Single Molecule Projects
Trapping Nanoparticles in Solution: The Anti-Brownian ELectrokinetic
(ABEL) Trap
We have developed a new type of trap for nanoscale particles in solution,
the ABEL trap. It is interesting to have first demonstrated this trap in 2005, 100 years after Einstein's annus mirabilis,
in which one of his key papers of that year addressed the mechanisms
for Brownian motion: Annalen der Physik 17, 549 (1905).
Nanoscale objects in solution (such as proteins and DNA) are
continually bombarded by thermally agitated molecules of solvent.
This bombardment makes nanoscale objects jiggle around. The smaller
an object is, the faster (and farther) it jiggles. This jiggling,
also known as Brownian motion, makes the task of studying nano-objects
in solution very difficult: the opbjects just don't hold still.
The Anti-Brownian Electrokinetic trap (ABEL trap) eliminates
the Brownian motion of one object in solution, allowing detailed
examination of its properties. The ABEL trap works by tracking
the tiny Brownian displacements of the object, and then using
a feedback loop to apply electric fields to the solution to exactly
cancel these displacements.
To trap very tiny objects, we have to apply the feedback extremely
quickly--if there is too much delay, the object escapes before
the ABEL trap can bring it back to the target position. We recently
optimized the feedback so that we could trap _individual_ fluorescently
labeled protein molecules in solution. These molecules (as small
as 10 nm in diameter) are the first proteins trapped in solution
and the smallest objects ever trapped in solution. This achievement
opens the possibility of studying individual proteins free-floating
in solution. We also trapped individual fluorescent cadmium selenide
nanocrystals. These nanocrystals may potentially be used as nanoscale
light sources. Single molecules of DNA can also be trapped, which
show shape fluctuations at equilibrium in solution.
The ABEL trap gives scientists a new handle on the nano-world.
This idea should have applications in diverse areas, including
the trapping and study of single biomolecules, nanoscale fabrication,
and statistical physics/mechanics. Current projects are addressing conformational changes in trapped biomolecules, photophysics of antenna proteins, and the counting of protein subunits.
Press
summaries of the ABEL trap are also available.
Detailed Study: Conformations
of a Single DNA Molecule in Equilibrium
Related Publications
High speed hardware version of the ABEL trap: Controlling Brownian Motion of Single Proteins and Single Fluorophores in Aqueous Buffer, Optics Express 16, 6941-6956 (2008) [PDF]
Dynamics of Single DNA Molecules in Equilibrium, Proc. Nat. Acad. Sci. (USA) 104, 12596-12602 (published online May 11, 2007) [PDF] [Movie] [Supporting Information] [Journal Link]
Internal Mechanical Response of a Polymer in Solution, Phys. Rev. Lett. 98, 116001-(1-4) (2007)
[PDF] [Supporting Information]
Suppressing Brownian Motion of Individual Biomolecules in Solution (Proc. Nat. Acad. Sci. (USA) v. 103, 4362 (2006)) [PDF] [Journal link] [Supporting Material and Movies].
An All-Glass Microfluidic Cell for the ABEL Trap: Fabrication and Modeling (Proc. SPIE v. 5930, 59300S-1-S-8 (2005)) [PDF]
Control of Nanoparticles with Arbitrary Two-Dimensional Force Fields (AEC, Phys. Rev. Lett. v. 94, 188102 (2005)) [PDF]
The Anti-Brownian ELectrophoretic Trap: Fabrication and Software (Proc. SPIE v. 5699, pp. 296-305 (2005))
[PDF]
Method for trapping and manipulating
nanoscale objects in solution (Appl. Phys. Lett. v. 86, 093109
(2005)) [Slide]
[PDF]
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