The electroactive multilayer films of polyelectrolytes and Prussian blue nanoparticles and their application for H2O2 sensors

Peroxidase (POD) Mimicking Activity of Different Types of Poly(ethyleneimine)-Mediated Prussian Blue Nanoparticles

Prussian blue nanoparticles (PBNPs) have been identified as a promising candidate for biomimetic peroxidase (POD)-like activity, specifically due to the metal centres (Fe3+/Fe2+) of Prussian blue (PB), which have the potential to function as catalytically active centres. The decoration of PBNPs with desired functional polymers (such as amino- or carboxylate-based) primarily facilitates the subsequent linkage of biomolecules to the nanoparticles for their use in biosensor applications. Thus, the elucidation of the catalytic POD mimicry of these systems is of significant scientific interest but has not been investigated in depth yet. In this report, we studied a series of poly(ethyleneimine) (PEI)-mediated PBNPs (PB/PEI NPs) prepared using various synthesis protocols. The resulting range of particles with varying size (~19-92 nm) and shape combinations were characterised in order to gain insights into their physicochemical properties. The POD-like nanozyme activity of these nanoparticles was then investigated by utilising a 3,3',5,5'-tetramethylbenzidine (TMB)/H2O2 system, with the catalytic performance of the natural enzyme horseradish peroxidase (HRP) serving as a point of comparison. It was shown that most PB/PEI NPs displayed higher catalytic activity than the PBNPs, with higher activity observed in particles of smaller size, higher Fe content, and higher Fe2+/Fe3+ ratio. Furthermore, the nanoparticles demonstrated enhanced chemical stability in the presence of acid, sodium azide, or high concentrations of H2O2 when compared to HRP, confirming the viability of PB/PEI NPs as a promising nanozymatic material. This study disseminates fundamental knowledge on PB/PEI NPs and their POD-like activities, which will facilitate the selection of an appropriate particle type for future biosensor applications.

Polyelectrolytes Assembly: A Powerful Tool for Electrochemical Sensing Application

The development of sensing coatings, as important sensor elements that integrate functionality, simplicity, chemical stability, and physical stability, has been shown to play a major role in electrochemical sensing system development trends. Simple and versatile assembling procedures and scalability make polyelectrolytes highly convenient for use in electrochemical sensing applications. Polyelectrolytes are mainly used in electrochemical sensor architectures for entrapping (incorporation, immobilization, etc.) various materials into sensing layers. These materials can often increase sensitivity, selectivity, and electronic communications with the electrode substrate, and they can mediate electron transfer between an analyte and transducer. Analytical performance can be significantly improved by the synergistic effect of materials (sensing material, transducer, and mediator) present in these composites. As most reported methods for the preparation of polyelectrolyte-based sensing layers are layer-by-layer and casting/coating methods, this review focuses on the use of the latter methods in the development of electrochemical sensors within the last decade. In contrast to many reviews related to electrochemical sensors that feature polyelectrolytes, this review is focused on architectures of sensing layers and the role of polyelectrolytes in the development of sensing systems. Additionally, the role of polyelectrolytes in the preparation and modification of various nanoparticles, nanoprobes, reporter probes, nanobeads, etc. that are used in electrochemical sensing systems is also reviewed.

Supported lipid bilayers with encapsulated quantum dots (QDs) via liposome fusion: effect of QD size on bilayer formation and structure

Understanding interactions between functional nanoparticles and lipid bilayers is important to many emerging biomedical and bioanalytical applications. In this paper, we report incorporation of hydrophobic cadmium sulphide quantum dots (CdS QDs) into mixed 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) liposomes, and into their supported bilayers (SLBs). The QDs were found embedded in the hydrophobic regions of the liposomes and the supported bilayers, which retained the QD fluorescent properties. In particular, we studied the effect of the QD size (2.7-5.4 nm in diameter) on the formation kinetics and structure of the supported POPC/POPE bilayers, monitored in situ using quartz crystal microbalance with dissipation monitoring (QCM-D), as the liposomes ruptured onto the substrate. The morphology of the obtained QD-lipid hybrid bilayers was studied using atomic force microscopy (AFM), and their structure by synchrotron X-ray reflectivity (XRR). It was shown that the incorporation of hydrophobic QDs promoted bilayer formation on the PEI cushion, evident from the rupture and fusion of the QD-endowed liposomes at a lower surface coverage compared to the liposomes without QDs. Furthermore, the degree of disruption in the supported bilayer structure caused by the QDs was found to be correlated with the QD size. Our results provide mechanistic insights into the kinetics of the rupturing and formation process of QD-endowed supported lipid bilayers via liposome fusion on polymer cushions.

Poly(l-glutamic acid)-g-poly(ethylene glycol) external layer in polyelectrolyte multilayer films: Characterization and resistance to serum protein adsorption

Formation of protein-resistant surfaces is a major challenge in the design of novel biomaterials and an important strategy to prevent protein adsorption is the formation of protein-resistant coatings. It can be achieved by proper modification of surfaces, e.g., by immobilization of hydrophilic polymers such as poly(ethylene glycol) (PEG). An appropriate method to immobilize PEG at charged surfaces is the adsorption of copolymers with PEG chains grafted onto polyelectrolyte backbone. The growing interest in the use of polyelectrolyte multilayer coatings in biomedical applications to improve biocompatibility and/or to prepare coating with antiadhesive properties has been the main reason for these studies. Therefore the aim was to produce protein resistant polyelectrolyte multilayer films. They were formed via the layer-by-layer approach, while their pegylation by the deposition of pegylated polyanion, PGA-g-PEG, as an external layer. The influence of PEG chain length and grafting density of PGA-g-PEG copolymers on the protein antiadhesive properties of pegylated polyelectrolyte multilayer films was investigated. To monitor the formation of pegylated and non-pegylated multilayer films, adsorption of the following proteins: HSA, Fibrinogen, and FBS were measured by quartz crystal microbalance (QCM - D). We found that protein adsorption onto all pegylated polyelectrolyte multilayers was significantly reduced in comparison to non-pegylated ones. Long-term performance tests confirmed the stability and the durability of the protein resistant properties of the pegylated multilayers. Antiadhesive properties of tested surfaces pegylated by PGA-g-PEG were compared to the available data for pegylated polycation PLL-g-PEG.

Interfacial and structural characteristics of polyelectrolyte multilayers used as cushions for supported lipid bilayers

The surface properties of polyelectrolyte multilayers (PEMs) obtained via sequential adsorption of oppositely charged polyions from their solutions and used as cushions for supported lipid bilayers were investigated. Five types of polyelectrolytes were used: cationic polyethyleneimine (PEI), poly(diallyldimethylammonium)chloride (PDADMAC), and poly-l-lysine hydrobromide (PLL); and anionic polysodium 4-styrenesulfonate (PSS) and poly-l-glutamic acid sodium (PGA). The wettability and surface free energy of the PEMs were determined by contact angle measurements using sessile drop analysis. Electrokinetic characterisation of the studied films was performed by streaming potential measurements of selected multilayers and the structure of the polyelectrolyte multilayer was characterized by synchrotron X-ray reflectometry. The examined physicochemical properties of the PEMs were correlated with the kinetics of the formation of supported lipid bilayers atop the PEM cushion.