Core-satellite Assemblies Research Articles

A highly active SERS sensing substrate: core–satellite assembly of gold nanorods/nanoplates

Regiospecific core–satellite assembly of gold nanoplates (AuNPs)/gold nanorods (AuNRs) can be fabricated via ss-DNA hybridization. SERS behavior of the DNA driven assembly has been explored from inducing transition between para-ATP and DMAB through plasmon-assisted catalysis, suggesting that the core–satellite assembly can be utilized as highly active optical substrate. Moreover, a Raman label tagged thymine-rich DNA functionalized AuNRs/AuNPs assembly can be employed as in situ SERS sensing of mercury ions at the ultrasensitive ppt level, which indicates that the core–satellite assembly is appropriate as a versatile SERS substrate for the application of optical chemical or biosensing.

DNA functionalized gold nanorods/nanoplates assembly as sensitive LSPR-based sensor for label-free detection of mercury ions

Core–satellite assembly, i.e., gold nanoplates (AuNPs) surrounded by gold nanorods (AuNRs), has been obtained by Thymine–Hg2+–Thymine (T–Hg2+–T) coordination. A novel label-free localized surface plasmon resonance (LSPR) detection of mercury ions can be performed via the core–satellite assembly. The proposed detection protocol exhibits good linear correlation between wavelength shifts of the plasmon band and concentrations of mercury ions over the range from 10nM to 0.2μM. Moreover, the detection limit (3σ) for the probes is 2.2nM, which is better than colorimetric detection via random aggregation of gold nanoparticles.

Stimuli-responsive plasmonic core–satellite assemblies: i-motif DNA linker enabled intracellular pH sensing

We report stimuli-responsive core-satellite assemblies of binary gold nanoparticles, linked by i-motif DNA, for live cell plasmonic imaging of pH changes in the endocytic pathway.

Quantitative Amplification of Cy5 SERS in ‘Warm Spots’ Created by Plasmonic Coupling in Nanoparticle Assemblies of Controlled Structure

Metal nanoparticle assemblies of well-defined structure are investigated as substrates for quantitative surface enhanced Raman scattering (SERS). The ∼100 nm structures are composed of oligonucleotide-functionalized gold nanoparticles of two sizes; a large particle serves as a template for assembly of multiple small particles. Satellite structure formation is driven by hybridization of linker oligonucleotides to thiolated single-stranded DNA bound to the particle surfaces and is verified by transmission electron microscopy and Rayleigh scattering spectroscopy. Raman scattering spectra are collected from dispersed particles and core−satellite assemblies (CSA) formed with core particles that incorporate Cy5 in the core particle surface strands. Quenching of Cy5 fluorescence allows Raman spectra to be clearly detected both from dispersed and assembled core−satellite structures. Raman scattering from Cy5 in the coupled assemblies is amplified by a factor of 8, relative to the Raman scattering collected from dispersed cores. The amplification of Raman scattering from Cy5 on the core particle surface is quantitatively consistent with the amplification expected on the basis of surface field intensities that increase when satellite particles assemble at controlled distance from the core. Raman scattering per core-satellite structure is determined by calibrating measured intensities using methanol as a Raman intensity standard. The number of Cy5 molecules per core−satellite structure contributing to the Raman scattering is determined from analysis of the spatial nonuniformity of the simulated core surface field distribution. The Raman cross section of the immobilized Cy5 species is estimated from the Raman scattering per CSA using the Cy5 coverage per core particle and the calculated mean electromagnetic enhancement on the surface of the CSA. While uncertainties in Cy5 coverage, properties of the Raman standard, core−satellite geometry, and concentration contribute modest errors in the Raman cross section estimates, weak electromagnetic enhancement allows the cross sections of the immobilized Cy5 molecules to be assessed without the usual orders of magnitude uncertanties associated with strongly enhanced near fields.

Robust Detection of Plasmon Coupling in Core-Satellite Nanoassemblies Linked by DNA

Plasmon coupling is investigated in aqueous phase nanoassemblies composed of 13 nm gold “satellite” particles tethered by duplex DNA to a 50 nm gold “core” particle. The structures are comprised of a large core nanoparticle and small satellite particles such that formation of core-satellite assemblies can be detected through measurement of scattering spectra, even when an excess of unbound satellite particles are present. Rayleigh scattering spectra collected from bulk samples reveal enhanced scattering and/or red shifting of the plasmon resonance upon formation of assemblies, with the extent and character of the response determined by the number of base pairs in the duplex DNA tether. Distance-dependence of the coupling is investigated also through simulation using structural models based upon observed satellite coverage and prior measurements of interparticle separation in DNA-linked nanoparticle materials. Spectral differences between scattering from linked and unlinked assemblies are found to differ s...

Plasmon coupling in binary metal core–satellite assemblies

Controlled plasmon coupling is observed in nanoparticle assemblies composed of 20 nm silver ‘satellite’ nanoparticles tethered by reconfigurable duplex DNA linkers to a 50 nm gold ‘core’ particle. The assemblies incorporate silver nanoparticle–oligonucleotide conjugates prepared using a new conjugation method in which the recognition strand is anchored by a 10 base pair, double strand spacer that presents adjacent 3’- and 5’-thiols to the silver surface. Reconfiguration of the DNA linkers from a compact to an extended state results in decreased core–satellite coupling and a blue-shift in the gold core plasmon resonance. The structural basis for the observed resonance modulation is investigated through simulation of the scattering spectra of binary assemblies with various core–satellite separations. Additional simulations of core–satellite assemblies composed of gold satellite particles bound to silver cores and of assemblies composed entirely of silver particles are used to clarify the dependence of the coupling response on the composition of the components and their distribution within the assembly.

Reconfigurable Core−Satellite Nanoassemblies as Molecularly-Driven Plasmonic Switches

Molecular control of plasmon coupling is investigated in sub-100 nm assemblies composed of 13 nm gold "satellite" particles tethered by reconfigurable DNA nanostructures to a 50 nm gold "core" particle. Reconfiguration of the DNA nanostructures from a compact to an extended state results in blue shifting of the assembly plasmon resonance, indicating reduced interparticle coupling and lengthening of the core-satellite tether. Scattering spectra of the core-satellite assemblies before and after reconfiguration are compared with spectra calculated using a structural model that incorporates the core/satellite ratio determined by TEM imaging and estimates of tether length based upon prior measurements of interparticle separation in DNA linked nanoparticle networks. A strong correspondence between measured and simulated difference spectra validates the structural models that link the observed plasmon modulation with DNA nanostructure reconfiguration.