Fluorescent Superlattices of Gold Nanoparticles:A New Class of Functional Materials

Fluorescent three-dimensional(3-D)superlattices of dansyl glutathione protected gold nanoparticles,with potential applications in molecular detection,have been synthesized at an air/water interface by controlling the pH of the nanoparticle suspension.The number of fluorophores per nanoparticle was calculated to be~127.Morphologies of the superlattice crystals were examined using scanning electron microscopy(SEM).Most of the crystals observed were triangular in shape.High-resolution transmission electron microscopy(HRTEM)and small angle X-ray scattering(SAXS)were used to study the packing of nanoparticles in these crystals.Both these studies showed that the nanoparticles were arranged in a face-centered cubic(fcc)pattern with a particle-particle distance(center-center)of~10.5 nm.Evolution of the crystal morphologies with time was also examined.The fluorescence properties of these triangles were studied using confocal fluorescence imaging and confocal Raman mapping,which were in good agreement with the morphologies observed by SEM.The superlattice exhibits near-infrared(NIR)absorption in the range 1100-2500 nm.Easy synthesis of such functional nanoparticle-based solids makes it possible to use them in novel applications.We utilized the fluorescence of dansyl glutathione gold superlattice crystals for the selective detection of bovine serum albumin(BSA),the major protein constituent of blood plasma,based on the selective binding of the naphthalene ring of the dansyl moiety with site I of BSA.

The development of molecular and nano actinide decorporation agents

Internal contamination of actinides has led to significant health hazards to the public and workers in the context of nuclear power plant accidents,uranium ore mining,and reprocessing of the used fuel.An effective sequestering agent that is able to remove accidentally incorporated actinides in vivo with low toxicity is always in urgent need.The molecular decorporation ligands have been the most widely researched agents for the past few decades,while preliminary studies of functionalized nanoparticles have shown their clear advantages in metal binding selectivity,toxicity,and oxidative stress alleviation.Herein,the state-of-the-art of those two types of decorporation agents is presented with special attention being paid on the correlation between the solution and solid-state chemistry of those agents with actinides and the corresponding decorporation efficacies.

Selection and design of high affinity DNA ligands for mutant single-chain derivatives of the bacteriophage 434 repressor

Single-chain repressor RRTRES is a derivative of bacteriophage 434 repressor, which contains covalently dimerized DNA-binding domains (amino acids 1-69) of the phage 434 repressor. In this single-chain molecule, the wild type domain R is connected to the mutant domain RTRES by a recombinant linker in a head-to-tail arrangement. The DNA-contacting amino acids of RTRES at the -1, 1,2, and 5 positions of the α3 helix are T, R, E, S respectively. By using a randomized DNA pool containing the central sequence -CATACAAGAAAGNNNNNNTTT-. a cyclic, in vitro DNA-binding site selection was performed. The selected population was cloned and the individual members were characterized by determining their binding affinities to RRTRES. The results showed that the optimal operators contained the TTAC or TTCC sequences in the underlined positions as above, and that the Kd values were in the 1×10-12mol/L1×10-11mol/L concentration range. Since the affinity of the natural 434 repressor to its natural operator sites is in the 1×10-9 mol/L range, the observed binding affinity increase is remarkable. It was also found that binding affinity was strongly affected by the flanking bases of the optimal tetramer binding sites, especially by the base at the 5' position. We constructed a new homodimeric single-chain repressor RrREsRtRES and its DNA-binding specificity was tested by using a series of new operators designed according to the recognition properties previously determined for the RTRES domain. These operators containing the consensus sequence GTAAGAAARNTTACN or GGAAGAAARNTTCCN (R is A or G) were recognized by RTRESRTRES specifically, and with high binding affinity. Thus, by using a combination of random selection and rational design principles, we have discovered novel, high affinity protein-DNA interactions with new specificity. This method can potentially be used to obtain new binding specificity for other DNA-binding proteins.