The degradation of polyelectrolyte microcapsules formed on protein-free CaCO₃ particles consisting of polyallylamine (PAH) and polystyrene sulfonate (PSS) and the resulting yield of protein in the presence of various salts of different concentrations, as well as at two pH values, was studied by fluorescence spectroscopy; the protein was incorporated into prepared microcapsules by adsorption. It was found that a high concentration of sodium chloride (2 M) leads to considerable dissociation of PAH, which is apparently due to the loosening of polyelectrolytes under the action of ionic strength. At the same time, 0.2 M sodium chloride and ammonium sulfate of the same ionic strength (0.1 M) exert less influence on the amount of dissociated polymer. In the case of ammonium sulfate (0.1 M), the effect is due to the competitive binding of sulfate anions to the amino groups of the polyelectrolyte. However, unlike microcapsules formed on CaCO₃ particles containing protein, the dissociation of polyelectrolyte from microcapsules formed on protein-free particles increased with increasing temperature. Apparently, a similar effect is associated with the absence of a distinct shell, which was observed on microcapsules formed on protein-containing CaCO₃ particles. The high level of the presence of Fluorescein isothiocyanate (FITC)-labeled Bovine Serum Albumin (BSA) in the supernatant is explained by the large amount of electrostatically bound protein and the absence of a shell that prevents the release of the protein from the microcapsules. In 2 M NaCl, during the observation period, the amount of the released protein did not exceed 70% of the total protein content in the capsules, in control samples, this value does not exceed 8%, which indicates the predominantly electrostatic nature of protein retention in capsules formed on protein-free CaCO₃ particles. The increase in protein yield and peeling of PAH with increasing pH is explained by the proximity of pH 7 to the point of charge exchange of the amino group of polyelectrolyte, as a result of the dissociation of the microcapsule.

This work investigated changes in the biochemical parameters of multilayer membrane structures, emerging at their modification with multiwalled carbon nanotubes (MWCNTs). The structures were represented by polyelectrolyte microcapsules (PMCs) containing glucose oxidase (GOx). PMCs were made using sodium polystyrene sulfonate (polyanion) and poly(allylamine hydrochloride) (polycation). Three compositions were considered: with MWCNTs incorporated between polyelectrolyte layers; with MWCNTs inserted into the hollow of the microcapsule; and with MWCNTs incorporated simultaneously into the hollow and between polyelectrolyte layers. The impedance spectra showed modifications using MWCNTs to cause a significant decrease in the PMC active resistance from 2560 to 25 kOhm. The cyclic current–voltage curves featured a current rise at modifications of multilayer MWCNT structures. A PMC-based composition was the basis of a receptor element of an amperometric biosensor. The sensitivity of glucose detection by the biosensor was 0.30 and 0.05 μA/mM for PMCs/MWCNTs/GOx and PMCs/GOx compositions, respectively. The biosensor was insensitive to the presence of ethanol or citric acid in the sample. Polyelectrolyte microcapsules based on a multilayer membrane incorporating the enzyme and MWCNTs can be efficient in developing biosensors and microbial fuel cells.

Polyelectrolyte microcapsules, which are obtained by the method of alternate adsorption of oppositely charged polyelectrolytes onto colloidal particles of micron size, are widely used in science and industry. Nevertheless, the properties of microcapsules are still poorly understood. In particular, there is no information in the literature on the buffer capacity. However, information on the presence of a buffer capacity and an understanding of its mechanisms can both simplify the use of microcapsules and expand the scope of their application. In this regard, the buffer capacity of various types of microcapsules was studied. It was found that polyelectrolyte microcapsules consisting of polyallylamine, and polystyrene sulfonate have a buffer capacity. In addition, in an acidic medium, the buffer capacity of microcapsules containing BSA is significantly greater than that of microcapsules without protein. This is due to the fact that BSA contributes to the buffering of microcapsules. Differences in the behaviour of the buffer capacity of microcapsules with the composition (PAH/PSS)₃ and (PSS/PAH)₃ were found. In addition, a hypothesis has been proposed that regions of unbound polyallylamine are responsible for the buffering properties of polyelectrolyte microcapsules. This hypothesis is confirmed by the fact that incubation of microcapsules in 0.5 M NaCl increases the amount of unbound polyallylamine, which leads to an increase in the buffer capacity of microcapsules at alkaline pH values higher than the buffer capacity of capsules in an aqueous solution.

Phage therapy is a great alternative to antibiotic drugs, but it can’t effectively overcome the over-acidic medium of the stomach. We offer the use of polyelectrolyte microcapsules as a protective means of bacteriophage. It is necessary to understand the influence of polyelectrolytes on bacteriophage survival. The work studied the effect of polyanions and polycations on the coliprotetic bacteriophage’s viability. We have shown that polyallylamine decreased bacteriophage’s viability during increasing polyelectrolyte concentration and polyarginine had a lower inhibitory effect (then PAH) on the activity of the bacteriophage due to polyelectrolyte concentration from 0.05 to 5 mg/mL. It was shown that the inhibition of the bacteriophage by polyallylamine had an electrostatic nature and the use of high ionic strength prevented the formation of the PAH-protein capsid complex. Polystyrene sulfonate does not affect bacteriophage viability during increasing polyelectrolyte concentration from 0.05 mg/mL to 1 mg/mL. Polystyrene sulfonate decreases the viability of bacteriophage from 5 mg/mL of polyelectrolyte concentration. Dextran sulfate inhibits bacteriophage activity at 20–30%. Dextran inhibits bacteriophage activity by 80% at diapason concentration from 0.05 to 5 mg/mL and loses the inhibition effect from a concentration of 5 mg/mL.

Polyelectrolyte microcapsules (PMC) based on polyallylamine and polystyrene sulfonate are utilized in various fields of human activity, including medicine, textiles, and the food industry, among others. However, characteristics such as microcapsule size, shell thickness, and pore size are not sufficiently studied and systematized, even though they determine the possibility of using microcapsules in applied tasks. The aim of this review is to identify general patterns and gaps in the study of the morphology of polyelectrolyte microcapsules obtained by the alternate adsorption of polystyrene sulfonate and polyallylamine on different solid cores. First and foremost, it was found that the morphological change in polyelectrolyte microcapsules formed on different cores exhibits a significant difference in response to varying stimuli. Factors such as ionic strength, the acidity of the medium, and temperature have different effects on the size of the microcapsules, the thickness of their shells, and the number and size of their pores. At present, the morphology of the microcapsules formed on the melamine formaldehyde core has been most studied, while the morphology of microcapsules formed on other types of cores is scarcely studied. In addition, modern methods of nanoscale system analysis will allow for an objective assessment of PMC characteristics and provide a fresh perspective on the subject of research.

Polyelectrolyte microcapsules are used in the development of new forms of targeted delivery systems, self-healing materials, sensors, and smart materials. Nevertheless, their buffer capacity has not been practically studied, although that characteristic makes it possible to estimate the change in the state of protonation of the entire polyelectrolyte system. This is necessary both for creating a buffer barrier system for pH-sensitive compounds (metals, enzymes, polyelectrolytes, drugs) and for the correct interpretation of the results of research and studying of the PMC structure. The buffer capacity of a PMC can be affected by the concentration of microcapsules in solution and the number of shell layers since the listed parameters affect other physicochemical properties of the PMC shell. This includes, for example, the electrical conductivity, permeability (of ions), osmotic pressure, charge density, etc. In this regard, we studied the change in the buffer capacity of polyelectrolyte microcapsules depending on their concentration and the number of shell layers. As a result, it was found that with an increasing concentration of microcapsules, the buffering capacity of the PMC increases, but at the same time, in the pH range from 4 to 5.5, the calculated buffering capacity of 1 billion capsules decreases with increasing their concentration. This effect may be associated with a decrease in the available -NH₂ groups of the PMC’s shell. In addition, it was found that the main contribution to the buffer capacity of a PMC is made by the entire shell of the microcapsule and not just its surface. At the same time, the buffer capacity of the capsules has non-linear growth with an increase in the number of PMC shell layers. It is presumably associated either with a decrease in the polyelectrolyte layer with an increase in their number or with a decrease in the permeability of hydrogen protons.