High-speed reading of the genetic code should get a boost with the creation
of the world's first graphene nanopores - pores measuring approximately 2
nanometers in diameter - that feature a 'built-in' optical antenna.
Researchers with Berkeley Lab and the University of California (UC) Berkeley
have invented a simple, one-step process for producing these nanopores in a
graphene membrane using the photothermal properties of gold nanorods.
"With our integrated graphene nanopore with plasmonic optical antenna,
we can obtain direct optical DNA sequence detection," says Luke Lee, the
Arnold and Barbara Silverman Distinguished Professor at UC Berkeley.
Lee and Alex Zettl, a physicist who holds joint appointments with Berkeley
Lab's Materials Sciences Division and UC Berkeley's Physics Department, were
the leaders of a study in which a hot spot on a graphene membrane formed a
nanopore with a self-integrated optical antenna. The hot spot was created by
photon-to-heat conversion of a gold nanorod.
"We believe our approach opens new avenues for simultaneous electrical
and optical nanopore DNA sequencing and for regulating DNA translocation,"
says Zettl, who is also a member of the Kavli Energy Nanoscience Institute
Nanopore sequencing of DNA, in which DNA strands are threaded through
nanoscale pores and read one letter at a time, has been touted for its ability
to make DNA sequencing a faster and more routine procedure. Under today's
technology, the DNA letters are "read" by an electrical current
passing through nanopores fabricated on a silicon chip. Trying to read
electrical signals from DNA passing through thousands of nanopores at once,
however, can result in major bottlenecks. Adding an optical component to this
readout would help eliminate such bottlenecks.
"We obtain direct and enhanced optical signals at the junction of a
nanopore and its optical antenna," Lee says. "Simultaneously
correlating this optical signal with the electrical signal from conventional
nanopore sequencing provides an added dimension that would be an enormous
advantage for high-throughput DNA readout."
A key to the success of this study was the single-step photothermal
mechanism that enabled the creation of graphene nanopores with self-aligned
plasmonic optical antennas. The dimensions of the nanopores and the optical
characteristics of the plasmonic antennas are tunable, with the antenna
functioning as both optical signal transducer and enhancer. The atomically thin
nature of the graphene membrane makes it ideal for high resolution, high
throughput, single-molecule DNA sequencing. DNA molecules can be labeled with
fluorescent dyes so that each base-pair fluoresces at a signature intensity as
it passes through the junction of the nanopore and its optical antenna.
"In addition, either the gold nanoplasmonic optical antenna or the
graphene can be functionalized to be responsive to different base-pair
combinations," Lee says. "The gold plasmonic optical antenna can also
be functionalized to enable the direct optical detection of RNA, proteins,
protein-protein interactions, DNA-protein interactions, and other biological
The results of this study were reported in Nano Letters
in a paper
titled "Graphene Nanopore with a Self-Integrated Optical Antenna."
Lee is the corresponding author. Other co-authors in addition to Zettl were
SungWoo Nam, Inhee Choi, Chi-cheng Fu, Kwanpyo Kim, SoonGweon Hong and Yeonho
This research was primarily supported by the DOE Office of Science.