Wei Wei Wang

Bioelectronic Imaging Array Based on Bacteriorhodopsin Film

A photoreceptor array that exploits the light sensitive bacteriorhodopsin (bR) films has been manufactured on a flexible indium-tin-oxide (ITO) coated plastic film using electrophoretic sedimentation technique (EPS). The effective sensing area of each photoreceptor is 2 × 2 mm2, separated by 1 mm and arranged in a 4 × 4 array. A switched integrator with gain on the order of 1010 is used to amplify the signal to a suitable level. When exposed to light, the differential response characteristic is attributed to charge displacement and recombination within bR molecules, as well as loading effects of the attached amplifier. The peak spectral response occurs at 568 nm and is linear over the tested light power range of 200 ¿ W to 12 mW. The response remains linear at other tested wavelengths, but with reduced amplitude. Initial tests have indicated that responsivity among all photoreceptors is greater than 71% of the average value, 465.25 mV/mW. The differential nature of the signal generated by bR makes it a suitable sensing material for vision applications such as motion detection. The prototype array demonstrates this property by employing Reichardts delay-and-correlate algorithm. Furthermore, fabricating sensor arrays on flexible substrates introduces a new design approach that enables non-planar imaging surfaces.

Time and frequency response characteristics of bacteriorhodopsin-based photodetectors

The time and frequency response behavior of a new class of photodetectors based on a light-sensitive protein, known as bacteriorhodopsin (bR), is described. Each bR-based detector consists of an indium tin oxide (ITO) electrode/bR thin film/indium tin oxide (ITO) electrode structure. The response of the photodetector to square-wave and transient pulse illumination are both simulated using an equivalent resistor-capacitor (RC) circuit and experimentally observed. The investigative study demonstrates that the physical dimensions of the sensor surface, load resistance and capacitance, and the illumination conditions all have an impact on the transient response and gain-bandwidth characteristics. It is observed that changing the sensing area of the detector only affects the amplitude of the response, but not the bandwidth. Increasing the load resistance produces a higher gain, but reduces bandwidth. Increasing the load capacitance has the effect of dramatically reducing both gain and bandwidth. The observations and conclusions derived from this research provide design guidelines for developing hybrid photoelectric sensors and imaging arrays using bacteriorhodopsin thin films.

Light-addressable bacteriorhodopsin photocell

Bacteriorhodopsin (bR) thin films have been investigated in recent years as a viable biomaterial for constructing micro- or nanoscale optical devices. During illumination, the bR molecules in the thin film undergo a photocycle that is followed by a proton transport from the cytoplasmatic side to the extracellular side of the cell membrane. The photoelectric response induced by the charge displacement can be influenced by both the wavelength and intensity of the impinging light sources. A photocell based on the photoelectric properties of a thin bR film is described in this paper. The bR-based photocell is built as a sandwich-structural device with an ITO (Indium Tin Oxide) electrode/bR film/ITO electrode configuration. The photocell is fabricated by depositing the oriented bR film onto the grounded ITO electrode. The cytoplasmic side of the bR membrane is attached to the ITO conductive surface and the extracelluar side is placed in contact with the second ITO electrode that provides the signal input to the instrumentation circuit. A polyester thin film was used as the spacer separating the two ITO electrodes. The size of the active area of the photocell is about 10×10 mm. A HeNe laser coupled with an acoustic-optical scanning system is used as the light source. Experimental results confirm that the photoelectric response generated by the bR-photocell prototype is durable, stable, and highly sensitive to changes in light intensity. The sensitivity of the proposed signal transducer is 10.25mV/mW. The wavelength dependence of the photoelectric responses is similar to the optical absorption spectrum of bR membrane.

Biological Transducers Based on Bacteriorhodopsin for Smart Biosensor Applications

In this study, a biological photoelectric transducer based on bacteriorhodopsin (bR) is described. Purple membrane (PM) containing bR are deposited on a TiO₂ electrode surface and electrically oriented. The dried bR purple membrane film is then utilized to investigate the photoelectric response. The latter is induced by charge displacement of bR molecules in the purple membranes. The response is affected by both the wavelength and intensity of the incident light sources. The experimental results indicate that the generated photo-voltage is proportional to the intensity of the illumination light, and the photo-voltage measured under different wavelengths correspond to the absorption spectrum of bR.

Bidirectional Motion Detection Using Protein-Based Photoreceptors

� Abstract — A bidirectional, speed selective motion detector that exploits bioelectronic photoreceptors is described. Each photoreceptor is a multi-layered structure composed of a thin bacteriorhodopsin (bR) film sandwiched between two Indium Tin Oxide (ITO) electrodes. As a light sensitive protein, bR exhibits a differential response to temporal changes in the light intensity. The measured peak photovoltage is linear over a light power range of 10 -4 W to 10 -1 W. The photoreceptor responsivity is measured over frequencies from 4 Hz to 400 Hz. Binary pulse correlation is used to identify the direction of movement and the pulse widths are used to compute the speed. The measured range of speed, in two directions, is 20 mm/s to 80 mm/s.

Flexible photocell array based on bacteriorhodopsin film

A bendable photocell array that exploits bioelectronic photoreceptors based on bacteriorhodopsin (bR) is described in this paper. Fabricating such a sensor array on a flexible plastic substrate introduces a new design approach that enables lightweight and durable non-planar sensing devices to be created with curved or spherical geometries. In this research, purple membrane patches obtained from wild-type bR are deposited onto a polyethylene terephthalate (PET) substrate coated with a patterned ITO layer using Electrophoretic Sedimentation (EPS) technique. The current prototype consists of a flexible 4x4 pixel array and an amplification circuit that magnifies the small electrical signal arising from the charge displacement and recombination within the dried bR film. Each individual pixel is a 2mm x 2mm square separated by a 1mm distance between neighboring elements. The measured photoelectric response of an individual pixel is approximately linear over the light power range between 200μW and 12mW. These bR photocells respond primarily to visible light with a spectral peak response at 568nm. The response times of the photoelectric signals can reach up to the microsecond range. Preliminary tests have demonstrated that photoresponse characteristics are maintained while the flexible substrate is deformed up to a 10mm bending radius. Unfortunately, dried bR photocells are inherently susceptible to electrical noise because of their extremely high film resistance, necessitating the employment of a noise-filtering amplifier. The image processing capabilities of bR are demonstrated in a motion detection application. Specifically, Reichardts delay-and-correlate algorithm is implemented and is used to detect both the speed and direction of a moving light spot.

Spherical imaging array based on bioelectronic photoreceptors

The performance of wide field-of-view (FOV) and omni-directional sensors are often limited by the complex optics used to project three-dimensional world points onto the planar surface of a charged-couple device (CCD) or CMOS array. Recent advances in the design and development of a spherical imaging system that exploits the fast photoelectric signals generated by dried bacteriorhodopsin (bR) films are described in this paper. The bendable, lightweight and durable bR-based photocell array is manufactured on an indium-tin-oxide (ITO) coated plastic film using Electrophoretic Sedimentation technique (EPS). The effective sensing area of each pixel in the preliminary prototype is 2x2 mm2, separated by 1mm and arranged in a 4x4 array. When exposed to light, the differential response characteristic is attributed to charge displacement and recombination within the bR molecule, as well as loading effects of the attached amplifier. The peak spectral response occurs at 568nm and is linear over the tested light power range of 200μW to 12mW. Response remains linear at the other tested wavelengths, but at reduced signal amplitude. Excess material between the bR sensing elements can be cut from the plastic substrate to increase structure flexibility and permit the array of photodetectors to be wrapped around the exterior, or adhered to the interior, of a sphere.

Protein-based photocell for high-speed motion detection

A high-speed motion detection system that utilizes bioelectronic photocells is described in this paper. Each individual photocell consists of a sandwich-structural device with an ITO (indium tin oxide) electrode/bR film/ITO electrode configuration. During illumination, the molecules in the thin bacteriorhodopsin (bR) film undergo a multi-state photocycle followed by a proton transport from the cytoplasmic side to the extracellular side of the cell membrane. Both the wavelength and intensity of the impinging light source influence the charge displacement and, thereby, the current flow. Experimental studies show that the bR photodetector measured by the current mode exhibits a wide dynamic range and very fast response time. The photoelectric response is approximately linear over the light power range of muW to W. The response time is related to the bR photocycle kinetics and has been measured in mus. The responsivity of the experimental photocell is ISO mV/mW at 570nm. In addition, the device exhibits a high degree of differential photosensitivity to change in incident light intensity. These photoelectric properties make bR film a viable material for designing spatio-temporal motion detection systems. Issues related to the design and fabrication of a high-resolution and high-speed motion detection system for machine vision applications are discussed

Photonic transistor based on bacteriorhodopsin films

Light activated optical circuits have several key advantages over conventional electronics because they are free from electrical current losses, resistive heat dissipation, and friction forces that greatly diminish system performance and efficiency. The effects of current leakage and power loss are also crucial design constaints in developing micro-electromechanical (MEMS) technology. An essential device for creating viable micro-optical circuitry is a robust photonic transistor that can act as a small signal switch and amplifier. The proposed photonic transistor is based on the complementary suppression-modulated light transmission properties of thin bacteriorhodopsin (bR) films. The light transmission properties exhibited by the thin film are controlled using the variable wavelength and intensity of the impinging light soruces. The light transmisison properties of the bR film are illustrated using a mathematical model for the two-state photoreaction system. The two-state model represents the longest lifetime in the bR photocycle, largest change in absorption maxima, and high photochemical stability. The optical response is proportional to changes in the light transmission properties of the biometrical, and therefore represents a viable material for creating optoelectronic devices.