Showing papers by "Enakshi Bhattacharya published in 2013"

Fabrication of Ultrathin Silicon Nanoporous Membranes and Their Application in Filtering Industrially Important Biomolecules

Abstract: Ultrathin silicon nanoporous membranes with multiple pores were fabricated using batch processes involving chemical vapor deposition and rapid thermal annealing. Transmission electron microscope images showed the existence of nanopores with an average pore size of 13 nm. Measurement of ionic conduction of electrolytes with varying conductivity across the membranes confirmed the existence of pores and the repeatability of the process. The functional diameter of the pores was determined by analyzing the permeability of several industrially and medically important globular biomolecules of varying sizes such as α-amylase, bovine serum albumin, catalase and xanthine oxidase. Biomolecules with hydrodynamic diameters up to 8 nm passed through the nanopores, whereas the passage of the larger molecules was hindered. The surface charges on the molecules determine the functional diameter of the pores, and hence the permeability, as substantiated by varying the pH of the buffer solution. The filtered proteins were found to be uncleaved from sodium dodecyl sulfate polyacrylamide gel electrophoresis, and the enzyme assay of the filtered amylase showed that the activity remained unchanged.

A Miniaturized pH Sensor With an Embedded Counter Electrode and a Readout Circuit

Abstract: 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.

Digital Microfluidics and its Integration with a Fluidic Microreactor

Abstract: We present the steps to fabricate a Digital Microfluidics (DMF) platform for handling fluidic sample delivery. This is followed by the integration of the DMF chip with a microreactor that is an Electrolyte Insulator Semiconductor Capacitor (EISCAP) biosensor. DMF is used for handling basic fluidic operations like droplet transportation, and splitting and dispensing smaller droplets from a reservoir. All the droplet operations on DI water droplets mentioned above are possible with AC actuation at ~35 V rms but this result in electrolysis on the transportation of an electrolyte droplet. DC actuation is used to solve the problem of electrolysis and to transport the electrolyte droplets. Interdigitated electrode geometry improves the device performance. The DMF substrate is used to deliver fluidic samples via a through hole in the DMF wafer to a bulk micromachined EISCAP biosensor bonded to the DMF wafer. The dimension of the through hole and the extent of its coverage with the control electrode are optimized for the successful delivery of the fluidic samples to the bonded biosensor below. The devices are tested by delivering droplets of electrolyte to the bonded reactor below. Capacitance-Voltage (C-V) measurement done on the integrated device confirms the successful delivery of the electrolyte to the microreactor. This integration technique can manipulate fluid handling work on the DMF substrate without compromising the functionality of the fluidic reactor.

Compact silicon biosensor for the clinical range estimation of blood serum triglycéride

Abstract: Electrolyte Insulator Semiconductor Capacitor (El S CAP) is a transducer that can detect triglycerides (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.