The U.S. military has a continued interest in the development of handheld, field-usable sensors and test kits for a variety
of diagnostic applications, such as traumatic brain injury (TBI) and infectious diseases. Field-use presents unique
challenges for biosensor design, both for the readout unit and for the biological assay platform. We have developed
robust biosensor devices that offer ultra-high sensitivity and also meet field-use needs. The systems under development
include a multiplexed quantitative lateral flow test strip for TBI diagnostics, a field test kit for the diagnosis of pathogens
endemic to the Middle East, and a microfluidic assay platform with a label-free reader for performing complex
biological automated assays in the field.
We describe the development of a label-less ellipsometric imaging microarray reader. The ability of the ellipsometric microarray reader to measure binding of sample to microarray surface is verified using oligonucleotide complementary DNA (cDNA) microarrays. Polarized light illuminates the microarray surface through a glass substrate at an angle beyond the critical angle and changes in the polarization of totally internally reflected light resulting from binding events on the microarray surface are measured. This polarization change is used to measure the thickness of biomolecules bound to the microarray. A prototype ellipsometric imaging microarray reader is constructed and calibrated, and the performance is evaluated with cDNA microarrays. The microarray reader measures changes in refractive index changes as small as 0.0024 and thickness changes as small as 0.28 nm. The optimization of angle of incidence and substrate refractive index necessary to achieve high sensitivity is also described. This ellipsometric technique offers an attractive alternative to fluorescence-microarray readers in some genomic, proteomic, diagnostic, and sensing applications.
Microarrays are being widely used in genomic, proteomic, and diagnostic applications. The binding events to the microarrays are measured with fluorescent labels. Fluorescent microarray readers offer high sensitivity and normalization of the reference and test samples. The use of labels increases the number of steps involved in array testing, concerns about storage labels, and cost of additional labeling steps. This paper describes an alternative approach that does not require the use of fluorescent or other labels. The binding events on the microarray introduce changes in polarization of the illuminated light which is measured to determine the concentrations of biomolecules bound to the microarray. Oligonucleotide microarrays were synthesized and tested on the imaging microarray reader. The refractive index changes of 0.006 and changes in thickness of 1 nm are demonstrated at a spatial resolution of 20 μm over a field of view of 1 cm2. This ellipsometric technique offers an attractive alternative to fluorescence-based measurement and could be very valuable in some of the genomic, proteomic, diagnostic, and sensing applications.
We report here on bacterial biofilm detection with an optical fiber probe and a compact detection system. This probe was tested on cells of the Pseudomonas aeruginosa and other species of bacteria in planktonic and sessile forms. Optical signal changes corresponding to the number density of the bacterial cells were measured.
Current blood tests cannot provide rapid support for field medical emergencies that require blood in excess of the tested supply, especially, when additional blood needs to be drawn from the available walking pool. A fluorescence-based rapid infectious disease screening system, based on a disposable disk with an array of wash-free, one-step, membrane strips and an array of optical probes can be used to quantify a panel of transmissible diseases in parallel with high specificity, high sensitivity, and operational simplicity. We have designed and constructed a sandwich membrane assay platform and a laboratory prototype optoelectronic measuring device and used this combined system to quantify hepatitis C antibody over the concentration range of 2 ng/ml to 100 ng/ml in 3 to 5 minutes.
All immunosensors currently described in literature are irreversible. Intelligent Optical Systems, Inc. has developed a revolutionary method for producing reversible immunosensors. In this method, the antibody and a labeled analog (structurally and functionally similar to the antigen) are coimmobilized on the sensor surface. Under equilibrium conditions, the labeled analog interacts with immobilized antibody to produce a sensor response. However, in the presence of antigen (analyte), the equilibrium is disturbed as the analyte competes for the binding sites of the immobilized antibody. This produces a measurable sensor response. The equilibrium is shifted back by washing the analyte away with a wash buffer, and the bound analog interacts with the immobilized antibody. Polarization and intensity based measurements are used to design the analog. Photoinduced electron transfer is used to create fluorescent analogs that provide enhancements in fluorescence intensity that can be measured. This principle can be extended to the detection of bacteria.
We report initial experimental results on the fabrication of multicore near-field optical (NFO) fiber probes after investigating several multicore NFO probe designs. Fluorescence measurement data demonstrating optical distinction between individual adjacent channels of a three- core NFO is presented. Our results demonstrate that simultaneous multiparameter sensing in side single living cells shall soon be a reality.
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