Today, the venerable Petri dish for culturing living cells is still in wide use even though it has not changed substantially since it was invented in the 19th century by Julius Richard Petri. Now Caltech wants to bring the Petri dish into the 21st century. By disassembling a smartphone and using its camera and display to monitor and illuminate, Caltech's "smart" Petri dish can monitor cell culture activity 24/7.
Researchers use Petri dishes to grow samples of selected micro-organisms, often merely to multiply their number enough to determine their type. For instance, a sample from a throat swab might be cultured in a Petri dish with a medical technician monitoring it until enough has grown to use in tests to see what variety of bug is making the patient's throat sore.
Often, after samples are grown, they are transferred to many other Petri dishes in which individual tests can be run to determine which drug works best. Here again, a lab technician must visually inspect each Petri dish to see if the culture is still growing--showing immunity to the drug--or whether growth is suppressed by the drug. Many other related uses of Petri dishes are made in other biological research areas, but they all share the same disadvantage of requiring trained technicians to monitor growth.
Caltech wants to change all that by making the Petri dish smart. And what better way to do that than to use the microelectronic components from a smartphone to automate their monitoring? Dubbed "ePetri" the new smart cell-culture dish was announced this month in the prestigious "Proceedings of the National Academy of Sciences."
To be sure, medical test automation is also being pursued by drug companies and other researchers using expensive microchip arrays that can culture as many as a million separate samples simultaneously. However, the Caltech invention shows how even the humblest research lab can profit from individual ePetri dishes using inexpensive smartphone components.
Individual Petri dishes are usually inserted into an incubator with dozens of other samples, each of which must be manually removed and periodically inspected to visually inspect and record how much growth has occurred since the last inspection. The ePetri dish, on the other hand, can monitor cell growth 24/7 as well as allow a technician sitting at a computer to quickly inspect it without removing it from the incubator. This not only saves time, but also reduces the risk of contamination.
"We can directly track the cell culture or bacteria culture within the incubator," said doctoral candidate Guoan Zheng who works in the Caltech lab of electrical engineer and bioengineering professor Changhuei Yang. "The data from the ePetri dish automatically transfers to a computer outside the incubator by a cable connection."
Caltech’s ePetri dish uses inexpensive smartphone components.
The poor-man's ePetri dish was assembled atop a standard cell phone image sensor chip in a rig constructed from, believe it or not, Lego building blocks. The cell culture is placed directly on the image sensor chip, thus eliminating the need for the expensive camera and lens system that is used to monitor cultures in multi-well microchip arrays. The smartphone's screen was mounted above the ePetri dish to illuminate it. A smartphone's Android app was then used to monitor growth 24/7 and record the images, which are accessed on a computer directly connected to the ePetri by USB.
For the future, the researchers want to integrate the ePetri dish with a built-in incubator so that a handheld lab-on-a-chip-type device could be used in a doctor’s office or in the field for remote diagnostics.
Other researchers contributing to the work included Caltech biologist Michael Elowitz, postdoctoral scholar Yaron Antebi and doctoral candidate Seung Ah Lee. Funding came from the Coulter Foundation.