Disk Spinning Unit (DSU) From Olympus

The Olympus Disk Spinning Unit (DSU) is a relatively recent technological advancement in the field of microscopy-based cellular research that employs fluorophores. The principle is based upon a small disk that has defined slits in it. When this disk is inserted into the light path and spins (~3,000 rpm) it has the effect of creating a virtual pinhole, which partially mimics a truly confocal microscope.

There are five different DSU disks (DISK-1 to -5), which have varying slit width and spacing and are used depending on both the specimen thickness and objective lenses used. Although a trained user can easily interchange the DSU disks, it is essential that the disk be tightened sufficiently as even a slight off-axis wobble has the potential of producing significantly blurry images.

We have been using an Olympus DSU with an Olympus IX-81 research microscope on a semi-daily basis for the past 4 years and have been very pleased with it. Our lab works on polarized cultured renal epithelial cells and we image both apical and basolateral aspects of these cells. We found that regular wideflour imaging of multiple Z-focal planes results in poor quality images due to the inherent fuzziness caused by the out-of-focus light. However, with the DSU in place we are able to acquire far superior image stacks from which we can generate clean axial projections in the Z-plane.

Although primarily advantageous for thicker biological specimens, we have also found the DSU to be useful at higher magnifications (e.g. oil-based 63 – 100x objectives) in studies where we are interested in the co-localization of two or more distinct fluorophore-labeled cellular proteins.

One of the disadvantages of the DSU is that the generation of a virtual pinhole results in a significant (~95%) decrease in the amount of light reaching the sample. As a result, we found that weak fluorescent signals were not ideal for DSU-mediated image acquisition using our CCD camera (Qimaging Retiga EXi). However, with the advent of more sensitive EM (electron multiplying)-CCD cameras this should become significantly less of a concern. Furthermore, researchers interested in confocal based live cell imaging would gain considerable benefit from a DSU; traditional laser based confocal systems cannot be used for live cell imaging due to the intensity of the lasers and the slow scan times.

The Olympus DSU would more than adequately serve the needs of a budget-conscious research lab that generates a lot of image data utilizing fluorophore-labeled biological samples and is interested in the ability to acquire confocal images, especially in a live cell imaging setting.