Showing papers by "Anju Chadha published in 2009"

The role of different anions in ionic liquids on Pseudomonas cepacia lipase catalyzed transesterification and hydrolysis

Abstract: Lipase Pseudomonas cepacia (PS) catalyzed transesterification of ethyl 3-phenylpropanoate with eleven alcohols was investigated in three ionic liquids [ILs], [Bmim]BF4, [Bmim]PF6, and [Bmim]Tf2N, consisting of an identical cation and different anions. The yields were higher in hydrophobic ILs [Bmim]Tf2N (55–96%) and [Bmim]PF6 (22–95%), than in hydrophilic [Bmim]BF4 (0–19%). The incubation of lipase PS in hydrophobic ILs for a period of 20–300 days at room temperature resulted in an increased yield of 62–98% in [Bmim]Tf2N and 45–98% in [Bmim]PF6, respectively. The lipase PS-hydrophobic IL mixture was recycled five times without any decrease in the yield of the products. In another set of experiments, the hydrolytic activity of the enzyme was determined after incubation in each of the three ILs and in hexane for 20 days at room temperature. It was found to be 1.8- and 1.6-fold higher in [Bmim]Tf2N and [Bmim]PF6, respectively, remained unchanged in [Bmim]BF4 and was 1.6 times lower in hexane as compared to the non-incubated enzyme.

MEMS Composite Porous Silicon/Polysilicon Cantilever Sensor for Enhanced Triglycerides Biosensing

Abstract: 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.

Miniaturization of EISCAP sensor for triglyceride detection

Abstract: 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 microm x 1,500 microm x 100 microm which can hold an electrolyte volume of 0.1 microl. 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.

Novel applications of silicon and porous silicon based EISCAP biosensors

Abstract: We report the fabrication of potentiometric electrolyte-insulator capacitor (EISCAP) biosensors based on silicon and porous silicon (PS) substrates with oxide and stacked oxide-nitride 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.