Membrane capacitance

The ion controlled diode was an initial attempt to isolate the active electronics from the chemical solution by producing a metallic-like via that allows the isolation of the chemically sensitive region from an area where electronic components could be deposited (41,42). However, the limited precision of the non-standard microfabrication techniques made this process difficult and costly. Since this device is still essentially a capacitive membrane-insulator-semiconductor structure like the chemfet, the same problems of hermetic isolation of the gate remain. 

Fig. 3. Heat production is an important consideration for devices using electric fields in the liquid near cells. This figure shows the theoretical distribution of heat production in and around a spherical cell at the centre of a quadrupole electrode chamber in a solution of low electrical conductivity (top) and high conductivity (bottom). The heat production is given by gE2 where g is the conductivity of the solution or cell component and E is the (local) electric field strength. The contour interval is 7% of the maximum in each case. The cell is modelled as an electrically conductive sphere enveloped by an insulating but capacitive membrane.

The models of Figures 4.30—4.32 will exhibit Maxwell—Wagner dispersion. The anisotropy of Figure 4.32 disappears at high frequencies because the capacitive membranes are short-circuited. For example, when anisotropy is caused by air in the lungs, the anisotropy may persist at virtually all frequencies. 

The admittance time constant is uniquely defined by ty, independent of G, as if the circuit were voltage driven. The admittance parameter therefore has the advantage that the measured characteristic frequency determining xy is directly related to the capacitance (membrane effects) and series resistance in tissue. The same is not true for impedance the impedanee is defined by both ty and X2. 

Capacitive membranes sensor typically is based upon the deformation of the membrane due to the interaction between bio-probe molecules at the functionalized surface and the corresponding bio-targets. The working mechanism is similar as how cantilever surface stress sensors operate. Surface stress-based sensor is comprised of stretchable membrane over which surfaces is functionalized by bio-probes. The interaction with the corresponding bio-targets results in surface stress and finally makes the membrane deform. Figure 3 shows the schematic structure... 

The miniaturized capacitive arrays play a critical role in the development of microsystems in biomedical applications since it can provide much higher sensitivity compared to the single-element capacitive sensor. Each capacitor of capacitance-based membrane sensor array is composed of a stretchable electrode. Satyanarayana et al. introduce a 3 x 3 array of individual sensor unit cells with an area of 1 cm [2]. Tsouti et al. reported a capacitive membrane-based sensor array made up of 256 elements with an area 1.44 cm [3]. Despite the large number of elements, only 32 contacting pad are used to address all the elements. The sensing units of the array have already been described in the capacitive membrane sensor section. The stretchable electrodes of the device are deposited on a silicon membrane and the counter electrode is fabricated... 

Examples of capacitive biosensors arrays. Image of the capacitive membrane array which consists of 16 rows of... 

Sivaramakrishnan S, Rajamani R, Pappenfus TM (2008) Electrically stretched capacitive membranes for stiffness sensing and analyte concentration measurement. Sens Actuators B 135 262-267... 

The electrostatic free energy of a macromolecule embedded in a membrane in the presence of a membrane potential V can be expressed as the sum of three separate terms involving the capacitance C of the system, the reaction field Orffr), and the membrane potential field p(r) [73],... 

Simple considerations show that the membrane potential cannot be treated with computer simulations, and continuum electrostatic methods may constimte the only practical approach to address such questions. The capacitance of a typical lipid membrane is on the order of 1 j.F/cm-, which corresponds to a thickness of approximately 25 A and a dielectric constant of 2 for the hydrophobic core of a bilayer. In the presence of a membrane potential the bulk solution remains electrically neutral and a small charge imbalance is distributed in the neighborhood of the interfaces. The membrane potential arises from... 

The primary reference method used for measuring carbon monoxide in the United States is based on nondispersive infrared (NDIR) photometry (1, 2). The principle involved is the preferential absorption of infrared radiation by carbon monoxide. Figure 14-1 is a schematic representation of an NDIR analyzer. The analyzer has a hot filament source of infrared radiation, a chopper, a sample cell, reference cell, and a detector. The reference cell is filled with a non-infrared-absorbing gas, and the sample cell is continuously flushed with ambient air containing an unknown amount of CO. The detector cell is divided into two compartments by a flexible membrane, with each compartment filled with CO. Movement of the membrane causes a change in electrical capacitance in a control circuit whose signal is processed and fed to a recorder. 

As first shown by Hladky and Haydon 7,8), it is possible to observe the current due to a single transmembrane channel by using extensions of the planar lipid hilaver approach of Mueller and Rudin 9). The basic system is shown in Fig. 2 and is commonly referred to as the black lipid membrane (BLM) method. This is because, as the lipid in the hole between the two chambers thins, the areas that have become planar bilayers are seen as black. Additional terms are bilayer lipid membranes or planar lipid bilayer membranes. These lipid bilayer membranes, particularly those which are solvent free, have capacitances which are very close to those of biological membranes. 

A = approximate area of the bilayer lipid membrane G = membrane conductance Gj = specific membrane conductance Cm = membrane capacitance C, = specific membrane capacitance. 

The speed of impulse propagation is determined by the time required for edl charging in neighboring membrane sections and depends on EDL capacitance and... 

This chapter is devoted to the behavior of double layers and inclusion-free membranes. Section II treats two simple models, the elastic dimer and the elastic capacitor. They help to demonstrate the origin of electroelastic instabilities. Section III considers electrochemical interfaces. We discuss theoretical predictions of negative capacitance and how they may be related to reality. For this purpose we introduce three sorts of electrical control and show that this anomaly is most likely to arise in models which assume that the charge density on the electrode is uniform and can be controlled. This real applications only the total charge or the applied voltage can be fixed. We then show that predictions of C < 0 under a-control may indicate that in reality the symmetry breaks. Such interfaces undergo a transition to a nonuniform state the initial uniformity assumption is erroneous. Most... 

Membrane thickness fluctuations were initially discussed in the local approach by Hladky and Gruen (HG) [102] in conjunction with their possible effect on membrane capacitance. They are directly related to the spectrum of 5-modes ... 

Initially the effect of applied voltage on membrane capacitance was attributed to the uniform electrostriction, in the manner of the elastic capacitor model [1,103], The effect of undulations was first considered by Leikin [78], In Ref. 89 the combined effect of undulations and uniform compression is studied, including the possible influence of nonlocality. The differential capacitance C is presented as... 

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