Chemically modified field effect transistors with nitrite or fluoride selectivity

Polysiloxanes with different types of polar substituents are excellent membrane materials for nitrite and fluoride selective chemically modified field effect transistors (CHEMFETs). Nitrite selectivity has been introduced by incorporation of a cobalt porphyrin into the membrane; fluoride selectivity has been obtained with a uranyl salophen derivative as the anion receptor. Polysiloxanes with acetylphenoxypropyl or phenylsulfonylpropyl substituents are the best sensing membranes. The nitrite selective CHEMFETs exhibit Nernstian responses and a high selectivity over chloride and bromide (log KPotNO2,j = –2.9 and –2.7 respectively, based on a phenylsulfonylpropyl functionalized polysiloxane). Also the sensitivity and selectivity of the fluoride selective CHEMFETs is better with the polysiloxane membranes than with plasticized PVC membranes. Even in the presence of 0.1 M of the more lipophilic chloride, bromide, or nitrate ions an almost Nernstian response and a detection limit of 0.25 mM is obtained for fluoride (log KF,jPot = –2.5).