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Aptamers are a new class of synthetic DNA/RNA oligonucleotides generated from in vitro selection to selectively bind with various molecules. Due to their molecular recognition capability for proteins, aptamers are becoming promising reagents in protein detection and new drug development. In this study, the specific interaction between the protein immunoglobulin E (IgE) and its 37-nt aptamer has been measured directly by atomic force microscopy. The single-molecule unbinding force between IgE and the aptamer is determined using the Poisson statistical method. The individual unbinding force between IgE and its monoclonal antibody has also been obtained and compared to that between IgE and the aptamer. The results reveal the high affinity of the aptamer to protein, which could match or even surpass that of the antibody to its antigen.

In this work, we synthesized amino acid-containing poly(phenylacetylene)s and demonstrated the possibility of tuning their hierarchical structures by internal and external perturbations. A valineacetylene adduct, 4-ethynylbenzoyl-L-valine methyl ester (5), was readily polymerized by [Rh(nbd)Cl]2, and the resultant "polyester" (1) was selectively hydrolyzed by KOH to its "polyacid" congener, poly(4ethynylbenzoyl-L-valine) (2). (Supra)molecular structures of the polymers were characterized by NMR, IR, UV, CD, and AFM techniques. The macromolecules took helical chain conformations in solutions. Their Cotton effects varied to different extents, when the polymer, solvent, and pH changed respectively from 1 to 2, from methanol to THF, and from neutral to basic. Upon evaporation of their methanol solutions, 1 and 2 self-assembled into micellar spheres and helical cables, respectively. Changing the solvent of 1 to THF changed its folding structure to helical cables, while increasing the pH of the methanol solution of 2 led to the formation of random threads. The denaturation from helical cables to random threads is probably caused by the cleavage of interstrand hydrogen bonds by base-mediated ionization of carboxyl groups of the valine pendants.

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A dynamic light scattering sensor for Pb(2+) was constructed with oligonucleotide-modified gold nanoparticles based upon its cleavage property for DNAzyme.