Immersion freezing of supercooled water drops containing glassy volcanic ash particles

AbstractThe freezing temperatures of hundreds of water drops with radii 20–50μm containing known average concentrations of suspended, mostly micron- to submicron-sized, volcanic ash particles composed of SiO2-rich glass were recorded using optical microscopy. As expected, the ash suppresses supercooling, and in contrast to earlier studies of much larger ash particles, the median freezing temperature clearly scales with the available ash surface area per drop. The heterogeneous nucleation rate coefficient per unit mass of ash (jm) increases exponentially with decreasing temperature (T) (increasing supercooling) with a possible change in the slope of a plot of logjm against T at T=245±1K. Although uncertainties in the ash surface area limit quantitative comparisons, we conclude that volcanic glass is a less effective ice-nucleating agent than feldspar crystals and more similar to other minerals previously studied

Cationized magnetoferritin enables rapid labeling and concentration of Gram-positive and Gram-negative bacteria in magnetic cell separation columns

In order to identify pathogens rapidly and reliably, bacterial capture and concentration from large sample volumes into smaller ones are often required. Magnetic labeling and capture of bacteria using a magnetic field hold great promise for achieving this goal, but the current protocols have poor capture efficiency. Here, we present a rapid and highly efficient approach to magnetic labeling and capture of both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria using cationized magnetoferritin (cat-MF). Magnetic labeling was achieved within a 1-min incubation period with cat-MF, and 99.97% of the labeled bacteria were immobilized in commercially available magnetic cell separation (MACS) columns. Longer incubation times led to more efficient capture, with S. aureus being immobilized to a greater extent than E. coli. Finally, low numbers of magnetically labeled E. coli bacteria (<100 CFU per ml) were immobilized with 100% efficiency and concentrated 7-fold within 15 min. Therefore, our study provides a novel protocol for rapid and highly efficient magnetic labeling, capture, and concentration of both Gram-positive and Gram-negative bacteria. IMPORTANCE Antimicrobial resistance (AMR) is a significant global challenge. Rapid identification of pathogens will retard the spread of AMR by enabling targeted treatment with suitable agents and by reducing inappropriate antimicrobial use. Rapid detection methods based on microfluidic devices require that bacteria are concentrated from large volumes into much smaller ones. Concentration of bacteria is also important to detect low numbers of pathogens with confidence. Here, we demonstrate that magnetic separation columns capture small amounts of bacteria with 100% efficiency. Rapid magnetization was achieved by exposing bacteria to cationic magnetic nanoparticles, and magnetized bacteria were concentrated 7-fold inside the column. Thus, bacterial capture and concentration were achieved within 15 min. This approach could be extended to encompass the capture and concentration of specific pathogens, for example, by functionalizing magnetic nanoparticles with antibodies or small molecule probes

Ultra-fast stem cell labelling using cationised magnetoferritin

Efficient magnetic labelling of stem cells is achieved within a one minute incubation period using cationised magnetoferritin.</p

Dual Control of Molecular Conductance through pH and Potential in Single-Molecule Devices

One of the principal aims of single-molecule electronics is to create practical devices out of individual molecules. Such devices are expected to play a particularly important role as novel sensors thanks to their response to wide ranging external stimuli. Here we show that the conductance of a molecular junction can depend on two independent stimuli simultaneously. Using a scanning tunnelling microscope break-junction technique (STM-BJ), we found that the conductance of 4,4′-vinylenedipyridine (44VDP) molecular junctions with Ni contacts depends on both the electrochemically applied gate voltage and the pH of the environment. Hence, not only can the Ni|44VDP|Ni junction function as a pH-sensitive switch, but the value of the pH at which switching takes place can be tuned electrically. Furthermore, through the simultaneous control of pH and potential the STM-BJ technique delivers unique insight into the acid–base reaction, including the observation of discrete proton transfers to and from a single molecule