Tunable colloidal spinners: Active chirality and hydrodynamic interactions governed by rotating external electric fields.

The rotational dynamics of microparticles in liquids have a wide range of applications, including chemical microreactors, biotechnologies, microfluidic devices, tunable heat and mass transfer, and fundamental understanding of chiral active soft matter which refers to systems composed of particles that exhibit a handedness in their rotation, breaking mirror symmetry at the microscopic level. Here, we report on the study of two effects in colloids in rotating electric fields: (i) the rotation of individual colloidal particles in rotating electric field and related to that (ii) precession of pairs of particles. We show that the mechanism responsible for the rotation of individual particles is related to the time lag between the external field applied to the particle and the particle polarization.

Quantifying intuition: Bayesian approach to figures of merit in EXAFS analysis of magic size clusters.

Analysis of the extended X-ray absorption fine structure (EXAFS) can yield local structural information in magic size clusters even when other structural methods (such as X-ray diffraction) fail, but typically requires an initial guess - an atomistic model. Model comparison is thus one of the most crucial steps in establishing atomic structure of nanoscale systems and relies critically on the corresponding figures of merit (delivered by the data analysis) to make a decision on the most suitable model of atomic arrangements. However, none of the currently used statistical figures of merit take into account the significant factor of parameter correlations.

Engineering a DNA origami mediated multicolour quantum dot platform for sub-diffraction spectral separation imaging.

The validation of super-resolution optical imaging techniques requires well-defined reference samples that can be used repeatedly and reliably as model standards. Here, we engineer a DNA origami scaffold-mediated multicolour quantum dot hybrid nanostructure and test it using a recently proposed Quantum Dot-based spectral separation technique. We show that multivalent DNA structures offer a robust and precise nanoscale quantum dot placement scaffold, while the spectral resolution method provides relatively simple and fast image acquisition capabilities using any standard confocal or fluorescence microscope capable of spectral signal separation and a single excitation laser wavelength.

2D colloids in rotating electric fields: A laboratory of strong tunable three-body interactions.

Many-body forces play a prominent role in structure and dynamics of matter, but their role is not well understood in many cases due to experimental challenges. Here, we demonstrate that a novel experimental system based on rotating electric fields can be utilised to deliver unprecedented degree of control over many-body interactions between colloidal silica particles in water. We further show that we can decompose interparticle interactions explicitly into the leading terms and study their specific effects on phase behaviour.

Mean-field model of melting in superheated crystals based on a single experimentally measurable order parameter.

Melting is one of the most studied phase transitions important for atomic, molecular, colloidal, and protein systems. However, there is currently no microscopic experimentally accessible criteria that can be used to reliably track a system evolution across the transition, while providing insights into melting nucleation and melting front evolution. To address this, we developed a theoretical mean-field framework with the normalised mean-square displacement between particles in neighbouring Voronoi cells serving as the local order parameter, measurable experimentally.

Fluorescent Convertible Capsule Coding Systems for Individual Cell Labeling and Tracking.

In modern biomedical science and developmental biology, there is significant interest in optical tagging to study individual cell behavior and migration in large cellular populations. However, there is currently no tagging system that can be used for labeling individual cells on demand with subsequent discrimination in between and long-term tracking of individual cells. In this article, we demonstrate such a system based on photoconversion of the fluorescent dye rhodamine B co-confined with carbon nanodots in the volume of micron-sized polyelectrolyte capsules.

DNA-driven dynamic assembly of MoS nanosheets.

Controlling the assembly of molybdenum disulfide (MoS) layers into static and dynamic superstructures can impact on their use in optoelectronics, energy, and drug delivery. Toward this goal, we present a strategy to drive the assembly of MoS layers via the hybridization of complementary DNA linkers. By functionalizing the MoS surface with thiolated DNA, MoS nanosheets were assembled into mulitlayered superstructures, and the complementary DNA strands were used as linkers.

Molecular nature of breakdown of the folic acid under hydrothermal treatment: a combined experimental and DFT study.

Using a combination of experimental Raman, FTIR, UV-VIS absorption and emission data, together with the corresponding DFT calculations we propose the mechanism of modification of the folic acid specifically under the hydrothermal treatment at 200 °C. We established that folic acid breaks down into fragments while the pteridine moiety remains intact likely evolving into 6-formylpterin with the latter responsible for the increase in fluorescence emission at 450 nm. The results suggest that hydrothermal approach can be used for production of other purpose-engineered fluorophores.

Universal Effect of Excitation Dispersion on the Heat Capacity and Gapped States in Fluids.

The change in dispersion of high-frequency excitations in fluids, from an oscillating solidlike to a monotonic gaslike one, is shown for the first time to affect thermal behavior of heat capacity and the q-gap width in reciprocal space. With in silico study of liquified noble gases, liquid iron, liquid mercury, and model fluids, we established universal bilinear dependence of heat capacity on q-gap width, whereas the crossover precisely corresponds to the change in the excitation spectra. The results open novel prospects for studies of various fluids, from simple to molecular liquids and melts.

Analysis of the atomic structure of CdS magic-size clusters by X-ray absorption spectroscopy.

Magic-size clusters are ultra-small colloidal semiconductor systems that are intensively studied due to their monodisperse nature and sharp UV-vis absorption peak compared with regular quantum dots. However, the small size of such clusters (<2 nm), and the large surface-to-bulk ratio significantly limit characterisation techniques that can be utilised. Here we demonstrate how a combination of EXAFS and XANES analyses can be used to obtain information about sample stoichiometry and cluster symmetry.

Site-specific release of reactive oxygen species from ordered arrays of microchambers based on polylactic acid and carbon nanodots.

Non-destructive, controllable, remote light-induced release inside cells enables studying of time- and space-specific surface-mediated delivery of bioactive compounds, which is an important approach in a wide range of biomedical tasks, especially those related to the control of cell growth, regenerative medicine, and self-disinfecting structures such as catheters. In this regard, the elaboration of encapsulation and controlled release of oxidative species is in high demand due to its versatile applications. One of the obvious candidates for such species is hydrogen peroxide.

Strange attractors induced by melting in systems with nonreciprocal effective interactions.

Newton's third law-the action-reaction symmetry-can be violated for effective interbody forces in open and nonequilibrium systems that are ubiquitous in areas as diverse as complex plasmas, colloidal suspensions, active and living soft matter, and social behavior. While studying monolayer complex plasma (confined charged particles in an ionized gas) with nonreciprocal interactions mediated by plasma flows, in silico we found that an interplay between melting and thermal activation drastically transforms the collective dynamics: the order-disorder transition modifies the system's thermal steady state so that the crystal tends to melt, whereas the fluid tends to freeze, jumping chaotically between the two states. We identified this collective chaotic behavior as strange attractors formed in a monolayer complex plasma and link the strange attractor behavior to the specifics of interparticle interactions.

Polylactic Acid-Based Patterned Matrixes for Site-Specific Delivery of Neuropeptides On-Demand: Functional NGF Effects on Human Neuronal Cells.

The patterned microchamber arrays based on biocompatible polymers are a versatile cargo delivery system for drug storage and site-/time-specific drug release on demand. However, functional evidence of their action on nerve cells, in particular their potential for enabling patterned neuronal morphogenesis, remains unclear. Recently, we have established that the polylactic acid (PLA)-based microchamber arrays are biocompatible with human cells of neuronal phenotype and provide safe loading for hydrophilic substances of low molecular weight, with successive site-specific cargo release on-demand to trigger local cell responses.

Laser-triggered drug release from polymeric 3-D micro-structured films via optical fibers.

Photosensitive polymeric three-dimensional microstructured film (PTMF) is a new type of patterned polymeric films functionalized with an array of sealed hollow 3D containers. The microstructured system with enclosed chemicals provides a tool for the even distribution of biologically active substances on a given surface that can be deposited on medical implants or used as a cells substrate. In this work, we proposed a way for photothermally activating and releasing encapsulated substances at picogram amounts from the PTMF surface in different environments using laser radiation delivered with a multimode optical fiber.

Direct Experimental Evidence of Longitudinal and Transverse Mode Hybridization and Anticrossing in Simple Model Fluids.

A significant number of key properties of condensed matter are determined by the spectra of elementary excitations and, in particular, collective vibrations. However, the behavior and description of collective modes in disordered media (e.g.

Investigating the Effect of Reaction Time on Carbon Dot Formation, Structure, and Optical Properties.

Carbon dots, a young member of the carbon nanomaterial family, are quasi-spherical nanoparticles, which have fluorescent properties as their key characteristic. A wide range of starting materials and synthetic routes have been reported in the literature, divided into two main categories: a top-down and bottom-up approach. Moreover, a series of different parameters that affect the properties of carbon dots have been investigated, including temperature, starting pH, as well as precursor concentration.

X-ray total scattering study of magic-size clusters and quantum dots of cadmium sulphide.

Four types of magic-size CdS clusters and three different CdS quantum dots have been studied using the technique of X-ray total scattering and pair distribution function analysis. We found that the CdS quantum dots could be modelled as a mixed phase of atomic structures based on the two bulk crystalline phases, which is interpreted as representing the effects of random stacking of layers. However, the results for the magic-size clusters are significantly different.

Luminescent carbon nanoparticles separation and purification.

Nowadays luminescent carbon-based nanoparticles can be synthesized by a wide range of physical and chemical methods from a large variety of carbon-based sources. However, in most of the cases the product of synthesis is a complex mixture of compounds, which results in significant challenges in understanding the structure and optical properties of the reaction products. Consequently, a number of separation and purification methodologies have been developed to alleviate these challenges.

Gel electrophoresis separation and origins of light emission in fluorophores prepared from citric acid and ethylenediamine.

We investigated light emission of hydrothermally treated citric acid and ethylenediamine (EDA) with various precursor ratios using gel-electrophoresis. We show that this relatively simple approach can deliver significant insights into the origins of photoluminescence. We found that products of the synthesis consist of both positively and negatively charged species and exhibit large dispersion in electrophoretic mobility (i.

Defect-governed double-step activation and directed flame fronts.

Defects play a crucial role in physics of solids, affecting their mechanical, electromagnetic, and chemical properties. However, influence of thermal defects on wave propagation in exothermic reactions (flame fronts) still remains poorly understood at the molecular level. Here, we show that thermal behavior of the defects exhibits essential features of double-step exothermic reactions with preequilibrium.

Experimental validation of interpolation method for pair correlations in model crystals.

Accurate analysis of pair correlations in condensed matter allows us to establish relations between structures and thermodynamic properties and, thus, is of high importance for a wide range of systems, from solids to colloidal suspensions. Recently, the interpolation method (IM) that describes satisfactorily the shape of pair correlation peaks at short and at long distances has been elaborated theoretically and using molecular dynamics simulations, but it has not been verified experimentally as yet. Here, we test the IM by particle-resolved studies with colloidal suspensions and with complex (dusty) plasmas and demonstrate that, owing to its high accuracy, the IM can be used to experimentally measure parameters that describe interaction between particles in these systems.

Manipulating the Optical Properties of Carbon Dots by Fine-Tuning their Structural Features.

As a new class of sustainable carbon material, "carbon dots" is an umbrella term covering many types of materials. Herein, a broad range of techniques was used to develop the understanding of hydrothermally synthesized carbon dots, and it is shown how fine-tuning the structural features by simple reduction/oxidation reactions can drastically affect their excited-state properties. Structural and spectroscopic studies found that photoluminescence originates from direct excitation of localized fluorophores involving oxygen functional groups, whereas excitation at graphene-like features leads to ultrafast phonon-assisted relaxation and largely quenches the fluorescent quantum yields.

One step hydrothermal functionalization of gold nanoparticles with folic acid.

A new fundamental concept for one-step in-situ functionalization of gold nanoparticles (GNPs) with folic acid using hydrothermal treatment is described. Hydrothermal treatment has been tuned to increase the light emission from the pterin moiety of folic acid molecule, while retain its structure and functionality, thus providing a simple route to multimodal tags for a variety of in vitro and in vivo biomedical applications. Successful functionalization of GNPs with the biological ligand is confirmed by specific binding with anti-folic acid antibody.

Carbon dot aggregates as an alternative to gold nanoparticles for the laser-induced opening of microchamber arrays.

Carbon dots (CDs) are usually used as an alternative to other fluorescent nanoparticles. Apart from fluorescence, CDs also have other important properties for use in composite materials, first of all their ability to absorb light energy and convert it into heat. In our work, for the first time, CDs have been proposed as an alternative to gold nanostructures for harvesting light energy, which results in the opening of polymer-based containers with biologically active compounds.