Transformations of chemical energy into mechanical work (and back again) are widely used by the Nature to govern a broad spectrum of fundamental biochemical reactions and processes, including transcription, signal transduction in cell membranes, and the operation of myosin motors in muscles. Changes in mechanical stress can be either a driving force or a consequence of chemical transformations, and in the latter case can serve as a measurable quantity for characterising these processes.
The remarkable revolution of the microelectronics industry has driven the miniaturisation of devices. Scaling down the dimensions of traditional devices to measure surface stress from the micron to the nanoscale, has significantly increased their sensitivity to probe chemical reactions and subtle physical transformations in the active layer of the sensor. Differential measurements with reference cantilevers have proven to be essential for biospecific measurements. Nanomechanical cantilever sensors have been used to probe a wide variety of chemical and biological processes such as deprotonation reactions, DNA hybridisation, protein recognition and cell adhesion. Yet in spite of significant experimental advances, the fundamental physics of the mechanotransduction mechanisms, that underpins this promising new technology, has remained elusive.
Researchers at the London Centre for Nanotechnology, led by Principal Investigator Dr Rachel McKendry have pioneered the study of biomolecular reactions on cantilever arrays. Recent work in Rachel’s group by Dr Maria Sushko and Dr Moyu Watari, in collaboration with Professor Alex Shluger and Professor John Harding (Sheffield) has brought important new insights into the basic physics of the mechanotransduction mechanism. Systematic experimental work by Dr. Moyu Watari using model alkanethiol self-assembled monolayers revealed how the cantilever bending signal depends on the chain length, terminal group of the monolayer, and also the pH and ionic strength of the buffer environment.
The scientific breakthrough has been made by combining these important experimental studies with the development of the first theoretical model of nanomechanical sensing by Dr. Maria Sushko. This multiscale multilayer model combines beam mechanics, mesoscopic soft-matter theory and atomistic modelling to predict the translation of molecular signals at the nanoscale into the micromechanical response of the cantilever device. The model shows that the cantilever response to biochemical changes in its active layer is a complex combination of competing biochemical, elastic and entropic contributions. Excellent quantitative agreement was found between experimental measurements and theoretical predictions.
The interdisciplinary team says that this multiscale model, which crosses the boundaries of materials science, physics and chemistry, reveals fundamental new physics at the nanoscale and can be used to engineer devices with significantly improved biomolecular detection sensitivity in silico. The fundamental advances made by Drs. Sushko, Watari and McKendry are the major step towards the transition from the proof-of-concept experiments to cantilever-based devices for routine medical diagnostics.
Figure 1: First quantitative model of nanomechanical biosensing, which links mesoscopic response of the BioMEMS device to specific chemical, elastic and entropic properties at the nanoscale. These concepts envision novel surface chemistries and device geometries “in silico” with significantly improved detection sensitivities for nanomechanical biosensing.
Notes to Editors:
 “Physics of Nanomechanic Biosensing on Cantilever Arrays” Advanced Materials (2008)
M.L. Sushko1, J.H. Harding2, A.L. Shluger1, R.A. McKendry1, M.Watari1
- London Centre for Nanotechnology, University College London
- Department of Engineering Materials, University of Sheffield
 M. Watari, J. Galbraith, H.-P. Lang, M. Sousa, M. Hegner, C. Gerber, M. A. Horton, and R. A. McKendry, J. Am. Chem. Soc., 129, 601 (2007).
2. About the London Centre for Nanotechnology
The London Centre for Nanotechnology is a joint enterprise between University College London and Imperial College London. In bringing together world-class infrastructure and leading nanotechnology research activities, the Centre aims to attain the critical mass to compete with the best facilities abroad. Furthermore by acting as a bridge between the biomedical, physical, chemical and engineering sciences the Centre will cross the 'chip-to-cell interface' - an essential step if the UK is to remain internationally competitive in biotechnology. Website: www.london-nano.com
3. About University College London
Founded in 1826, UCL was the first English university established after Oxford and Cambridge, the first to admit students regardless of race, class, religion or gender, and the first to provide systematic teaching of law, architecture and medicine. In the government's most recent Research Assessment Exercise, 59 UCL departments achieved top ratings of 5* and 5, indicating research quality of international excellence.
UCL is in the top ten world universities in the 2007 THES-QS World University Rankings, and the fourth-ranked UK university in the 2007 league table of the top 500 world universities produced by the Shanghai Jiao Tong University. UCL alumni include Marie Stopes, Jonathan Dimbleby, Lord Woolf, Alexander Graham Bell, and members of the band Coldplay. Website: www.ucl.ac.uk