Two types of fluorescent pH indicators, a hydroxycoumarin and an aminocoumarin dye, are incorporated by means of long paraffinic chain substituents to neutral, anionic, and cationic micelles. The apparent pK values for the dyes in the micelles are compared to the pK values in aqueous solution. Shifts of the apparent pK are found for charged as well as for uncharged micelles, being different for the two indicators. A comparison of the pK shifts of the indicators in neutral micelles to pK shifts in a series of mixed solvents of different dielectric constant (t) leads us to attribute the shifts in the neutral system to a reduced polarity at the micelle surface for which a value of e 32 is estimated. With respect to charged micelles this polarity effect is responsible for part of the apparent pK shift. It may be revealed by comparing the results for the two indicator types.The value of the effective dielectric constant is found to be similar to that in the neutral micelle. The remaining part of the apparent pK shift may be taken as a measure of the electrical potential at the surface of the charged micelles. Some examples of potential measurements for various counterions are presented. A thermodynamical section attempts to present clear definitions of (and relations between) terms as "apparent pK'\ "interfacial pK", "interfacial pH", and "acidity function".

An identified neuron of the leech, a Retzius cell, has been attached to the open gate of a p-channel field-effect transistor. Action potentials, spontaneous or stimulated, modulate directly the source-drain current in silicon. The electronic signals match the shape of the action potential. The average voltage on the gate was up to 25 percent of the intracellular voltage change. Occasionally weak signals that resemble the first derivative of the action potential were observed. The junctions can be described by a model that includes capacitive coupling of the plasma membrane and the gate oxide and that accounts for variable resistance of the seal.

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A hybrid circuit of a semiconductor chip and synaptically connected neurons was implemented and characterized. Individual nerve cells from the snail Lymnaea stagnalis were immobilized on a silicon chip by microscopic picket fences of polyimide. The cells formed a network with electrical synapses after outgrowth in brain conditioned medium. Pairs of neurons were electronically interfaced for noninvasive stimulation and recording. Voltage pulses were applied to a capacitive stimulator on the chip to excite the attached neuron. Signals were transmitted in the neuronal net and elicited an action potential in a second neuron. The postsynaptic excitation modulated the current of a transistor on the chip. The implementation of the silicon-neuron-neuron-silicon circuit constitutes a proof-of-principle experiment for the development of neuroelectronic systems to be used in studies on neuronal signal processing, neurocomputation, and neuroprosthetics.