Charlene A. Sanders

Stand-off tissue-based biosensors for the detection of chemical warfare agents using photosynthetic fluorescence induction.

Tissue biosensors made from immobilized whole-cell photosynthetic microorganisms have been developed for the detection of airborne chemical warfare agents and simulants. The sensor read-out is based on well-known principles of fluorescence induction by living photosynthetic tissue. Like the cyanobacteria and algae from which they were constructed, the sensors are robust and mobile. The fluorescence signal from the sensors was stable after 40 days, storage and they can be launched or dropped into suspected danger zones. Commercially available hand-held fluorometric detector systems were used to measure Photosystem II (PSII) photochemical efficiency of green algae and cyanobacteria entrapped on filter paper disks. Toxic agents flowing in the gas stream through the sensors can alter the characteristic fluorescence induction curves with resultant changes in photochemical yields. Tabun (GA), sarin (GB), mustard agent, tributylamine (TBA) (a sarin stabilizer), and dibutyl sulfide (DBS) (a mustard agent analog) were tested. Upper threshold limits of detectability for GA, TBA, and DBS are reported. With additional research and development, these biosensors may find application in stand-off detection of chemical and perhaps biological warfare agents under real-world conditions.

In Situ Characterization of Stimulating Microelectrode Arrays: Study of an Idealized Structure Based on Argus II Retinal implants

The development of a retinal prosthesis for artificial sight includes a study of the factors affecting the structural and functional stability of chronically implanted microelectrode arrays. Although neuron depolarization and propagation of electrical signals have been studied for nearly a century, the use of multielectrode stimulation as a proposed therapy to treat blindness is a frontier area of modern ophthalmology research. Mapping and characterizing the topographic information contained in the electric field potentials and understanding how this information is transmitted and interpreted in the visual cortex is still very much a work in progress. In order to characterize the electrical field patterns generated by the device, an in vitro prototype that mimics several of the physical and chemical parameters of the in vivo visual implant device was fabricated. We carried out multiple electrical measurements in a model “eye,” beginning with a single electrode, followed by a 9-electrode array structure, both idealized components based on the Argus II retinal implants. Correlating the information contained in the topographic features of the electric fields with psychophysical testing in patients may help reduce the time required for patients to convert the electrical patterns into graphic signals.

Metabolic Prosthesis for Oxygenation of Ischemic Tissue

This communication discloses new ideas and preliminary results on the development of a metabolic prosthesis for local oxygenation of ischemic tissue under physiologically neutral conditions. We report for the first time selective electrolysis of physiological saline by repetitively pulsed, charge-limited electrolysis for the production of oxygen and suppression of free chlorine. Using 800-mu A amplitude current pulses and < 200 mus pulse duration, we demonstrate prompt oxygen production and delayed chlorine production at the surface of a fused 0.85-mm diameter spherical platinum electrode. The data, interpreted in terms of the ionic structure of the electric double layer, suggest a strategy for in situ production of metabolic oxygen via a new class of ldquosmartrdquo prosthetic implants for ischemic disease such as diabetic retinopathy. We also present data indicating that collateral pH drift, if any, can be held constant using a feedback-controlled three-electrode electrolysis system that chooses an anode and cathode pair based on pH data provided by a local sensor.

Dynamic Interactions of Retinal Prosthesis Electrodes withNeural Tissue and Materials Science in Electrode Design

Visual sensation communicates greater information about the environment than any other sense. It is a carefully integrated neural interpretation of chemical and electrical signals that are initiated by photons of light and culminate in cerebral processes that create and map a complex range of visual percepts. Useful visual sensation is dependent upon the efficient functioning of all the links in the visual pathway and the transfer of the signal from image to visual cortex without interruption. Artificial sight refers to a number of experimental photochemical and photoelectrical devices that mimic the function of specialized cells in the optical neuronal network and assume their role if they become impaired by injury or degenerative disease. One such device, presently under development, is a microelectrode array retinal prosthesis for the treatment of people who are blind from retinitis pigmentosa (RP) or age-related macular degeneration (AMD). In both diseases, the photoreceptor cells (rods and cones) are gradually destroyed. Patients affected by photoreceptor degeneration slowly lose visual acuity and eventually become blind. Without viable photoreceptor cells, there are few options for regaining vision. Defective cells may be replaced by removing the retina and transplanting a new retina from a compatible donor. Clinical studies of transplant procedures and immunological studies of transplant survival and rejection are presently under way [1]. The only other viable option is an electronic visual prosthesis. The retinal prosthesis (Figure 11.1) is an intraocular electronic device that can be permanently implanted on the inner retinal surface

Application of photosynthesis to artificial sight

Using the technique of Kelvin force microscopy, we have performed the first measurements of photovoltages from single photosynthetic reaction centers. The measured values, typically 1 V or more, are sufficiently large to trigger a neural response. The goal of this project is insertion of purified Photosystem I (PSI) reaction. centers or other photoactive agents into retinal cells where they will restore photoreceptor function to people who suffer from age-related macular degeneration (AMD) or retinitis pigmentosa (RP), diseases that are the leading causes of blindness world-wide. Although the neural wiring from eye to brain is intact, these patients lack photoreceptor activity. It is the ultimate goal of this proposal to restore photoreceptor activity to these patients using PSI as the optical trigger. In principle, the approach should work. PSI is a robust integral membrane molecular photovoltaic device. Depending on orientation, it can depolarize or hyperpolarize the cell membrane with sufficient voltage to trigger an action potential.

Nanoscale photosynthesis, the photophysics of neural cells, and artificial sight

Using the technique of Kelvin force microscopy, we have performed the first measurements of photovoltages from single photosynthetic reaction centers. The measured values, typically 1 V or more, are sufficiently large to trigger a neural response. The goal of this project is insertion of purified Photosystem I (PSI) reaction centers or other photoactive agents into retinal cells where they will restore photoreceptor function to people who suffer from age-related macular degeneration (AMD) or retinitis pigmentosa (RP), diseases that are the leading causes of blindness world-wide. Although the neural wiring from eye to brain is intact, these patients lack photoreceptor activity. It is the ultimate goal of this proposal to restore photoreceptor activity to these patients using PSI as the optical trigger. In principle, the approach should work. PSI is a robust integral membrane molecular photovoltaic device. Depending on orientation, it can depolarize or hyperpolarize the cell membrane with sufficient voltage to trigger an action potential.