Credit: Kansas State Univ.
It’s a cloak that surpasses all others: a microscopic carbon cloak made of
graphene that could change the way bacteria and other cells are imaged.
assistant professor of chemical engineering at Kansas State Univ., and his
research team are wrapping bacteria with graphene to address current challenges
with imaging bacteria under electron microscopes. Berry’s method creates a carbon cloak that
protects the bacteria, allowing them to be imaged at their natural size and
increasing the image’s resolution.
Graphene is a form of carbon that is only one atom thick, giving it several
important properties: it’s impermeable, it’s the strongest nanomaterial, it’s
optically transparent, and it has high thermal conductance.
“Graphene is the next-generation material,” Berry said. “Although only an atom
thick, graphene does not allow even the smallest of molecules to pass through.
Furthermore, it’s strong and highly flexible so it can conform to any
Berry’s team has been researching graphene
for three years, and Berry
recently saw a connection between graphene and cell imaging research. Because
graphene is impermeable, he decided to use the material to preserve the size of
bacterial cells imaged under high-vacuum electron microscopes.
The research results appear in the paper “Impermeable Graphenic Encasement
of Bacteria,” appears in Nano
The current challenge with cell imaging occurs when scientists use electron
microscopes to image bacterial cells. Because these microscopes require a high
vacuum, they remove water from the cells. Biological cells contain 70% to 80%
water, and the result is a shrunken cell. As a result, it is challenging to
obtain an accurate image of the cells and their components in their natural
and his team created a solution to the imaging challenge by applying graphene.
The graphene acts as an impermeable cloak around the bacteria so that the cells
retain water and don’t shrink under the high vacuum of electron microscopes.
This provides a microscopic image of the cell at its natural size.
The carbon cloaks can be wrapped around the bacteria using two methods. The
first method involves putting a sheet of graphene on top of the bacteria, much
like covering up with a bed sheet. The other method involves wrapping the
bacteria with a graphene solution, where the graphene sheets swaddle the
bacteria. In both cases the graphene sheets were functionalized with a protein
to enhance binding with the bacterial cell wall.
Under the high vacuum of an electron microscope, the wrapped bacteria did not
change in size for 30 minutes, giving scientists enough time to observe them.
This is a direct result of the high strength and impermeability of the graphene
Graphene’s other extraordinary properties enhance the imaging resolution in
microscopy. Its electron-transparency enables a clean imaging of the cells.
Since graphene is a good conductor of heat and electricity, the local
electronic-charging and heating is conducted off the graphene cloak, giving a
clear view of the bacterial cell well. Unwrapped bacterial cells appear dark with
an indistinguishable cell wall.
“Uniquely, graphene has all the properties needed to image bacteria at
high resolutions,” Berry
said. “The project provides a very simple route to image samples in their
native wet state.”
The process has potential to influence future research. Scientists have
always had trouble observing liquid samples under electron microscopes, but
using carbon cloaks could allow them to image wet samples in a vacuum.
Graphene’s strong and impermeable characteristics ensure that wrapped cells can
be easily imaged without degrading them. Berry
said it might be possible in the future to use graphene to keep bacterium alive
in a vacuum while observing its biochemistry under a microscope.
The research also paves the way for enhanced protein microscopy. Proteins
act differently when they are dry and when they are in an aqueous solution. So
far most protein studies have been conducted in dry phases, but Berry’s research may
allow proteins to be observed more in aqueous environments.