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Magnetic nanoparticles (MNPs) hold significant potential for a wide range of applications, however, surface modification or bio-conjugation of MNPs often leads to their aggregation and instability. To address this, we proposed a facile method using a layer-by-layer (LbL) coating technique with polyallylamine hydrochloride (PAH) and poly(styrene sulfonic acid) sodium salt (PSS), so as to maintain the dispersion stability and functionality of MNPs. This method enabled us to develop the powerful MNPs towards to their use in the electrochemical biosensor, by combining both the redox probes (ferrocene (Fc), anthraquinone (AQ), or monocarboxymethylene blue (MB)) and bio-probes (IgG). The redox molecules were effectively anchored to the MNPs under the organic solvents, while such functionalized MNPs surface were subsequently protected by the LbL coating process prior to dispersing in high ionic strength solutions (e.g. Phosphate-buffered saline). And the out-layer of polyelectrolyte shell allowed biomolecules to attach to the MNP surface without chemical cross-linking. Our results demonstrated that the TEM size of MNPs@Fc, MNP@AQ and MNP@MB after LbL coating were characterized as 11.0 ± 2.0 nm, 10.5 ± 2.1 nm and 12.4 ± 2.2 nm and these developed redox MNPs of MNPs@Fc, MNPs@AQ and MNPs@MB were characterized by square wave voltammetry (SWV) with their redox intensity of 0.64 ± 0.10 µA, 23.25 ± 0.73 µA and 0.48 ± 0.13 µA, respectively. In addition, the binding efficiency of adsorption between the MNPs and IgG was up to 78%, evidenced by SDS-PAGE gel analysis. This facile method offered a versatile and effective way to functionalize MNPs, combining redox and biological properties for potential applications in disease diagnosis and point-of-care diagnostics.

Tissue adhesives are regularly used for wound healing, bleeding control and sealing internal organ leakages. However, currently available tissue adhesives are often cytotoxic. Polycations containing primary amines are generally known to induce cytotoxicity. Complex coacervates, composed of oppositely charged polyelectrolytes, may offer a biocompatible alternative. In this study, primary amines of polyallylamine hydrochloride (pAH) were reacted with glycidyltrimethylammonium chloride (GTMAC) following an epoxide ring nucleophilic substitution to obtain pAH with quaternary ammonium pendant groups (q-pAH). These polycations were combined with negatively charged polysulfopropyl methacrylate (pSPMA) to form complex coacervates. The biocompatibility of the individual polyelectrolytes and resulting complex coacervates was studied using A549 cells through Live/Dead, MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) and LDH (lactate dehydrogenase) assays. Additionally, adhesion to porcine tissues was evaluated. Quaternization of pAH strongly reduced the critical salt concentration (CSC) of the coacervate system, while remaining easy to process and injectable. The cytocompatibility of q-pAH/pSPMA was increased compared to pAH/pSPMA, mainly caused by the reduction of the required salt concentration. Nevertheless, quaternization did not reduce the cytotoxicity of the polycation itself. Complexation with pSPMA effectively reduced cytotoxicity through charge neutralization. Upon direct contact of A549 cells with q-pAH/pSPMA coacervates improved biocompatibility was observed compared to pAH/pSPMA, which could not be fully attributed to effects of reduced salt levels. Both coacervates formed stable, gel-like patches upon the salt switch and these adhered to various tissues. Reduction of complex coacervate cytotoxicity by polycation quaternization can be included in future designs of medical adhesives. Graphical Abstract

A method to identify and quantify amines in polymers by X-ray photoelectron spectroscopy using the energetic distribution of N1s atomic orbitals is presented in this work. The N orbital energetic states were obtained and associated with the atomic chemical states of amines through their formation energy. Pyrrole and allylamine plasma polymers were used as test polymers of this method because they potentially have primary, secondary and tertiary amines in their structure; although, additional unsaturated and oxidized amines were also found in the test polymers as a function of the synthesis power. The participation percentages of amines obtained with this method indicated that secondary amines had the greatest participation in the polymers followed by unsaturated and tertiary amines. The lowest participation belonged to primary amines or to the oxidized amines found during the analyses. This method is new and can be applied to other materials in solid state, not only to polymers, with enough stability to resist the X-ray beams of the XPS spectrometers.

In this work we have investigated the effect of surface modification of fibres on the overall mechanical properties of high-density papers. Paper sheets were prepared by a combination of heat-pressing and polyelectrolyte Layer-by-Layer (LbL) modification of different softwood fibres. LbLs of Polyallylamine Hydrochloride (PAH) and Hyaluronic Acid (HA) were adsorbed onto unbleached kraft fibres and bleached Chemo-ThermoMechanical Pulp (CTMP) to improve the strength of the fibre–fibre joints in papers made from these fibres. Additionally, different sheet-making procedures were used to prepare a range of network densities with different degrees of fibre–fibre interaction in the system. The results demonstrate that interfacial adhesion within fibre–fibre joints plays a pivotal role in the network's performance, even at higher paper densities. Hygroexpansion measurements and fracture zone imaging with Scanning Electron Microscopy (SEM) further support the claim that stronger interactions between the fibres allow for a better utilisation of the inherent fibre properties. Surface treatments and network densification significantly improved the paper sheets' mechanical properties. Specifically, LbL-treatments alone increased specific stiffness up to 60% and specific strength by over 100%. This improvement is linked to the build-up of residual stresses during drying. Due to a high interaction between the fibres during water removal the fibres become constrained, leading to increased stretching of fibre segments. Strengthened fibre joints intensify this constraint, further increasing the stretch and, consequently, the paper's strength.

Silver nanoparticles were immobilized on magnetic polyallylamine (PAA) decorated g-C 3 N 4 by using Heracleum persicum extract as a biological reducing and stabilizing agent. The resulting nanocomposite, Fe 3 O 4 -g-C 3 N 4 -TCT-PAA-Ag, was then characterized using BET, VSM, XRD, TGA, FTIR, TEM, EDS and ICP. The catalytic performance of the synthesized nanocatalyst was considered in the reduction of rhodamine B, and methyl orange in the presence of sodium borohydride in the aqueous medium at room temperature. The results showed that Fe 3 O 4 -g-C 3 N 4 -TCT-PAA-Ag nanocomposite could promote both reduction reactions efficiently in very short reaction times (70–100 s). In addition, Fe 3 O 4 -g-C 3 N 4 -TCT-PAA-Ag could be magnetically recovered and recycled for several cycles with no significant decrease in its catalytic performance. Using the experimental results, the rate constant, enthalpy, and entropy of the reduction reactions of both dyes were estimated.

The main objective of the present study was to prepare and evaluate dissolvable microneedle patch containing nanoparticles of tetanus toxoid without the use of any adjuvant and its immunopotentiation activity. Immunization with microneedles is a novel approach in vaccines delivery with advantages such as convenience, simple, and non-invasive therapy. The gelatin nanoparticles were prepared by a layer-by-layer coating method using polystyrene sulfonate (PSS), polyallylamine hydrochloride (PLA), and PLGA. The filtered gelatin nanoparticles were later dispersed in the aqueous PVP K10 solution and integrated into a mold to develop microneedles. The nanoparticles and their dissolvable microneedle patches were evaluated using particle size, surface charge, entrapment efficiency, SEM analysis, in-vitro, and in-vivo studies. The particle size was found in the order of PLGA-coated nanoparticles > layered gelatin nanoparticles > aminated gelatin nanoparticles > gelatin nanoparticles and aminated gelatin nanoparticles showed maximum entrapment efficiency (92.6 ± 3.25%). The microscopic SEM images showed the spherical-shaped particle formation, verifies that the nanoparticles were formed. The gelatin nanoparticles followed the prolonged release for the period of 8 h whereas the nanoparticle-loaded dissolvable microneedles showed the controlled release pattern for 24 h. Aminated nanoparticulate microneedle showed the highest antibody production against tetanus toxoid. Hence, the nanoparticulate dissolvable microneedles-based immunopotentiation can be used as an alternative for delivery of tetanus toxoid.

A fluorometric turn-on assay is described for ascorbic acid (AA). It is based on the controlled release of polyallylamine-stabilized gold nanoclusters (polyallylamine-AuNCs) from MnO nanosheets. In an aqueous solution of near-neutral pH value, the positively charged capped AuNCs are adsorbed on the surface of the negatively charged MnO nanosheets. The adsorption leads to the quenching of the fluorescence of the AuNCs. However, in the presence of AA, MnO is reduced to Mn . This causes the destruction of the MnO nanosheets. As a result, the fluorescence of the polyallylamine-AuNCs at 615 nm is recovered. This method for determination of AA is inexpensive, sensitive, and selective. It works in the 0.01 to 200 μM concentration range and has a 3.2 nM detection limit (for S/N = 3). Graphical abstract Gold nanoclusters (AuNCs) and polyallylamine can form polyallylamine-AuNCs to enhance the orange fluorescence of AuNCs. MnO nanosheets can absorb polyallylamine-AuNCs, and this results in fluorescence quenching of polyallylamine-AuNCs. Ascorbic acid (AA) can reduce MnO nanosheets, in this results in the fluorescence recovery of polyallylamine-AuNCs.

This work describes a novel L-lactate biosensor based on the immobilization of L-lactate dehydrogenase enzyme on the screen-printed electrode modified with a ternary composite based on gold nanoparticles, electrochemically-reduced graphene oxide, and poly (allylamine hydrochloride). The enzyme was stabilized by crosslinking with glutaraldehyde. Applied working potential, pH and NAD+ concentration were optimized. The biosensor reports a specific sensitivity of 1.08 µA/mM·cm2 in a range up to 3 mM L-lactic acid with a detection limit of 1 µM. The operational and long-term stability as well as good selectivity allowed the L-lactic acid measurement in dairy products and wine samples.

Complex coacervation is an electrostatically-driven phase separation phenomenon that is utilized in a wide range of everyday applications and is of great interest for the creation of self-assembled materials. Here, we utilized turbidity to characterize the effect of salt type on coacervate formation using two vinyl polyelectrolytes, poly(acrylic acid sodium salt) (pAA) and poly(allylamine hydrochloride) (pAH), as simple models for industrial and biological coacervates. We confirmed the dominant role of salt valence on the extent of coacervate formation, while demonstrating the presence of significant secondary effects, which can be described by Hofmeister-like behavior. These results revealed the importance of ion-specific interactions, which are crucial for the informed design of coacervate-based materials for use in complex ionic environments, and can enable more detailed theoretical investigations on the role of subtle electrostatic and thermodynamic effects in complex coacervation.

The gut microbiota plays a critical role in chronic kidney disease (CKD) and hypertension. Trimethylamine-N-oxide (TMAO) and trimethylamine (TMA) are gut microbiota-derived metabolites, and both are known uraemic toxins that are implicated in CKD, atherosclerosis, colorectal cancer and cardiovascular risk. Therefore, the detection and quantification of TMAO, which is a metabolite from gut microbes, are important for the diagnosis of diseases such as atherosclerosis, thrombosis and colorectal cancer. In this study, a new “colour-switch” method that is based on the combination of a plasma separation pad/absorption pad and polyallylamine hydrochloride-capped manganese dioxide (PAH@MnO2) nanozyme was developed for the direct quantitative detection of TMAO in whole blood without blood sample pretreatment. As a proof of concept, a limit of quantitation (LOQ) of less than 6.7 μM for TMAO was obtained with a wide linear quantification range from 15.6 to 500 μM through quantitative analysis, thereby suggesting potential clinical applications in blood TMAO monitoring for CKD patients.