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Posted: Jul 13, 2006

Constructing smart nanomaterials with DNA molecules

(Nanowerk Spotlight) Researchers at the University of Illinois at Urbana-Champaign have shown that, by employing small pieces of DNA molecules called aptamers, nanomaterials can be smart enough to assemble or disassemble only in the presence of programmable signals such as "AND" or "OR", with controllable cooperativity.
Tremendous progress has been made in making individual nanomaterials. To realize the full potentials of nanoscale science and technology, one must learn how to assemble or disassemble these materials at a specific location in response to a need for such materials. Most work focuses on nanomaterials assembly in response to external signals or stimuli, such as temperature, pH, etc. Biomaterials, on the other hand, are assembled under almost constant external variables such as temperature and pH.
Instead, Professor Yi Lu from the Department of Chemistry at the University of Illinois, and his group came up with the first examples of controlled assembly (and disassembly) of smart materials in response to internal signals, sometimes to multiple stimuli.
Together with first author Juewen Liu he recently published a paper, titled "Smart Nanomaterials Responsive to Multiple Chemical Stimuli with Controllable Cooperativity" in the June 27, 2006 online edition of Advanced Materials.
"Since 2003, my group has been focusing on learning from Nature to control nanomaterials assembly in response to internal stimuli" Lu explains to Nanowerk. "In this paper, we went a step further by demonstrating that nanoparticle assembly and disassembly can be programmed like a computer code in response to "AND" or "OR" of two chemical stimuli. Their cooperativity, i.e. the requirement of two molecules working together to affect the aggregation states of nanoparticles, can also be controlled."
Lu's group took advantage of the high binding properties of aptamers to assemble nanoparticles and demonstrated that small molecules can regulate the assembly state of DNA functionalized gold nanoparticles. Aptamers are nucleic acids that can bind to target molecules with high affinity and specificity. The range of molecules that aptamers can selectively bind to rivals that of antibodies and they can be selected to target essentially any molecule of choice.
By incorporating aptamers to nanomaterials, Lu's group has demonstrated smart materials responsive to adenosine, cocaine, and K+. Because of the generality of the designs, materials responsive to any combination of the three chemicals can be prepared. More importantly, the cooperativity between the molecules is controllable.
"Fine-control of nanomaterials assembly or disassembly has always been a huge challenge" says Lu. "Our work is a step in the right direction. For instance, a short-term application is better colorimetric sensors for molecules such as adenosine and cocaine, since controlled assembly in response to those stimuli resulted in dramatic color changes. Adding "AND" and "OR" to such a process make sensing less vulnerable to false positive results."
By replacing the gold nanoparticles with other nanomaterials, such as quantum dots, nanotubes, or polymers, smart materials suitable for a diverse range of applications can be obtained.
The principles demonstrated in Lu's work may also apply to controlled assembly of nanoelectronics or nanophotonics in the long-term future.
By , Copyright Nanowerk LLC

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