A smart Petri dish does away with the need for bulky microscopes and significantly reduces human labor time, while improving the way in which bacterial culture growth can be recorded.

Imaging sensor chips, similar to those in built-in cameras of cell phones, transform the way cell cultures are imaged by serving as a platform for the smart Petri dish. The device, dubbed ePetri, was built by engineers at the California Institute of Technology (Caltech; Pasadena, CA, USA) using a Google smart phone, 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. As the image sensor takes pictures of the culture, the information is sent out to the laptop, enabling scientists to acquire and save images of the cells as they are growing in real time. The technology is particularly useful for imaging confluent cells--those that grow very close to one another and typically cover the entire Petri dish.

Biologists use Petri dishes primarily to grow cells. In the medical field, they are used to identify bacterial infections, such as tuberculosis. Conventional use of a Petri dish requires that the cells being 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.

"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," explained Guoan Zheng, lead author of the study and a graduate student in electrical engineering at Caltech. "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."

Changhuei Yang, senior author of the study and professor of electrical engineering and bioengineering at Caltech, and his team believe that the ePetri system will open up a whole range of new approaches to many other biological systems. For example, ePetri could provide microscopy-imaging capabilities for other portable diagnostic lab-on-a-chip tools.

The team is working to build a self-contained system that would include its own small incubator. This would make the system more useful as a desktop diagnostic tool that could be housed in a doctor's office, reducing the need to send bacteria samples out to a lab for testing.

The device is described in a paper that appears online in the Proceedings of the National Academy of Sciences (PNAS) in September 2011.

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