Multi-Parameter Characterization of Liquid-to-Ice Phase Transition Using Bulk Acoustic Waves.

The detection of the liquid-to-ice transition is an important challenge for many applications. In this paper, a method for multi-parameter characterization of the liquid-to-ice phase transition is proposed and tested. The method is based on the fundamental properties of bulk acoustic waves (BAWs). BAWs with shear vertical (SV) or shear horizontal (SH) polarization cannot propagate in liquids, only in solids such as ice. BAWs with longitudinal (L) polarization, however, can propagate in both liquids and solids, but with different velocities and attenuations. Velocities and attenuations for L-BAWs and SV-BAWs are measured in ice using parameters such as time delay and wave amplitude at a frequency range of 1-37 MHz. Based on these measurements, relevant parameters for Rayleigh surface acoustic waves and Poisson's modulus for ice are determined. The homogeneity of the ice sample is also detected along its length. A dual sensor has been developed and tested to analyze two-phase transitions in two liquids simultaneously. Distilled water and a 0.9% solution of NaCl in water were used as examples.

Gluconobacter Oxydans-Based MFC with PEDOT:PSS/Graphene/Nafion Bioanode for Wastewater Treatment.

Microbial fuel cells (MFCs) are a variety of bioelectrocatalytic devices that utilize the metabolism of microorganisms to generate electric energy from organic matter. This study investigates the possibility of using a novel PEDOT:PSS/graphene/Nafion composite in combination with acetic acid bacteria Gluconobacter oxydans to create a pure culture MFC capable of effective municipal wastewater treatment. The developed MFC was shown to maintain its activity for at least three weeks. The level of COD in municipal wastewater treatment was reduced by 32%; the generated power was up to 81 mW/m2 with a Coulomb efficiency of 40%. Combining the MFC with a DC/DC boost converter increased the voltage generated by two series-connected MFCs from 0.55 mV to 3.2 V. A maximum efficiency was achieved on day 8 of MFC operation and was maintained for a week; capacitors of 6800 µF capacity were fully charged in ~7 min. Thus, G. oxydans cells can become an important part of microbial consortia in MFCs used for treatment of wastewaters with reduced pH.

Modification of thermally expanded graphite and its effect on the properties of the amperometric biosensor.

The work considered the properties of a biosensor based on a novel nanomaterial-modified thermally expanded graphite (TEGM). The main focus was on whether the procedure of additional graphite thermal expansion would affect the electrochemical properties of biosensors based on membrane fractions of acetic acid bacteria Gluconobacter oxydans. Raman spectroscopy, scanning electron microscopy and electrochemical analysis were used for the study. Raman spectra showed that the formation of TEGM led to its stratification into smaller particles and a better orderly layered structure with high "graphenization" degree. Modification of TEG led to the formation of additional cavities into which bacterial cells or bacterial membrane fractions could be immobilized and affect the electrical conductivity of the biosensors positively. Calculation of the heterogeneous charge transfer constants showed that processes occurring on the electrodes are quasi-reversible. The limiting stage of these processes is the transfer of an electron from a biological component on the electrode surface, not the diffusion of the analyte from the solution to the active centers of the enzyme. We showed the possibility of developing third-generation mediator-free biosensors for glucose detection based on TEGM, as well as of second-generation mediator biosensors for glucose, ethanol and glycerol detection.

The Peculiarities of the Acoustic Waves of Zero-Order Focusing in Lithium Niobate Plate.

In this research, beam focusing in lithium niobate plate was studied for fundamental anti-symmetric (A0) and symmetric (S0) Lamb waves, and the shear-horizontal (SH0) wave of zero-order. Using the finite element method, appropriate configuration of the interdigital transducer with arc-like electrodes was modeled accounting for the anisotropy of the slowness curves and dispersion of the modes in the plate. Profiles of the focalized acoustic beams generated by the proposed transducer were theoretically analyzed. Based on the result of the analysis, relevant delay lines were fabricated and transfer functions (insertion loss) of the line were measured for SH0 wave in YX-lithium niobate plate. Using an electron scanning microscope, distribution of the electric fields of the same wave were visualized. The results of this study may be useful for hybrid devices and sensors combining nano and acoustoelectronic principles.

Bioelectrochemical Properties of Enzyme-Containing Multilayer Polyelectrolyte Microcapsules Modified with Multiwalled Carbon Nanotubes.

This work investigated changes in the biochemical parameters of multilayer membrane structures, emerging at their modification with multiwalled carbon nanotubes (MWCNTs). The structures were represented by polyelectrolyte microcapsules (PMCs) containing glucose oxidase (GOx). PMCs were made using sodium polystyrene sulfonate (polyanion) and poly(allylamine hydrochloride) (polycation). Three compositions were considered: with MWCNTs incorporated between polyelectrolyte layers; with MWCNTs inserted into the hollow of the microcapsule; and with MWCNTs incorporated simultaneously into the hollow and between polyelectrolyte layers. The impedance spectra showed modifications using MWCNTs to cause a significant decrease in the PMC active resistance from 2560 to 25 kOhm. The cyclic current-voltage curves featured a current rise at modifications of multilayer MWCNT structures. A PMC-based composition was the basis of a receptor element of an amperometric biosensor. The sensitivity of glucose detection by the biosensor was 0.30 and 0.05 µA/mM for PMCs/MWCNTs/GOx and PMCs/GOx compositions, respectively. The biosensor was insensitive to the presence of ethanol or citric acid in the sample. Polyelectrolyte microcapsules based on a multilayer membrane incorporating the enzyme and MWCNTs can be efficient in developing biosensors and microbial fuel cells.

Super high sensitive plate acoustic wave humidity sensor based on graphene oxide film.

The changes of density and elastic modules due to water vapor adsorption are measured for graphene oxide film at room temperature. Dominant mechanism for acoustic wave humidity sensing by the film is shown to be related with variation of its electric conductivity. Basing on the data, super high sensitive humidity sensor employing high-order Lamb wave with large coupling constant, standard lithium niobate plate, and graphene oxide sorbent film is developed. The minimal detectable level of the sensor is as low 0.03% RH, response times are 60/120s, and reproducibility is ±2.5%. The sensor is completely selective towards H2, CO, CH4, NO, O2.