Anju Chadha

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.

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.

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.