Facility for combined optical trapping, single-molecule fluorescence and microfluidics experiments on DNA
This instrument is built around an inverted optical microscope and designed for experiments on DNA with lengths ranging from ~2 to 20 micron. It consists of three modalities. (i) The sample is contained in a multichannel microfluidic flow cell, which allows for rapid buffer exchange. (ii) It employs two independently steerable optical traps (1064 nm, 3 Watt total power). One of the traps can be moved actuated via computer control. Force / displacement is measured by means of a position-sensitive detector and read out using a 24 bit ADC board. Force feedback is available for force-clamp measurements on the ~10 Hz time scale. (iii) Fluorescence arising from proteins or labels bound to the DNA can be detected, with single-fluorophore accuracy. Excitation light is provided by 473 nm, 532 nm and 633 nm continuous-wave lasers (powers up to 25 mW). Fluorescence images are detected using an EMCCD camera. Optical filters are available for detection of EGFP/fluorescein/Alexa 488, Cy3/Alexa 555, and Cy5/Alexa 647.
Some essential parts of the laser setup are displayed below: