A device useful in diagnostics in which a biochemical species is attached to the surface of a sensor, especially to the gate of a field effect transistor. In such a "BIOCHEMFET" it has been a problem to attach two or more biochemical species to the surface of the sensor, especially to the gates of a multi-gated FET. It has now been found possible to bond a group having a photoactivatable function covalently to the sensor surface, photo-expose the resultant modified surface selectively, e.g. through a mask, and bond the biochemical species, e.g. a hapten, antigen, antibody, lectin or enzyme, to the photoactivated function. In this way the biochemical species becomes attached in selected areas only. In view of the success of this technique realized under conditions of miniaturization, the invention makes possible "printed circuits for proteins". In addition to the device are the process of manufacture thereto, use for diagnostic purposes and a diagnostic kit of the device and a partner capable of binding to the biochemical species.

A quartz crystal microbalance assay in which the binding of analyte to a surface on or near a quartz crystal microbalance (QCM) is detected by a conjugate which comprises an enzyme capable of catalyzing the conversion of a substrate to a product capable of accummulating on or reacting with a surface of the QCM leading to a mass change and, hence, a change in resonant frequency.

There is provided a novel method of testing for the presence of an analyte in a fluid suspected of containing the same. In this method, in the presence of the analyte, a substance capable of modifying certain characteristics of the substrate is bound to the substrate and the change in these qualities is measured. While the method may be modified for carrying out quantitative differential analyses, it eliminates the need for washing analyte from the substrate which is characteristic of prior art methods.

Several types of new microelectronic devices including diodes, transistors, sensors, surface energy storage elements, and light-emitting devices are disclosed. The properties of these devices can be controlled by molecular-level changes in electroactive polymer components. These polymer components are formed from electrochemically polymerizable material whose physical properties change in response to chemical changes, and can be used to bring about an electrical connection between two or more closely spaced microelectrodes. Examples of such materials include polypyrrole, polyaniline, and polythiophene, which respond to changes in redox potential. Each electrode can be individually addressed and characterized electrochemically by controlling the amount and chemical composition of the functionalizing polymer. Sensitivity of the devices may be increased by decreasing separations between electrodes as well as altering the chemical environment of the electrode-confined polymer. These very small, specific, sensitive devices provide means for interfacing electrical and chemical systems while consuming very little power.

A sensor uses an immobilized affinity component capable of interacting with analyte species and being associated with a conducting polymer such that the interaction of the affinity component and the analyte induces change in the electrical properties of the polymer. An AC signal is applied to the polymer, and the induced change in impedance resulting from the interaction is measured. The impedance is measured at a frequency or frequencies corresponding to a peak or peaks in the relationship between frequency and impedance change for the polymer and the analyte. The measurement may be made by reference to the imaginary or real component of impedance. The polymer may be in the form of a layer bridging two electrodes between which the impedance is measured. The two electrodes may together define an interdigitated electrode assembly.