A Novel Thermo-FET Sensing System for Binary Chemical Solvent Monitoring Applications

This article introduces a new field-effect transistor (FET)-based sensing system designed to monitor charge/polarity changes during the evaporation of microsize water droplets containing polar substances such as ethanol and methanol. The system utilizes a high transconductance interdigital open-gate junction FET (ID-OGJFET) with a sizeable direct-on-channel sensing area (>16 mm2) in direct contact with the liquid droplet. A new electrofluidic package has also been developed to facilitate sample access on the FET chip, which prevents leakage and connects the sensor to readout systems. An experimental procedure is designed to demonstrate the functionality and applicability of this FET platform sensing system for chemical analysis, such as measuring the concentration of ethanol or methanol in water using the evaporation-based sensing mechanism enabled by the ID-OGJFET. Real-time video capture is employed for monitoring and control. The sensor measures ethanol and methanol concentrations ranging from 0% to 100% with steps of 10% EtOH/MetOH in water, utilizing the evaporation-based sensing mechanism and current output of the ID-OGJFET sensor. The minimum meaningful measured concentration is 1% (v/v) for ethanol and 1.49% (v/v) for methanol. The combined uncertainty analysis of methanol’s concentration predictions ranged from 3.29 to 77.91 s. The expanded uncertainty varied from 6.58 to 155.82 s at a 95% confidence level for concentrations from 0% v/v to 100% with 10% intervals. For ethanol, the combined uncertainties ranged from 4.68 to 98.95 s. The expanded uncertainties, calculated with a coverage factor 2, varied from 9.36 to 197.90 s at a 95% confidence level.