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Multi-Component Nano-Structures with Tunable Optical Properties

Scientists at Brookhaven National Laboratory report the first successful assembly of 3-D multi-component nanoscale structures with tunable optical properties that incorporate light-absorbing and -emitting particles. This work, using synthetic DNA as a programmable component to link the nanoparticles, demonstrates the versatility of DNA-based nanotechnology for the fabrication of functional classes of materials, particularly optical ones, with possible applications in solar-energy conversion devices, sensors, and nanoscale circuits.

Like earlier work conducted by the research team, this technique makes use of the high specificity of binding between complementary strands of DNA to link particles together in a precise way.

In the current study, the DNA linker molecules had three binding sites. The two ends of the strands were designed to bind to complementary strands on “plasmonic” gold nanoparticles — particles in which a particular wavelength of light induces a collective oscillation of the conductive electrons, leading to strong absorption of light at that wavelength. The internal part of each DNA linker was coded to recognize a complementary strand chemically bound to a fluorescent dye molecule. This setup resulted in the self-assembly of 3-D body centered cubic crystalline structures with gold nanoparticles located at each corner of the cube and in the center, with dye molecules at defined positions in between.

The scientists also demonstrated that the assembled structures can be dynamically tuned by altering the salt concentration of the solution in which they are formed. Changes in salinity alter the length of the negatively charged DNA molecules, leading to reversible contraction and expansion of the whole lattice by about 30 percent in length.

The expansion and contraction of the crystal lattice allowed for a dramatic modulation of an optical response: a three-fold increase in the emission rate of the fluorescent molecules was observed.

These results were determined using a combination of small angle x-ray scattering at NSLS and time-resolved fluorescent methods at the CFN.

An understanding of these interactions could be relevant for developing novel optical materials for photovoltaic, photocatalysis, computing, and light-emitting applications.

H. Xiong, M.Y. Sfeir, O. Gang, “Assembly, Structure, and Optical Response of Three-Dimensional Dynamically Tunable Multicomponent Superlattices,” Nano Letters, 10(11), 4456 (2010).

Top: Brookhaven scientists used DNA linkers with three binding sites (black “strings”) to connect gold nanoparticles (orange and red spheres) and fluorescent dye molecules (blue spheres) tagged with complementary DNA sequences. These units are self-assembled to form a body-center cubic lattice with nanoparticles at the corners and in the center, and fluorescent dye molecules in between.

Bottom: Brookhaven Lab researcher Oleg Gang

Figure 1 Oleg Gang