Jul 14, 2009
Tiny bead gathers data inside living cell
A traditional photonic-force microscope (PFM) – an instrument that uses optical trapping to measure intracellular properties such as stiffness or viscoelastic moduli – results in huge sets of data, which require tedious numerical analysis. To get around the problem, researchers in Switzerland and Poland have teamed up to develop an analog signal processor that can attain real-time capabilities while retaining the richness of the traditional PFM data.
The system is devoted to intracellular measurements and is fully interactive through the use of a haptic joystick. The force-feedback mechanism allows the user to interactively guide an optically trapped bead and obtain the stiffness matrix of a liquid or biological sample with high spatial resolution (a few nanometres) and an update frequency of 1 kHz.
Using specialized analog hardware along with a dedicated algorithm, the researchers can extract the full 3D stiffness matrix of the optical trap in real time, including the off-diagonal cross-terms. The hardware is also capable of simultaneously recording data for subsequent offline analysis, which allows the team to check that a good correlation exists between the classical analysis of stiffness and the system's real-time measurements.
Instantaneous stiffness measurements are displayed in real time on a graphical user interface. The whole system has been built and is operational. Early results have been reported in Nanotechnology that confirm the consistency of the real-time measurements with offline computations.
This work was financed by GEBERT RüF STIFTUNG.
About the author
Andrzej Kulik is a research associate based at the Institute of Physics of Condensed Matter – EPFL. From August 2009 he will be working at the Institute of Physics of Biological Systems, Laboratory of Physics of Living Matter – EPFL.