Nonstick and laser-safe gold aids laser trapping of biomolecules

Jun 17, 2009
The gold posts in this colorized micrograph, averaging 450 nanometers in diameter, are used to anchor individual biomolecules such as DNA for studies of their mechanical properties. The background surface is glass coated with a protein to prevent unwanted sticking. Credit: D.H. Paik/JILA

Biophysicists long for an ideal material -- something more structured and less sticky than a standard glass surface—to anchor and position individual biomolecules. Gold is an alluring possibility, with its simple chemistry and the ease with which it can be patterned. Unfortunately, gold also tends to be sticky and can be melted by lasers. Now, biophysicists at JILA have made gold more precious than ever—at least as a research tool—by creating nonstick gold surfaces and laser-safe gold nanoposts, a potential boon to laser trapping of biomolecules.

JILA is a joint institute of the National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder.

JILA’s successful use of gold in optical-trapping experiments, reported in Nano Letters, could lead to a 10-fold increase in numbers of single molecules studied in certain assays, from roughly five to 50 per day, according to group leader Tom Perkins of NIST. The ability to carry out more experiments with greater precision will lead to new insights, such as uncovering diversity in seemingly identical molecules, and enhance NIST’s ability to carry out mission work, such as reproducing and verifying piconewton-scale force measurements using DNA, Perkins says. (A one-kilogram mass on the Earth’s surface exerts a force of roughly 10 newtons. A piconewton is 0.000 000 000 001 newtons. See “JILA Finds Flaw in Model Describing DNA Elasticity” NIST Tech Beat, Sept. 13, 2007.)

Perkins and other biophysicists use laser beams to precisely manipulate, track and measure molecules like DNA, which typically have one end bonded to a surface and the other end attached to a micron-sized bead that acts as a “handle” for the laser. Until now, creating the platform for such experiments has generally involved nonspecifically absorbing fragile molecules onto a sticky glass surface, producing random spacing and sometimes destroying biological activity. “It’s like dropping a car onto a road from 100 feet up and hoping it will land tires down. If the molecule lands in the wrong orientation, it won’t be active or, worse, it will only partially work,” Perkins says.

Ideally, scientists want to attach biomolecules in an optimal pattern on an otherwise nonstick surface. Gold posts are easy to lay down in desired patterns at the nanometer scale. Perkins’ group attached the DNA to the gold with sulfur-based chemical units called thiols (widely used in nanotechnology), an approach that is mechanically stronger than the protein-based bonding techniques typically used in biology. The JILA scientists used six thiol bonds instead of just one between the DNA and the gold posts. These bonds were mechanically strong enough to withstand high-force laser trapping and chemically robust enough to allow the JILA team to coat the unreacted gold on each nanopost with a polymer cushion, which eliminated undesired sticking. “Now you can anchor DNA to gold and keep the rest of the gold very nonstick,” Perkins says.

Moreover, the gold nanoposts were small enough—with diameters of 100 to 500 nanometers and a height of 20 nanometers—that the scientists could avoid hitting the posts directly with lasers. “Like oil and water, traditionally tweezers and gold don’t mix. By making very small islands of gold, we positioned individual molecules where we wanted them, and with a mechanical strength that enables more precise and additional types of studies,” Perkins says.

Citation: D.H. Paik, Y. Seol, W. Halsey and T.T. Perkins. Integrating a high-force optical trap with nanoposts and a robust gold-DNA bond. Nano Letters. Publication Date (Web): June 3, 2009 DOI: 10.1021/nl901404s.

Source: National Institute of Standards and Technology (NIST)

Explore further: Nanocontainers for nanocargo: Delivering genes and proteins for cellular imaging, genetic medicine and cancer therapy

add to favorites email to friend print save as pdf

Related Stories

Gold Nanoparticles Prove to Be Hot Stuff

Aug 31, 2006

Gold nanoparticles are highly efficient and sensitive “handles” for biological molecules being manipulated and tracked by lasers, but they also can heat up fast—by tens of degrees in just a few nanoseconds—which ...

JILA Finds Flaw in Model Describing DNA Elasticity

Sep 17, 2007

DNA, the biomolecule that provides the blueprint for life, has a lesser-known identity as a stretchy polymer. JILA scientists have found a flaw in the most common model for DNA elasticity, a discovery that will improve the ...

Adenine ‘Tails’ Make Tailored Anchors for DNA

Dec 22, 2006

Researchers from the National Institute of Standards and Technology, the Naval Research Laboratory and the University of Maryland have demonstrated a deceptively simple technique for chemically bonding single ...

Gold Nanostars Outshine the Competition

Oct 15, 2008

(PhysOrg.com) -- Novel nanoparticles being tested at the National Institute of Standards and Technology have researchers seeing stars. In a recent paper,* NIST scientists used surface-enhanced Raman spectroscopy ...

Electric Jolt Triggers Release of Biomolecules, Nanoparticles

Sep 11, 2006

Johns Hopkins researchers have devised a way to use a brief burst of electricity to release biomolecules and nanoparticles from a tiny gold launch pad. The technique could someday be used to dispense small amounts of medicine ...

Recommended for you

Twisted graphene chills out

Sep 17, 2014

(Phys.org) —When two sheets of graphene are stacked in a special way, it is possible to cool down the graphene with a laser instead of heating it up, University of Manchester researchers have shown.

Researchers use liquid inks to create better solar cells

Sep 17, 2014

(Phys.org) —The basic function of solar cells is to harvest sunlight and turn it into electricity. Thus, it is critically important that the film that collects the light on the surface of the cell is designed ...

User comments : 0