Abstract
The concepts of transistor recording of electroactive cells are considered, when the response is determined by a current-induced voltage in the electrolyte due to cellular activity. The relationship to traditional transistor recording, with an interface-induced response due to interactions with the open gate oxide, is addressed. For the geometry of a cell-substrate junction, the theory of a planar core-coat conductor is described with a one-compartment approximation. The fast electrical relaxation of the junction and the slow change of ion concentrations are pointed out. On that basis, various recording situations are considered and documented by experiments. For voltage-gated ion channels under voltage clamp, the effects of a changing extracellular ion concentration and the enhancement/depletion of ion conductances in the adherent membrane are addressed. Inhomogeneous ion conductances are crucial for transistor recording of neuronal action potentials. For a propagating action potential, the effects of an axon-substrate junction and the surrounding volume conductor are distinguished. Finally, a receptor-transistor-sensor is described, where the inhomogeneity of a ligand–activated ion conductance is achieved by diffusion of the agonist and inactivation of the conductance. Problems with regard to a development of reliable biosensors are mentioned.
Highlights
The electrolyte-oxide-semiconductor field-effect transistor (EOSFET) has been introduced as an ion sensitive sensor (ISFET), where the interaction of ions with the gate oxide induces a changed source-drain current at a constant gate voltage applied to a reference electrode in the bath electrolyte [1].A more specific interface-induced response can be achieved for biological analytes when the gate oxide is modified by suitable coatings [2]
Three issues are addressed in particular: (i) the cell-substrate junction is described as a planar capacitive core-coat conductor, which allows relating the cellular currents with changes of the electrical potential and changes of ion concentrations in the junction; (ii) in certain situations, the current-induced response is superposed by the interface-induced response of an ion-sensitive gate due to changed ion concentrations; and (iii) the inhomogeneous distribution of ion conductances in the cell membrane is crucial for a current-induced transistor response with intact electrogenic cells
They play a minor role for transient activations of ion conductances as with firing neurons and can be avoided if the ion sensitivity of the gate oxide is suppressed
Summary
The electrolyte-oxide-semiconductor field-effect transistor (EOSFET) has been introduced as an ion sensitive sensor (ISFET), where the interaction of ions with the gate oxide induces a changed source-drain current at a constant gate voltage applied to a reference electrode in the bath electrolyte [1]. The present paper describes the concepts of current-induced transistor sensorics for electroactive cells with a focus on planar cell-substrate junctions. Three issues are addressed in particular: (i) the cell-substrate junction is described as a planar capacitive core-coat conductor, which allows relating the cellular currents with changes of the electrical potential and changes of ion concentrations in the junction; (ii) in certain situations, the current-induced response is superposed by the interface-induced response of an ion-sensitive gate due to changed ion concentrations; and (iii) the inhomogeneous distribution of ion conductances in the cell membrane is crucial for a current-induced transistor response with intact electrogenic cells. The structure of the paper is as follows: First, the physics of the EOSFET is considered in to identify the current-induced and the interface-induced transistor response with electrogenic cells.
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