Michael E. Knotts

Time-resolved luminescent lateral flow assay technology.

We here report a detection technology that integrates highly sensitive time-resolved luminescence technique into lateral flow assay platform to achieve excellent detection performance with low cost. We have developed very bright, surface-functionalized and mono-dispersed phosphorescent nanoparticles of long lifetime under ambient conditions. The phosphorescent nanoparticles have been used to conjugate with monoclonal antibody for C-reactive protein (CRP), an inflammatory biomarker. Lateral flow immunoassay devices have been developed using the conjugate for highly sensitive detection of CRP. The CRP assay can achieve a detection sensitivity of <0.2 ngmL(-1) in serum with a linear response from 0.2 to 200 ngmL(-1) CRP. We have also developed a low cost time-resolved luminescence reader for the lateral flow immunoassay (LFIA) devices. The reader does not use expensive band pass filter and still provide very low detection background and high detection sensitivity on solid substrates such as nitrocellulose membranes. The reader can detect less than 2.5 ng phosphorescent particles captured on a nitrocellulose membrane strip with more than three orders of magnitude linear detection dynamic range. The technology should find a number of applications, ranging from clinical diagnostics, detection of chemical and biological warfare agents, to food and environmental monitoring.

Experimental characterization of mm-wave detection by a micro-array of Golay cells

We present experimental results for an uncooled imaging focal plane array technology that consists of a polymer/metal/polymer layered membrane suspended over a micro-fabricated array of cavities. The device operation is Golay-like (heating of air in the cavity causes a detectable deflection of the membrane proportional to incident EM power), but potentially offers both greater sensitivity and more read-out options (optical or electrical) than a traditional Golay cell through tailoring of the membrane properties. The membrane is formed from a layer-by-layer deposition of polymer with one or more monolayers of gold nanoparticles (or other metal) that help control the membranes elasticity and deformation-dependent optical reflectivity/electrical conductivity. Baseline capabilities of the device have been established through optical measurements of membrane deflection due to incident mm-wave radiation modulated at 30 Hz (corresponding to a video refresh rate). The device demonstrates an NEP of 300 nW/√Hz at 105 GHz for a 19-layer membrane (9 poly/1 Au/9 poly) suspended over an array of 80 μm diameter cavities (depth = 100 μm) etched in a 500 μm thick substrate of Si. Calculations of membrane sensitivity show that this NEP could be reduced to ~ 100 pW/√Hz with enlarged cavity diameters on the order of 600 μm.

Improved night vision demonstrator program status

Although existing night vision equipment provides a significant improvement in target detection in low light conditions, there are several limitations that limit their effectiveness. Focus is a significant problem for night vision equipment due to the low f-number optics required to obtain sufficient sensitivity as well as the dynamic nature of night vision applications, which requires frequent focus adjustments. The Georgia Tech Research Institute has developed a prototype next-generation night vision device called the Improved Night Vision Demonstrator (INVD) in order to address these shortfalls. This paper will describe the design of the INVD system as well as an analysis of its performance.

Photoconductive terahertz source with array feed for enhanced emission

Charge screening limits the output power of photoconductive sources of terahertz-frequency (far-infrared) radiation. We demonstrate a means of obtaining a significant increase in output power using a coherent array of two sources operated near saturation.

Demonstration of enhanced emission and time delay beam steering using photoconductive terahertz source with multiple spot feed

Excitation of electrically biased photoconductive switches with femtosecond optical pulses is a well established method of generating wide bandwidth (0.5 to 2.5 THz) pulses of terahertz frequency radiation. This method of pulse generation draws energy from the bias power supply to accelerate optically injected charge carriers, giving rise to a current pulse that can radiate into free space; nevertheless, the output power is limited by both poor coupling of the radiation out of the substrate and by charge carrier screening. By optimizing the electrode structures and illumination geometries it may be possible to address both of these limitations. To explore this idea, we have experimentally studied illumination with coherent array of two sources spaced by less than a wavelength and operated near saturation in a semi-insulating GaAs source. By illuminating with an array of N=2 spots, we demonstrate a doubling in output terahertz power with no increase in input optical power. This result is consistent with results that have been shown for optical excitation that has been stretched along the anode using cylindrical lenses; however, the array of two spots permits steering the beam by adjusting the relative time of arrival of the two exciting pulses. Experimental evidence of this beam steering is presented. With proper electrode design, this approach may ultimately enable an N-fold increase in output power with an array of N spots, the formation of narrow beams, and the adjustment of beam direction by control of the relative time of arrival of the exciting optical pulses.

Scalability of line excitation THz arrays

A new THz array method is proposed based on the photoconductive line excitation. We present experimental demonstration of the scalability of the radiated THz power based on the number of antenna elements illuminated.

Hands-Free Focus Night Vision Technology Demonstration

The Georgia Tech Research Institute is currently developing a device to demonstrate a hands-free focus technology for head-mounted night vision sensors. The demonstrator device will integrate a computational imaging technique that increases depth of field with a digital night vision sensor. The goal of the demonstrator is to serve as a test bed for evaluating the critical performance/operational parameters necessary for the hands-free focus technology to support future tactical night vision concepts of operation. This paper will provide an overview of the technology studies and design analyses that have been performed to date as well as the current state of the demonstrator design.