– Construction:
– ChemFETs have source, drain, and gate electrodes.
– The gate potential controls current flow between the source and drain.
– ChemFETs use a semi-permeable membrane with receptors at the gate.
– Threshold voltage of ChemFETs depends on analyte concentration gradient.
– Ionophores are often used to facilitate analyte ion mobility.
– Applications:
– ChemFETs detect target analytes in liquid or gas phases.
– They require reversible binding of analyte with a receptor in the gate membrane.
– ChemFETs are widely used for anion or cation selective sensing.
– More focus has been on cation-sensing than anion-sensing ChemFETs.
– Anion-sensing in ChemFETs is complex due to various factors.
– Practical limitations:
– ChemFET bodies are generally robust.
– The need for a separate reference electrode makes the system bulkier.
– The system may become more fragile due to the additional electrode.
– History:
– Dutch engineer Piet Bergveld pioneered the adaptation of MOSFET into a sensor.
– Bergveld invented the ISFET in 1970, a precursor to ChemFETs.
– ChemFETs are based on the ISFET concept developed in the 1970s.
– ChemFETs detect any chemical, unlike ISFETs that only detect ions.
– There is some ambiguity regarding the distinction between ChemFETs and ISFETs.
– See also:
– Chemiresistor.
– EOSFET.
– Electronic nose.
A ChemFET is a chemically-sensitive field-effect transistor, that is a field-effect transistor used as a sensor for measuring chemical concentrations in solution. When the target analyte concentration changes, the current through the transistor will change accordingly. Here, the analyte solution separates the source and gate electrodes. A concentration gradient between the solution and the gate electrode arises due to a semi-permeable membrane on the FET surface containing receptor moieties that preferentially bind the target analyte. This concentration gradient of charged analyte ions creates a chemical potential between the source and gate, which is in turn measured by the FET.
