Smart Petri Dish Provides Lensless Imaging

Using a smartphone and some Lego blocks, engineers at California Institute of Technology have created a new way to analyze cell cultures on the fly.

Because the phone’s imaging chip is used as a quasi petri dish, the Caltech team has dubbed its product ePetri. The technology is described in the online edition of the Proceedings of the National Academy of Sciences.

Petri dishes are primarily used to grow cells, and they help identify bacterial infections such as tuberculosis. Conventional use of a petri dish requires that the cells to be cultured be placed in an incubator to grow. As the sample grows, it is removed — often numerous times — from the incubator to be studied under a microscope.

The ePetri, however, does away with bulky microscopes and significantly reduces human labor time, while improving the way in which the culture growth can be recorded.

In a new smart petri dish, a culture is placed on the image sensor chip (left), while a cell 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 outside the incubator. (Photo: Guoan Zheng, California Institute of Technology)

“Our ePetri dish is a compact, small, lens-free microscopy imaging platform. We can directly track the cell culture or bacteria culture within the incubator,” said Guoan Zheng, lead author of the study. “The data from the ePetri dish automatically transfers to a computer outside the incubator by a cable connection. Therefore, this technology can significantly streamline and improve cell culture experiments by cutting down on human labor and contamination risks.”

The team 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, while 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 outside the incubator, which saves images of the cells as they are growing in real time. The technology is adept at imaging confluent cells — those that grow very close to one another and that typically cover the entire petri dish.

“Until now, imaging of confluent cell cultures has been a highly labor-intensive process in which the traditional microscope has to serve as an expensive and suboptimal workhorse,” said Changhuei Yang, senior author of the study. “What this technology allows us to do is create a system in which you can do wide-field-of-view microscopy imaging of confluent cell samples. It capitalizes on the use of readily available image sensor technology, which is found in all cell phone cameras.”

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 use in basic research.

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 its lens’s limitations, a researcher effectively wears blinders and can focus on only one region of the petri dish at a time, Elowitz said. By using the ePetri platform, however, Elowitz could follow the stem-cell changes over the entire surface of the device.

“It radically reconceives the whole idea of what a light microscope is,” he said. “Instead of a large, heavy instrument full of delicate lenses, Yang and his team have invented a compact lightweight microscope with no lens at all, yet one that can still produce high-resolution images of living cells. Not only that, it can do so dynamically, following events over time in live cells, and across a wide range of spatial scales from the subcellular to the macroscopic.”

For more information, visit: www.caltech.edu