science-fiction fantasy of nanotechnology building
novel structures, devices, and materials at the atomic
or molecular scale is becoming a reality. For the
great potential of nanoscience and nanotechnology to be
fully realized, however, research efforts must cross many
disciplines, from electrical engineering, mechanical engineering,
materials science, and computer science to bioengineering,
chemistry, and physics.
is this cross-disciplinary approach fostered more than
at UC Berkeley. Each month, Lab Notes is proud
to present the work of nanotechnology researchers from
the College of Engineering and our collaborators across
New DNA Detectors Bridge the (Nano)Gap
by David Pescovitz
A bio-nano breakthrough at UC Berkeley may someday lead to devices that diagnose disease, detect evidence of bioterrorism, and aid in the discovery of new drugs. Most impressive though is that these devices, based on a DNA-sensing chip in development at Berkeley, will fit in your pocket.
Lee's collaborative pioneering research in nanotechnology, biophysics, and
bioengineering will establish new tools to detect and treat a variety of
diseases. Click for
Bioengineering professor Luke Lee, co-director of the Berkeley Sensor and Actuator Center, and his students recently demonstrated a tiny chip that instantly identifies DNA by its electrical properties.
Already available DNA microarrays, or "gene chips," enable the analyses
of DNA samples to identify biological substances. The silicon or
glass chips are embedded with tens of thousands of different fragments
of DNA whose double helix structure has been separated into single
strands. Each bit of reference DNA consists of a specific sequence
of bases the four letters that spell out the genetic code
that are unique to the disease or pathogen, for instance,
that the user is attempting to identify.
The sample-of-interest is also separated into single strands and then introduced onto the chip for analysis. Because certain letters in DNA always connect to specific other letters, the sample will only bind, or hybridize, with its complementary strand. By detecting which reference fragment the DNA sample binds most tightly to, the user can identify the DNA in question. The hassle though comes in trying to detect when the DNA strands bind, or hybridize.
"Most of the DNA detection systems commercially available today are based on optical detection," Lee says. "You have to label the DNA with a fluorescent molecule, excite it with a laser, and then detect the fluorescence."
Reference DNA sits inside this 50 nanometer wide gap. Click for larger
Other magnetic and electrochemical methods in development also require labeling steps and external detection apparatus. Not only are those processes time-consuming, Lee explains, but the detection apparatus is currently bulky and expensive.
Lee's approach is to replace the optics with electronics. Using
novel nanotechnology batch-fabrication techniques, Lee creates polysilicon
chips riddled with nanogap junctions, chasms just 50 nanometers
wide. Immobolized within each nanogap is a single strand of reference
DNA. A voltage is then applied across the nanogap and a measurement
is taken of the capacitance the ability of the conductors
to store charge. The capacitance is determined by the dielectric
(insulating) property of the material in the nanogap, which changes
as a result of hybridization.
"Then you add the sample DNA and measure the difference after hybridization," Lee says. "You look for a complementary match based on the electrical signal."
Currently, Lee and his team are working to improve the sensitivity
of their device. The next step in the research, he says, is to design
a nanofluidic system, essentially nanoscale plumbing, to control
the flow of the DNA samples through the nanogap junction arrays.
"Our work," Lee says, "is really at the interface between solid-state
electronics and soft-state biopolymers," molecules formed by living
BioPOEMS at UC Berkeley
"Nano-Microscope Spots Single Molecules"
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