Scientists have developed a sterilizing
graphene filter that captures microbes
and their harmful products from the air
and destroys them. 

They envisage the
device being useful in hospitals and
other healthcare settings.

Scientists may have found a way to trap and kill
bacteria in hospital settings.

Each year, around 1 in 25 patients in the United
States acquire at least one infection due to hospital
care, according to the Centers for Disease Control
and Prevention (CDC).

A recent paper in the journal ACS Nano describes
the self-sterilizing graphene filter and how it
performed in tests.

The device is the brainchild of study senior author
James M. Tour, Ph.D., and his team at Rice
University in Houston TX, where Tour holds
professorships in materials science and
nanoengineering, as well as chemistry and computer
science.

"So many patients become infected by bacteria
and their metabolic products, which, for example,
can result in sepsis while in the hospital," says
Prof. Tour.

The filter incorporates laser-induced graphene (LIG)
technology. Graphene is a form of carbon that is
extremely thin, very strong, and able to conduct
electricity.

Graphene has many applications, which, in addition
to medicine, can range from digital electronics to
aerospace engineering.

LIG is a porous graphene foam that forms when an
industrial laser cutter heats the surface of a sheet of
polyimide, a common high strength polymer.

Since Prof. Tour and his team discovered the
process for making LIG in 2014, it has given rise to
many applications ranging from electronics to art.

The team found that they could adapt LIG for use as
a filter by forming graphene on both sides of the
polyimide. This produces a thin – but strong – 3D
lattice of the polymer that reinforces the graphene
foam.

Eventually, they found that they could build a filter
comprising thick forests of conductive graphene
fibers on beds of interleaved sheets.

Because of its structure, the foam filter can
capture microorganisms, such as bacteria and
fungi, along with other airborne contaminants,
such as spores, prions, and various toxic
compounds that are present in aerosols, droplets,
and particles.

The filter traps and destroys what it captures by
periodically heating up to a temperature of 350°C
(660°F) as a result of electricity passing through it.
It does not need much power to reach this
temperature, and it only takes a few seconds to
cool down again.

Destroys harmful
molecules
The 350°C temperature is hot enough to kill
microorganisms and any byproducts that could feed
new microbes, as well as any "molecules that can
cause adverse biological reactions and diseases,"
note the authors.

"These molecules include pyrogens, allergens,
exotoxins, endotoxins, mycotoxins, nucleic acids,
and prions," they add.

"We need more methods," Prof. Tour explains, "to
combat the airborne transfer of not just bacteria but
also their downstream products, which can cause
severe reactions among patients."

"Some of these products, like endotoxins, need to
be exposed to temperatures of 300°C in order to
deactivate them," he adds.

Prof. Tour suggests that destroying bacteria-
producing molecules would significantly reduce the
risk of them spreading among patients, resulting in
shorter hospitalizations, less sickness, and fewer
deaths.

He and his team believe that a single custom-built
LIG filter could replace the two filters that hospitals
currently have to install in their ventilation systems
to comply with federal regulations.

In their study paper, the researchers describe how
they tested the LIG filter using a commercial
vacuum air filtration system that works by sucking
air at a rate of 10 liters per minute.

They ran the test for 90 hours without stopping. The
results showed that the heating method succeeded
in sterilizing the filters of all the pathogens and
their byproducts.

Potentially longer lasting
air filter
From culturing tests, the team also found that
bacteria did not pass through the LIG filter. The
tests involved culturing bacteria on a membrane
downstream of the filter.

The researchers also incubated used filters for 130
hours after the 90 hours of use and examined them.
They compared the results with those of incubated
filters that had not undergone any heating.
The results showed that the used LIG filters, which
had undergone repeated bouts of heating to
temperatures above 300°C, had not regrown any
bacteria during the incubation. This was not the
case with the unheated LIG filters.
The team suggests that the ability to self-sterilize
could give LIG filters a longer life so that users
would not need to replace them as often as the
more conventional air filters.
Prof. Tour also foresees a use for LIG filters in
commercial airplanes.