The team at Caltech built the Petri dish platform prototype using a Google smart phone, a commercially available cell-phone image sensor and Lego building blocks. The result is a system that lets researchers acquire and save images of the cells as they are growing, in real time.
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.
The ePetri removes the need for microscopes, which biologists have been using to observe growing cultures since the late 1800s. The culture is placed on the image-sensor chip, while the phone’s LED screen is used as a scanning light source. The chip automatically transfers data to a computer via cable, all from inside the incubator.
‘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. ‘Therefore, this technology can significantly streamline and improve cell culture experiments by cutting down on human labour and contamination risks.’
‘Until now, imaging of confluent cell cultures has been a highly labour-intensive process in which the traditional microscope has to serve as an expensive and suboptimal workhorse,’ said Changhuei Yang, senior author of the study and professor of electrical engineering and bioengineering at Caltech. ‘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 capitalises on the use of readily available image-sensor technology, which is found in all cell-phone cameras.’
Allowing scientists to view the entire petri dish at once is an important advantage for Caltech biologist Professor Michael Elowitz, who is using 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 other more specialised cells. Using a conventional microscope with its lens’s limitations, a researcher effectively wears blinders and is only able to focus on one region of the petri dish at a time, said Prof. Elowitz.
‘It radically re-conceives the whole idea of what a light microscope is,’ said Prof. Elowitz. ‘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 sub-cellular to the macroscopic.’