Graphene camera to help 'see' electric signals in heart, brain

Scientists have developed a highly sensitive camera system with graphene film that can help map tiny electric fields in a liquid - an advance that will allow more extensive and precise imaging of electrical signals in our hearts and brains.
The ability to visually depict the strength and motion of very faint electrical fields may also aid in the development of 'lab-on-a-chip' devices that use very small quantities of fluids on a microchip-like platform to diagnose disease or aid in drug development.
The setup could potentially be adapted for sensing or trapping specific chemicals and for studies of light-based electronics.

"This was a completely new, innovative idea that graphene could be used as a material to sense electrical fields in a liquid," said Jason Horng, from Kavli Energy NanoSciences Institute, a joint institute at Lawrence Berkeley National Laboratory (Berkeley Lab) and University of California, Berkeley in the US.
"The basic concept was how graphene could be used as a very general and scalable method for resolving very small changes in the magnitude, position, and timing pattern of a local electric field, such as the electrical impulses produced by a single nerve cell," said Halleh B Balch, a PhD student at UC Berkeley.

"One of the outstanding problems in studying a large network of cells is understanding how information propagates between them," Balch said.

Other techniques developed to measure electrical signals from small arrays of cells can be difficult to scale up to larger arrays and in some cases cannot trace individual electrical impulses to a specific cell.
"This new method does not perturb cells in any way, which is fundamentally different from existing methods that use either genetic or chemical modifications of the cell membrane," said Bianxiao Cui, from Stanford University.
The new platform should more easily permit single-cell measurements of electrical impulses traveling across networks containing 100 or more living cells, researchers said.

Researchers first used infrared light to understand the effects of an electric field on graphene's absorption of infrared light.
In the experiment, they aimed an infrared laser through a prism to a thin layer called a waveguide.
The waveguide was designed to precisely match graphene's light-absorbing properties so that all of the light was absorbed along the graphene layer in the absence of an electric field.
Researchers then fired tiny electrical pulses in a liquid solution above the graphene layer that very slightly disrupted the graphene layer's light absorption, allowing some light to escape in a way that carried a precise signature of the electrical field.

They captured a sequence of images of this escaping light in thousandths-of-a-second intervals and these images provided a direct visualisation of the electrical field's strength and location along the surface of the graphene.