Self-assembled nanobiocatalyst. Phosphate-mediated cross-linking of redox polyelectrolytes and glucose oxidase leads to self-assembled nanostructures with higher output power density per mol of mediator, thus enabling more efficient biofuel cells.

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The type and concentration of ions present in a solution containing an electroactive polyelectrolyte shape its configuration, adsorption, and electrochemical response.

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We present an electrochemical sandwich‐type assay based on the splitting of an aptamer into two fragments. Gold nanoparticles are modified with one of the fragments and a redox polyelectrolyte. The first is used as the recognition element, while the other for the electrochemical signal generation. The split‐aptamer used here can detect adenosine, used as a model system for recognizing small molecules. The multiple binding sites on the nanoparticle, along with the high number of redox probes, yield a selective and sensitive assay for adenosine, achieving a limit of detection of 3.1 nM and a linear range up to 75 nM. The obtained results are analyzed in terms of the nanoparticle and electrode architectures. The assay can be easily extended to other small molecules and sandwich assays, representing a promising tool for detecting metabolites at the nanomolar level.

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High-power density output in enzymatic fuel cells is a key feature to reduce the size of self-powered implantable medical devices. Electron transfer mediated through redox polyelectrolytes allows the transport of electrons from enzymes away from the electrode, improving the current output. It is known that doping ions in polyelectrolytes introduce relevant characteristics in the generation of assemblies regarding mass adsorption and stiffness. In this work, binary 1:1 sodium salts (NaX; X = F–, Cl–, Br–, NO3 –, ClO4 –) were studied as doping ions of two redox polyelectrolytes (osmium-based branched polyethyleneimine and osmium-based linear polyallylamine) to enhance the adsorption and electron transfer process in glucose oxidase/redox polyelectrolyte assemblies. Cyclic voltammetry, polarization modulation infrared reflection absorption spectroscopy, quartz crystal microbalance with dissipation, and atomic force microscopy were used to understand the growth mechanism of these films and their performance. Ion hydrophobicity plays a key role, bromide being the one that generates the greater absorption and the best electron transfer efficiency for both redox polyelectrolytes. Branched polyethyleneimine doped with bromide was the best combination for the construction of bioanodes. Its application on an O2–glucose enzymatic fuel cell yields a power density output of 2.5 mW cm–2, achieving state-of-the-art performance.