To identify a disease, build a better Petri dish
Here is something that couldn’t have been done a decade ago; researchers at the California Institute of Technology have designed and built an extremely portable imaging system for observing living cells in culture. This article on Science Daily reports a study published in the biomedical journal PNAS, that offers an inexpensive way to keep an eye on microorganisms growing in the incubator. The technique, called subpixel perspective sweeping microscopy (SPSM), uses a current model smartphone LCD screen for illumination. In the prototype device mocked up in the picture, a 6 mm by 4 mm plastic culture device (picture D) is directly attached to a CMOS detector, which is assembled into a manifold constructed from LEGO bricks to hold the smartphone/light source (picture E/F). The inherent problem with this approach is that current CMOS imaging devices have a resolution limit of approximately 2 micron pixel size, which would make for a very pixelated image when enlarged without optical magnification. To solve this, the researchers used the smartphone LCD screen to tilt and shift the illumination of the Petri dish during image acquisition. The degree of shift of illumination is smaller than the 2 micron pixel size, and consequently a series of low resolution “shadow” images are generated. These images are combined by software to generate a single, higher-resolution image that achieves a much improved limit of resolution that is comparable to optical magnification.
So, what do the pictures look like? Actually, very nice indeed. Panel A to the right indicates the field of view of the ePetri dish using the image detection scheme. To put this in perspective, the researchers have indicated the field of view of a standard 40x objective by putting a small circle at the bottom of that image. Note that using the ePetri approach, the entire dish is observed at once, and can be done so in real time. Panels B1 and C1 demonstrate the raw images obtained using the ePetri system, which appear pixelated due to the limit of resolution by the CMOS sensor. Combination of approximately 200 separate shadowed images was used to produce the images in B2 and C2 respectively. For comparison, Panel D shows an image acquired microscopically using a standard 40x magnification objective, and demonstrates a comparable level of detail. The ePetri setup has the advantage of capturing a much larger region in a single image.
I’ve already noticed ambitious BIO230 students holding their cameraphones up to the oculars of our microscopes to capture images for their lab notebooks. The ubiquity and precision of these devices is already changing the way we look at the world, even in Microbiology lab.