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.

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.

In this paper, we describe an electrochemical sensing platform—ElectroSens—for the detection of Zn based on self-assembled polyelectrolyte multilayers on the carbon fiber (CF) electrode surface. The CF-extended surface facilitates the usage of a small volume electrochemical cell (1 mL) without stirring. This approach allows making a low-cost three-electrode platform. Working electrode modification with layer-by-layer assembly of polyethyleneimine (PEI), poly(sodium 4-styrenesulfonate) (PSS), and mercury nitrate layers eliminates solution toxicity and provides stable stripping voltammetry measurements. The stable, robust, sustainable, and even reusable Ag/AgCl reference electrode consists of adsorbed 32 PEI-KCl/PSS-KCl bilayers on the CF/silver paste separated from the outer solution by a polyvinyl chloride membrane. The polyelectrolyte-based sensor interface prevents adsorption of protein molecules from biological liquids on the CF surface that leads to a sensitivity increase of up to 2.2 μA/M for Zn 2+ detection and provides a low limit of detection of 4.6 × 10 –8 M. The linear range for Zn detection is 1 × 10 –7 to 1 × 10 –5 M. A portable potentiostat connected via wireless to a smartphone with an android-based software is also provided. The ElectroSens demonstrates reproducibility and repeatability of data for the detection of Zn in blood and urine without the digestion step.

We demonstrate that our bio-electrochemical platform facilitates the reduction of detection time from the 3-day period of the existing tests to 15 min. Machine learning and robotized bioanalytical platforms require the principles such as hydrogel-based actuators for fast and easy analysis of bioactive analytes. Bacteria are fragile and environmentally sensitive microorganisms that require a special environment to support their lifecycles during analytical tests. Here, we develop a bio-electrochemical platform based on the soft hydrogel/eutectic gallium–indium alloy interface for the detection of Streptococcus thermophilus and Bacillus coagulans bacteria in various mediums. The soft hydrogel-based device is capable to support bacteria’ viability during detection time. Current–voltage data are used for multilayer perceptron algorithm training. The multilayer perceptron model is capable of detecting bacterial concentrations in the 104 to 108 cfu/mL range of the culture medium or in the dairy products with high accuracy (94%). Such a fast and easy biodetection is extremely important for food and agriculture industries and biomedical and environmental science.

The new detection SERS platform is applicable for the quick and easy formation of sensing devices for food, agriculture, and environmental science. For quantitative sensing, it is important that a...