Miklos Erdosy

Electroanalytical and biocompatibility studies on carboxylated poly(vinyl chloride) membranes for microfabricated array sensors.

Potassium ion-selective and pH membrane electrodes based on neutral carrier ionophores for K+ (valinomycin) and H+ (TDDA and ETH 5294), respectively, immobilized in carboxylated PVC (PVC-COOH) with normal (classical) and reduced amounts of plasticizer, were investigated with respect to their general analytical performances (linear range, slope, detection limit, selectivity, internal membrane resistance), their biocompatibility and cellular responses. The analytical performance of potassium selective electrodes was not affected by reducing the plasticizer content from 66% (m/m) to about 33% (m/m) while that of pH electrodes was significantly changed at the lower plasticizer concentration level. The adhesive properties of PVC-COOH membranes to an inert substrate such as polyimide-coated Kapton are greatly improved by reducing the plasticizer content of the membrane. In addition, as was reported earlier by this group, improved biocompatibility was observed with these membranes relative to those with increased plasticizer content. A ratio of 1:1 m/m for PVC-COOH to plasticizer is recommended for the construction of planar ISEs without massive use of internal solution.

Aliphatic polyurethane as a matrix for pH sensors: effects of native sites and added proton carrier on electrical and potentiometric properties

The potentiometric and impedance characteristics of polymeric membranes, based on aliphatic polyurethane (Tecoflex) as a matrix, are described and interpreted by theory and experiments for H(+) and alkali metal ion-sensitive sensors. Both dummy plasticized membranes and proton carrier-loaded membranes can show pH response. The pH response of dummy membranes is due to protonated natural negative sites in the polyurethane matrix. The electrodes with added proton carrier show improved rejection of Li(+), Na(+), and K(+) responses and give useful analytical responses. Optimal performance requires control of negative site concentration by addition of lipophilic salt (e.g. tetraphenylborate derivatives). Impedance analyses show surface-rate semicircles and, depending on the bathing electrolyte solution, appearance of a diffusional Warburg impedance. In addition to these time-dependence surface region effects, changes in the bulk membrane resistance with soaking time can be well correlated with equilibrium water content of plasticized membranes.

Ion-selective microchemical sensors with reduced preconditioning time. Membrane biostability studies and applications in blood analysis

Abstract Progress on solution of two general problems regarding the use of in vivo planar microchemical sensors is reported. These are issues of short term and long term response stability. Reduction of preconditioning time (hydration period), i.e., the time needed by the planar microchemical sensors based on Kapton® substrate to achieve the optimal analytical performances, has been achieved. By storing the electrodes in containers with humid atmospheres (100% humidity) their short time responses, e.g. measured potential, when placed in samples to be analyzed, are practically constant after one minute of immersion. The electrode sensitivity, potential reproducibility and membrane resistance of both pH and K+ sensors were evaluated and compared before and after placing them in whole blood samples for specified periods of time. Blood serum samples were successfully assayed and the results compared with those obtained with a pH glass electrode and a blood gas analyzer, respectively. The long term stability o...

Electroanalytical and surface characterization of encapsulated implantable membrane planar microsensors

Abstract The selective polymeric membranes of planar microsensors sensitive to inorganic analytes of biomedical interest (e.g., H + , K + ), fabricated on a flexible polyimide (Kapton ® DuPont) substrate using a combination of thin-film, thick-film and packaging technologies, were encapsulated with a biocompatible polymeric material such as poly(2-hydroxyethylmethacrylate) (poly-HEMA), The electroanalytical characteristics of these sensors (linear activity ranges, slopes of the calibration curves, response times, membrane resistances, and selectivities) are not significantly different when compared with those of non-coated membrane sensors. The encapsulated membrane electrodes show improved analytical characteristics after exposure to whole blood samples for specified periods of time. The long-term stability of the membranes for in vivo use was investigated by the cage implant system; the membrane biostability and cell adhesion, at 1, 3, 7, and 14 days of subcutaneous implantation in Sprague-Dawley rats, were evaluated by scanning electron microscopy.

Potentiometric responses of ion-selective membranes containing mixtures of two different ionophores

Research related to optical sensors (optodes) directed the attention towards plasticized polymeric membranes containing more than one ionophore at the same time. Studying the potentiometric behavior of such membrane systems helps to characterize the effect of cross-contamination in multi-electrode systems used for biomedical applications. In this article, a theoretical model is introduced, which describes the potentiometric behavior of membranes doped with two different ion carriers. The theory is compared to those results obtained with a model system containing both K+ and H+-ionophores in the membrane phase. The study has also been extended to ion-selective membranes containing two other ion-selective carriers in different ratios. These results give guidelines to optimize the physical arrangement of potentiometric multi-electrode systems.

Calcium Selective Polymeric Membranes for Microfabricated Sensor Arrays

Abstract The potentiometric and impedance characteristics of various selective Ca2+ polymeric membranes are described and interpreted by theory and experiments for Ca2+ microfabricated sensor arrays. These are designed for further biomedical applications with an emphasis on potential in situ applications. The polymeric materials used in the present studies consist of either carboxylated PVC or aliphatic polyurethane. Both materials showed good adherence properties to the polyimide-coated Kapton substrate used in planar sensor fabrication. The impedance analysis, performed in the frequency range from 65,000 Hz to 0.1 Hz, revealed the bulk geometrical response at high frequencies. Measured Rbulk corresponds to the unperturbed bulk resistance. That, in turn, depends on mobilities and concentrations of Ca2+ complex and mobile sites. Decreases in Rbulk correlated well with sensor behavior during the preconditioning (hydration) period. Studies of blood interactions with these sensors proved that the main sensor...

Mechanism of transport in carrier-based ion-selective electrodes

Inert, passive, overplasticized poly(vinyl chloride) membranes loaded naturally or artificially with trapped, hydrophobic sites, and with added carriers (neutral or charged) show the ‘closed circuit’ carrier mechanism when perturbed by a.c. and d.c. voltages. These solvent polymeric membranes behave like homogeneous phases, as observed by impedance spectroscopy. The interfacial ion exchange processes have been analysed and data favour direct aqueous ion hopping to surface carriers in the membrane phase, subject to electroneutrality constraints. In potentiometry, carriers serve as selective reagents, establish the interfacial space charge and potential differences, but only show carrying properties when perturbed. Transport then occurs, in most cases, by motion of ion-carrier complexes, not by ion hopping. Exceptions are pH membranes where carriers are fixed in space and protons hop. Effects of hydrophobic additives can be analysed to interpret different cases recently observed for charged carriers.New results cover the interpretation of monotonic I–t curves (with decreasing slope) and monotonic I–t curves with a shoulder (decreasing–increasing–decreasing slope). Ohmic, non-ohmic and limiting current characters of I–V curves are emphasized to distinguish characteristics of fixed from mobile, trapped, site behaviour.