Polymer membranes sensors

Figure 25. Polymer membrane sensor re.sponse against let-rachloroethene. The membrane contains polyelhylenoxide. 2-l1uorophenyl-2-nitrophcnylelhcr, lelraoclylammoniumbro-...

Explosive Detection by Fluorescent Electrospun Polymer Membrane Sensor... 

Shen, H., Habara, M., Toko, K., 2008. Development of caffeine detection using taste sensor with Upid/polymer membranes. Sensor. Mater. 20, 171-178. 

SENSORS BASED ON FREE-STANDING MOLECULARLY IMPRINTED POLYMER MEMBRANES. COMPUTATIONAL MODELLING OF SYNTHETIC MIMICKS OF BIORECEPTORS... 

For example, Novasina S.A. (www.novasina.com), a Swiss company specializing in the manufacture of devices to measure humidity in air, has developed a new sensor based on the non-synthetic application of an ionic liquid. The new concept makes simple use of the close correlation between the water uptake of an ionic liquid and its conductivity increase. In comparison with existing sensors based on polymer membranes, the new type of ionic liquid sensor shows significantly faster response times (up to a factor of 2.5) and less sensitivity to cross contamination (with alcohols, for example). Each sensor device contains about 50 pi of ionic liquid, and the new sensor system became available as a commercial product in 2002. Figure 9-1 shows a picture of the sensor device containing the ionic liquid, and Figure 9-2 displays the whole humidity analyzer as commercialized by Novasina S.A.. 

Dubois, P., Rosset, S., Koster, S., Bufom, J.M., Stauffer, J., Mikhailov, S., Dadras, M., Rooij, Nico- F. de., and Shea, H., Microactuators based on ion-implanted dielectric electroactive polymer membranes (EAP), Presented at 13th International Conference on Solid-State Sensors, Actuators and Microsystems, Seoul, Korea, June 5-9, 2005, 2048. 

Mohr G.J., Wolfbeis O.S., Application of Potential-Sensitive Fluorescent Dyes in Anion-Sensitive and Cation-Sensitive Polymer Membranes, G Sensor Actuat B-Chem. 1997 37 103. 

The optical sensors are composed of ion-selective carriers (ionophores), pH indicator dyes (chromoionophores), and lipophilic ionic additives dissolved in thin layers of plasticized PVC. Ionophores extract the analyte from the sample solution into the polymer membrane. The extraction process is combined with co-extraction or exchange of a proton in order to maintain electroneutrality within the unpolar polymer membrane. This is optically transduced by a pH indicator dye (chromoionophore)10. 

In the case of co-extraction, a selective anion-carrier (ionophore) extracts the analyte anion into the lipophilic sensor membrane. In order to maintain electroneutrality, a proton is co-extracted into the membrane where it protonates a pH indicator dye contained in the polymer membrane. Due to protonation, the dye undergoes a change in either absorption or fluorescence. (Figure 6 and Tables 13 and 14). 

B. Fu, E. Bakker, J.H. Yun, V.C. Yang, and M.E. Meyerhoff, Response mechanism of polymer membrane-based potentiometric polyion sensors. Anal. Chem. 66, 2250-2259 (1994). 

The principle of pH electrode sensing mechanisms which are based on glass or polymer membranes is well investigated and understood. Common to all potentiometric ion selective sensors, a pH sensitive membrane is the key component for a sensing mechanism. When the pH sensitive membrane separates the internal standard solution with a constant pH from the test solution, the potential difference E across the membrane is determined by the Nemst equation ... 

Polymer-based pH sensors are not suitable for continuous in-vivo measurements due to the poor biocompatibility of plasticizers used in the polymer membrane. To minimize such a problem, surface treatment or using a reduced amount of plasticizers has been proposed [71]. In order to improve stability and adhesion, polyurethane has been used as an alternative to PVC membranes in the construction of pH sensing membranes [72, 73],... 

S. Ryu, J. Shin, G. Cha, R. Hower, and R. Brown, Polymer membrane matrices for fabricating potentio-metric ion sensors, in Technical Digest 5th Int. Mtg. on Chemical Sensors, vol. 2, pp. 961-964. Rome, Italy, July 11-14 (1994). 

H.J. Yoon, J.H. Shin, S.D. Ixe, H. Nam, G.S. Cha, T.D. Strong, and R.B. Brown, Solid-state ion sensors with a liquid junction-free polymer membrane-based reference electrode for blood analysis. Sens. Actuators B. 64, 8-14 (2000). 

In a further development, an ADH-MB-NAD/polypyrrole electrode, a platinum counter electrode and an Ag/AgCl reference electrode were assembled and covered with a gas-permeable polymer membrane to form an gaseous ethanol sensor. This appears to be the first time that a complete enzyme sensor for gaseous ethanol has been fabricated in such a manner with NAD incorporated in immobilized form. 

Sensors based on the above reaction scheme have been developed for Al3+, Zn2+, Cu2+, Ca2+, Pb2+, Hg2"1", K+, Li+, etc. A polycation, protamine sensor has also been developed using 2/7/-dichlorofluorescein octadecyl ester (DCFOE) doped in polymer membranes. However, most of these sensors are pH dependent due to the pH dependence of the cation complexation reactions. The cation ion indicators can be immobilized on any solid support, such as silica, cellulose, ion-exchange resin, porous glass, sol-gel, or entrapped in polymer membranes. 

The fourth type of mediator-based cation optical sensing is using potential sensitive dye and a cation selective ionophore doped in polymer membrane. Strong fluorophores, e.g. Rhodamine-B C-18 ester exhibits differences in fluorescence intensity because of the concentration redistribution in membranes. PVC membranes doped with a potassium ionophore, can selectively extract potassium into the membrane, and therefore produce a potential at the membrane/solu-tion interface. This potential will cause the fluorescent dye to redistribute within the membrane and therefore changes its fluorescence intensity. Here, the ionophore and the fluorescence have no interaction, therefore it can be applied to develop other cation sensors with a selective neutral ionophore. 

H. Chen and E. Wang, Urea optical sensors based on ammonium ion selective polymer membranes, Anal. Lett., 33(6) (2000) 997-1011. 

Fig. 15.11). The sensor has response times of 6-15 min, depending on the membrane thickness, and the polymer membranes maintained their recognition characteristics over 6 months.

Sergeyeva TA, Piletsky SA, Brovko AA, Slinchenko EA, Sergeeva LM, El skaya AV. Selective recognition of atrazine by molecularly imprinted polymer membranes. Development of conductometric sensor for herbicides detection. Anal Chim Acta 1999 392 105-111. 

Recent research in the field of polymer membrane ion-selective electrodes [389-391], has revealed that their se-lectivities [392-396] and limits of detections [394-397] could be improved by several orders of magnitude. The review of Bakker and Pretsch [398] summarized recent progress in the development and application of potentiometric sensors with low detection limit in the range 10-8-10-11 M. 

Many different types of techniques for protein immobilization have been developed using, in most cases, enzyme sensors. Early studies of enzyme biosensors often employed thick polymer membranes (thickness 0.01-1 mm) in which enzymes are physically entrapped or chemically anchored. The electrode surface was covered with the enzyme-immobilized polymer membranes to prepare electrochemical enzyme sensors. Although these biosensors functioned appropriately to... 

Redox potential pH Ionic activities Inert redox electrodes (Pt, Au, glassy carbon, etc.) pH-glass electrode pH-ISFET iridium oxide pH-sensor Electrodes of the first land and M" /M(Hg) electrodes) univalent cation-sensitive glass electrode (alkali metal ions, NHJ) solid membrane ion-selective electrodes (F, halide ions, heavy metal ions) polymer membrane electrodes (F, CN", alkali metal ions, alkaline earth metal ions)... 

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