F.D. Ovcharenko Institute of Biocolloidal Chemistry

Electrochemical enzyme-based biosensors are one of the largest and commercially successful groups of biosensors. Integration of nanomaterials in the biosensors results in significant improvement of biosensor sensitivity, limit of detection, stability, response rate and other analytical characteristics. Thus, new functional nanomaterials are key components of numerous biosensors. However, due to the great variety of available nanomaterials, they should be carefully selected according to the desired effects. The present review covers the recent applications of various types of nanomaterials in electrochemical enzyme-based biosensors for the detection of small biomolecules, environmental pollutants, food contaminants, and clinical biomarkers. Benefits and limitations of using nanomaterials for analytical purposes are discussed. Furthermore, we highlight specific properties of different nanomaterials, which are relevant to electrochemical biosensors. The review is structured according to the types of nanomaterials. We describe the application of inorganic nanomaterials, such as gold nanoparticles (AuNPs), platinum nanoparticles (PtNPs), silver nanoparticles (AgNPs), and palladium nanoparticles (PdNPs), zeolites, inorganic quantum dots, and organic nanomaterials, such as single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), carbon and graphene quantum dots, graphene, fullerenes, and calixarenes. Usage of composite nanomaterials is also presented.

Extraction is an important operation in food engineering, enabling the recovery of valuable soluble components from raw materials. With increasing energy costs and environmental concerns, industry specialists are looking for improved techniques requiring less solvents and energy consumption. Enhancing Extraction Processes in the Food Industry is a

Fluorosurfactants are the most effective compounds to lower the surface tension of aqueous solutions, but their wetting properties as related to low energy hydrocarbon solids are inferior to hydrocarbon trisiloxane surfactants, although the latter demonstrate higher surface tension in aqueous solutions. To explain this inconsistency available data on the adsorption of fluorosurfactants on liquid/vapour, solid/liquid and solid/vapour interfaces are discussed in comparison to those of hydrocarbon surfactants. The low free energy of adsorption of fluorosurfactants on hydrocarbon solid/water interface should be of a substantial importance for their wetting properties.

The objective of this study was to investigate the effects of pulsed electric field (PEF) and high-voltage electrical discharges (HVED) application on the efficiency of aqueous extraction of total soluble matter and polyphenols from grape skins ( Vitis vinifera L.) at different temperatures within 20-60 degrees C. The highest level of polyphenol concentration C was reached after about 60 min of extraction for HVED treatment: C(HVED) = 21.4 +/- 0.8 micromol of gallic acid equivalent (GAE)/g of dry matter (DM). Almost the same level of C was reached after 180 min of extraction for the PEF-treated skins. These levels exceeded the value C = 19.1 +/- 0.5 micromol of GAE/g of DM for the untreated samples. The difference between degrees Brix values for HVED-treated and untreated systems decreased with temperature increase (from 40 to 60 degrees C), but a large difference in the total amount of polyphenols was observed for HVED-treated and untreated systems. The activation energies were W(u) = 31.3 +/- 3.7 kJ/mol and W(PEF) = 28.9 +/- 5.5 kJ/mol for untreated and PEF-treated systems, respectively.

The recent progress in theoretical and experimental studies of simultaneous spreading and evaporation of liquid droplets on solid substrates is discussed for pure liquids including nanodroplets, nanosuspensions of inorganic particles (nanofluids) and surfactant solutions. Evaporation of both complete wetting and partial wetting liquids into a nonsaturated vapour atmosphere are considered. However, the main attention is paid to the case of partial wetting when the hysteresis of static contact angle takes place. In the case of complete wetting the spreading/evaporation process proceeds in two stages. A theory was suggested for this case and a good agreement with available experimental data was achieved. In the case of partial wetting the spreading/evaporation of a sessile droplet of pure liquid goes through four subsequent stages: (i) the initial stage, spreading, is relatively short (1-2 min) and therefore evaporation can be neglected during this stage; during the initial stage the contact angle reaches the value of advancing contact angle and the radius of the droplet base reaches its maximum value, (ii) the first stage of evaporation is characterised by the constant value of the radius of the droplet base; the value of the contact angle during the first stage decreases from static advancing to static receding contact angle; (iii) during the second stage of evaporation the contact angle remains constant and equal to its receding value, while the radius of the droplet base decreases; and (iv) at the third stage of evaporation both the contact angle and the radius of the droplet base decrease until the drop completely disappears. It has been shown theoretically and confirmed experimentally that during the first and second stages of evaporation the volume of droplet to power 2/3 decreases linearly with time. The universal dependence of the contact angle during the first stage and of the radius of the droplet base during the second stage on the reduced time has been derived theoretically and confirmed experimentally. The theory developed for pure liquids is applicable also to nanofluids, where a good agreement with the available experimental data has been found. However, in the case of evaporation of surfactant solutions the process deviates from the theoretical predictions for pure liquids at concentration below critical wetting concentration and is in agreement with the theoretical predictions at concentrations above it.

The effect of the pulsed electric field (PEF) pretreatment on convective drying of red beetroot tissue was investigated at the drying temperatures Td in the interval 30–100°C. The degree of material damage Z under the PEF and thermal treatment was studied. Dependence of the electrical characteristic damage time τE on the electric field strength E and the thermal characteristic damage time τT on temperature Td is discussed. The drying rate is shown to be maximal for highly disintegrated tissues; PEF pretreatment allowed reduction of the drying temperature by 20–25°C. PEF pretreatment results in greater degree of tissue shrinkage and hence increase in rehydration time; however, the textural properties of rehydrated samples with and without PEF treatment are seen to be similar. The benefit of PEF pretreatment for drying at moderate temperatures with preservation of colorants is also demonstrated.

INTRODUCTION: Nanoscale gold particles (AuNPs) have wide perspectives for biomedical applications because of their unique biological properties, as antioxidative activity and potentials for drug delivery. AIMS AND OBJECTIVES: The aim was to test effects of AuNPs using suggested heart failure rat model to compare with proved medication Simdax, to test gold nanoparticle for drug delivery, and to test sonoporation effect to increase nanoparticles delivery into myocardial cells. MATERIAL AND METHODS: We performed biosafety and biocompatibility tests for AuNPs and conjugate with Simdax. For in vivo tests, we included Wistar rats weighing 180-200 g (n = 54), received doxorubicin in cumulative dose of 12.0 mg/kg to model advance heart failure, registered by ultrasonography. We formed six groups: the first three groups of animals received, respectively, 0.06 ml Simdax, AuNPs, and conjugate (AuNPs-Simdax), intrapleurally, and the second three received them intravenously. The seventh group was control (saline). We performed dynamic assessment of heart failure regression in vivo measuring hydrothorax. Sonoporation of gold nanoparticles to cardiomyocytes was tested. RESULTS: We designed and constructed colloidal, spherical gold nanoparticles, AuNPs-Simdax conjugate, both founded biosafety (in cytotoxicity, genotoxicity, and immunoreactivity). In all animals of the six groups after the third day post-medication injection, no ascites and liver enlargement were registered (P < 0.001 vs controls). Conjugate injection showed significantly higher hydrothorax reduction than Simdax injection only (P < 0.01); gold nanoparticle injection showed significantly higher results than Simdax injection (P < 0.05). AuNPs and conjugate showed no significant difference for rat recovery. Difference in rat life continuity was significant between Simdax vs AuNPs (P < 0.05) and Simdax vs conjugate (P < 0.05). Sonoporation enhances AuNP transfer into the cell and mitochondria that were highly localized, superior to controls (P < 0.01 for both). CONCLUSIONS: Gold nanoparticles of 30 nm and its AuNPs-Simdax conjugate gave positive results in biosafety and biocompatibility in vitro and in vivo. AuNPs-Simdax and AuNPs have similar significant cardioprotective effects in rats with doxorubicin-induced heart failure, higher than that of Simdax. Intrapleural (local) delivery is preferred over intravenous (systemic) delivery according to all tested parameters. Sonoporation is able to enhance gold nanoparticle delivery to myocardial cells in vivo.

Electroacoustic characterization of concentrated dispersed systems requires an adequate theory of dynamic electrophoretic mobility which takes into account particle−particle interaction. The concept of the “cell model” provides convenient and comprehensive means for creating this theory. There are two different versions of the electrokinetic cell model. The first one was introduced by Levine and Neale, the second one by Shilov and Zharkikh. The Levine−Neale cell model gives a large discrepancy with experimental data as it was shown by O'Brien and Hunter. We suggest several reasons indicating that the Shilov−Zharkikh cell model is more adequate than the Levine−Neale one. First of all, it gives transition to the Smolichowski law for electroosmosis which is valid for concentrated systems. The Shilov−Zharkikh cell model yields a symmetrical Onsager relationship between kinetic coefficients as well as the Maxwell−Vagner law for electric conductivity. In addition, the Shilov−Zharkikh cell model predicts much stronger volume fraction dependence of dynamic electrophoretic mobility. Such strong dependence corresponds to O'Brien−Hunter experimental data which could not be explained by the Levine−Neale cell model. We developed two versions of the theory using different constrains. The first version is valid only at low frequency, but it takes into account surface conductivity. The second version neglects surface conductivity. At the same time this second version takes into account inertia effects which makes it valid at high frequencies. We do not address a question of the appropriate frame of references for the dynamic electrophoretic mobility. All calculations are performed in the frame of references which is associated with the liquid.

The simultaneous spreading and evaporation of droplets of aqueous trisiloxane (superspreader) solutions onto a hydrophobic substrate has been studied both experimentally, using a video-microscopy technique, and theoretically. The experiments have been carried out over a wide range of surfactant concentration, temperature, and relative humidity. Similar to pure liquids, four different stages have been observed: the initial one corresponds to spreading until the contact angle, θ, reaches the value of the static advancing contact angle, θad. Duration of this stage is rather short, and the evaporation during this stage can be neglected. The evaporation is essential during the next three stages. The next stage after the spreading, which is referred to herein as the first stage, takes place at constant perimeter and ends when θ reaches the static receding contact angle, θr. During the next, second stage, the perimeter decreases at constant contact angle θ = θr for surfactant concentration above the critical wetting concentration (CWC). The static receding contact angle decreases during the second stage for concentrations below CWC because the concentration increases due to the evaporation. During the final stage both the perimeter and the contact angle decrease. In what follows, we consider only the longest stages I and II. The developed theory predicts universal curves for the contact angle dependency on time during the first stage, and for the droplet perimeter on time during the second stage. A very good agreement between theory and experimental data has been found for the first stage of evaporation, and for the second stage for concentrations above CWC; however, some deviations were found for concentrations below CWC.

The forces acting in colloidal suspensions and affecting their stability and aggregation kinetics are considered. The approximations used for these forces in numerical simulations and the importance of the balanced account for both colloidal forces and hydrodynamic interactions are discussed. As an example the results of direct numerical simulations of kinetics of aggregation either with account for hydrodynamic interaction between particles or without it are compared by varying the parameters of the interaction potential between particles and fraction of solid. Simulations are based on the Langevin equations with pairwise interaction between particles and take into account Brownian, hydrodynamic and colloidal forces. It is confirmed that the neglecting of hydrodynamic interaction results in an accelerated growth of aggregates. The results of numerical simulations of aggregation kinetics are compared with well known analytical solutions.

There has been a substantial increase in the number of publications in the field of wetting and spreading since 2010. This increase in the rate of publications can be attributed to the broader application of wetting phenomena in new areas. It is impossible to review such a huge number of publications; that is, some topics in the field of wetting and spreading are selected to be discussed below. These topics are as follows: (i) Contact angle hysteresis on smooth homogeneous solid surfaces via disjoining/conjoining pressure. It is shown that the hysteresis contact angles can be calculated via disjoining/conjoining pressure. The theory indicates that the equilibrium contact angle is closer to a static receding contact angle than to a static advancing contact angle. (ii) The wetting of deformable substrates, which is caused by surface forces action in the vicinity of the apparent three-phase contact line, leading to a deformation on the substrate. (iii) The kinetics of wetting and spreading of non-Newtonian liquid (blood) over porous substrates. We showed that in spite of the enormous complexity of blood, the spreading over porous substrate can be described using a relatively simple model: a power low-shear-thinning non-Newtonian liquid. (iv) The kinetics of spreading of surfactant solutions. In this part, new results related to various surfactant solution mixtures (synergy and crystallization) are discussed, which shows some possible direction for the future revealing of superspreading phenomena. (v) The kinetics of spreading of surfactant solutions over hair. Fundamental problems to be solved are identified.

Generation of cohesive motion was observed during the dissolution of mm-sized drops of dicholoromethane into aqueous surfactant solutions. This system shows pulsating drops, multi-armed rotors, and polygonal shapes. The sharp tips of these patterns eject much smaller droplets to form expanding halos or swirling chains. The daughter droplets also undergo cascades of secondary and higher-order splitting events. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

An interpretation is given for the cofield rotation observed in low-frequency electrorotation experiments using polystyrene particles in electrolyte solution. It is shown that the main cause of the particle rotation is the electroosmotic velocity of the electrolyte inside the thin double layer, rather than the torque exerted by the rotating electric field on the out of phase part of the induced dipole moment.

Electrical conductivity, optical transmittance and microstructure of multiwalled carbon nanotubes (MWCNTs) dispersed in nematic liquid crystal 4-ethoxybenzylidene-4'-n-butylaniline (EBBA) were studied in the temperature range between 287 and 363 K. The concentration C of MWCNTs was varied within 0.01–1% wt. The percolation threshold with a noticeable increase in electrical conductivity (by many orders of magnitude) was observed in the vicinity of C ≈ 0.1% wt. The heating–cooling hysteretic behaviour of electrical conductivity and optical transmittance thermal pre-history effects were studied. These effects reflected strong agglomeration and rearrangement of nanotubes during the thermal incubation. The estimates show that transient behaviour during the thermal incubation can be caused by Brownian motion of MWCNTs. The solidification of MWCNT + EBBA composite in the nematic range extended by conditions of supercooling was also studied as a function of temperature using electrical conductivity measurements. The solidification lag-time dependence on supercooling temperature followed the classical heterogeneous nucleation law, with MWCNTs serving as centres of EBBA solidification.

Long-time auto-oscillation of the surface tension can evolve when in an aqueous system a diethyl phthalate droplet is placed under the free water surface. The experimental conditions for development of surface tension auto-oscillations are described. Based on a theoretical analysis the mechanism of these auto-oscillations is proposed. The mechanism of the auto-oscillations results from a switching between diffusion and convection transfer of diethyl phthalate in the solution. A periodic Marangoni flow on the water surface resulting from a surface layer instability is discussed. The solubility of the amphiphile in the water and its surface activity are the main characteristics that determine the system behavior.

The electro-optical response and the microstructure of multiwalled carbon nanotubes dispersed in nematic liquid crystals with negative dielectric anisotropy are investigated. In contrast to undoped liquid crystals, the liquid crystal dispersions of carbon nanotubes are characterized by the irreversible electro-optic response or the so-called electro-optical memory effect. This effect is that the light transmittance through the sandwiched layer of the dispersion placed between two crossed polarizers considerably increases after the electric field application cycle. The state of memory persisted over months of our observation. The memory is caused by the incomplete relaxation of liquid crystal molecules from the random planar to the initial homeotropic state after the field is off. It is pointed out that the stabilization of the planar state is due to the network of small nanotube aggregates formed in the liquid crystal disturbed by electro-hydrodynamic flows. It is revealed that the efficiency of electro-optical memory depends on the network morphology and the efficiency of electro-hydrodynamic flows in a liquid crystal.

The percolation behaviour of conductive composites containing particles of different sizes was analysed. A composite was simulated as the media containing small conductive particles distributed in the channels between large insulative particles, where each large particle is covered by n monolayers of the filler particles. The simulations were done for the cases of two-dimensional (2D) and three-dimensional (3D) lattices. It was shown that the percolation filler concentration x* versus the particle size ratio λ = R/r and the number of monolayers n may be approximated as , where d is the space dimensionality; is the site random percolation threshold; neff is the effective number of monolayers, which decreases with increase in n and neff → n in the limit of n → ∞. The scaling behaviour of the percolation threshold inside the layers confined by the large particles was analysed. The data obtained at different values of λ and n gave the same correlation length exponent values as for the classical random percolation both for 2D and 3D cases. Analysis of the electrical conductivity behaviour near the percolation threshold in 2D systems showed the existence of the obvious differences at different values of λ and n, though the conductivity exponents s and t retained their universal values typical for the random percolation. The accuracy of the developed theoretical approach was experimentally tested for the polyvinyl chloride–copper (PVC–Cu) and polycarbonate–copper (PC–Cu) composites.

Abstract During multivalent ions insertion processes, intense electrostatic interaction between charge carriers and host makes the high‐performance reversible Al 3+ storage remains an elusive target. On account of the strong electrostatic repulsion and poor robustness, Prussian Blue analogues (PBAs) suffer severely from the inevitable and large strain and phase change during reversible Al 3+ insertion. Herein, we demonstrate an entropy‐driven strategy to realize ultralong life aqueous Al‐ion batteries (AIBs) based on medium entropy PBAs (ME‐PBAs) host. By multiple redox active centers introduction, the intrinsic poor conductivity can be enhanced simultaneously, resulting in outstanding capabilities of electrochemical Al 3+ storage. Meanwhile, the co‐occupation at metal sites in PBA frameworks can also increase the M−N bond intensity, which is beneficial for constraining the phase change during consecutive Al 3+ reversible insertion, to realize an extended lifespan over 10,000 cycles. Based on the calculation at different operation states, the fluctuation of ME‐PBA lattice parameters is only 1.2 %. Assembled with MoO 3 anodes, the full cells can also deliver outstanding electrochemical properties. The findings highlight that, the entropy regulation strategy could uncover the isochronous constraint on both strain and phase transition for long‐term reversible Al 3+ storage, providing a promising design for advanced electrode materials for aqueous multivalent ions batteries.

Over the past years, both food researchers and food industry have shown an increased interest in finding techniques that can estimate modifications in quality, nutritional, and thermophysical properties of food products during processing and/or storage. For instance, differential scanning calorimetry (DSC) has attracted the interest of scientific community because only a small amount of sample is needed for analysis. Moreover, it does not require any specific sample preparation, and is a repeatable and reliable method. In addition, DSC methodology needs a short time for experiments compared with other techniques used for the same purpose. At this stage of investigation, there is a need to evaluate the commonly accepted and new emerging DSC applications to establish the optimum conditions of emerging processing. This paper reviews the current and new insights of DSC technique for the estimation of quality, nutritional, and thermophysical properties of food products during conventional and emerging processing and/or subsequent storage. The estimation of different properties in several food matrices after processing and/or storage is also discussed.

Jamming phenomena on a square lattice are investigated for two different models of anisotropic random sequential adsorption (RSA) of linear $k$-mers (particles occupying $k$ adjacent adsorption sites along a line). The length of a $k$-mer varies from 2 to 256. The effect of $k$-mer alignment on the jamming threshold is examined. For completely ordered systems where all the $k$-mers are aligned along one direction (e.g., vertical), the obtained simulation data are very close to the known analytical results for one-dimensional systems. In particular, the jamming threshold tends to the R\'enyi's parking constant for large $k$. In the other extreme case, when $k$-mers are fully disordered, our results correspond to the published results for short $k$-mers. It was observed that for partially oriented systems the jamming configurations consist of the blocks of vertically and horizontally oriented $k$-mers ($v$ and $h$ blocks, respectively) and large voids between them. The relative areas of different blocks and voids depend on the order parameter $s$, $k$-mer length, and type of the model. For small $k$-mers ($k\ensuremath{\leqslant}4$), denser configurations are observed in disordered systems as compared to those of completely ordered systems. However, longer $k$-mers exhibit the opposite behavior.