Positrons are the antimatter version of electrons and so their fate in a matter world is ultimately to annihilate. However, prior to this, a positron may combine with an electron to form a matter-antimatter hybrid called positronium. This is akin to a hydrogen atom with the proton replaced by a positron. Fundamental to our understanding of the physical universe, positron and positronium are these days also acknowledged as being fantastically useful in practical applications such as probing material properties and medical diagnostics. However, there is still much that we do not know for sure about the details of the interactions of these particles with ordinary matter. For example if, in a collision with an atom or molecule, a positron captures an electron, in which directions is the positronium likely to travel and with what probability? More...
Published: Jun 17, 2015 12:35:19 PM
How light of different colours is absorbed by carbon dioxide (CO2) can now be accurately predicted using new calculations developed by a UCL-led team of scientists. This will help climate scientists studying Earth’s greenhouse gas emissions to better interpret data collected from satellites and ground stations measuring CO2. More...
Published: Jun 15, 2015 10:29:10 AM
New research from UCL has uncovered additional second laws of thermodynamics which complement the ordinary second law of thermodynamics, one of the most fundamental laws of nature. These new second laws are generally not noticeable except on very small scales, at which point, they become increasingly important. More...
Published: Feb 10, 2015 11:55:53 AM
Within the Atomic, Molecular, Optical and Positron Physics (AMOPP) group, we have a program of research aimed at applying physics techniques to biological and life science questions.
Molecular complexes that perform vital functions in live cells can be labelled with fluorescent tags which emit light when illuminated by the appropriate excitation light. Fluorescence microscopy provides valuable information about the location, number and arrangement of these complexes in the cell. When carried out in live cells (in vivo), it allows dynamic monitoring maintaining the native biological context and functionality in the living cell. Videos can be acquired with spatial resolutions of a few hundred nanometres and at tens of millisecond time scales, which, after image processing involving single-particle tracking, can help elucidate the mechanisms and functions of the biological complexes of interest.
Force sensing and manipulation using optical tweezers and magnetic traps
Optical tweezers are a useful and important tool with many applications in the physical and life sciences. By strongly focussing a laser beam, microscopic objects can be trapped and manipulated at the beam waist. The group of Dr. Phil Jones uses optical tweezers for trapping a variety of objects interesting for life sciences or soft matter, including microscopic bubbles and carbon nanotubes. More information about this research can be found in the optical tweezers website.
Magnetic traps: tailored magnetic trapping potentials can be used for confining and manipulating micrometre-sized particles in solution. The particles can be previously functionalised and attached to biological complexes so that the magnetic traps can then be employed to exert and measure forces relevant to the function of the complexes. Combined with fluorescence microscopy, this technique provides a powerful tool for studies at the single molecule level and in real time in live cells. In this way, Physics can be applied to biomedical problems important to human health, in particular, those related to cell-surface interactions. For instance, we can try to understand the forces involved in the activity of cell-surface receptor molecules, such as those key to cancer growth, immune response or viral infection. The group of Dr. Isabel Llorente-Garcia applies fluorescence microscopy and magnetic force spectroscopy and manipulation to the study of mechanisms of receptor-mediated virus entry in live cells.
Ultrafast laser spectroscopy of biological systems
Ultrafast lasers - lasers that produce pulses of light as short as a few femtoseconds (1 femtosecond is 10-15 s)- can be used in experiments for single and multi-photon induced fluorescence as a means of investigating molecular probe dynamics in biological systems.
These very short pulses of laser light can be used to measure the orientation and very fast rotation of molecules ('probes') when they are placed in an environment that restricts their motion. The probe is a chromophore, a molecule that absorbs light of one colour and re-emits is at a different one. By analysing the light emitted by the chromophore, particularly its polarisation, we can obtain information about the way the molecule is moving ('tumbling' and 'wobbling' motion), and so deduce the nature of the environment surrounding it.
Highly ordered molecular environments can commonly be found in the biological sciences, for example, in cell membranes. This technique can be used to detect and measure changes in the biological environment from changes in the motion of the probe molecules.
Dr Angus Bain works
on the development of various picosecond and femtosecond laser spectroscopy techniques,
as well as on novel developments in time resolved stimulated emission depletion
(STED), time resolved polarised fluorescence techniques for the study of
Förster resonance energy transfer (FRET) in biological systems and super
resolution fluorescence microscopy via fluorescence lifetime image
reconstruction with low power continuous wave stimulated emission depletion (CW
Theoretical biophysics - quantum phenomena in biomolecular functions
It is well known that quantum mechanics explains the structure, stability and spectroscopy of the molecular components of living systems. What remains unknown (and controversial) is whether there are quantum coherent dynamics relevant for their biological functionality - features that have been selected by evolution. In order to achieve a theoretical understanding of the possible roles of quantum phenomena in biomolecular functions, Dr Alexandra Olaya-Castro works on theoretical studies of quantum approaches to photosynthetic complexes, non-classical features of electronic and vibrational dynamics in biomolecules, counting statistics and noise characterisation in charge and exciton transfer processes, and quantum thermodynamics of biomolecular processes.
For more information on Biological Physics research areas and people within the Physics Department, please see: