Topological-defect-induced surface charge heterogeneities in nematic electrolytes

M. Ravnik and J. C. Everts

Phys. Rev. Lett. 2020, 125, 037801

We show that topological defects in an ion-doped nematic liquid crystal can be used to manipulate the surface charge distribution on chemically homogeneous, charge-regulating external surfaces, using a minimal theoretical model. In particular, the location and type of the defect encodes the precise distribution of surface charges and the effect is enhanced when the liquid crystal is flexoelectric. We demonstrate the principle for patterned surfaces and charged colloidal spheres. More generally, our results indicate an interesting approach to control surface charges on external surfaces without changing the surface chemistry.

Screened Coulomb interactions of general macroions with nonzero particle volume

J. C. Everts

Phys. Rev. Research 2020, 2, 033144

A semianalytical approach is developed to calculate the effective pair potential of rigid arbitrarily shaped macroions with a nonvanishing particle volume, valid within linear screening theory and the mean-field approximation. The essential ingredient for this framework is a mapping of the particle to a singular charge distribution with adjustable effective charge and shape parameters determined by the particle surface electrostatic potential. For charged spheres, this method reproduces the well-known Derjaguin-Landau-Verwey-Overbeek (DLVO) potential. Further exemplary benchmarks of the method for more complicated cases, like tori, triaxial ellipsoids, and additive torus-sphere mixtures, leads to accurate closed-form integral expressions for all particle separations and orientations. The findings are relevant for determining the phase behavior of macroions with experiments and simulations for various particle shapes.

Fabrication of nanocages on nickel using femtosecond laser ablation and trace level detection of malachite green and Nile blue dyes using surface enhanced Raman spectroscopic technique

B. Chandu, M. Sree Satya Bharati, P. Albrycht, S.V. Rao

Optics and Laser Technology, 2020, 131, 106454

Over the last decade several research groups have accomplished the fabrication of 2D periodic and 3D nanocage like structures on different materials using diverse lithographic approaches. Herein, we present the detailed studies on the fabrication of femtosecond (fs) laser‐induced periodic/ripple‐like surface structures on nickel (Ni) substrate in distilled water whereas 3D-like (nanocages) features on Ni substrates in acetone by tailoring the laser processing parameters (pulse energy). The morphological studies of simultaneously obtained Ni nanoparticles (NPs)/nanostructures (NSs) in distilled water/acetone were meticulously studied using transmission electron microscope (TEM) and field emission scanning electron microscope (FESEM). The fabricated Ni periodic/3D-like structures were gold (Au) plated using thermal evaporation technique and subsequently utilized as surface enhanced Raman scattering (SERS) active sensors for detecting the traces of various analyte molecules such as malachite green (MG) and Nile blue (NB). The grooved Ni-Au substrates allowed us to detect extremely low concentrations of MG (500 pM) and NB (5 nM) and, significantly, utilizing a simple, portable Raman spectrometer. Moreover, the substrates have demonstrated superior reproducibility as well as multi-utility nature with a relative standard deviation (RSD) of <17%. Additionally, Au- coated Ni grooved SERS substrates have demonstrated superior sensitivity and reproducibility in comparison to commercially available Ag-based SERS sensors (SERSitive, Poland). The proposed method of fabricating ripple and nanocages of Ni SERS platforms are highly viable to overcome the cost and one-time usage of substrates for on-site detection of several analyte molecules using a portable/hand-held Raman spectrometer.

Nanoparticle enhanced laser induced breakdown spectroscopy of liquid samples by using modified surface-enhanced Raman scattering substrates

D. J. Palásti, P. Albrycht, P. Janovszky, Z. Geretovszky, G. Galbács

Spectrochimica Acta - Part B Atomic Spectroscopy, 2020, 166, 105793

An assessment of the feasibility of using modified surface enhanced Raman scattering substrates (Ag nanoparticles on indium‑tin-oxide glass) for quantitative nanoparticle-enhanced laser induced breakdown spectroscopy (NELIBS) was carried out. Substrates were prepared with different surface coverage from various nanoparticle sizes, and their laser ablation behaviour was tested in detail. It was found that use of those combinations are most beneficial in terms of the signal enhancement factor, which provide the shortest interparticle distances. With the application of 266 nm laser wavelength, long (ms-range) gate width, and optimized laser pulse energy, the best NELIBS signal enhancement was found to be about a factor of three. By using liquid sample deposition by spraying, which was found to provide an even distribution of liquid samples on the substrate surface, successful calibration for Mn, Zn and Cr was performed. The NELIBS signal repeatability from five repeated measurements was found to be comparable to that of LIBS (5–10% RSD). These observations indicate that the NELIBS signal enhancement approach can be used in quantitative analytical applications for liquid samples, if i) the substrate fabrication procedure has good repeatability, ii) surface coverage and nanoparticle size is tightly controlled, iii) a homogenous liquid sample deposition is achieved.

Transport of nanoprobes in multicellular spheroids

M. Pilz, K. Kwapiszewska, T. Kalwarczyk, G. Bubak, D. Nowis and R. Hołyst

Nanoscale, 2020, 12, 19880-19887

The efficient delivery of drugs to cells depends on their diffusion through the extracellular matrix (ECM) of tissues. Here we present a study on the diffusion of nanoprobes of radius from 1 nm to over 100 nm in the ECM of spheroids of three cell types (HeLa, MCF-7 and fibroblasts). We quantified the nanoparticle transport in the spheroids’ proliferating zone. We determined the size-dependent viscosity of the ECM. We revealed that nanoobjects up to 10 nm in radius exhibited unobstructed diffusion in the ECM, regardless of the spheroid type. The presented length-scale dependent viscosity profiles for spheroids pave the way for advanced modelling of drug administration through tissues.

Nanoscale Viscosity of Cytoplasm Is Conserved in Human Cell Lines

K. Kwapiszewska , K. Szczepański, T. Kalwarczyk, B. Michalska, P. Patalas-Krawczyk, J. Szymański, T. Andryszewski, M. Iwan, J. Duszyński and R. Hołyst

J. Phys. Chem. Lett. 2020, 11, 16, 6914–6920

Metabolic reactions in living cells are limited by diffusion of reagents in the cytoplasm. Any attempt to quantify the kinetics of biochemical reactions in the cytosol should be preceded by careful measurements of the physical properties of the cellular interior. The cytoplasm is a complex, crowded fluid characterized by effective viscosity dependent on its structure at a nanoscopic length scale. In this work, we present and validate the model describing the cytoplasmic nanoviscosity, based on measurements in seven human cell lines, for nanoprobes ranging in diameters from 1 to 150 nm. Irrespective of cell line origin (epithelial–mesenchymal, cancerous–noncancerous, male–female, young–adult), we obtained a similar dependence of the viscosity on the size of the nanoprobes, with characteristic length-scales of 20 ± 11 nm (hydrodynamic radii of major crowders in the cytoplasm) and 4.6 ± 0.7 nm (radii of intercrowder gaps). Moreover, we revealed that the cytoplasm behaves as a liquid for length scales smaller than 100 nm and as a physical gel for larger length scales.

Recent Progress in the Detection of Bacteria Using Bacteriophages: A Review

J. Paczesny, Ł. Richter and R. Hołyst

Viruses, 2020, 12(8), 845

Bacteria will likely become our most significant enemies of the 21st century, as we are approaching a post-antibiotic era. Bacteriophages, viruses that infect bacteria, allow us to fight infections caused by drug-resistant bacteria and create specific, cheap, and stable sensors for bacteria detection. Here, we summarize the recent developments in the field of phage-based methods for bacteria detection. We focus on works published after mid-2017. We underline the need for further advancements, especially related to lowering the detection (below 1 CFU/mL; CFU stands for colony forming units) and shortening the time of analysis (below one hour). From the application point of view, portable, cheap, and fast devices are needed, even at the expense of sensitivity.

Photoluminescent, Ferromagnetic, and Hydrophobic Sponges for Oil–Water Separation

K. Yin, D. Lu, B. Sun, T. Kalwarczyk, R. Hołyst, J. Hao, H. Li and J.Hao

ACS Omega, 2020, 5, 25, 15077–15082

To find a facile way to produce a hydrophobic sponge that can effectively absorb oils is urgent to resolve the environmental pollution and ecological disaster caused by oil spillage. Here, alkylated carbon dots (C dots) were prepared from pyrolysis of a mixture of dodecylamine and citric acid followed by purification through silica gel column chromatography. Polyurethane sponge was modified by alkylated C dots by a simple dip-coating method, which endows the photoluminescent and hydrophobic sponge with good absorption capacities for various oils and nonpolar organic solvents with high recyclability. The water contact angle of the modified sponge can reach 138.8°. Interestingly, the sponge enables visual absorption under UV irradiation in the dark, which has not been achieved by other carbon-based adsorbents. The sponge was further made ferromagnetic by introducing alkylated Fe3O4 nanoparticles into its structure, which allowed controllable oil–water separation.

Single-molecule brightness analysis for the determination of anticancer drug interactions with DNA

Y. Zhou, K. Bielec, P. Pasitsuparoad and R. Hołyst

Analyst, 2020, 145, 6600-6606

Anthracyclines are one of the most studied anticancer drugs approved for medical treatment. The equilibrium constant (K) of the reaction between these drugs with DNA in both in vitro and in vivo experiments lacks consensus. The K values vary from 104 up to 108 M−1, which suggest a 1000-fold error in determining the effective concentration needed to form the drug–DNA complex. Until 2014, only one study by García [J. Phys. Chem. B, 2014, 118, 1288–1295] showed that the binding of anthracycline representative doxorubicin occurs in two reactions. We support this result by brightness analysis at a single molecular level for the four most common anthracyclines: doxorubicin, daunorubicin, epirubicin, and idarubicin.

Ions in an AC Electric Field: Strong Long-Range Repulsion between Oppositely Charged Surfaces

Ł. Richter, P. J. Żuk, P. Szymczak, J. Paczesny, K. M. Bąk, T. Szymborski, P. Garstecki, H. A. Stone, R. Hołyst and C. Drummond

Phys. Rev. Lett., 2020, 125, 056001

Two oppositely charged surfaces separated by a dielectric medium attract each other. In contrast we observe a strong repulsion between two plates of a capacitor that is filled with an aqueous electrolyte upon application of an alternating potential difference between the plates. This long-range force increases with the ratio of diffusion coefficients of the ions in the medium and reaches a steady state after a few minutes, which is much larger than the millisecond timescale of diffusion across the narrow gap. The repulsive force, an order of magnitude stronger than the electrostatic attraction observed in the same setup in air, results from the increase in osmotic pressure as a consequence of the field-induced excess of cations and anions due to lateral transport from adjacent reservoirs.

Scaling equation for viscosity of polydimethylsiloxane in ethyl acetate: From dilute to concentrated solutions

A. Agasty, A. Wisniewska, T. Kalwarczyk, K. Koynov and R. Holyst

Polymer Volume, 2020, 203, 122779

Rheology of polymer solutions suffers from lack of universal model of viscosity applicable across wide range of concentrations. Here we build such a model on the basis of measured viscosity of polydimethylosiloxane (PDMS) in ethyl acetate in a wide range of polymer concentrations: from dilute up to highly concentrated solutions. The relationship between viscosity and different polymer parameters in solution such as coil size, correlation length ξ, monomer–solvent and monomer–monomer interaction parameter were established experimentally as a function of concentrations [from 0.001g∕cm3 to 8.000g∕cm3], temperature [in a range 283–303K] and molecular masses [9–139kg∕mol]. Entanglement onset at the crossover from dilute to semi-dilute solution as well as the solvent–monomer contact reduction at the crossover from semi-dilute to concentrated regime are captured by the model. This model is in accordance with the Eyring rate theory for activated processes.

TMAO, a seafood-derived molecule, produces diuresis and reduces mortality in heart failure rats

M. Gawrys-Kopczynska, M. Konop, K. Maksymiuk, K. Kraszewska, L. Derzsi, K. Sozanski, R. Holyst, M. Pilz and E. Samborowska

ELIFE 2020, 9

Trimethylamine-oxide (TMAO) is present in seafood which is considered to be beneficial for health. Deep-water animals accumulate TMAO to protect proteins, such as lactate dehydrogenase (LDH), against hydrostatic pressure stress (HPS). We hypothesized that TMAO exerts beneficial effects on the circulatory system and protects cardiac LDH exposed to HPS produced by the contracting heart. Male, Sprague-Dawley and Spontaneously-Hypertensive-Heart-Failure (SHHF) rats were treated orally with either water (control) or TMAO. In vitro, LDH with or without TMAO was exposed to HPS and was evaluated using fluorescence correlation spectroscopy. TMAO-treated rats showed higher diuresis and natriuresis, lower arterial pressure and plasma NT-proBNP. Survival in SHHF-control was 66% vs 100% in SHHF-TMAO. In vitro, exposure of LDH to HPS with or without TMAO did not affect protein structure. In conclusion, TMAO reduced mortality in SHHF, which was associated with diuretic, natriuretic and hypotensive effects. HPS and TMAO did not affect LDH protein structure.

Joint effect of surfactants and cephalexin on the formation of Escherichia coli filament

S. Hou, Z. Jia, K. Kryszczuk, D. Chen, L. Wang, R. Hołyst and X. Feng

Ecotoxicology and Environmental Safety, 2020, 199, 110750

Both antibiotics and surfactants commonly exist in natural environment and have generated great concerns due to their biological influence on the ecosystem. A major concern lies in the capacity of antibiotics to induce bacterial filaments formation, which has potential health risks. However, their joint effect is not clear so far. Here, we studied the joint effect of cephalexin (Cex), a typical antibiotic, and differently charged surfactants on the formation of E. coli filaments. Three kinds of surfactants characterized by different charges were used: cationic surfactant (CTAB), anionic surfactant (SDS) and nonionic surfactant (Tween). Data showed that Cex alone caused the formation of E. coli filaments, elongating their maximum profile from ca. 2 μm (a single E. coli cell) to tens of micrometers (an E. coli filament). A joint use of surfactants with Cex could produce even longer E. coli filaments, elongating the maximum length of the bacteria to larger than 100 μm. The capacity order of different surfactants under their optimum concentrations to produce elongated E. coli filaments was Tween > SDS > CTAB. The E. coli filaments were characterized with a normal DNA distribution and a good cell membrane integrity. We measured the stiffness of bacterial cell wall by atomic force microscopy and correlated the elongation capacity of the E. coli filaments to the stiffness of cell wall. Zeta potential measurement indicated that inserting into or being bound to the cell surface in a large quantity was tested not to be the major way that surfactants interacted with bacteria

Cell extract gels as an example of active matter

A. Wisniewska, T. Kalwarczyk, J. Szymanski, K. Kryszczuk, K. Matula and R. Holyst

Rheologica Acta 2020, 59, 575–582

Cell lysates (cellular extracts) constitute a perfect imitation of the intracellular environment that can provide insight into cellular response to external stimuli. However, most of the presented results are performed for diluted lysates that do not reflect the actual properties of a crowded cellular environment. Here, we report for the first time the measurement of the viscosity and shear storage modulus of highly concentrated Escherichia coli (E. coli) lysates with and without adenosine triphosphate (ATP). By cleavage of DNA content, we showed the value of shear storage modulus GG′ decreases by 19–31% in comparison to control samples. The addition of molecules that provides energy (ATP) allowed to rebuild the structure of the lysate by reversibly increasing viscous properties over elastic ones. When the energy delivered in the form of ATP is consumed by the unliving bacterial lysate, the system returns to its initial state.

Self-Stabilized Giant Aggregates in Water from Room-Temperature Ionic Liquids with an Asymmetric Polar–Apolar–Polar Architecture

G. Zhang, H. Zhu, J. Chen, M. Chen, T. Kalwarczyk, R. Hołyst, H. Li and J. Hao

J. Phys. Chem. B 2020, 124, 22, 4651–4660

We report the assembly of four imidazolium bromides, each of which bears a naphthyl on one side of the imidazolium cation and a branched alkyl chain on the other. This design creates a new type of amphiphilic ionic liquid with an apolar–polar–apolar structure and a low melting point (mp, <−20 °C), which has not been achieved by reported counterparts bearing linear alkyl chains. In solvent-free states, microphase segregation occurs where polar and apolar domains arrange bicontinuously as proved by molecular dynamics (MD) simulations. When dispersed in water, self-stabilized giant aggregates formed with ultrahigh colloidal stability (up to years). MD simulations provide clues of discrete bicontinuous phases within the giant aggregates. These newly discovered self-assemblies provide a heterogeneous reservoir that can accommodate guest molecules including the highly apolar fullerene C60, paving the way for a wide range of potential applications.

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