A critical evaluation of direct electrical protein detection methods

During the last decennia many protein-related electrical phenomena have been studied and applied in a variety of measuring systems, from simple metal electrodes with adsorbed proteins to sophisticated systems with lipid bilayers. Many of the investigations concern the monitoring of immuno reactions. The basis underlying electrical effects of the observed phenomena are the protein modulated dielectric constant, conductivity, electrical potential, ion permeability and ion mobility. In this paper special attention is paid to the capacitive measurements with EIS systems as well as impedance and potential measurements with FET devices. The Donnan theory is treated and applied to the static ImmunoFET operation, explaining the relatively small effects which have been reported. Finally, an alternative approach is described in which the ImmunoFET is applied in a dynamic way, to circumvent the drawbacks of the static measurements

Exploiting the dynamic properties of FET-based chemical sensors

After a long period of mainly static application of ISFETS, other more sophisticated applications are being developed, based on the exploitation of the dynamic properties of ISFETS. Examples are the use of flow-through cells with sample injection and the integration of a pH actuator electrode for very fast titration in a microvolume. The development of an immunoFET makes use of induced transient phenomen

The merit of using silicon for the development of hearing aid microphones and intraocular pressure sensors

An important design rule for a hearing aid is the requirement of a large signal to noise ratio, which is mainly determined by that of the microphone and its preamplifier. It will be shown that in order to increase the signal to noise ratio it is favourable to integrate the preamplifier with the microphone, which implies that the microphone should be made of silicon, preferably with a single wafer technology. For the development of a tonometer for the measurement of intraocular pressure, the application of a silicon force sensor rationalizes that also the flattening of the eye globe is measured with a silicon applanation sensor, instead of by optical means which is the present practice. A sensor construction has been developed, which combines a force, pressure and applanation sensor, all made in silicon

The future of biosensors

Since the development of the glucose sensor by Clark and Lyons in 1962, generally recognized as the first biosensor, many types of sensors have been developed in which a physical or chemical transducer is provided with a layer containing a biological sensing element. The resulting device is called a biosensor, aimed to produce an electronic signal as a function of the concentration of a chemical or biochemical constituent of a liquid, not necessarily of biological origin. Among the many proposed concepts, the integration of biologically active materials with a silicon chip is one of the most intriguing approaches, because it seems the most comprehensive integration between biology and electronics. In this paper the resulting biochips, mainly based on the field-effect principle as the coupling mechanism between the two domains, will be described and discussed with an outlook on the future

The impact of MOSFET-based sensors

The basic structure as well as the physical existence of the MOS field-effect transistor is without doubt of great importance for the development of a whole series of sensors for the measurement of physical and chemical environmental parameters.\ud \ud The equation for the MOSFET drain current already shows a number of parameters that can be directly influences by an external quantity, but small technological variations of the original MOSFET configuration also give rise to a large number of sensing properties. All devices have in common that a surface charge is measured in a silicon chip, depending on an electric field in the adjacent insulator.\ud \ud FET-based sensors such as the GASFET, OGFET, ADFET, SAFET, CFT, PRESSFET, ISFET, CHEMFET, REFET, ENFET, IMFET, BIOFET, etc. developed up to the present or those to be developed in the near future will be discussed in relation to the considerations mentioned above

The influence of tensile forces on the deflection of circular diaphragms in pressure sensors

It is known that the deflection of a diaphragm is determined by two mechanisms, bending moments or bending stress and tensile forces or membrane stress.\ud \ud Usually the influence of tensile forces is not taken into account when calculating the mechanical properties of thin diaphragms. Hence the mathematical description thus obtained will only be valid if the deflection of the diaphragm is small compared with its thickness and if lateral stress is absent.\ud \ud In this paper we will consider uniformly loaded circular diaphragms, which are assumed to be isotropic, and present the results of a study on the influence of bending stress and tensile stress, which together determine the diaphragm deflection.\ud \ud Starting from theoretical considerations, a simulation program is developed of which several results are presented and discussed

Comparison of electrode impedances of Pt, PtIr (10% Ir) and Ir-AIROF electrodes used in electrophysiological experiments

In tissue impedance measurements with the 4-electrode assembly, unexpected difficulties may occur because a combination of electrode impedance and stray capacitance in the array of four electrodes, can lead to serious measuring failures in the low-frequency range. An optimal solution to this problem can be obtained if the electrode impedances are frequency independent. A comparative study of the electrode impedances of Pt and PtIr electrodes and of a new electrode material (Ir-AIROF) is reported. It is shown that the impedance of Ir-AIROF electrodes is relatively low and almost frequency independent. Therefore the use of Ir-AIROF electrodes provides a solution to the problem mentioned above

A classification of chemically sensitive semiconductor devices

A general scheme is presented for classifying chemically sensitive semi-conductor devices (CSSDs). CSSDs reported in the literature up to now, as well as related physicochemical phenomena, are briefly discussed and shown to fit in the scheme