Semiconductor chemical and biochemical sensors

Abstract In this paper, problems related to the fabrication of semiconductor (bio)chemical sensors and microreactors, including modification of the surface of different materials (semiconductors, dielectric materials, polymers) to create a sensing membrane on the transducer's surface and immobilise bioreceptors namely enzymes are discussed

Comparison of Urea Determination in Biological Samples by EnFETs Based on pH and pNH4 Detection

In this paper urea biosensors based on detection of pH and ammonium ions are presented. As transducers pH-sensitive ion-selective field effect transistors (ISFETs) and chemically modified FETs (ChemFETs) snsitive to ammonium ions were used.Results concerning urea determination by the bisensors in blood plasma and in dialysate show that the biosensors can be applied for urea monitoring in the effluent dialysate. However in the case of pNH4 based EnFETs a special pre-treatment (dilution with tris/HCl buffer) of the samples is necessary

An influence of polyHEMA gate layer on properties of ChemFETs

A complex deposition procedure of the hydrogel layer of modified poly(2-hydroxyethyl methacrylate) (polyHEMA) covalently linked to the silicon nitride surface and covering only the gate area of the ISFET, was optimized for photolithographic technology, using standard silicon wafers of 3” diameter. The influence of hydrogel composition and layer thickness on the sensors’ parameters was investigated. It was shown, that ISFETs covered with more than 100 μm thick polyHEMA layers in restricted pH-range could be practically insensitive to pH. Regarding mechanical stability of ion-selective sensors, a polyHEMA layer of ca. 20 μm thickness was found to be the best suitable for further manufacturing of durable ion selective sensors (Chemically modified Field-Effect Transistors – ChemFETs). The weak buffering properties of the thin polyHEMA layers had no disadvantageous influence on the sensors’ function

Surface Modification for Microreactor Fabrication

In this paper, methods of surface modification of different supports, i.e. glass andpolymeric beads for enzyme immobilisation are described. The developed method ofenzyme immobilisation is based on Schiff’s base formation between the amino groups onthe enzyme surface and the aldehyde groups on the chemically modified surface of thesupports. The surface of silicon modified by APTS and GOPS with immobilised enzymewas characterised by atomic force microscopy (AFM), time-of-flight secondary ion massspectroscopy (ToF-SIMS) and infrared spectroscopy (FTIR). The supports withimmobilised enzyme (urease) were also tested in combination with microreactors fabricatedin silicon and Perspex, operating in a flow-through system. For microreactors filled withurease immobilised on glass beads (Sigma) and on polymeric beads (PAN), a very high andstable signal (pH change) was obtained. The developed method of urease immobilisationcan be stated to be very effective

New ISFET interface circuit design with temperature compensation

An integrated and new interface circuit with temperature compensation has been developed to enhance the ISFET readout circuit stability. The bridge-type floating source circuit suitable for sensor array processing has been proposed to maintain reliable constant drain–source voltage and constant drain current (CVCC) conditions for measuring the threshold voltage variation of ISFET due to the corresponding hydrogen ion concentration in the buffer solution. The proposed circuitry applied to Si3N4 and Al2O3-gate ISFETs demonstrate a variation of the drain current less than 0.1 mA and drain–source voltage less than 1 mV for the buffer solutions with the pH value changed from 2 to 12. In addition, the scaling circuitry with the V T temperature correction unit (extractor) and LABVIEW software are used to compensate the ISFET thermal characteristics. Experimental results show that the temperature dependence of the Si3N4-gate ISFET sensor improved from 8 mV/1C to less than 0.8 mV/1C