Anju Chadha

We report the fabrication of potentiometric electrolyteinsulator capacitor (EISCAP) biosensors based on silicon and porous silicon (PS) substrates with oxide and stacked oxidenitride dielectrics. These biosensors have been calibrated for the detection and estimation of bioanalytes like tributyrin and urea, based on enzymatic reactions and have a linear detection range from 0.1 mM to 20 mM of the bioanalyte concentration. These improved sensitivity EISCAP sensors were used for the estimation of the total acid content in rancid butter, estimation of enzyme (Lipase) activity and to estimate total triglyceride levels in blood serum. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

We report fabrication of potentiometric biosensors with silicon for the estimation of triglycerides and urea based on enzymatic reactions. The sensor is an Electrolyte-Insulator-Semiconductor capacitor (EISCAP) that shows a shift in the measured CV with changes in the pH of the electrolyte. Enzyme mediated biological reactions involve changes in the pH of the electrolyte and an EISCAP can be effectively used for detection of biological compounds. Optimization of the conditions for the enzymatic reaction and calibration of the sensor are included. Effect of replacing silicon with porous silicon is discussed.

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 composite porous silicon/polysilicon microcantilever for biosensing applications with enhanced sensitivity is reported. It is fabricated by surface micromachining of polysilicon cantilevers followed by the formation of the surface porous layer after release by Reaction Induced Vapor Phase Stain Etch. The microcantilevers with porous surface layer are characterized by their morphology that exhibits a dual macro and nanostructure for very effective immobilization of biomolecules. The current work focuses on the fabrication of composite porous silicon/polysilicon microcantilevers, characterization of their morphology and resonance frequency, as well as demonstration of improved immobilization of enzyme resulting in enhanced sensing of triglycerides. © 2009 IEEE.

Lipase from Pseudomonas cepacia was covalently immobilized on crystalline silicon, porous silicon and silicon nitride surfaces. The various stages of immobilization were characterized using FTIR (Fourier transform infrared) spectroscopy. The surface topography of the enzyme immobilized surfaces was investigated using scanning electron microscopy (SEM). The quantity of the immobilized active enzyme was estimated by the para-nitrophenyl palmitate (pNPP) assay. The immobilized lipase was used for triglyceride hydrolysis and the acid produced was detected by a pH sensitive silicon nitride surface as a shift in the C-V (capacitance-voltage) characteristics of an electrolyte-insulator-semiconductor capacitor (EISCAP) thus validating the immobilization method for use as a biosensor. © 2008 Elsevier 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 detection of micromolar levels of triglycerides using surface micromachined polysilicon cantilever beams. Enzymatic hydrolysis of triglycerides produces glycerol which alters the viscosity and density of the solution. This affects the dynamic properties of cantilever beams immersed in the solution. The change in the resonance frequency of the cantilever beams in the solution is measured using Doppler Vibrometry and the concentration of triglyceride is determined by comparing with a predetermined calibration plot. © 2007 IEEE.

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.

In this paper we discuss the fabrication and characterization of miniaturized triglyceride biosensors on crystalline silicon and porous silicon (PS) substrates. The sensors are miniaturized Electrolyte Insulator Semiconductor Capacitors (mini-EISCAPs), which primarily sense the pH variation of the electrolyte used. The lipase enzyme, which catalyses the hydrolysis of triglycerides, was immobilized on the sensor surface. Triglyceride solutions introduced into the enzyme immobilized sensor produced butyric acid which causes the change in pH of the electrolyte. Miniaturized EISCAP sensors were fabricated using bulk micromachining technique and have silicon nitride as the pH sensitive dielectric layer. The sensors are cubical pits of dimensions 1,500 μm × 1,500 μm × 100 μm which can hold an electrolyte volume of 0.1 μl. The pH changes in the solution can be sensed through the EISCAP sensors by monitoring the flatband voltage shift in the Capacitance-Voltage (C-V) characteristics taken during the course of the reaction. The reaction rate is found to be quite high in the miniature cells when compared to the sensors of bigger dimensions. © 2008 Springer Science+Business Media, LLC.