Anju Chadha

Estimation of triglyceride concentration is important for the health and food industries. Use of solid state biosensors like Electrolyte Insulator Semiconductor Capacitors (EISCAP) ensures ease in operation with good accuracy and sensitivity when compared to conventional sensors. In this paper we report on packaging of miniaturized EISCAP sensors on silicon. The packaging involves glass to silicon bonding using adhesive. Since this kind of packaging is done at room temperature, it cannot damage the thin dielectric layers on the silicon wafer unlike the high temperature anodic bonding technique and can be used for sensors with immobilized enzyme without denaturing the enzyme. The packaging also involves a teflon capping arrangement which helps in easy handling of the bio-analyte solutions. The capping solves two problems. Firstly, it helps in the immobilization process where it ensures the enzyme immobilization happens only on one pit and secondly it helps with easy transport of the bio-analyte into the sensor pit for measurements. © 2010 Copyright SPIE - The International Society for Optical Engineering.

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 biosensor for triglycerides has been developed with porous silicon. Porous silicon was made from p-type crystalline silicon and it was thermally oxidized. Lipase enzyme was used to hydrolyze triglycerides, which results in the formation of acid. This causes a change in the pH of the solution. Here, the enzyme lipase was immobilized into the pores of the oxidized porous silicon via physical adsorption. Electrolyte-oxide-semiconductor (EOS) structure was realized with enzyme solution, oxidized porous silicon, porous silicon and crystalline silicon. The concentration of triglycerides in the electrolyte was determined by characterizing the above EOS structure for capacitance-voltage (C-V) measurements.

Electrolyte Insulator Semiconductor Capacitor (El S CAP) is a transducer that can detect triglycérides (TGs) in blood serum through an enzymatic response that changes the pH of the electrolyte (blood serum). This change in pH is transformed by the EISCAP to a shift in the capacitance-voltage (C-V) characteristics of the device which in turn can be mapped to the amount of TG in blood serum. We have developed a miniaturized biochip with immobilized enzyme integrated with a thin film counter electrode for the estimation of TG in blood serum within the clinical range. The miniaturized devices are tested using blood serum sample to estimate the TG concentration and compared with clinical data. © 2013 IEEE.

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.

Aluminium coated polysilicon (Al-polySi) nanoresonator has been used to design a urea biosensor. The etching characteristic of Al by the ammonium hydroxide from urea hydrolysis in the presence of urease was used to estimate the urea concentration. Urease immobilized on Al coated polySi indicated smoothening of the surface with increasing urea concentration, confirming the etching of Al. The nanoresonator could estimate between 10-1000 nM concentrations of urea. The sensing was not affected in the presence of interferents such as uric acid and ascorbic acid, thus making it specific for urea. The sensor was found to be highly sensitive and specific and can have potential application in the field of medical diagnostics and environmental monitoring.

A novel composite porous silicon/polysilicon microcantilever for biosensing applications with enhanced sensitivity is reported. It is fabricated by surface mi cromachining 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 demonstration of improved immobilization of enzymes resulting in enhanced sensing of triglycerides. © 2008 IEEE.