FPGA-based real-time position-clamp control in optical tweezers, The Sequel: doi:10.1063/1.3257693 (first part here)

Some very early testing of fluorescence imaging in our optical tweezers instrument. A 10 kb long piece of DNA (ca 3 um long when stretched) is held between two optically trapped microspheres. The DNA is coated with a fluorescent dye (SYBR-gold) which is exited by a 488 nm blue laser and the fluorescence signal is [...]

I’m testing an EMCCD camera. This is a video of fluorescently labeled DNA through a 100x epi-fluorescence microscope. Or you can try a slightly better quality wmv-download (82 Mb) Once we’ve had time to practice some more, it should look much cooler, something like these DNA-curtains, or DNA-ejection from bacteriophage lambda. But it’s a start. Also [...]

I need this seldom enough to forget how it’s done – but then it’s annoying to have to think/google for the solution again when I do need it… So I’ll document here. The task is to generate uniformly distributed numbers within a circle of radius R in the (x,y) plane. At first polar coordinates seems [...]

I presented one slide and a 3 minute video as a case-study during the  keynote presentation at Helsinki NIDays 2009 this morning.

Here a DNA-molecule is being stretched between two optically trapped polystyrene micron-sized beads. We’re using an FPGA-based real-time controller for steering the upper trap. It’s programmed with a PI-loop which aims to keep the force acting on the lower bead constant. Around 10s into the video we switch on the feedback-loop and we see the [...]

A ~48 000 base-pair long (ca 16 um) piece of DNA is stretched between two optically trapped ca 2 um diameter polystyrene beads. Bright-field real-time view through a 100x microscope. Scale-bar in microns on the right.

Were stretching a 13 kb DNA-construct between two optically trapped beads. This isn’t a video of the experiment itself, but of some entangled beads we found in an old sample. The beads are 3 or 2 micron in diameter, and we hold on to the middle big bead with the optical trap while moving around [...]