Polyion-sensitive membrane electrodes: Fundamental and applied studies

The potentiometric response of polycation sensitive membrane electrodes (polyion sensors) toward two classes of polycationic dendrimers was investigated: poly(amidoamine) (PAMAM) dendrimers and poly(propyleneimine) (PPI) dendrimers. It was found that the polycation sensor equilibrium EMF response toward these dendrimers is highly pH-dependent. Various dendrimer derivatives were synthesized to investigate the role of interior tertiary amine and terminal primary amine sites in the EMF response as a function of pH. Both the internal tertiary amines and the terminal primary amines contributed to the EMF response when those sites were ionized. Under non-equilibrium conditions, sub-mug/mL (nanomolar) concentrations of these dendrimers were readily detected. The interaction of these dendrimers with various polyanions (e.g., DNA) was investigated by a simple titration method, as monitored with polycation or polyanion sensors. The titration endpoints were independent of the DNA length (for each given dendrimer generation), but increased with dendrimer generation on a charge basis (dendrimer:DNA). In the interest of finding a suitable titrant for dendrimers (to enable dendrimer quantitation in solution), various polyanionic polysaccharides investigated in previous polyion sensor research were tested. Ultimately, a polyanionic polyoxometalate (paratungstate) was found to give useful titration curves for both classes of dendrimers. Quantitation of PAMAM and PPI dendrimers at the sub-mug/mL level was readily accomplished in aqueous samples by this new method.; The detection of pentosan polysulfate (PPS) in plasma (1-10 mug/ML PPS) was accomplished by a simple titration method where protamine, a polycationic peptide that binds with PPS, is used as the titrant, and monitored with polycation sensors. The PPS-protamine binding phenomenon was also used to generate a novel protease assay, where the protamine in the polyelectrolyte complex serves as the assay substrate. Upon cleavage of the protamine, the PPS is liberated for subsequent detection by polyanion sensors. In addition to the determination of PPS, another polyanionic polysaccharide was investigated: o-desulfated heparin (ODSH). This is the first report of electrochemical ODSH detection, which was accomplished by a simple potentiometric titration method. The determination of mug/mL levels of ODSH was investigated in buffer, plasma, and whole blood. This methodology was then applied to animal toxicokinetic studies of ODSH.