Phase Behavior and Electrochemical Properties of Highly Asymmetric Redox Coacervates.

This work reports the phase behavior and electrochemical properties of liquid coacervates made of ferricyanide and poly(ethylenimine). In contrast to the typical polyanion/polycation pairs used in liquid coacervates, the ferricyanide/poly(ethylenimine) system is highly asymmetric because poly(ethylenimine) has approximately 170 charges per molecule, while ferricyanide has only 3. Two types of phase diagrams were measured and fitted with a theoretical model. In the first type of diagram, the stability of the coacervate was studied in the plane given by the concentration of poly(ethylenimine) versus the concentration of ferricyanide for a fixed concentration of added monovalent salt (NaCl). The second type of diagram involved the plane given by the concentration of poly(ethylenimine) vs the concentration of the added monovalent salt for a fixed poly(ethyleneimine)/ferricyanide ratio. Interestingly, these phase diagrams displayed qualitative similarities to those of symmetric polyanion/polycation systems, suggesting that coacervates formed by a polyelectrolyte and a small multivalent ion can be treated as a specific case of polyelectrolyte coacervate. The characterization of the electrochemical properties of the coacervate revealed that the addition of monovalent salt greatly enhances charge transport, presumably by breaking ion pairs between ferricyanide and poly(ethylenimine). This finding highlights the significant influence of added salt on the transport properties of coacervates. This study provides the first comprehensive characterization of the phase behavior and transport properties of asymmetric coacervates and places these results within the broader context of the better-known symmetric polyelectrolyte coacervates.

Unexpected enhancement of pH-stability in Au3+/Ag+ loaded H-bonded layer-by-layer thin films.

In this work, a polymeric film was synthesized through a layer-by-layer (LBL) self-assembly technique using polyacrylic acid (PAA) and polyethylene oxide (PEO), resulting in the formation of a hydrogen-bonded LBL film. The formation of these films was evaluated by PMIRRAS and QCM-D. The synergy of these techniques allowed the understanding of the mechanism of formation of the film by showing the H-bonding formation and film growth. Au and Ag metal ions were successfully incorporated into the films, as corroborated by the combination of the information obtained by XRR and PMIRRAS. The films were exposed to increasing pH, showing a pronounced improvement in stability in films loaded with Au ions, extending the stability from pH 4 to 10. This behavior allows the use of this system in a wider range of applications, including the possibility of working in biological conditions. On the other hand, films loaded with Ag disintegrated at pH above 4. At acidic pH (below 3), these films released the Ag ions, which may be useful for the preparation of antibacterial stimuli-responsive nanomaterials. In both cases, the films were adequate to produce metal nanoparticles by metal loading and in situ reduction.

Development of a Redox-Polymer-Based Electrochemical Glucose Biosensor Suitable for Integration in Microfluidic 3D Cell Culture Systems.

The inclusion of online, in situ biosensors in microfluidic cell cultures is important to monitor and characterize a physiologically mimicking environment. This work presents the performance of second-generation electrochemical enzymatic biosensors to detect glucose in cell culture media. Glutaraldehyde and ethylene glycol diglycidyl ether (EGDGE) were tested as cross-linkers to immobilize glucose oxidase and an osmium-modified redox polymer on the surface of carbon electrodes. Tests employing screen printed electrodes showed adequate performance in a Roswell Park Memorial Institute (RPMI-1640) media spiked with fetal bovine serum (FBS). Comparable first-generation sensors were shown to be heavily affected by complex biological media. This difference is explained in terms of the respective charge transfer mechanisms. Under the tested conditions, electron hopping between Os redox centers was less vulnerable than H2O2 diffusion to biofouling by the substances present in the cell culture matrix. By employing pencil leads as electrodes, the incorporation of these electrodes in a polydimethylsiloxane (PDMS) microfluidic channel was achieved simply and at a low cost. Under flow conditions, electrodes fabricated using EGDGE presented the best performance with a limit of detection of 0.5 mM, a linear range up to 10 mM, and a sensitivity of 4.69 µA mM-1 cm-2.

Enzymes hosted in redox-active ionically cross-linked polyelectrolyte networks enable more efficient biofuel cells.

Redox mediators are pivotal players in the electron transfer process between enzymes and electrodes. We present an alternative approach for redox mediation based on branched polyethyleneimine (BPEI) modified with an osmium complex. This redox polyelectrolyte is crosslinked with phosphate to produce colloidal particles with a diameter of ca. 1 µm, which, combined with glucose oxidase (GOx), can form electroactive assemblies through either layer by layer assembly (LbL) or one-pot drop-casting (OPDC). The addition of NaCl to these colloidal systems induces the formation of films that otherwise poorly grow, presenting an outstanding catalytic current. The system was tested as a bioanode delivering a power output of 148 µW per nmol of mediator. These results are explained in terms of the interactions of the ions with the polyelectrolyte and represent a new route for the development of bioelectrochemical devices involving redox mediators and enzymes.

Efficient decolorization of recalcitrant dyes at neutral/alkaline pH by a new bacterial laccase-mediator system.

Laccases and laccase-mediator systems (LMS) are versatile catalysts that can oxidize a broad range of substrates coupled to the sole reduction of dioxygen to water. They possess many biotechnological applications in paper, textile, and food industries, bioethanol production, organic synthesis, detection and degradation of pollutants, and biofuel cell development. In particular, bacterial laccases are getting relevance due to their activity in a wide range of pH and temperature and their robustness under harsh conditions. However, the enzyme and the redox mediator's availability and costs limit their large-scale commercial use. Here we demonstrate that ß-(10-phenothiazyl)-propionic acid can be used as an efficient and low-cost redox mediator for decolorizing synthetic dyes by the recombinant laccase SilA from Streptomyces ipomoeae produced in E. coli. This new LMS can decolorize more than 80% indigo carmine and malachite green in 1 h at pH = 8.0 and 2 h in tap water (pH = 6.8). Furthermore, it decolorized more than 40% of anthraquinone dye remazol brilliant blue R and 80% of azo dye xylidine ponceau in 5 h at 50 °C, pH 8.0. It supported at least 3 decolorization cycles without losing activity, representing an attractive candidate for a cost-effective and environmentally friendly LMS functional at neutral to alkaline pH.

The effect of ionic strength and phosphate ions on the construction of redox polyelectrolyte-enzyme self-assemblies.

Layer by layer assembly of polyelectrolytes with proteins is a convenient tool for the development of functional biomaterials. Most of the studies presented in the literature are based on the electrostatic interaction between components of opposite charges, limiting the assembly possibilities. However, this process can be tuned by modifying the environment where the main constituents are dissolved. In this work, the electron transfer behavior between an electroactive polyelectrolyte (polyallylamine derivatized with an osmium complex) and a redox enzyme (glucose oxidase) is studied by assembling them in the presence of phosphate ions at different ionic strengths. Our results show that the environment from which the assembly is constructed has a significant effect on the electrochemical response. Notably, the polyelectrolyte dissolved in the presence of phosphate at high ionic strength presents a globular structure which is preserved after adsorption with substantial effects on the buildup of the multilayer system, improving the electron transfer process through the film.