A novel flexible ion-selective sensor for potassium and sodium detection was proposed. Flexible ion-selective electrodes with pseudo-liquid internal solution on contrary to the system with a solid contact provided a more stable analytical signal. Such advantages were achieved because of polyelectrolyte (PEI/PSS) layers adsorption on the conduct substrate with a layer-by-layer technique. Such an approach demonstrated that ion-selective electrodes save sensitivity with Nernstian dependence: 56.2 ± 1.4 mV/dec aNa+ and 56.3 ± 1.9 mV/dec aK+, as well as a fast time of response for potassium (5 s) and sodium (8 s) was shown. The sensing platform proposed demonstrates a better time of response and is close to the Nernstian value of sensitivity with a sensor low cost. The results proposed confirm a pseudo-liquid junction for the ion-selective electrode. Biocompatibility of an ion-selective sensing platform was demonstrated at potassium potentiometric measurements in Escherichia coli biofilms. Potassium levels in a biofilm were measured with potentiometry and showed agreement with the previous results.

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The present study of nanoelectrochemical sensors prepared by directed electrochemical nanowire assembly (DENA) is defined by the requirements of electrochemical analysis, where the transducer function of metallic nanowires is synergetically combined with their electrochemical catalytic activity with respect to a particular analyte. We show for the first time that this technique can be employed for metals (Pd, Au) and their bimetallic compositions to create various multicomponent sensor nanomaterials on a single chip without the use of multistep lithography for the spatially resolved analysis of solutions. The nanostructures of various compositions can be individually addressed when used in liquid media, so that the particular surface properties of the individual nanoarray elements can be used for the electrochemical analysis of specific analytes. The sensor application of these devices in electrolytes and cell culture conditions has been demonstrated for the first time. As an example, the Pd-Au nanowires prepared by DENA were used for a non-enzymatic analysis of H2O2 with a linear concentration interval of 10-6-10-3 M, sensitivity of 18 µA M-1 and detection limit of 3×10-7 M at as low absolute value of the detection potential as-0.05 V. This sensor was also proven for the detection of hydrogen peroxide in HL-1 cell culture, demonstrating good biocompatibility and support for the cell culture conditions. Using various DENA-grown electrochemical compositions on a single chip, a novel multisensor platform is proposed for the determination of various analytes in electrolyte solutions for biocompatible sensor arrays, flexible multianalyte environmental and technological process monitoring, and healthcare areas.

In the present work, transparent holographic poly­(diallyldimethylammonium chloride) (PDADMAC)/heparin and PDADMAC/poly­(styrenesulfonate) (PSS) films were synthesized via polyelectrolyte coacervates. PDADMAC/heparin films were obtained without temperature treatment. Thin holographic free-standing films with a 1 μm grating period and uniform surface of a polyelectrolyte complex were readily and quickly made by pressing polyelectrolyte coacervate, the hydrated viscoelastic fluid-like form of polyelectrolyte complex precursor, between a flat surface and holographic mask. Heparin replaces PSS in film composition to prepare the sheer film. Thus, the PDADMAC/heparin holographic film demonstrates transparency and reversible response for humidity under diffraction detection. In addition to diffraction humidity signal measurements, the cobalt­(II) chloride was impregnated in polyelectrolyte coacervate to make an additional colorimetric signal response. In this case, the free-standing film serves both as the substrate for the hygroscopic salt and as a diffraction humidity sensor. The PDADMAC/heparin/Co­(II) chloride film demonstrates a linear humidity range from 50 to 90%. Additionally, due to hydrated inorganic salt ion size, cobalt chloride prevents film porosity, which initiates under film swelling. Based on the results and calculations obtained, the study proposes the mechanism of water incorporation, including the reptation model and polyelectrolyte complex behavior. Results of density functional theory calculations prove that binding of cobalt aqua complexes [Co­(H2O)6]2+ with the dimeric associates heparin/PDADMAC via noncovalent interactions (hydrogen bonds) additionally is much more energetically favorable compared with the alternative association of heparin/PDADMAC with water molecules.