Jiri Janata

Hydrogen, Calcium, and Potassium Ion-Sensitive FET Transducers: A Preliminary Report

The application of integrated circuit technology to the field of physiological data acquisition may produce a significant impact on patient monitoring, diagnosis and therapeutic medical decisions. Biomedical sensors based on IC technology have several potential advantages not available in present biomedical sensors. These include small size, reliability, rapid time response, multi-sensor chip, and onchip signal processing to achieve high to low impedance transformation, temperature compensation, signal multiplexing, etc.

Encapsulation of polymeric membrane-based ion-selective field effect transistors

Abstract The use of polymeric membrane-based ISFETs in solution requires a method of encapsulating the package while leaving the gates of the chip open for a subsequent membrane deposition. The choice of encapsulants and the method are governed by the general device package, by the geometry and layout of the chip and by the intended use. In view of this, there seems to be no universal recipe for encapsulation. Two examples of the ISFET encapsulation approach described in this paper are an adaptation of the tape authomated bonding process and a dry film photoresist wafer encapsulation. Both of these processes, when fully developed, permit some degree of automation in the ISFET assembly.

Electrochemistry of chemically sensitive field effect transistors

Abstract : It is shown that ISFETs are closely related to conventional ion selective electrodes. The time response characteristics of these devices are examined in detail. The possibility of their use as direct charge sensors is critically evaluated. (Author)

A study of insulator materials used in ISFET gates

Abstract Experiments with aqueous electrolyte-insulator-semiconductor structures showed that Si 3 N 4 is a satisfactory insulator on silicon whereas thermally grown SiO 2 is not. The results can be explained in terms of microcrack formation in SiO 2 . The breakdown voltage was found to be relatively independent of the SiO 2 thickness and crack sizes were estimated to be of the order of a few tens of angstroms. No electrically significant bulk hydration effects were found to occur in either insulator in mildly acidic solutions.

In vivo continuous monitoring of ionized calcium in dogs using ion sensitive field effect transistors.

The authors have used calcium ion (Ca++) sensitive field effect transistor (ISFET) probes to monitor in vivo changes in Ca++ activity in the venous blood of dogs in response to infusions of sodium citrate or calcium chloride. During eight experiments, Ca++ activity changes were monitored in response to sodium citrate infusions simulating infusion of 1, 2, or 4 units of citrate preserved blood per 6 min. The ISFET probe recorded decreases in Ca++ activity during all infusions. Periodic serum samples were analyzed off-line using an in vitro ion selective electrode instrument. Analysis of variance showed no statistically significant differences between off-line sample and ISFET Ca++ activities (p greater than 0.05). A second experiment tested the use of the Ca++ ISFET as a control sensor for maintaining a desired Ca++ level. These studies provided a range of Ca++ activity values for comparison of off-line and ISFET values. Infusion rates of sodium citrate or calcium chloride needed to maintain venous Ca++ activity at 1.0 mEq/L or 3.0 mEq/L for periods of 30 min ranged from 440 to less than 1 mg/min during maintenance periods. Observation of hemodynamics during the calcium ion control maneuvers suggests that calcium ion may be used to improve cardiovascular performance during critical care situations that involve cardiovascular instability.

Continuous monitoring of interstitial fluid potassium during hemorrhagic shock in dogs

Interstitial fluid potassium ion activity (IF K+) may be an accurate indicator of adequacy of cellular perfusion because normal transmembrane K+ gradient appears to be related to oxygen-dependent energy supply, and with a large gradient, even a small absolute increase in IF K+ may represent an easily detected percentage increase in that compartment. Ion sensitive field effect transistor (ISFET) devices combine integrated circuit and ion selective electrode technology to produce electrochemical sensors which are sufficiently small, rugged, and biocompatible to allow placement in the interstitium for continuous in vivo monitoring in unparalyzed subjects.K+ ISFETs were mounted at the tips of 19 gauge vascular catheters. In each of 10 dogs, 1 such probe was inserted in a central vein and another was surgically placed between medial thigh muscle fascicles. Shock (MAP = 40 mm Hg) was produced and maintained for 1 h by exsanguination into citrated blood bags. Shed blood was then reinfused. Continuous monitoring of arterial pressure, serum potassium activity (S K+) and IF K+v and intermittent determinations of cardiac output (thermodilution) and S K+ (off-line clinical analyzer) were continued for another 5 h. Mean IF K+ rapidly and monotonically increased from a control value of 3.6 to 5.1 mEq/L after 1 h of shock (p < 0.005), and then temporarily returned to a value indistinguishable from control within 2 h after resuscitation. During most of these same intervals and events, variations in S K+ were statistically indistinguishable (p > 0.05) from control values.It is concluded that ISFET probes can reliably and continuously monitor IF K+ in vivo for extended intervals. The consistently observed increase in IF K+ in response to hemorrhage, a phenomenon invisible systemically (S K+), suggests that such probes may provide clinically valuable information regarding perfusion related events at the cellular level during onset of and resuscitation from hypoperfusion states.

Diffusional impedance of stationary microelectrodes

Abstract The diffusional impedance of a stationary disk microelectrode is derived. High and low frequency expressions are given, and an approximate solution, which covers both the high and low frequencies is also derived. The complex impedance plots of microdisk electrodes are discussed. Geometrical considerations lead to the concept of the “effective diffusional area”, which is a useful tool for the prediction of microelectrode behavior. This notion is applied to evaluate some features of ring microelectrodes.

Homogeneous reaction involving components of different redox couples—I. theoretical considerations and digital simulation

Abstract : Coupled heterogeneous electron transfer/homogeneous reactions occur in the electro-oxidation of certain anilines, and in association reactions of hydrocarbon anions with metal cations. If the adduct A sub m sub R is electroinactive, the resulting voltammogram is distorted in a way which is characteristic of the value of m. The derivation of the theoretical fluxes for these reactions and calculated normal potential pulse voltammograms are presented. The results are derived from both limiting flux and digital simulation considerations. (Author)

Fluctuation analysis at ITIES

Abstract Fluctuation equilibrium analysis is a technique which can be used to obtain information about double layer capacitance and charge transfer resistance of an interface. As such it is similar to the low amplitude impedance analysis which is a common method of investigation of electrochemical systems. The fundamental difference between the two approaches lies in the fact that the former investigates the system under the conditions of true equilibrium, i.e. without applied perturbation. The advantage of using fluctuation analysis in the study of ITIES is that it can be extended to lower frequencies (0.1–20,000 Hz) than are conveniently accessible by conventional impedance spectroscopy. Moreover, there is no danger of induced mechanical oscillations due to periodical changes of surface tension which may occur when a sinusoidal perturbation signal is applied to the ITIES interface. It is possible that the characteristic features of the low frequency part of the spectrum in the nitrobenzene/ water system are due to slow kinetics of solvation of the picrate anion.

Homogeneous reaction involving components of different redox couples—II. polarographic studies of the interactions of alkali metal cations with athracene and fluoranthene dianions in N,N-dimethylformamide and acetonitrile

Abstract The polarographic behavior of mixtures of anthracene (An), fluoranthene (Fa) and alkali metal cations in N,N -dimethylformamide (DMF) or acetonitrile (ACN) indicates that the electrogenerated dianion of the hydrocarbon reacts with the metal cation in the diffusion layer to form ion complexes. This results, in the case of sodium or lithium cations with anthracene in both DMF and ACN, in the appearance of inverted polarographic waves. In the case of other alkali metal cations (K + , Rb + ), the intensity of the polarographic wave due to the reduction to the hydrocarbon dianion is simply decreased. The stoichiometries and mechanisms of the interactions are discussed. In the presence of proton donors such as water, a competing reaction for the dianion results. The polarograms are simulated by digital approximation techniques.