A new technique that combines electron microscopy and laser technology enables programmable, arbitrary shaping of electron beams. It can potentially be used for optimizing electron optics and for adaptive electron microscopy, maximizing sensitivity while minimizing beam-induced damage. This ... more
How to separate nanoparticles by “shape”
New strategy to separate molecules
In our daily lives, the purpose and function of an item is defined by either its material, e.g. a rain jacket is fabricated of water-proof material, or its shape, e.g. a wheel is round to enable a rolling motion. What is the impact of the two factors on the nanoscale? The impact of material, i.e. the chemistry of the building block, has been excessively varied and the impact on polymer properties investigated leading to new functional materials, as for example slush powders. On the contrary, the impact of ’shape’ has not been elucidated yet, since we are lacking reliable shape-sensitive separation techniques. Scientists of the University of Vienna and the International School of Advanced Studies in Triest, have overcome this hurdle.
The researchers developed a strategy how to separate knotted ring polymers from unknotted ones. Polymers are long molecules, consisting of the periodic repetition of a building block called a monomer. Lisa Weiß and Christos Likos of the University of Vienna together with Cristian Micheletti and Mattia Marenda of the International School of Advanced Studies (SISSA) investigated the influence of topology, which is the mathematical precise expression for ‘shape’, on polymers and how to separate them. Distinct topologies in polymer science are the unknot, which can be imagined as a closed pearl necklace, each pearl representing a monomer, or various knotted structures captured on a ring polymer, corresponding to knotting a necklace and permanently closing it afterwards.
The key idea is to use modulated nanochannels; i. e., channels of a small radius, which is increasing and decreasing periodically along the channel axis. On such length and time scales thermal motion, known as well as Brownian motion, is an important player, determining the magnitude of diffusion, a term describing the random displacement of polymers.
Without flow, the channel modulation inverts the ranking of diffusivities compared to an unconfined system, such that the fastest diffusing species in bulk is the slowest in a modulated channel. Unfortunately, due to the random nature of diffusion, it cannot be employed for separation. Therefore, the researchers applied weak flows, using special simulation techniques, which correctly take into account the solvent mediated momentum transfer. For sufficiently small flow strengths they can indeed separate distinctly knotted molecules.
This mechansim is based on the fact that the average transport velocity due to flow is smaller compared to the random displacement per typical polymer time scale, and polymers have enough time to diffusively explore the channel cross-section before being transported to the next chamber. As long as this condition is met, unknotted polymers can be transported up to ten times as fast as their knotted counterparts, leading to a reliable separation. Interestingly, the size of the constriction is not of crucial importance. Nevertheless, the ratio of constriction size to the average size of a knot can be used to control whether the knot is leading or trailing behind the rest of the polymer, establishing thereby preference for different translocation modes.
The collaboration took place in the framework of the Marie-Curie research network Nanotrans, allowing to combine the Viennese knowledge on hydrodynamics with the knot expertise based in Trieste.
- separation techniques
Researchers determine the structure and dynamics of proteins using NMR (Nuclear Magnetic Resonance) spectroscopy. Until now, however, much higher concentrations were necessary for in-vitro measurements of the biomolecules in solution than found in our body's cells. An NMR method enhanced by ... more
A small group of researchers including Dennis Kurzbach from the Faculty of Chemistry of the University of Vienna just published in "Nature Protocols" an advanced NMR (Nuclear Magnetic Resonance) method to monitor fast and complicated biomolecular events such as protein folding. For example, ... more
The structure of a biomolecule can reveal much about its functioning and interaction with the surrounding environment. The double-helical structure of DNA and its implications for the processes of transmission of genetic information form an obvious example. In a new study by SISSA - Scuola ... more
Anyone who has been on a sailing boat knows that tying a knot is the best way to secure a rope to a hook and prevent its slippage. The same applies to sewing threads where knots are introduced to prevent them slipping through two pieces of fabric. How, then, can long DNA filaments, which ha ... more
"Interphase" refers to the period in the cell cycle in which chromosomes spend most of their time. During this phase, in between mitoses, chromosomes live "dissolved'' in the nucleus where they carry out the processes required for the duplication of genetic material. Our current knowledge r ... more
- 1Elusive carbonic acid: it really exists!
- 2A new tool for estimating people’s total exposure to potentially harmful chemicals is developed by Mount Sinai researchers
- 3Advances in spectroscopy
- 4New Molecular Microscopy Uncovers how Breast Cancer Spreads
- 5Imaging cells: New method enables clear, precise look inside
- 6Smarter sensor sniffs out target gases
- 7Can smartphones predict mortality risk?
- 8SARS-CoV-2 detection in 30 minutes using gene scissors
- 9Fighting tumours with magnetic bacteria
- 10Seeing concentrations of toxins with the naked eye
- Distinguish sugars with eye-catching and stretchy rainbow film
- Neuroscientists illuminate how brain cells deep in the cortex operate in fre ...
- Tomography shows high potential of copper sulphide solid-state batteries
- Sinonasal cancer: AI facilitates breakthrough in diagnostics
- Hope for first blood test to detect deadly heart inflammation
- Growth of Nanoholes Visible for the First Time Thanks to Helium Scattering
- New light for shaping electron beams
- Three Eyes See More than Two - monitoring a catalytic reaction with three different microscopies under exactly the same conditions in real time
- Sniffing out carcinogens in foodstuffs
- Miniaturized Lab-on-a-Chip for real-time Chemical Analysis of Liquids