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.

This 8-channel pressure-gauge card is a step towards proper control of fluid flow in microfluidic devices. The transducers (0-1 psi) are around 30 eur each and made by Honeywell. The mV-level signal from a Wheatstone bridge in the transducer is amplified by an instrumentation amplifier (INA111) to around 0-10 V for input to a 16-bit [...]

Wallin, A.E., Salmi, A., Tuma, R. (2007). Step Length Measurement–Theory and Simulation for Tethered Bead Constant-Force Single Molecule Assay. Biophysical Journal, 93(3), 795-805. DOI: 10.1529/biophysj.106.097915 A lot of single molecule experiments are carried out in the configuration shown above. The idea is to mechanically probe a bio-molecule (such as DNA or RNA) or find out [...]

I’ve worked on steering our Optical Tweezers instrument using Acousto Optical Deflectors. Here’s an example of what it can do. We’re trapping four 1 um silica microspheres in water using a single 1064nm laser that is time shared between the beads (it hops between them at a fast rate). Then we can program the AODs [...]