Ion- and bio-sensors based on functionalized poly(vinyl chloride) membranes.

Abstract

Research concerning the development and study of new types of polymeric matrices for the preparation of ion-selective electrode (ISE) membranes and biosensors is described. Neutral carriers (e.g., nonactin and tridodecylamine) and charged carriers (e.g., 5,10,15,20-tetraphenyl (porphyrinato) tin (IV) dichloride, Sn(TPP)Cl$\sb2$) are employed to test the feasibility of using these new polymeric matrices to prepare ISE membranes. The enzyme urease and anti-urease antibody are covalently immobilized on the surface of various ISE membranes to prepare enzyme- and immuno-type bioelectrodes. Functionalized polymers, carboxylated-PVC (PVC-COOH) and aminated-PVC (PVC-NH$\sb2$) are chosen as models for these studies. The presence of membrane carboxyl and amino groups are shown to have little effect on the potentiometric performance of pH and ammonium selective neutral carrier-based electrodes, particularly when the mole ratio of carrier (nonactin)/NH$\sb2$ is $\geq$0.62. On the other hand, the salicylate response of a charged carrier-based sensor is essentially eliminated when PVC-COOH is used as the membrane matrix. The preparation and potentiometric pH response properties of blank membranes (no carriers) formulated with various aminated-PVC products are also described. Products containing secondary and/or primary amino groups are obtained by modifying PVC with mono- and/or diamines, respectively. Blank membranes prepared with either type of aminated-polymer exhibit nearly Nernstian potentiometric pH response over various pH ranges. In general, membranes based on diamino products exhibit pH response over a wider range (5.0 $\leq$ pH $\leq$ 10.5) than membranes formulated with monoamino products (5.0 $\leq$ pH $\leq$ 8.0). These potentiometric results are used to estimate the basicity of the various primary and secondary amino sites in the membrane phases. To prepare model biosensors, the enzyme urease is immobilized on nonactin/PVC-NH$\sb2$ and blank PVC-NH$\sb2$ membrane surfaces via glutaraldehyde crosslinking methods. The ion-selective membranes are shown to retain their potentiometric response toward selected ions and the resulting urea electrodes based on NH$\sb4\sp{+}$ or H$\sp{+}$ sensors exhibit rapid response to different levels of urea in aqueous solutions. Finally, the preparation and properties of anti-urease antibodies (polyclonal and monoclonal) that have potential applications in the design of new biosensors are described. A faster microtiter plate assay is investigated for the screening of anti-urease antibody production and for examining the antibodies' effect on urease catalytic activity. Novel biosensors are prepared by immobilizing anti-urease antibodies that do not inhibit enzymatic activity on the surface of a nonactin/PVC-NH$\sb2$ ammonium electrode.