No abstract

The fabrication of pH-sensitive ISFET devices in an unmodified two-metal commercial CMOS technology (1.0 m from Atmel-ES2) is reported. The ISFET devices have a gate structure compatible with the CMOS process, with an electrically floating electrode consisting on polysilicon plus the two metals. The passivation oxynitride layer acts as the pH-sensitive material in contact with the liquid solution. The devices have shown good operating characteristics, with a 47 mV/pH response. The use of a commercial CMOS process allows the straightforward integration of signal-processing circuitry. An ISFET amplifier circuit has been integrated with the ISFET sensors.

The low but known risk of bacterial contamination has emerged as the greatest residual threat of transfusion-transmitted diseases. Label-free detection of a bacterial model, Escherichia coli, is performed using nonfaradic electrochemical impedance spectroscopy (EIS). Biotinylated polyclonal anti-E. coli is linked to a mixed self-assembled monolayer (SAM) on a gold electrode through a strong biotin-neutravidin interaction. The binding of one antibody molecule for 3.6 neutravidin molecules is determined using the surface plasmon resonance (SPR). The detection limit of E. coli found by SPR is 10(7) cfu/mL. After modeling the impedance Nyquist plot of E. coli/anti-E. coli/mixed SAM/gold electrode for increasing concentrations of E. coli (whole bacteria or lysed bacteria), the main parameter that is modified is the polarization resistance RP. A sigmoid variation of RP is observed when the log concentration of bacteria (whole or lysed) increases. A concentration of 10 cfu/mL whole bacteria is detected by EIS measurements while 103 cfu/mL is detected for lysed E. coli.