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Tiopronin monolayer-protected silver nanoparticles with different core sizes (average diameter = 2, 5, 20 nm) were prepared by using different mole ratios of silver nitrate/tiopronin. Ligands on the silver particles were partially displaced by fluorescein-labeled thiolate single-stranded oligonucleotides or their complementary unlabeled oligonucleotides through ligand exchange. The fluorophores on silver particles showed a surface-enhanced fluorescence (SEF) dependent on the size of metallic cores. The particles could be coupled through hybridizations of oligonucleotides bound on the particles. The coupled particles were aggregated due to multiple displacements of oligonucleotides on each particle, resulting in stronger SEF. The dye-labeled oligonucleotides were assembled on the silver islands on the solid substrate, and the complementary oligonucleotide-displaced particles were coupled via oligonucleotide hybridization. The couplings between particles and islands resulted in an obvious fluorescence enhancement.
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PMID:Surface-enhanced fluorescence of fluorescein-labeled oligonucleotides capped on silver nanoparticles. 1685 86

Tiopronin-protected silver nanoparticles (average diameter = 5 nm) were partially displaced by (2-mercapto-propionylamino) acetic acid 2,5-dioxo-pyrrolidin-1-ylesters via ligand exchange, and the succinimide-terminated silver particles were bound to amine-labeled Dextran 3000 (1 amine/per chain) or Dextran 10 000 (2.5 amine/per chain), respectively. The particle-Dextran 10 000 adducts were self-aggregated by interactions of multiple amines on Dextran and multi-functionalized ligands on the particle. The transverse plasmon band was blue shifted while the longitudinal plasmon at 575 nm increased, corresponding to the compact aggregation of particles. The particle-Dextran 3000 adducts, which were not aggregated, were coupled to Concanavalin A (Con A) to facilitate the aggregation of particles. The aggregated particles displayed an absorbance spectral change depending on the mole ratio of Con A/particle-Dextran 3000. The particle-Dextran 3000 adduct was released by a competitive complexation of glucose. This process was monitored by both the change in plasmon absorbance and wavelength, with the glucose concentration. The aggregation and dissociation of Con A/particle-Dextran complexes were also verified by TEM images.
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PMID:Aggregation of Silver Nanoparticle-Dextran Adducts with Concanavalin A and Competitive Complexation with Glucose. 3189 53