7 research outputs found
Imaging three-dimensional rotational diffusion of plasmon resonant gold nanorods using polarization-sensitive optical coherence tomography
We demonstrate depth-resolved viscosity measurements within a single object using polarized optical scattering from ensembles of freely tumbling plasmon resonant gold nanorods (GNRs) monitored with polarization-sensitive optical coherence tomography. The rotational diffusion coefficient of the GNRs is shown to correlate with viscosity in molecular fluids according to the Stokes-Einstein relation. The plasmon resonant and highly anisotropic properties of GNRs are favorable for microrheological studies of nanoscale properties
Large-Scale Synthesis of Gold Nanorods through Continuous Secondary Growth
Gold
nanorods (GNRs) exhibit a tunable longitudinal surface plasmon
resonance (LSPR) that depends on the GNR aspect ratio (AR). Independently
controlling the AR and size of GNRs remains challenging but is important
because the scattering intensity strongly depends on the GNR size.
Here, we report a secondary (seeded) growth procedure, wherein continuous
addition of ascorbic acid (AA) to a stirring solution of GNRs, stabilized
by cetyltrimethylammonium bromide (CTAB) and synthesized by a common
GNR growth procedure, deposits the remaining (âŒ70%) of the
Au precursor onto the GNRs. The growth phase of GNR synthesis is often
performed without stirring, since stirring has been believed to reduce
the yield of rod-shaped nanoparticles, but we report that stirring
coupled with continuous addition of AA during secondary growth allows
improved control over the AR and size of GNRs. After a common primary
GNR growth procedure, the LSPR is âŒ820 nm, which can be tuned
between âŒ700 and 880 nm during secondary growth by adjusting
the rate of AA addition or adding benzyldimethylhexadecylammonium
chloride hydrate (BDAC). This approach for secondary growth can also
be used with primary GNRs of different ARs to achieve different LSPRs
and can likely be extended to nanoparticles of different shapes and
other metals
Sign Inversion in Photopharmacology: Incorporation of Cyclic Azobenzenes in Photoswitchable Potassium Channel Blockers and Openers
Photopharmacology relies on ligands that change their pharmacodynamics upon photoisomerization. Many of these ligands are azobenzenes that are thermodynamically more stable in their elongated transconfiguration, which predominates in the dark. Often, they are biologically active in this form and lose activity upon irradiation and photoisomerization to their cis-isomer. Recently, cyclic azobenzenes, so-called diazocines, have emerged. They are thermodynamically more stable in their bent cisÂâform than in their elongated trans-form. Incorporation of these switches into a variety of photopharmaceuticals could convert dark-active ligands into dark-inactive ligands, which is preferred in most biological applications. This âpharmacological sign-inversionâ is demonstrated for a photochromic blocker of voltage-gated potassium channels, termed CAL, and a photochromic opener of G-protein-coupled inwardly rectifying potassium (GIRK) channels, termed CLOGO.<br /
Bulky Adamantanethiolate and Cyclohexanethiolate Ligands Favor Smaller Gold Nanoparticles with Altered Discrete Sizes
Use of bulky ligands (BLs) in the synthesis of metal nanoparticles (NPs) gives smaller core sizes, sharpens the size distribution, and alters the discrete sizes. For BLs, the highly curved surface of small NPs may facilitate growth, but as the size increases and the surface flattens, NP growth may terminate when the ligand monolayer blocks BLs from transporting metal atoms to the NP core. Batches of thiolate-stabilized Au NPs were synthesized using equimolar amounts of 1-adamantanethiol (AdSH), cyclohexanethiol (CySH), or <i>n</i>-hexanethiol (C6SH). The bulky CyS- and AdS-stabilized NPs have smaller, more monodisperse sizes than the C6S-stabilized NPs. As the bulkiness increases, the near-infrared luminescence intensity increases, which is characteristic of small Au NPs. Four new discrete sizes were measured by MALDI-TOF mass spectrometry, Au<sub>30</sub>(SAd)<sub>18</sub>, Au<sub>39</sub>(SAd)<sub>23</sub>, Au<sub>65</sub>(SCy)<sub>30</sub>, and Au<sub>67</sub>(SCy)<sub>30</sub>. No Au<sub>25</sub>(SAd)<sub>18</sub> was observed, which suggests that this structure would be too sterically crowded. Use of BLs may also lead to the discovery of new discrete sizes in other systems