Joseph T. Smith

Application of Flexible OLED Display Technology for Electro-Optical Stimulation and/or Silencing of Neural Activity

This paper presents a new biophotonic application for large-area, high-resolution, flexible organic light-emitting diode (OLED) display technology currently used to manufacture low-cost color flexible displays on plastic substrates. The new concept uses a fully addressable high resolution flexible OLED pixel array on a thin, mechanically compliant biocompatible plastic substrate to selectively stimulate and/or silence small groups of neurons on either the cortical surface or, alternatively, within the deep brain. Optical measurements from a 455 nm blue flexible OLED test structure demonstrated the ability to emit 1 mW/mm2 of instantaneous light intensity using a 13 V, 20 Hz pulse, which meets the minimum reported intensity at ~ 450 nm to induce optical stimulation in genetically modified neural tissue. Biocompatibility was successfully demonstrated by the ability to grow human epithelial cells on the surface of a full TFT process flow plastic flexible display substrate. Additionally, a new active matrix array display architecture was designed to support pulsed mode OLED operation. These preliminary results demonstrate the initial viability of extending flexible plastic substrate OLED display technology to the development of large-area, high-resolution emissive active matrix arrays for chronic optogenetic applications.

Flexible ISFET Biosensor Using IGZO Metal Oxide TFTs and an ITO Sensing Layer

This letter presents the fabrication details and measured performance of a prototype flexible extended-gate ion-sensitive field effect transistor (ISFET) biosensor, manufactured using a metal oxide indium-gallium-zinc oxide thin film transistor and an indium-tin oxide sensing layer on a 125- μm thick flexible plastic substrate. ISFET drain current was shown to respond correctly to the pH buffer concentration with repeatable pH sensitivity observed over multiple cycles. These results demonstrate the initial viability of directly extending flexible plastic substrate organic light emitting diode display technology to the production of low-cost, plastic ISFET biosensors.

Application of Flexible OLED Display Technology to Point-of-Care Medical Diagnostic Testing

This paper presents a new concept combining flexible organic light-emitting diode (OLED) display technology with fluorescent biorecognition microarray technology to fabricate point-of-care immunobiosensors. Our approach is designed to leverage commercial OLED display technology to reduce pre-functionalized biosensor substrate costs to pennies per cm2 combined with leveraging the display industries ability to manufacture an immense number of low-cost consumer electronic products annually. For this work, we demonstrate that our new approach using high brightness flexible OLED display technology combined with a charge integrating readout circuit and optical filters can offer point-of-care diagnostic sensitivity at or below 10 pg/mL, which approaches the lower limit of detection (LLOD) of typical clinical laboratory instrumentation.

Flexible digital x-ray technology for far-forward remote diagnostic and conformal x-ray imaging applications

Today’s flat panel digital x-ray image sensors, which have been in production since the mid-1990s, are produced exclusively on glass substrates. While acceptable for use in a hospital or doctor’s office, conventional glass substrate digital x-ray sensors are too fragile for use outside these controlled environments without extensive reinforcement. Reinforcement, however, significantly increases weight, bulk, and cost, making them impractical for far-forward remote diagnostic applications, which demand rugged and lightweight x-ray detectors. Additionally, glass substrate x-ray detectors are inherently rigid. This limits their use in curved or bendable, conformal x-ray imaging applications such as the non-destructive testing (NDT) of oil pipelines. However, by extending low-temperature thin-film transistor (TFT) technology previously demonstrated on plastic substrate- based electrophoretic and organic light emitting diode (OLED) flexible displays, it is now possible to manufacture durable, lightweight, as well as flexible digital x-ray detectors. In this paper, we discuss the principal technical approaches used to apply flexible display technology to two new large-area flexible digital x-ray sensors for defense, security, and industrial applications and demonstrate their imaging capabilities. Our results include a 4.8″ diagonal, 353 x 463 resolution, flexible digital x-ray detector, fabricated on a 6″ polyethylene naphthalate (PEN) plastic substrate; and a larger, 7.9″ diagonal, 720 x 640 resolution, flexible digital x-ray detector also fabricated on PEN and manufactured on a gen 2 (370 x 470 mm) substrate.

Flexible amorphous silicon PIN diode x-ray detectors

A low temperature amorphous silicon (a-Si) thin film transistor (TFT) and amorphous silicon PIN photodiode technology for flexible passive pixel detector arrays has been developed using active matrix display technology. The flexible detector arrays can be conformed to non-planar surfaces with the potential to detect x-rays or other radiation with an appropriate conversion layer. The thin, lightweight, and robust backplanes may enable the use of highly portable x-ray detectors for use in the battlefield or in remote locations. We have fabricated detector arrays up to 200 millimeters along the diagonal on a Gen II (370 mm x 470 mm rectangular substrate) using plasma enhanced chemical vapor deposition (PECVD) a-Si as the active layer and PECVD silicon nitride (SiN) as the gate dielectric and passivation. The a-Si based TFTs exhibited an effective saturation mobility of 0.7 cm2/V-s, which is adequate for most sensing applications. The PIN diode material was fabricated using a low stress amorphous silicon (a-Si) PECVD process. The PIN diode dark current was 1.7 pA/mm2, the diode ideality factor was 1.36, and the diode fill factor was 0.73. We report on the critical steps in the evolution of the backplane process from qualification of the low temperature (180°C) TFT and PIN diode process on the 150 mm pilot line, the transfer of the process to flexible plastic substrates, and finally a discussion and demonstration of the scale-up to the Gen II (370 x 470 mm) panel scale pilot line.

Application of flat panel OLED display technology for the point-of-care detection of circulating cancer biomarkers

Point-of-care molecular diagnostics can provide efficient and cost-effective medical care, and they have the potential to fundamentally change our approach to global health. However, most existing approaches are not scalable to include multiple biomarkers. As a solution, we have combined commercial flat panel OLED display technology with protein microarray technology to enable high-density fluorescent, programmable, multiplexed biorecognition in a compact and disposable configuration with clinical-level sensitivity. Our approach leverages advances in commercial display technology to reduce pre-functionalized biosensor substrate costs to pennies per cm2. Here, we demonstrate quantitative detection of IgG antibodies to multiple viral antigens in patient serum samples with detection limits for human IgG in the 10 pg/mL range. We also demonstrate multiplexed detection of antibodies to the HPV16 proteins E2, E6, and E7, which are circulating biomarkers for cervical as well as head and neck cancers.

Disposable point-of-use optical biosensor for multiple biomarker detection

This work explored the viability of a new miniaturized fluorescence measurement-based sensor architecture using organic light emitting diode (OLED) display and photodiode active matrix array technology for point-of-use diagnosis of multiple disease biomarkers in a low cost disposable configuration. Sensor feasibility and optical performance were evaluated using a bright 0.3mW/mm2 2 × 2 mm, 455nm blue OLED emitter test structure configured first with orthogonally crossed linear polarizing film; and second, with band-pass and long-pass optical filters. Preliminary measurement results indicated that this type of sensor architecture requires optical filters to approach the sensitivity of laboratory fluorescence-based instrumentation.

Optically Seamless Flexible Electronic Tiles for Ultra Large-Area Digital X-Ray Imaging

This paper presents a new flexible electronics assembly technique that combines individual digital X-ray detectors to create a much larger composite digital X-ray detector. The new assembly technique uses multiple flexible digital X-ray detectors manufactured on a thin, transparent, and flexible plastic substrate, which are overlapped to create the larger composite X-ray detector. The assembly technique, illustrated in a mechanical mockup, is optically seamless, and has the ability to scale up to extremely large X-ray imaging arrays. Feasibility and preliminary imaging performance were demonstrated by tiling several 16 × 16 pixel resolution prototype flexible X-ray detector test structures. Optical losses under typical digital radiography conditions were also measured by overlapping a plastic substrate flexible X-ray detector onto a commercial glass substrate digital X-ray imaging array. Approximately 5% signal loss was observed in the transparent plastic overlap region, and the seam edge imaging artifact was demonstrated to be correctable using commercial gain calibration. A key medical imaging application for this technology is single-exposure, low-dose, and full-body digital radiography.

Development of a testbed for flexible a-Si:H photodiode sensing arrays

Large area, flexible sensing arrays for imaging, biochemical sensing and radiation detection are now possible with the development of flexible active matrix display technology. In particular, large-area flexible imaging arrays can provide considerable advancement in defense and security industries because of their inherent low manufacturing costs and physical plasticity that allows for increased adaptability to non-planar mounting surfaces. For example, a flexible array of photodetectors and lenslets formed into a cylinder could image simultaneously with a 360 degree view without the need for expensive bulky optics or a gimbaled mount. Here we report the design and development of a scalable 16x16 pixel testbed for flexible sensor arrays using commercial-off-the-shelf (COTS) parts and demonstrate the capture of a shadow image with an array of photodiodes and active pixel sensors on a plastic substrate. The image capture system makes use of an array of low-noise, InGaZnO active pixel amplifiers to detect changes in current in 2.4 μm-thick reverse-biased a-Si:H PIN diodes. A thorough characterization of the responsivity, detectivity, and optical gain of an a- Si:H photodiode is also provided. At the back end, analog capture circuitry progressively scans the array and constructs an image based on the electrical activity in each pixel. The use of correlated-double-sampling to remove fixed pattern noise is shown to significantly improve spatial resolution due to process variations. The testbed can be readily adapted for the development of neutron, alpha-particle, or X-ray detection arrays given an appropriate conversion layer.

Characterization of a compact and highly sensitive fluorescence-based detection system for point-of-care applications

This work details the design and characterization of a low-cost, portable and highly sensitive fluorescence detection system intended for use in a compact and disposable point-of-care (POC) device. The detection device leverages time integration to improve the signal to noise ratio (SNR) compared to instantaneous measurements. It also eliminates complicated focusing optics and electronics typically found in bulky and expensive laboratory-scale devices. Characterization was performed by measuring a series of logarithmically scaled dilutions of 1 μm Nile Red fluorescent microspheres immobilized on microscope slides. This approach eliminates assay dependencies and elucidates the actual system performance. A theoretical model that predicts the time-integrated output voltage profile of the sensor was developed; this prediction is useful for evaluating any lens-free fluorescent system based on a set of filters and choice of fluorophore. By relating the fluorophore concentration, system design parameters, and the output voltage, the model matches well with the empirical data and the limit of determination (LOD) for Nile Red is 20 particles. This system provides a sensitive and potentially low-cost device for fluorescent diagnosis in an integrated and compact/miniaturized POC device, lab-on-chip or a table-top reader.