Researchers at the Marine Biological Laboratory have designed a microscope that allows scientists to see the alignment of molecules in a sample as it spins at high speed in a centrifuge. With this device, scientists will be able to see the changes that occur in living cells as they experience forces up to 10,000 times that of the Earth's gravity.
The device, called a centrifuge polarizing microscope, works by synchronizing a polarized laser pulse to the motion of the centrifuge. Much like a strobe light, an extremely short pulse (about 6 ns) illuminates the specimen each time it flashes by the microscope objective. The resulting image has a resolution of better than 1 µm, and the polarized illumination gives it a sensitivity of better than a nanometer retardance. Thus scientists can see the alignment of a few strands of protein, DNA or membranes as the force of the centrifuge causes them to stratify.
According to Shinya Inoué, who developed the device with researchers from Hamamatsu and Olympus, the synchronization is crucial to its success. The laser pulses must be very short and be timed so that as the sample passes the objective, the image remains still.
Inoué explained that the microscope, which has been in development for about a year, could have far-reaching implications in biology and in nonbiological applications. He said that an interesting possibility is to use it to study sickle-cell anemia, a disease that causes hemoglobin in some red blood cells to crystallize and form a characteristic crescent-shaped cell.
Inoué's group at the Marine Biology Laboratory is using the device to study the polymerization state of microtubules and their force-generating mechanisms for moving organelles in living cells.
He said the microscope also has potential for studying liquid crystals and the suspension of molecules in emulsions. "We just finished developing the instrument," Inoué said. "We haven't really explored its potential yet, but it should be useful anywhere that polarized light is used to examine molecular alignment and density-dependent stratification."
The device uses a frequency-doubled Nd:YAG laser from New Wave Research of Sunnyvale, Calif. Hama-matsu Photonics K.K. furnished the control circuitry for the laser and a video camera that has a fiber optic faceplate in addition to its charge-
coupled device. The faceplate overcomes the interference of light from the highly monochromatic laser. Olympus Optical Co. Ltd. provides the microscope optics and mechanics,
Inoué said they will continue their work on microtubules, but that he is eager to explore other applications and hopes to combine the microscope with contrast enhancement methods other than polarized light.