multiple self-consistent solutions to the coupled Schrödinger and Poisson equations found for diodes that combine heterostructure tunneling barriers with n−-n+-n− spacer layers.