ION-SENSITIVE FIELD-EFFECT TRANSISTORS WITH ULTRATHIN LANGMUIR-BLODGETT MEMBRANES

Novel ISFET devices coated with ultrathin Langmuir-Blodgett (LB) membranes are suitable for sodium detection in liquids. Successful deposition of a Na+-ion sensitive LB film onto structured ISFET surfaces has been achieved. The LB material consists of a rod-like LB polymer mixed with a commercially available sodium ionophore. A thin additional LB covering layer increases the sensor stability in contact with the electrolytes. The ISFET sensors show a nearly Nernstian sodium sensitivity of more than 52 mV/pNa in the range 10(-3) to 1 mol/l over a period of at least 30 days. A maximum response time after concentration changes of less than 1 min was determined. Selectivities were investigated to interfering ions like K+, Ca2+, Mg2+ and H+. The obtained results are in good agreement with the sensor properties of capacitive silicon/SiO2 structures coated with LB membranes of the same kind.