Martijn M.G. Antonisse

Potentiometric anion selective sensors

In comparison with selective receptors (and sensors) for cationic species, work on the selective complexation and detection of anions is of more recent date. There are three important components for a sensor, a transducer element, a membrane material that separates the transducer element and the aqueous solution, and the receptor molecule that introduces the selectivity. This review deals with potentiometric transduction elements that convert membrane potentials into a signal. The structure and properties of membrane materials is discussed. The nature of the anion receptor ultimately determines the selectivity. Both coordination chemistry and hydrogen bonding have been used to design anion receptor molecules. The integration of all three elements by covalent linkage of all elements in durable sensorsystem concludes the review.

Neutral anion receptors: design and application

After the development of synthetic cation receptors in the late 1960s, only in the past decade has work started on the development of synthetic neutral anion receptors. Combination and preorganization of different anion binding groups, like amides, urea moieties, or Lewis acidic metal centers lead to receptor molecules that strongly bind inorganic anions with high selectivity. Combined with neutral cation ligands, ditopic receptors were obtained for the complexation of inorganic salts. The molecular complexation properties of anion receptors has been transduced into macroscopic properties in membrane separation processes and in sensors for selective anion detection.

H2PO4 -selective CHEMFETs with uranyl salophene receptors

Abstract Chemically modified field effect transistors (CHEMFETs) with ion-selective membranes which incorporate lipophilic uranyl salophene derivatives exhibit H2PO−4 selectivities strongly deviating from the Hofmeister series. Selectivity is obtained over much more lipophilic anions such as NO−3 ( log K Pot H 2 PO 4 , NO 3 =−1.3 ) and Cl− ( log K Pot H 2 PO 4 , Cl =−1.8 ). Modification of the uranyl salophene derivatives with additional hydrogen bond accepting methoxy substituents results in lowered detection limits and an improved selectivity over Cl−, Br−, SO2−4 and OH−.

Durable nitrate-selective chemically modified field effect transistors based on new polysiloxane membranes

Polysiloxane copolymers with different amounts and types of substituents have been synthesized and characterized. Polar substituents determine the polarity and methacrylate groups allow cross-linking and covalent binding of electroactive species. These chemically well-defined homogeneous polymers have been applied as ion-selective membrane material in nitrate-selective field effect transistors (CHEMFETs). The selectivity of the CHEMFETs is influenced by the nature of the polar substituents in the polymer. The incorporation of methacrylate moieties in the polysiloxane allows covalent attachment of quaternary ammonium sites to the membrane matrix and this enlarges the durability of the sensor.

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).

Polysiloxane based CHEMFETs for the detection of heavy metal ions

The development of polysiloxane based chemically modified field effect transistors (CHEMFETs) for heavy metal ions is described. Different polar siloxane copolymers have been synthesized via an anionic copolymerization of hexamethylcyclotrisiloxane, [3-(methacryloxy)propyl]pentamethylcyclotrisiloxane and pentamethylcyclotrisiloxanes with a pendant polar group, e.g. ester, ether, amide, keto or cyan group. Well-structured monomodal molecular weight polymers were obtained with molecular weight distributions from 1.3 to 1.7. The siloxane copolymers were used as sensing membranes for Ag+, Cd2+ sand Pb2+ selective CHEMFETs. The intrinsic elastomeric properties of the polysiloxane membrane makes the use of a plasticizer superfluous, which should have a favourable effect on the durability of these CHEMFETs. Siloxane copolymers with 3-cyanopropyl side groups are already intrinsically selective for Ag+ ions and this can be further enhanced by the addition of an Ag+ selective ionophore I. Good Cd2+ selectivity was obtained for CHEMFETs with 3-acetoxypropyl functionalized siloxane membranes in which the Cd2+ selective ionophore 2 was incorporated. CHEMFETs with a [3-(p-acetylphenoxy)propyl]polysiloxane membrane containing the Pb2+ selective ionophore 3 showed good selective responses towards Pb2+.

Chemically Modified Field-Effect Transistors for Measurement of Ion Activities in Aqueous Solution

Chemically modified field effect transistors for the selective detection of several cation and anion activities in aqueous solution are described. For obtaining sensors of high durability, novel polysiloxane membranes have been developed which contain different side groups to tune their intrinsic properties. These polysiloxane membranes show good performance in life time experiments. The ion selectivity has been tuned by incorporation of various novel ion receptor molecules, yielding sensors with high selectivities for sodium, potassium, lead, cupper, cadmium, silver, nitrate, nitrite, fluoride, and dihydrogen phosphate.

Optical detection of complexation of labeled saccharides to macrocyclic synthetic receptors

The interaction of optically labeled saccharides with resorcin[4]arenes as synthetic saccharide receptors has been investigated by determination of the partition of the saccharides over an aqueous and 1-octanol phase in the absence and presence of the synthetic receptor. It is shown that the complexation of merocyanine labeled glucose, galactose and ribose with the resorcin[4]arenes can be optically detected and that the chosen receptors have a modest selectivity towards the labeled glucose.

Chemical sensors based on field effect transistors; selective recognition of cations and anions

Microsensors based on chemically modified field effect transistors (CHEMFETs) for the detection of ions require a durable chemoselective membrane layer with receptor molecules of high selectivity. This contribution describes recent advances in the development of polysiloxane polymer membranes, in the design of cation and anion selective receptors, and their application in CHEMFETs to obtain sensors with improved durability.