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Biosensors bring together the strengths of biochemical interactions combined with electronic detection and can be used for medical diagnostics, environmental analysis, food quality control, drug detection, etc. Silicon based sensors have the advantages of being compact and thus requiring small sample quantity for testing, ease in signal processing and possibility of circuit integration and also lower costs if made by batch processing. Electrolyte–Insulator-Semiconductor capacitors (EISCAP) show a shift in the measured capacitance voltage (CV) characteristic with changes in the pH of the electrolyte. Many biological reactions, especially enzyme mediated ones, involve changes in the pH of the electrolyte and an EISCAP can be effectively used for the detection of biological compounds. We started with developing an EISCAP sensor that was able to detect presence of urea in milk and triglycerides (TGs) in blood serum. Miniaturization of the sensor to reduce the sample volume and the analysis time can lead to low cost diagnostic bio-chips. We discuss the problems encountered on miniaturizing the EISCAPs and ways to address them. These include the scaling of the device, choice and integration of the electrode for stable measurements, improved process for immobilization of the enzymes and the measurements on the miniaturized EISCAPs. Finally, a complete biosensor system, for the detection of TGs, based on the miniaturized EISCAP with an embedded counter electrode and the bio-receptor as well as a readout system is discussed. Estimation of TGs in blood serum samples using the sensor is compared with clinical data.


Enakshi Bhattacharya did her MSc (Physics) from IIT Bombay in 1980, PhD from TIFR Mumbai in 1985 and Post-doctoral work at the National Renewable Energy Laboratory (then SERI), USA from 1986-88. She was a faculty member in the Department of Physics, IIT Kanpur during 1988-91. Since 1991, she has been on the faculty of the Department of Electrical Engineering at IIT Madras and was a Visiting Scientist at the Micromachined Products Division of Analog Devices, USA from 1999-2000. She is interested in all forms of silicon: single crystal, poly, amorphous and porous and her current research areas are MEMS/NEMS and Biosensors.