4_08/2008Cover Picture: Small 8/2008

The cover picture shows the use of gold nanoparticles as a colorimetric probe for aptamer-based sensing. A DNA aptamer for cocaine is engineered into two pieces of random coil-like single-stranded oligonucleotides through elaborate design. These two oligonucleotides readily fold into a rigid aptamer structure in the presence of cocaine. Since gold nanoparticles possess markedly different affinities toward these two states, the ligand-induced structural variation of the aptamer can be translated into the different aggregation states of gold nanoparticles. Hence, the color of gold nanoparticles that arises from their surface plasmon resonance serves as a sensitive probe for the presence of the cocaine target. By using this strategy, micromolar cocaine can be detected within minutes. For more information, please read the Full Paper “Visual Cocaine Detection with Gold Nanoparticles and Rationally Engineered Aptamer Structures” by C. Fan et al. beginning on page 1196.

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