Dynamic position and force measurement for multiple optically trapped particles using a high-speed active pixel sensor

A high frame rate active pixel sensor designed to track the position of up to six optically trapped objects simultaneously within the field of view of a microscope is described. The sensor comprises 520 X 520 pixels from which a flexible arrangement of six independent regions of interest is accessed at a rate of up to 20 kHz, providing the capability to measure motion in multiple micron scale objects to nanometer accuracy. The combined control of both the sensor and optical traps is performed using unique, dedicated electronics (a field programmable gate array). The ability of the sensor to measure the dynamic position and the forces between six optically trapped spheres, down to femtonewton level, is demonstrated paving the way for application in the physical and life sciences. (C) 2009 American Institute of Physics. [doi:10.1063/1.3202381]