Robust detection of bacteria can significantly reduce risks of nosocomial infections, which are a serious problem even in developed countries (4.1 million cases each year in Europe). Here we demonstrate utilization of novel multifunctional bioconjugates as specific probes for bacteria detection. Bifunctional magnetic-fluorescent microparticles are coupled with bacteriophages. The T4 bacteriophage, due to its natural affinity to bacterial receptors, namely, OmpC and LPS, enables specific and efficient detection of Escherichia coli bacteria. Prepared probes are cheap, accessible (even in nonbiological laboratories), as well as versatile and easily tunable for different bacteria species. The magnetic properties of the bioconjugates facilitate the separation of captured target bacteria from other components of complex samples and other bacteria strains. Fluorescence enables simple analysis. We chose flow cytometry as the detection method as it is fast and widely used for biotests. The capture efficiency of the prepared bioconjugates is close to 100% in the range of bacteria concentrations from tens to around 10⁵ CFU/mL. The limit of detection is restricted by flow cytometry capabilities and in our case was around 10⁴ CFU/mL.

We show that surface-enhanced Raman spectroscopy (SERS) coupled with principal component analysis (PCA) can serve as a fast, reliable, and easy method for detection and identification of food-borne bacteria, namely Salmonella spp., Listeria monocytogenes, and Cronobacter spp., in different types of food matrices (salmon, eggs, powdered infant formula milk, mixed herbs, respectively). The main aim of this work was to introduce the SERS technique into three ISO (6579:2002; 11290–1:1996/A1:2004; 22964:2006) standard procedures required for detection of these bacteria in food. Our study demonstrates that the SERS technique is effective in distinguishing very closely related bacteria within a genus grown on solid and liquid media. The advantages of the proposed ISO-SERS method for bacteria identification include simplicity and reduced time of analysis, from almost 144 h required by standard methods to 48 h for the SERS-based approach. Additionally, PCA allows one to perform statistical classification of studied bacteria and to identify the spectrum of an unknown sample. Calculated first and second principal components (PC-1, PC-2) account for 96, 98, and 90% of total variance in the spectra and enable one to identify the Salmonella spp., L. monocytogenes, and Cronobacter spp., respectively. Moreover, the presented study demonstrates the excellent possibility for simultaneous detection of analyzed food-borne bacteria in one sample test (98% of PC-1 and PC-2) with a goal of splitting the data set into three separated clusters corresponding to the three studied bacteria species. The studies described in this paper suggest that SERS represents an alternative to standard microorganism diagnostic procedures.

Multifunctional core/shell type nanomaterials composed of nanocrystalline, lanthanide doped fluorides and gold nanoparticles (Au NPs) were successfully prepared. The products were synthesized to combine luminescence properties of the core NPs, i.e., LnF₃/SiO₂–NH₂ and KLn₃F₁₀/SiO₂–NH₂, and plasmonic activity of the shell Au NPs within a single nanomaterial. The luminescent lanthanide NPs (10 or 150–200 nm) were separated from the gold NPs (6–30 nm) using an amine modified silica shell (thickness ≈30 nm). The synthesized products exhibited bright green (Tb³⁺) and red (Eu³⁺) emission under UV light irradiation. Surface modification with Au NPs influenced the product emission and luminescence decay characteristics. The luminescent-plasmonic nanomaterials were used as platforms for surface enhanced Raman scattering (SERS) measurements. 4-Mercaptobenzoic acid, choline, and T4 bacteriophages were utilized as SERS probes. For all synthesized nanomaterials, the SERS spectra for all probes studied exhibited higher intensity in comparison with the spectra measured using a commercial SERS substrate. Cytotoxicity of the products was evaluated in fibroblast cells. The results obtained showed biocompatibility of the synthesized nanomaterials in a dose-dependent manner.

Electrostatic repulsions can drive crystallization in many-particle systems. For charged colloidal systems, the phase boundaries as well as crystal structure are highly tunable by experimental parameters such as salt concentration and pH. By using projections of the colloid–ion mixture to a system of (soft) repulsive spheres and the one-component plasma (OCP), we study the hitherto unexplained experimentally observed reentrant melting of electrostatically repelling colloids upon increasing the colloid density. Our study shows that the surface chemistry should involve a competition between adsorption of cations and anions to explain the observed density-induced reentrant melting.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.