The region ion sensitive field effect transistor, a novel bioelectronic nanosensor

A novel type of bioelectronic region ion sensitive field effect transistor (RISFET) nanosensor was constructed and demonstrated on two different sensor chips that could measure glucose with good linearity in the range of 0-0.6 mM and 0-0.3 mM with a limit of detection of 0.1 and 0.04 mM, respectively. The sensor is based on the principle of focusing charged reaction products with an electrical field in a region between the sensing electrodes. For glucose measurements, negatively charged gluconate ions were gathered between the sensing electrodes. The signal current response was measured using a low-noise pico ammeter (pA). Two different sizes of the RISFET sensor chips were constructed using conventional electron beam lithography. The measurements are done in partial volumes mainly restricted by the working distance between the sensing electrodes (790 and 2500 nm, respectively) and the influence of electrical fields that are concentrating the ions. The sensitivity was 28 pA/mM (2500 nm) and 830 pA/mM (790 nm), respectively. That is an increase in field strength by five times between the sensing electrodes increased the sensitivity by 30 times. The volumes expressed in this way are in low or sub femtoliter range. Preliminary studies revealed that with suitable modification and control of parameters such as the electric control signals and the chip electrode dimensions this sensor could also be used as a nanobiosensor by applying single enzyme molecule trapping. Hypotheses are given for impedance factors of the RISFET conducting channel. (c) 2007 Elsevier B.V. All rights reserved

Signal frequency studies of an environmental application of a 65 nm region ion sensitive field effect transistor sensor

A rapid and sensitive novel type of bioelectronic Region Ion Sensitive Field Effect Transistor (RISFET) nanosensor was constructed on a chip with a 65 nm sensing electrode gap. The RISFET nanosensor was demonstrated for the environmental pesticide analysis of neurotoxic organocarbamate/carbofuran. The linear range for carbofuran analysis is ac signal frequency dependent, studied in the range (500 down-0.5 Hz, 50 mV(peak-peak) ac) and a bias voltage applied between the bottom capacitor plate and the electrodes. The signal current response is measured using a low-noise pico ammeter. The inhibition of acetylcholinesterase (AChE) by carbofuran was detectable in a logarithmic linear range (0.1-100nM) at 1.08 Hz, with a lower limit of detection of inhibition 0.1 nM with 10 min incubation time. The sensor is based on the principle of focusing charged reaction products with an electrical field in a region between the sensing electrodes. The current measurement by the sensor electrodes is correlated to the composition of the sample. The carbofuran detection is based on the ability to inhibit the enzyme AChE. The RISFET sensor chip is fabricated using conventional electron beam lithography. The encompassed sensor volume in the "nanocell" is in the attoliter range. (c) 2007 Elsevier B.V. All rights reserved