KEYWORDS: Sensors, Photodiodes, Transducers, Silicon, Chemical analysis, Diodes, Microfluidics, Photodetectors, Chemiluminescence, Digital signal processing
Results will be reported from efforts to develop a self-contained micromachined microfluidic detection system for the
presence of specific target analytes under the US Office of Naval Research CIED Basic Research Program. Our efforts
emphasize improving/optimizing a dedicated micromachined sensor array with integrated photodetectors that are
coupled to chemically sensitized chemiluminescent receptors. Here we will review our work on the fabrication of
integrated photodiodes within an array of micromachined silicon pyramidal cavities that will contain the
chemiluminescent compounds. One particular advantage of such approach over a conventional planar photodiode would
be its collection efficiency without the use of external optical components. This should allow a more compact and
robust system to be constructed by integrating photodetection and fluidics into a single chip-based platform.
Additionally, overview of accessing the photodiode using wireless coupling to a resonant chemically sensitive tag will
be discussed.
Results will be reported from efforts to develop a self-contained micromachined microfluidic detection system for the presence of specific target analytes under the US Office of Naval Research Counter IED Basic Research Program. Our efforts include improving/optimizing a dedicated micromachined sensor array with integrated photodetectors and the synthesis of chemiluminescent receptors for nitramine residues. Our strategy for developing chemiluminescent synthetic receptors is to use quenched peroxyoxalate chemiluminescence; the presence of the target analyte would then trigger chemiluminescence. Preliminary results are encouraging as we have been able to measure large photo-currents from the reaction. We have also fabricated and demonstrated the feasibility of integrating photodiodes within an array of micromachined silicon pyramidal cavities. One particular advantage of such approach over a conventional planar photodiode would be its collection efficiency without the use of external optical components. Unlike the case of a normal photodetector coupled to a focused or collimated light source, the photodetector for such a purpose must couple to an emitting source that is approximately hemispherical; hence, using the full sidewalls of the bead's confining cavity as the detector allows the entire structure to act as its own integrating sphere. At the present time, our efforts are concentrating on improving the signal-to-noise ratio by reducing the leakage current by optimizing the fabrication sequence and the design.
Under a recent US Office of Naval Research University Affiliated Research Center (UARC) Basic Research Program we have begun a number of activities that we hope will enhance future ability to detect the presence of explosives vapors and residues. Here we present initial work on the development of a microfluidic system for a new point chemical sensor allowing the rapid, accurate, and specific detection of vapors emitted by explosive materials. We have already extensively tested a micromachined platform with external optical excitation and detection. Our new chemical approach is to create a receptor with high affinity and selectivity to nitro-explosives. A series of chemiluminescent molecular signaling systems are proposed that are specifically directed toward detection of TNT, PETN, RDX, HMX, and CL-20. These will be used in a new micromachined platform that integrates photodetectors directly into a micromachined micro-fluidic bead platform for detection of the chemiluminescent signals. By integrating photodetectors into the sidewalls of our chemical sensor array, in immediate proximity to the sensing microbeads, we can eliminate all external optics currently required for optical signal collection. This should allow a more compact and robust system to be constructed by integrating photodetection and fluidics into a single chip-based platform. Additionally, a concept of accessing a photodiode using inductive coupling, i.e. non-contact wireless reading, is introduced and demonstrated.
Combination of micromachined platforms and chemically sensitive micro-beads have been demonstrated for use as multi-analyte chemical and biological agent detectors [1,2]. In many of these systems agarose beads have been used as the "container" of various chemical sensors and enzymes. This paper discusses a method of array assembly using such sub-millimeter size beads.
Combinations of micromachined platforms and chemically sensitive micro-beads have been demonstrated for use as multi-analyte chemical and biological agent detectors. Two critical requirements for bead-based chemical detection platforms are bead retention and assembly. Separate “cover layers” have been used in the past for retention, but this constrains fluid flow through the device, and may require the use of precision spacers. In addition, since chemical sensing molecules within the beads can be quite sensitive exposure to high temperatures or harsh chemicals used in micromachining must be avoided after beads are placed in the platform. Here we present a new device whose fabrication is completed before placing the beads, and that provides both bead confinement and a means for self-assembly of arrays. Simple micromachined flexible “fingers” are used for all functions. The micromachined fingers are designed to bend out of the way as a bead is placed into a micromachined storage well, but then snap back after the bead is fully inserted into the well. We have also demonstrated that by designing different sized openings over each well it is possible to construct self-assembling bead arrays.
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