The Petri dish has been around for more than a century and is a fundamental piece of equipment for biology experiments. The first Petri dishes were made of glass but are now more likely to be made of transparent polystyrene. These dishes, which have existed for more than 50 years and which have remained largely unchanged during this time, are supposed to be biodurable – that is, unaffected by biological cultures and solutions. However, Andrei Sommer and colleagues of the University of Ulm have now found that this is not true on the nanoscale.

The researchers came to their conclusion by employing a nanoindenter – a device that measures hardness variations on the surface of a material. They found that the surface at the bottom of the polystyrene dish becomes significantly softer when in contact with an aqueous solution. This leads to the production of a nanoscopic layer of reactive oxygen species (ROS) that can weaken biological cells, says Sommer.

“ROS are reactive intermediates derived from oxygen and can be molecules (such as hydrogen peroxide, for example), radicals or ions. ROS can oxidize lipids and inactivate enzymes, resulting in cell damage.”

A Petri dish made of quartz glass coated with a layer of transparent, biocompatible nanodiamond would overcome this problem because it does not encourage the formation of a nanoscopic layer of ROS, he adds.

Implications for in vitro fertilization

Most in vitro fertilization (IVF) is performed in polystyrene Petri dishes, so cell damage during such a procedure would be very serious indeed, continues Sommer. ROS is thought to play an important role during IVF in which egg and sperm cells are “incubated” in a Petri dish. ROS damage may be even more significant during a particular process known as intra-cytoplasmic sperm injection, in which egg cells are stripped of their cumulus cells – a ROS-protective cell layer – before a sperm cell is injected into them. Scientists believe that ROS during IVF come from cell metabolism itself, from breakdown products when cells die and the microenvironment in which the cells are placed.

Preliminary tests using mouse embryonic carcinoma and primary cells show that diamond-coated dishes could be ideal platforms for in vitro experiments. However, there is one important drawback in that quartz glass Petri dishes coated with nanodiamond are expensive to make.

Cutting costs

“Our new results expose the shortcomings of traditional polystyrene Petri dishes and so might serve as a model to eventually inspire a cheaper and more disposable solution based on plastic,” Sommer told nanotechweb.org. “For the moment, and to cut costs, we recommend coating existing polystyrene dishes with a suitable nanolayer to seal the plastic, thereby preventing it from softening. The result could be a hybrid material Petri dish with unrivalled biocompatibility.”

Richard Rawlins of Rush University Medical Center in Chicago, who was not involved in this work, agrees. “The negative impact of ROS on human in vitro fertilization procedures has been known for many years,” he explained. “To counteract this problem, the culture medium used in IVF typically contains ROS scavengers to negate ROS impact. Sommer and colleagues’ discovery, which highlights that ROS are still active at the nanoscale, is important. Coating either plasticware or glassware to prevent ROS formation may significantly improve the viability and quality of embryos produced in vitro, and may even benefit other procedures in medicine, such as in vitro production of stem cell lines.”

The work is detailed in the Journal of Bionic Engineering.