The current resolution of the SROFM is 0.75 microns, which is comparable to a light microscope at 20 times magnification, says Guoan Zheng, lead author of a recent paper on the work, published in the journal Lab on a Chip.

The sensor has pixels that are 3.2 microns on each side. A "super resolution" algorithm assembles multiple images (50 for each high-resolution image) to create an enhanced resolution image--as if the screen had pixels 0.32 microns in size. However, super-resolution techniques can only distinguish features that are separated by at least one pixel, meaning the final resolution must be at least twice the pixel size. This is why a .32 micron pixel size yields only a resolution of .75 microns.

Zheng's technique uses only a small portion of the chip, allowing him to capture cells at a relatively high frame rate of 300 frames per second. This yields a super-resolution "movie" of a cells at six frames per second.

Using a higher-resolution CMOS sensor should allow an even better ultimate resolution, says Seung Ah Lee, another collaborator on the project. Lee wants to get the resolution up to the equivalent of 40x magnification, so that the technique can be used for diagnosis of malaria via automated recognition of abnormal blood cells.

Aydogan Ozcan, a professor at UCLA who is developing a competing approach, says that Zheng's work is "a valuable advance for optofluidic microscopy," in that this system is simpler, offers higher resolution, and is easier to use than previous microscopes. However, Ozcan says that the technique has limitations.

The microfluidic channel must be quite small, says Ozcan, which means the approach can't be applied to particles that might vary greatly in size, and the channel must be built to accommodate the largest particle that might flow through it. Ozcan's own lensless microscope does not use microfluidic channels, and instead captures a "hologram" of the sample by interpreting the interference pattern of an LED lamp shining through it. This method has no such limitations.

"From my perspective, these are complementary approaches," says Ozcan, whose ultimate aim is cheap, cell-phone based medical diagnostic tools for the developing world.