Using microelectromechanical systems technology, a high-performance extended-gate field-effect transistor (EGFET)-based pesticide microsensor for organophosphorus and carbamate (CM) detection is developed. To minimize the whole pesticide-sensing system, we also integrated a planar Ti/Ag/AgCl/KCl-gel microreference electrode into the same silicon chip. The total dimensions of the proposed pesticide-sensing system are only 0.92 × 0.95 × 0.1 cm3. This EGFET-based microsensor for organophosphorus and CMs demonstrates extremely high sensitivity (194 and 268.1 mV/dec, respectively) and sensing linearity (0.993 and 0.974, respectively) and extremely low response time (120 and 300 s, respectively). The microsensor detection limit for both pesticides is 0.001 ppm.
We have developed an extended gate field-effect-transistor (EGFET)-based carbon dioxide (CO2) sensing system with a packaged Ti/Ag/AgCl/KCl-gel microreference electrode using microelectro-mechanical systems (MEMS) technology. The total dimensions of the proposed CO2 sensing system are only 2.8×1.5×0.1 cm, which is approximately 30 times smaller than a conventional CO2 sensing system (including the commercial Ag/AgCl RE). All of the manufacturing processes adopted in this work are compatible with standard planar technology and are very suitable for mass production. The presented planar reference electrode shows a very small offset voltage (−3.0 mV) and a very small potential drift (2.5 mV in 30,000 s) that is approximately equal to that of the commercial Ag/AgCl RE (1.6 mV in 30,000 s). Additionally, the implemented EGFET-based CO2 microsensor with a coated CO2 solid electrolyte and gas permeable membranes on the gate sensing area demonstrates a very high sensitivity (44.4 mV/decade) and very high sensing linearity (98.37%), while sensing CO2 concentrations ranging from 0.25 to 50 mM. Furthermore, a very small hysteresis voltage (7.5 mV) was obtained during the sensing cycle of 2.5–5–25–50–25–5–2.5 mM; this result was achieved by improving the surface planarization and enlarging the sensing area of the EGFET to 1 mm2.
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