Anju Chadha

A modified electrolyte-insulator-semiconductor-capacitor (EISCAP) developed in-house was used for the determination of triglycerides and urea in blood, in addition to urea in milk. The sensitivity of the sensor was 55 ± 0.5 mV per unit change of pH. The EISCAP was optimized to operate at 25 °C in 0.25 mM phosphate buffer (pH 6), 1 M KCl and 1 mg lipase for triglycerides and in 1 mM Tris-HCl buffer (pH 7.4), 0.5 M KCl and 0.5 U urease for urea. Comparisons of the results obtained from the developed biosensor and clinical records gave correlation coefficients of 0.979 and 0.974 for blood triglycerides and blood urea respectively. Similarly, estimation of milk urea determined using the sensor in comparison with the spectrophotometric method gave a correlation coefficient of 0.992. The sensor gave reproducible and reliable results up to six months. © 2011 Elsevier B.V. All rights reserved.

A novel, enzymatic, porous silicon (PS) based potentiometric method for estimating triglycerides is reported. Lipase, an enzyme, which hydrolyses triglycerides was immobilised on PS which was prepared from p-type (1 0 0) crystalline silicon and was thermally oxidized. On hydrolysis the triglycerides result in the formation of fatty acids which causes a change in the pH of the solution. Enzyme solution-oxidized PS-crystalline silicon structure was used to detect changes in pH during the hydrolysis of tributyrin as a shift in the capacitance-voltage (C-V) characteristics. Optimisation of the conditions for the enzymatic reaction and calibration of the sensor are included. © 2002 Elsevier Science B.V. All rights reserved.

A novel method for estimating triglycerides is reported. Porous silicon, prepared from p-type (100) crystalline silicon was thermally oxidized and used to immobilise lipase, an enzyme, which hydrolyses triglycerides resulting in the formation of fatty acids. This causes a change in the pH of the solution. Enzyme solution-oxidized porous silicon-crystalline silicon structure was used to detect changes in pH during the hydrolysis of tributyrin as a shift in the capacitance-voltage (C-V) characteristics. Detailed calibration of the sensor is included. © 2001 Elsevier Science B.V.

Sensitive biosensors for detection of triglyceride concentration are important. In this paper we report on two types of silicon based triglyceride sensors: an electrolyte-insulator-semiconductor capacitor (EISCAP) which is a potentiometric device and a polysilicon microcantilever. The detection principle for both sensors is based on the enzymatic hydrolysis of triglyceride though the sensing mechanisms are different: electronic for the EISCAP and mechanical for the microcantilever. The characteristics and performances of the two sensors are critically compared. The EISCAP sensor necessitates the presence of a buffer for stable measurements which limits the sensitivity of the sensor at low concentrations of the bioanalyte to 1 mM. The cantilever sensor works without a buffer which improves the lower level of sensitivity to 10 μm. Both sensors are found to give reproducible and reliable results. © 2008 Elsevier B.V. All rights reserved.

We report fabrication of a potentiometric biosensor on silicon for the estimation of tributyrin and urea based on enzymatic reactions. The sensor is an electrolyte-insulator-semiconductor capacitor (EISCAP) that shows a shift in the measured C-V with changes in the pH of the electrolyte. This pH shift can be induced by the enzyme-mediated hydrolysis of tributyrin and urea which results in acidic and basic solutions, respectively and an EISCAP can be effectively used for the detection of these bioanalytes. A silicon nitride based EISCAP was used for the first time to detect triglycerides and urea. The sensor was able to detect millimolar concentrations of the bioanalytes (tributyrin/urea). The most important features of the tributyrin and urea sensor are high sensitivity, long life-time, easily built at a low cost, micro-construction and short response time. Optimization of the conditions for the enzymatic reaction and calibration of the sensor are included. © 2004 Elsevier B.V. All rights reserved.

Electrolyte insulator semiconductor capacitors (EISCAPs) show a shift in the measured capacitance-voltage (C-V) characteristics with changes in the pH of the electrolyte and has the potential to be used as biosensors. The choice of an electrode to the EISCAP is important for reliable measurements. Here, we discuss a silicon-based EISCAP sensor bonded to a glass wafer with an embedded electrode. Three noble metal electrodes (Pt, Au, Ag) are studied for the ease of integration and performance and it is found that the chloridized Ag electrodes exhibit the highest pH sensitivity and the lowest electrode potential drift with time. A readout system that measures the pH of the electrolyte under test is developed and implemented in a programmable system on chip. Calibration of the EISCAP to account for sensor process variations is also incorporated. The pH measurement data on the miniaturized EISCAPs is presented. © 2001-2012 IEEE.