Smart petri dish analyzes cell growth
PASADENA, Calif. — Built from a smartphone, a commercially available cell phone image sensor and some Lego blocks, ePetri isn't like other petri dishes. The compact, lens-free microscopy imaging platform can track cell cultures and bacteria as they incubate.
Petri dishes have been used primarily to grow cells and to help identify bacteria at the center of infections such as tuberculosis. Their conventional use with cultures requires cells to be placed in an incubator. As a sample grows inside the platter, it is removed — often numerous times — from the incubator to be studied under a microscope.
A new ePetri prototype allows biologists and clinicians to study cell cultures as they grow. Images courtesy of Guoan Zheng.
The technology streamlines and improves cell culture experiments because data from the ePetri dish is automatically transferred to a computer outside the incubator by a cable connection, said ePetri developer Guoan Zheng, a California Institute of Technology graduate student. This eliminates possible contamination risks and cuts back on human labor.
Zheng and colleagues built the platform prototype using a Google smartphone, a commercially available cell phone image sensor and Lego building blocks. The culture is placed on the image sensor chip, and the phone's LED screen is used as a scanning light source. The device is placed in an incubator with a wire running from the chip to a laptop, which saves real-time images of cell growth. It is adept at imaging confluent cells — those that grow very close to one another and that typically cover the entire petri dish.
The ePetri imaging platform uses the LED screen of a smartphone as the scanning light source. The holder was built, in part, using Lego blocks.
Until now, confluent cell culture imaging has proved to be a labor-intensive process. With the new technology, scientists can use wide-field-of-view microscopy imaging on confluent cell samples.
"This lensless microscopy approach has several advantages," said Changhuei Yang, a professor of electrical engineering and bioengineering at Caltech. "Unlike other chip-scale microscopy work that is in progress, this approach allows imaging of confluent cell cultures without caveats or restrictions. As such, it enables us to fully realize the concept of a self-imaging petri dish with microscopy resolution."
In addition to simplifying medical diagnostic tests, the ePetri platform may be useful in areas such as drug screening and detection of toxic compounds. It has also proved to be practical for basic research. The device was described online Oct. 3 in the Proceedings of the National Academy of Sciences (doi: 10.1073/pnas.1110681108).
Michael Elowitz, a co-author on the study, has used the ePetri system to observe embryonic stem cells. Stem cells in different parts of a petri dish often behave differently, changing into various types of more specialized cells. Using a conventional microscope with the limitations of its lens, a researcher effectively wears blinders and can focus on only one region of the petri dish at a time, Elowitz said. The ePetri platform, however, allowed Elowitz to follow the stem-cell changes over the entire surface of the device.
Yang and his team believe that the ePetri system is likely to open a variety of new approaches to other biological systems as well. They are working to build a fluorescence-capable version and one that incorporates an incubator.
The incubator-ePetri combination is especially useful for clinicians, Yang explained. "Instead of having to send samples to a consolidated lab for incubation and analysis, a [general practitioner] can do culture growth and analysis with his or her lab easily."
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