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A physical model and an experimental method to quantitatively determine the binding constants between a model polycationic nonviral gene delivery vehicle poly-L-histidine (PLH) and calf thymus deoxyribonucleic acid (DNA) is described. The results suggest that the competitive interaction of the components of the polyelectrolyte complex with charged species could be responsible for the liberation of the DNA from the gene delivery vehicle.

Potentiometry, turbidimetry, and fluorescence spectroscopy were used to reveal the utility of different polycarboxybetaines (PCB) as positively charged components of polyelectrolyte complexes. The results indicated that PCB interacts efficiently with sodium poly(styrenesulfonate) forming polyelectrolyte complex with pH-controlled solubility, and this could be important in the development of bioseparation techniques.

Linear water-soluble polyelectrolytes, i.e., poly(methacrylate) polyanion and poly(N-ethyl-4-vinylpyridinium) polycation, were used as carriers for the reactants in immunoassay. The strength of ionic forces through distance and the cooperative binding of oppositely charged chains, the carriers interact with each other at an extremely high rate and affinity. These properties of the polyelectrolytes made it possible to carry out the immunochemical steps of the assay in true solution and then to quickly separate the resulting products from the reaction mixtures. The above approach was applied to an assay for the herbicide simazine. Both enzyme-linked immunosorbent assay (ELISA) and dot blot formats of the immunoassay were evaluated. In the ELISA format, the polycation was adsorbed on the surface of a microtiter plate. A tracer antigen (simazine) was allowed to interact in solution with components of the reaction mixture containing simazine - peroxidase conjugate, specific antibodies, and staphylococcal protein A conjugated with the polyanion, and then the mixture was added to the immobilized polycation. Quick separation of the immunoreactants was achieved due to formation of interpolyelectrolyte complexes between polycation and polyanion molecules. After washing, the microplate wells were rifled with a solution of substrate, and the optical density of the reaction products was measured. In the second format, a solution of the same reaction mixture (after incubation) was filtered through a porous membrane, with the polycation adsorbed. The subsequent addition of substrate led to the development of colored spots. Sensitivity of the dot blot format was close to that of the traditional ELISA format using the same reactants, i.e., 0.5 ng/mL. However, the assay was much faster (assay time decreased from 100-120 to 45 min). Sensitivities of the dot immunoassay were 1 ng/mL for densitometric detection and 10 ng/mL for visual detection with a duration of 20 min. The techniques developed here were used for simazine determination in water, milk, and juices.

The complex formation between polycarboxybetaines (PCB) and polyanions can be enhanced and efficiently controlled by the proper choice of alkyl spacer between charges in the betaine moieties. Practical ramifications of the revealed role of the alkyl spacer in polyelectrolyte complexation as well as the pH-induced stabilization of the complexes that occurs under enzyme-friendly conditions might extend to areas of biotechnology, specifically in bioseperation and gene delivery.

The approach based on conductivity measurements, which provides valuable information on the conformation of polyions in salt-free dilute aqueous solutions that correlates well with data obtained by other methods is discussed. The results shows that both symmetrical and nonsymmetrical ionenes are valuable polycations to reveal the effect of mean charge density and the charge distribution of the chains on their properties.