Alternating strings and clusters in suspensions of charged colloids

J. C. Everts, M. N. van der Linden, A. van Blaaderen and R. van Roij

Soft Matter, 2016, 12, 6610-6620

We report the formation of alternating strings and clusters in a binary suspension of repulsive charged colloids with double layers larger than the particle size. Within a binary cell model we include many-body and charge-regulation effects under the assumption of a constant surface potential, and consider their repercussions on the two-particle interaction potential. We find that the formation of induced dipoles close to a charge-reversed state may explain the formation of these structures. Finally, we will touch upon the formation of dumbbells and small clusters in a one-component system, where the effective electrostatic interaction is always repulsive.

Tuning Colloid-Interface Interactions by Salt Partitioning

J. C. Everts, S. Samin, and R. van Roij

Phys. Rev. Lett. 2016, 117, 098002

We show that the interaction of an oil-dispersed colloidal particle with an oil-water interface is highly tunable from attractive to repulsive, either by varying the sign of the colloidal charge via charge regulation or by varying the difference in hydrophilicity between the dissolved cations and anions. In addition, we investigate the yet unexplored interplay between the self-regulated colloidal surface charge distribution with the planar double layer across the oil-water interface and the spherical one around the colloid. Our findings explain recent experiments and have direct relevance for tunable Pickering emulsions.

ABO blood groups’ antigen–antibody interactions studied using SERS spectroscopy: towards blood typing

A. Kamińska, A. Kowalska A, P. Albrycht, E. Witkowska E, J. Waluk

Analytical Methods, 2016, 8(7), pp. 1463–1472

The article presents surface enhanced Raman scattering (SERS) technique associated with the principal component analysis (PCA) as a fast and reliable method for the study of interactions between the A, B, AB and O (abr. ABO) blood groups antigen and complementary monoclonal A and B antibodies. The possibility of simultaneous detection and differentiation within the ABO group was evaluated. Using 785 nm excitation wavelength, distinctive spectral changes among all types of the studied blood groups were found for mixtures of red blood cells (RBCs) with the A or B antibody. For PCA analysis, all the spectral data were divided into two main groups based on the type of antibody. The obtained PC scores in the area of antigen–antibody interactions (1311–1345 cm−1) allow differentiation within blood groups with accuracy from 96% to 98%. Additionally, for this region the characteristic marker bands of specific antigen–antibody interactions in relation to both ABO system and antibody were established. The results show excellent segregation of the obtained data and the possibility to use SERS for determination of ABO blood group. Our study proves that SERS is one of the most sensitive techniques for investigations of biological samples and may be used as a new tool that provides one-step comprehensive and reliable medical diagnosis.

Antibacterial and anticancer PDMS surface for mammalian cell growth using the Chinese herb extract paeonol(4-methoxy-2-hydroxyacetophenone)

J. Jiao, L.Sun, Z. Guo, S. Hou, R. Hołyst, Y. Lu and X. Feng

Scientific Reports 2016, 6, 38973

Polydimethylsiloxane (PDMS) is widely used as a cell culture platform to produce micro- and nano-technology based microdevices. However, the native PDMS surface is not suitable for cell adhesion and is always subject to bacterial pollution and cancer cell invasion. Coating the PDMS surface with antibacterial or anticancer materials often causes considerable harm to the non-cancer mammalian cells on it. We have developed a method to fabricate a biocompatible PDMS surface which not only promotes non-cancer mammalian cell growth but also has antibacterial and anticancer activities, by coating the PDMS surface with a Chinese herb extract, paeonol. Coating changes the wettability and the elemental composition of the PDMS surface. Molecular dynamic simulation indicates that the absorption of paeonol onto the PDMS surface is an energy favourable process. The paeonol-coated PDMS surface exhibits good antibacterial activity against both Gram-positive and Gram-negative bacteria. Moreover considerable antibacterial activity is maintained after the coated surface is rinsed or incubated in water. The coated PDMS surface inhibits bacterial growth on the contact surface and promotes non-cancer mammalian cell growth with low cell toxicity; meanwhile the growth of cancer cells is significantly inhibited. Our study will potentially guide PDMS surface modification approaches to produce biomedical devices.

Motion of Molecular Probes and Viscosity Scaling in Polyelectrolyte Solutions at Physiological Ionic Strength

K. Sozanski, A.Wisniewska, T. Kalwarczyk, A. Sznajder and R. Hołyst

PLOS ONE, 2016.

We investigate transport properties of model polyelectrolyte systems at physiological ionic strength (0.154 M). Covering a broad range of flow length scales—from diffusion of molecular probes to macroscopic viscous flow—we establish a single, continuous function describing the scale dependent viscosity of high-salt polyelectrolyte solutions. The data are consistent with the model developed previously for electrically neutral polymers in a good solvent. The presented approach merges the power-law scaling concepts of de Gennes with the idea of exponential length scale dependence of effective viscosity in complex liquids. The result is a simple and applicable description of transport properties of high-salt polyelectrolyte solutions at all length scales, valid for motion of single molecules as well as macroscopic flow of the complex liquid.

Photoactive Langmuir–Blodgett, Freely Suspended and Free Standing Films of Carboxylate Ligand-Coated ZnO Nanocrystals

J. Paczesny, M. Wolska-Pietkiewicz, I. Binkiewicz, M. Wadowska, Z. Wróbel, K. Matuła, W. Nogala, J. Lewiński and R.Hołyst

ACS Appl. Mater. Interfaces 2016, 8, 21, 13532–13541

A new possibility for the formation of macroscopic and photoactive structures from zinc oxide nanocrystals is described. Photoactive freely suspended and free-standing films of macroscopic area (up to few square millimeters) and submicrometer thickness (up to several hundreds of nanometers) composed of carboxylate ligand-coated zinc oxide nanocrystallites (RCO2–ZnO NCs) of diameter less than 5 nm are prepared according to a modified Langmuir–Schaefer method. First, the suspension of RCO2–ZnO NCs is applied onto the air/water interface. Upon compression, the films become turbid and elastic. The integrity of such structures is ensured by interdigitation of ligands stabilizing ZnO NCs. Great elasticity allows transfer of the films onto a metal frame as a freely suspended film. Such membranes are afterward extracted from the supporting frame to form free-standing films of macroscopic area. Because the integrity of the films is maintained by ligands, no abolishment of quantum confinement occurs, and films retain spectroscopic properties of initial RCO2–ZnO NCs. The mechanism of formation of thin films of RCO2–ZnO NCs at the air/water interface is discussed in detail.

The Hinge Region Strengthens the Nonspecific Interaction between Lac-Repressor and DNA: A Computer Simulation Study

L. Sun, M. Tabaka, S. Hou, L. Li, K. Burdzy ,A. Aksimentiev, Ch. Maffeo, X. Zhang and R. Hołyst

PLOS ONE, 2016.

LacI is commonly used as a model to study the protein-DNA interaction and gene regulation. The headpiece of the lac-repressor (LacI) protein is an ideal system for investigation of nonspecific binding of the whole LacI protein to DNA. The hinge region of the headpiece has been known to play a key role in the specific binding of LacI to DNA, whereas its role in nonspecific binding process has not been elucidated. Here, we report the results of explicit solvent molecular dynamics simulation and continuum electrostatic calculations suggesting that the hinge region strengthens the nonspecific interaction, accounting for up to 50% of the micro-dissociation free energy of LacI from DNA. Consequently, the rate of microscopic dissociation of LacI from DNA is reduced by 2~3 orders of magnitude in the absence of the hinge region. We find the hinge region makes an important contribution to the electrostatic energy, the salt dependence of electrostatic energy, and the number of salt ions excluded from binding of the LacI-DNA complex.

Ordering of bacteriophages in the electric field: Application for bacteria detection

Ł. Richter, K. Matula, A. Leśniewski, K. Kwaśnicka, J. Łos, M. Łoś, J. Paczesny and R. Hołyst

Sensors and Actuators B: Chemical, 2016, 224, 233-240

Only in USA the nosocomial infections cause around 100,000 deaths per year. Majority of them could have been avoided if the pathogens would be identified shortly after infection. However, classical approaches are laborious; can take up to even 72 h. Here we demonstrate a step towards a sensor for fast detection of bacteria. The sensor is based on layer of oriented T4 bacteriophages. The sensitivity of biosensors increases four times for ordered over disordered layer of bacteriophages. This results in the limit of detection of Escherichia coli in the range of 102–103 cfu/mL. Such value is much lower when compared to similar sensors based on physisorbed layer of phages and is of the same order of magnitude as probes with chemically immobilized bacteriophages described in the literature. Proper orientation of bacteriophages prevents receptor binding proteins from being blocked. For the purpose we utilized the electrostatic interactions upon application of electric potential to the surface on which phages are deposited.

How can macromolecular crowding inhibit biological reactions? The enhanced formation of DNA nanoparticles

S. Hou, P. Trochimczyk, L. Sun, A. Wisniewska, T. Kalwarczyk, X. Zhang, B. Wielgus-Kutrowska, A. Bzowska and R. Hołyst

Scientific Reports 2016, 6, 22033

In contrast to the already known effect that macromolecular crowding usually promotes biological reactions, solutions of PEG 6k at high concentrations stop the cleavage of DNA by HindIII enzyme, due to the formation of DNA nanoparticles. We characterized the DNA nanoparticles and probed the prerequisites for their formation using multiple techniques such as fluorescence correlation spectroscopy, dynamic light scattering, fluorescence analytical ultracentrifugation etc. In >25% PEG 6k solution, macromolecular crowding promotes the formation of DNA nanoparticles with dimensions of several hundreds of nanometers. The formation of DNA nanoparticles is a fast and reversible process. Both plasmid DNA (2686 bp) and double-stranded/single-stranded DNA fragment (66bp/nt) can form nanoparticles. We attribute the enhanced nanoparticle formation to the depletion effect of macromolecular crowding. This study presents our idea to enhance the formation of DNA nanoparticles by macromolecular crowding, providing the first step towards a final solution to efficient gene therapy.

Determination of equilibrium and rate constants for complex formation by fluorescence correlation spectroscopy supplemented by dynamic light scattering and Taylor dispersion analysis

X.Zhang, A. Poniewierski, A. Jelińska, A. Zagożdżon, A. Wisniewska, S. Hou and R. Hołyst

Soft Matter, 2016, 12, 8186-8194

The equilibrium and rate constants of molecular complex formation are of great interest both in the field of chemistry and biology. Here, we use fluorescence correlation spectroscopy (FCS), supplemented by dynamic light scattering (DLS) and Taylor dispersion analysis (TDA), to study the complex formation in model systems of dye–micelle interactions. In our case, dyes rhodamine 110 and ATTO-488 interact with three differently charged surfactant micelles: octaethylene glycol monododecyl ether C12E8 (neutral), cetyltrimethylammonium chloride CTAC (positive) and sodium dodecyl sulfate SDS (negative). To determine the rate constants for the dye–micelle complex formation we fit the experimental data obtained by FCS with a new form of the autocorrelation function, derived in the accompanying paper. Our results show that the association rate constants for the model systems are roughly two orders of magnitude smaller than those in the case of the diffusion-controlled limit. Because the complex stability is determined by the dissociation rate constant, a two-step reaction mechanism, including the diffusion-controlled and reaction-controlled rates, is used to explain the dye–micelle interaction. In the limit of fast reaction, we apply FCS to determine the equilibrium constant from the effective diffusion coefficient of the fluorescent components. Depending on the value of the equilibrium constant, we distinguish three types of interaction in the studied systems: weak, intermediate and strong. The values of the equilibrium constant obtained from the FCS and TDA experiments are very close to each other, which supports the theoretical model used to interpret the FCS data.

Influence of nanomechanical stress induced by ZnO nanoparticles of different shapes on the viability of cells

K. Matuła, Ł. Richter, W. Adamkiewicz, B. Åkerström, J. Paczesny and R. Hołyst

Soft Matter, 2016,12, 4162-4169

There is growing interest in nanostructures interacting with living organisms. However, there are still no general rules for the design of biocompatible nanodevices. Here, we present a step towards understanding the interactions between nanostructures and living cells. We study the influence of nanomechanical stress induced by zinc oxide (ZnO) nanostructures of different shapes on the viability of both prokaryotic (Gram-negative bacteria: Escherichia coli and Enterobacter aerogenes, and Gram-positive bacteria: Staphylococcus epidermidis and Corynebacterium glutamicum) and eukaryotic cells (yeast Saccharomyces cerevisiae and liver cancer cell line HepG2). Nanoparticles (NPs) and nanorods (NRs) of matching crystallographic structure (P63mc) and active surface area (in the order of 5 × 10−2 μm2) are almost non-toxic for cells under static conditions. However, under conditions that enable collisions between ZnO nanostructures and cells, NRs appear to be more damaging compared to NPs. This is due to the increased probability of mechanical damage caused by nanorods upon puncturing of the cell wall and membranes. Gram-positive bacteria, which have thicker cell walls, are more resistant to nanomechanical stress induced by NRs compared to Gram-negative strains and eukaryotic cells. The presented results may be exploited to improve the properties of nanotechnology based products such as implants, drug delivery systems, antibacterial emulsions and cosmetics.

Langmuir and Langmuir–Blodgett Films of Unsymmetrical and Fully Condensed Polyhedral Oligomeric Silsesquioxanes (POSS)

J. Paczesny, I. Binkiewicz, M. Janczuk, K. Wybrańska, Ł. Richter and R. Hołyst

J. Phys. Chem. C 2015, 119, 48, 27007–27017

The search for novel building blocks for preparation of nanostructures of unique properties is crucial for development of functional nanomaterials. Polyhedral oligomeric silsesquioxanes (POSS) may be regarded as organic–inorganic nanoparticles of unusual characteristics, i.e., monodisperse size, high temperature resistance, and small dielectric constant. Here, we study four derivatives of fully condensed polyhedral oligomeric octasilsesquioxanes. Seven corners of the POSS cages are substituted with isobutyl groups forming a hydrophobic tail, whereas the eighth substituent acts as a hydrophilic head due to a judiciously chosen functional group. Such design assures amphiphilic character of POSS molecules with well-defined hydrophilic head and hydrophobic tail. The combination of amphiphilicity, well-defined size and composition, and rheological properties of monolayers makes studied POSS interesting model for self-assembly, thin films, and interfacial investigations. The Langmuir–Blodgett technique is used as a method that provides the best control over the parameters of thin films formation. The functional hydrophilic group strongly influences the behavior of POSS at the air/water interface. The mercapto derivative, which seems most promising for preparation of complex nanostructures, appears to form aggregates and multilayer films. Three other studied derivatives (bearing glycerol unit, maleamic acid, and amino group) behave as classical amphiphiles at the air/water interface.

Small Crowders Slow Down Kinesin-1 Stepping by Hindering Motor Domain Diffusion

K. Sozański, F. Ruhnow, A. Wiśniewska, M. Tabaka, S. Diez, and R. Hołyst

Phys. Rev. Lett., 2015, 115, 218102

The dimeric motor protein kinesin-1 moves processively along microtubules against forces of up to 7 pN. However, the mechanism of force generation is still debated. Here, we point to the crucial importance of diffusion of the tethered motor domain for the stepping of kinesin-1: small crowders stop the motor at a viscosity of 5 mPas—corresponding to a hydrodynamic load in the sub-fN (104pN) range—whereas large crowders have no impact even at viscosities above 100 mPas. This indicates that the scale-dependent, effective viscosity experienced by the tethered motor domain is a key factor determining kinesin’s functionality. Our results emphasize the role of diffusion in the kinesin-1 stepping mechanism and the general importance of the viscosity scaling paradigm in nanomechanics.

Towards Organized Hybrid Nanomaterials at the Air/Water Interface Based on Liquid-Crystal/ZnO Nanocrystals

J. Paczesny M. Wolska‐Pietkiewicz, I. Binkiewicz, Z. Wróbel, M.Wadowska, K. Matuła, I. Dzięcielewski, D. Pociecha, J. Smalc‐Koziorowska, J. Lewiński and R. Hołyst

CHEMISTRY A EUROPEAN JOURNAL, 2015, 21, 16941-16947

The ability to self‐assemble nanosized ligand‐stabilized metal oxide or semiconductor materials offers an intriguing route to engineer nanomaterials with new tailored properties from the disparate components. We describe a novel one‐pot two‐step organometallic approach to prepare ZnO nanocrystals (NCs) coated with deprotonated 4‐(dodecyloxy)benzoic acid (i.e., an X‐type liquid‐crystalline ligand) as a model LC system (termed ZnO‐LC1 NCs). Langmuir and Langmuir–Blodgett films of the resulting hybrids are investigated. The observed behavior of the ZnO NCs at the air/water interface is rationalized by invoking a ZnO‐interdigitation process mediated by the anchored liquid‐crystalline shell. The ordered superstructures form according to mechanism based on a ZnO‐interdigitation process mediated by liquid crystals (termed ZIP‐LC). The external and directed force applied upon compression at the air/water interface and the packing of the ligands that stabilize the ZnO cores drives the formation of nanorods of ordered internal structure. To study the process in detail, we follow a nontraditional protocol of thin‐film investigation. We collect the films from the air/water interface in powder form (ZnO‐LC1 LB), resuspend the powder in organic solvents and utilize otherwise unavailable experimental techniques. The structural and physical properties of the resulting superlattices were studied by using electron microscopy, atomic force microscopy, X‐ray studies, dynamic light scattering, thermogravimetric analysis, UV/Vis absorption, and photoluminescence spectroscopy.

Motion of nanoprobes in complex liquids within the framework of the length-scale dependent viscosity model

T. Kalwarczyk, K. Sozanski, A. Ochab-Marcinek, J. Szymanski, M. Tabaka, S. Hou, and R. Hołyst

Advances in Colloid and Interface Science, 2015, 223, 55-63

This paper deals with the recent phenomenological model of the motion of nanoscopic objects (colloidal particles, proteins, nanoparticles, molecules) in complex liquids. We analysed motion in polymer, micellar, colloidal and protein solutions and the cytoplasm of living cells using the length-scale dependent viscosity model. Viscosity monotonically approaches macroscopic viscosity as the size of the object increases and thus gives a single, coherent picture of motion at the nano and macro scale. The model includes interparticle interactions (solvent-solute), temperature and the internal structure of a complex liquid. The depletion layer ubiquitously occurring in complex liquids is also incorporated into the model. We also discuss the biological aspects of crowding in terms of the length-scale dependent viscosity model.

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