Motivated to visualize calcium and neurotransmitters being released in brain tissue, which takes mere milliseconds, researchers from the University of Leicester, UK, have developed a “bolt-on” confocal system to improve the acquisition time of an existing camera and microscope. Using a low-cost light source, the new instrument matches the resolution of traditional confocal instruments but has a 100-fold increase in acquisition speed, sufficient to image high-speed calcium signaling in rat neurons.
Described in a paper published August 24 in PLoS One (1), the new instrument incorporates a digital micromirror device (DMD)—an inexpensive component found in consumer electronics like televisions and projectors— to define the patterns of sample illumination and detection. The DMD is an array of 1024 by 768 tiny mirrors that can each alternate between “on” or “off” and then can collect the light emitted from the sample.
The DMD used in the new instrument works on the same principle as the spinning disk technique—which uses an array of multiple pinholes arranged in a spiral that is spun to fill the image of a sample—except that the mirrors serve as pinholes. More importantly, the DMD is programmable. “You can choose the level of resolution that you want,” said study author Nicholas Hartell. “If you want something that’s very high resolution, you need to go a bit more slowly, but if you don’t mind losing a bit of resolution you can go incredibly fast.”
Although other groups incorporated DMDs in confocal instruments, none has reported major gains in image acquisition speed. In contrast, “we’ve used a system that allows us to turn the mirrors on and off much more rapidly,” said Hartell. Also, the optical configuration of mirrors that collect emitted light in the new instrument does so more efficiently than a lens-based system.
The new microscope is also relatively low-cost, partly because its light source, light-emitting diodes, is far less expensive than the lasers used in standard instruments. “Whereas, a bank of different wavelength lasers would cost tens of thousands of dollars, we can do [the light source] for probably about $100,” said Hartell.
In the new microscope, the detector now limits image acquisition. While Hartell’s group uses a charge-coupled device camera, a complementary metal-oxide semiconductor camera can be easily swapped in for an additional 10-fold boost in imaging speed. Now, his group is working with the University of Leicester’s Space Research Centre to incorporate an even faster detector, and he expects results within several months. Hartell’s team is also working to commercialize their instrument and have a potential partner to license the technology.
1. Martial, F.P., N.A. Hartell. 2012. Programmable illumination and high-speed, multi-wavelength, confocal microscopy using a digital micromirror. PLoS One 7(8): e43942
Related event: And if you're interested in microscopy, don't miss Daniel Larson from the National Cancer Institute speak about his work on the regulation and function of RNA in cells using multiphoton microscopy at our free virtual symposium. All registrants have a chance to win an iPad! So register today!