... understanding life in molecular detail

Dr Simon Connell

AFM, Lipid Membranes, Fibrin, Experimental biophysics, Nanomechanics


The development of Atomic Force Microscopy technology, and its application to problems in biophysics and soft-matter physics. Complementary techniques such as QCM-D, fluorescence microscopy and magnetic tweezers are used in conjunction with AFM to study phase transitions, molecular self-assembly, the higher level structure of protein assemblies, the mechanisms of fibrin clot formation and the mechanical properties of nanoscale structures such as fibrin protofibrils and proteins.

Current major projects include:
  • Phase behaviour, patterning and curvature in lipid membranes
  • Development of a high sensitivity low noise force sensor
  • Blood clotting mechanisms via molecular resolution imaging
  • Fibrin rheology, magnetic tweezers and single fibre nano-mechanics

My research is focussed on the development of AFM technology, and its application to problems in Biophysics and soft condensed matter Physics. I also manage the Atomic Force Microscopy Facility, which houses 7 state-of-the-art AFM systems, open to both internal and external users.

Phospholipid membranes – My research in this area focuses on understanding the phase behaviour of self-assembled lipid structures, including the study of lipid “rafts”. Originating in the fundamental determination of lipid phase diagrams vs composition, temperature and other experimental conditions, the dynamics and mechanisms of phase separation have been found to control the final structure. This precisely mapped behaviour can then be used to understand how membrane proteins, peptides, surfactants or nanoparticles may interact with biomimetic phospholipid bilayers. Of particular interest is the behaviour in unusual areas of the phase diagram, including critical points, 3-phase regions and edge-actants. Membranes may also be used as a controllable substrate for the immobilisation and study of biomolecular species in native enviroments. Recent instrumental developments include a combined AFM-epifluorescence micrsoscopy system, and an AFM heat-cool temperature stage capable of rapid quenching at rates of up to 10ï?°C per second. Force spectroscopy can be used to unambiguously assign the phase to a particular, domain, as well as measure the precise depth (or change in depth) of a bilayer, and even detect the presence of hydrogen bonding between lipid head groups.
lipid rafts

Stratum corneum lipids – The lipids in the outermost layers of skin, consisting of long chain ceramides, fatty acids and cholesterol, provide most of the skins barrier properties. Utilizing the experimental techniques developed studying cell membranes, we are exploring the structure and mechanics of this unusual multilayered system, which has some remarkable properties. We are currently investigating how external agents may affect the properties of this important barrier layer.

Fibrinogen structure and function – Using biophysical techniques (high resolution non-contact AFM imaging of molecular structure, magnetic tweezers, electron and fluorescence confocal optical microscopy, force spectroscopy) we are elucidating the mechanisms involved in thrombosis and haemostasis. We aim to discover the molecular mechanisms that regulate clot structure and mechanics across multiple length scales, from the level of individually associating fibrinogen monomers up to the final clot structure.

Low noise force spectroscopy – Dynamic force spectroscopy (DFS) is a powerful method able to probe the underlying features of the potential energy landscape of non-covalent interactions. This is achieved by applying a mechanical force in a defined direction to the particular interaction under study. Application of a force tilts the potential energy landscape exponentially increasing the unbinding or unfolding rate.We have recently development a novel force sensor based around the AFM in order to improve DFS. Using very soft cantilevers and radiation pressure actuation under fast feedback control, the system can be used to cool the cantilever to effective temperatures of <10 K in liquid water (by damping thermally induced motion). In another mode, termed constant velocity (CV)-AFM, the cantilever is locked in position, and the force determined via the pressure required to lock the lever. This provides a very fast response time < 1 ms, allowing the measurement of protein unfolding intermediates, and eliminates cantilever recoil, during which time measurable force data cannot be obtained

Detailed research programme                  Close ▲
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Lecturer (Leeds) 2010-present
BSc PhD (Portsmouth)

Postdoc (Helmholtz-Zentrum Berlin) 1999
Postdoc (Nottingham) 1999-2001
Postdoc (Leeds) 2001-2005
Senior Research Fellow (Leeds) 2005-2010

EC Stoner 8.32a
School of Physics
0113 343 8241
s.d.a.connell@leeds.ac.uk

http://www.mnp.leeds.ac.uk/sconnell/

Selected Publications

  1. ”Critical Point Fluctuations in Supported Lipid Membranes” Connell SD, Heath GR, Olmsted PD, Kisil A; Faraday Discussions (2013) 161:91-111

  2. Evidence that y’ fibrinogen directly interferes with protofibril growth:oimplications for fibrin structure and clot stiffness” J Thromb Haemost (2012), 10(6):1072-1080

  3. Mechanically unfolding protein L using a laser-feedback controlled cantilever” Crampton N, Alzahrani K, Beddard GS, Connell SD, Brockwell DJ, Biophys J (2011), 100(7), 1800-1809

  4. Atomic  Force Microscopy based molecular recognition of a fibrinogen receptor on human erythrocytes”, Carvalho FA, Connell SD, Miltenberger-Miltenyi G, Pereira SV, Tavares A, Ariens RAS, Santos NC (2010) ACS NANO 4(8), 4609-4620