AChemFET is achemically-sensitive field-effect transistor, that is afield-effect transistor used as asensor for measuringchemical concentrations insolution.[1] When the targetanalyte concentration changes, the current through thetransistor will change accordingly.[2] Here, the analyte solution separates the source andgate electrodes.[3] 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.[3] This concentration gradient of charged analyte ions creates a chemical potential between the source and gate, which is in turn measured by the FET.[4]
The schematic view of a ChemFET. Source, drain, and gate are the three electrodes used in a FET system. The electron flow takes place in a channel between the drain and source. The gate potential controls the current between the source and drain electrodes.
A ChemFET's source and drain are constructed as for anISFET, with the gate electrode separated from the source electrode by a solution.[4] The gate electrode's interface with the solution is a semi-permeable membrane containing the receptors, and a gap to allow the substance under test to come in contact with the sensitive receptor moieties.[5] A ChemFET'sthreshold voltage depends on the concentration gradient between the analyte in solution and the analyte in contact with its receptor-embedded semi-permeable barrier.[5]
Often,ionophores are used to facilitate analyte ion mobility through the substrate to the receptor.[6] For example, when targeting anions,quaternary ammonium salts (such astetraoctylammonium bromide) are used to provide cationic nature to the membrane, facilitating anion mobility through the substrate to the receptor moieties.[7]
ChemFETs can be utilized in either liquid or gas phase to detect target analyte, requiring reversible binding of analyte with a receptor located in the gate electrode membrane.[8][3] There is a wide range of applications of ChemFETs, including most notably anion or cation selective sensing.[5] More work has been done with cation-sensing ChemFETs than anion-sensing ChemFETs.[5] Anion-sensing is more complicated than cation-sensing in ChemFETs due to many factors, including the size, shape, geometry, polarity, and pH of the species of interest.[5]
The body of a ChemFET is generally found to be robust.[9][4] However, the unavoidable requirement for a separate reference electrode makes the system more bulky overall and potentially more fragile.
ChemFETs are based on a modified ISFET, a concept developed by Bergveld in the 1970s.[4] There is some confusion as to the relationship between ChemFETs and ISFETs. Whereas an ISFET only detects ions, a ChemFET detects any chemical (including ions).
^Wróblewski, Wojciech; Wojciechowski, Kamil; Dybko, Artur; Brzózka, Zbigniew; Egberink, Richard J.M; Snellink-Ruël, Bianca H.M; Reinhoudt, David N (2001). "Durability of phosphate-selective CHEMFETs".Sensors and Actuators B: Chemical.78 (1–3):315–319.Bibcode:2001SeAcB..78..315W.doi:10.1016/s0925-4005(01)00832-2.
^Antonisse, Martijn M. G.; Snellink-Ruël, Bianca H. M.; Engbersen, Johan F. J.; Reinhoudt, David N. (1 January 1998). "Chemically modified field effect transistors with nitrite or fluoride selectivity".Journal of the Chemical Society, Perkin Transactions 2 (4): 775.doi:10.1039/a709076e.ISSN1364-5471.
^Han, Jin-Woo; Rim, Taiuk; Baek, Chang-Ki; Meyyappan, M. (30 September 2015). "Chemical Gated Field Effect Transistor by Hybrid Integration of One-Dimensional Silicon Nanowire and Two-Dimensional Tin Oxide Thin Film for Low Power Gas Sensor".ACS Applied Materials & Interfaces.7 (38):21263–9.Bibcode:2015AAMI....721263H.doi:10.1021/acsami.5b05479.ISSN1944-8244.PMID26381613.
