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Bioelectronics is a progressing interdisciplinary research field that involves the integration of biomaterials with electronic transducers, such as electrodes, field-effect-transistors or piezoelectric crystals. Surface engineering of biomaterials, such as enzymes, antigen-antibodies or DNA on the electronic supports, controls the electrical properties of the biomaterial-transducer interface and enables the electronic transduction of biorecognition events, or biocatalyzed transformation, on the transducers. Bioelectronic sensing devices, biosensors of tailored sensitivities and specificities, are being developed.

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Photoisomerizable monolayers assembled onto electrode supports act as "command interfaces" for controlling the binding interactions of biomaterials with the functionalized surfaces. The light-induced binding and dissociation of the biomaterials to and from the electrodes, respectively, are electronically transduced. Two systems, including the photostimulated binding and dissociation of cytochrome c (Cyt c) and of anti-DNP antibody to and from functionalized surfaces, are discussed. The application of the systems as optobioelectronic devices and reversible immunosensors is addressed. A mixed monolayer consisting of pyridine and nitrospiropyran (1a) photoisomerizable units assembled on a Au-electrode acts as a command interface for the light-controlled association and dissociation of Cyt c to and from the monolayer. Cyt c binds to the pyridine/1a-monolayer electrode, resulting in electrical contact between the redox protein and the electrode. Photoisomerization of the mixed monolayer to the pyridine/protonated merocyanine state (1b) results in the electrostatic repulsion of Cyt c and its dissociation from the electrode support. This blocks the electrical contact between Cyt c and the electrode. By the cyclic photoisomerization of the mixed monolayer between the 1a and 1b states, reversible "ON"-"OFF" amperometric transduction of the affinity interactions between the redox protein and the interface is accomplished. Coupling of the photostimulated electrical contact between Cyt c and the electrode surface to the Cyt c-mediated bioelectrocatalyzed reduction of O(2) by cytochrome oxidase provides a means to amplify the transduced electronic signal. A photoisomerizable thiolated dinitrospiropyran (2a) monolayer, assembled on solid supports, acts as a light-active antigen interface that enables the photocontrolled binding and dissociation of anti-dinitrophenyl antibody (DNP-Ab) to and from the interface. The dinitrospiropyran (2a) layer acts as an antigen for the DNP-Ab, whereas the protonated dinitromerocyanine (2b) lacks antigen features for the DNP-Ab. By reversible photoisomerization of the monolayer between the 2a and 2b states, cyclic binding and dissociation of DNP-Ab to and from the monolayer interface is accomplished. The association and dissociation of the DNP-Ab to and from the 2a- and 2b-monolayer states are electronically transduced, using amperometric, Faradaic impedance and microgravimetric, quartz crystal microbalance analyses. The photostimulated binding of an antibody to a photoisomerizable antigen monolayer provides a novel method to design reversible immunosensor devices.

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Hebbian dynamics is used to derive the differential equations for the synaptic strengths in the neural circuitry of the locomotive oscillator. Initially, neural connection are random. Under a specified arborization hypothesis relating to the density of neural connections, the differential equations are shown to model the self-organization and the stability of the oscillator.

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We study the relation of neural development, organization, and activity to behavior. We provide a model of the locomotive oscillator, a neural system supplying alternating stimulation to extensor and flexor muscles creating an oscillatory motion. We propose a protocol by which this neural system starting from unstructured, unconnected neural populations develops structure and function. The protocol is studied by both computer simulation and mathematical analysis. Our main results are 1. The locomotive oscillator self-organizes and maintains its organization, assuming certain properties of the neural populations. 2. Imperfections disturbing the functional adequacy of the neural populations may lead to the deterioration and disappearance of the oscillatory behavior. 3. The locomotive oscillator may fail to organize if the development is not staged in time.

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