Mechanical and Biological Engineering
We are exploiting the unique material properties of gold nanorods to control biological processes.
Ultrafast laser excitation can rapidly heat gold nanorods, which can be utilized to release biomolecules.
Because the optical properties of gold nanorods are size and shape tunable, this permits tailoring the nanorod for strategically controlled release.
Ligand exchange of gold nanorods
We are studying ligand exchange methods so that functionalization with DNA and proteins is possible.
The most commonly used nanorod ligand, cetyltrimethylammonium bromide (CTAB) enables water solubility by forming a bilayer on the nanorod surface.
Due to its fluxional nature and bilayer configuration, CTAB can prevent straightforward biofunctionalization and stability in buffers.
Unfortunately, nanorod surface chemistry has lagged behind that of gold nanoparticles, and it is challenging to conjugate gold nanorods to proteins and DNA.
Therefore, we are exploring new approaches to exchange the CTAB on nanorods to molecules that form covalent bonds to the nanorod and result in monolayers on the surface.
We exploit two-phase ligand exchange strategies which have been employed successfully for ligand exchange of nanocrystals of various materials.
Thermal properties of gold nanorods
We are studying the thermal properties of gold nanorods and how it is influenced by the surface coating ligand.
Transient absorption spectroscopy is utilized to examine the thermal transport between gold nanorods and the solvent.
We find that the free ligand concentration can strongly influence thermal transport, particularly at its critical micelle concentration.
This work is in collaboration with the groups of Sarit K. Das and Gang Chen (Dept. of Mechanical Engineering).
Mechanism of triggered release from gold nanorods
We are studying release of simple molecules from gold nanorods by laser excitation, and studying the mechanism.
We find that the nature of the surface coating ligand can strongly influence release of simple molecules from the nanorods.
By using hydrophobic dyes that intercalates in the CTAB bilayer on the nanorod surface, we are exploring how laser excitation
acclerates the rate of exchange of the dye on and off the nanorod surface and determining power limits to prevent thermal damage of the payload. In addition, we probe how the concentration of free CTAB affects
the mechanism of release.
Selective release of multiple species from gold nanorods
The use of multiple drugs in drug cocktails has been sought for improving treatment efficacy of diseases such as malaria, cancer, and HIV. However, the differences in the chemical properties (such as molecular weights, solubilities) and pharmacokinetics of the components of a drug mixture can create challenges for loading, delivery, and release of multiple drugs. Even if a pre-determined synergistic ratio is encapsulated in a carrier, this ratio may not be maintained at a target upon delivery or during release. Therefore, for effective combination therapy, release rates and windows of each drug must be controlled independently. Nanoscale carriers have gained attraction, but achieving different release windows for each drug in a mixture requires engineering intricate architectures. Extending all of these strategies beyond two species or even changing the order of release is problematical.
An effective method to externally control release of each species independently and actively would ultimately lead to optimization of combination therapies for treatment. Since the longitudinal SPR of nanorods is tunable by changing NR aspect ratio, NRs with different aspect ratios can be excited independently at different wavelengths. We synthesize NRs of different aspect ratios and morphologies, short nanorods and "nanobones," with different DNA oligos and tune the laser wavelength in order to achieve orthogonal triggered release. The releases were efficient (~50-80%) and externally controllable by tuning the laser fluence, and released DNA is still functional.
S. Park, N. Sinha, K. Hamad-Schifferli, "Effective Size and Zeta Potential of Nanorods by Ferguson Analysis," Langmuir, 2010, 26 (16) 13071-13075.
J. D. Alper and K. Hamad-Schifferli, "Effect of ligand on thermal dissipation from gold nanorods," Langmuir, 2010, 26 (6), 3786-3789.
J. D. Alper, M. P. Crespo, K. Hamad-Schifferli, "Release mechanism of octadecyl rhodamine B chloride from Au nanorods by ultrafast laser pulses," Journal of Physical Chemistry C, 2009, 113 (15), 5967-5973.
A. Wijaya, S. B. Schaffer, I. G. Pallares, K. Hamad-Schifferli, "Selective release of multiple DNA oligonucleotides from gold nanorods," ACS Nano, 2009, 3(1), 80-86.
A. Wijaya and K. Hamad-Schifferli, "Ligand customization and DNA functionalization of gold nanorods via roundtrip phase transfer ligand exchange," Langmuir, 2008, 24, 9966-9969.
A. J. Schmidt,* J. D. Alper,* M. Chiesa, G. Chen, S. K. Das, K. Hamad-Schifferli, "Probing the gold nanorod-ligand-solvent interface by plasmonic absorption and thermal decay," Journal of Physical Chemistry C, 2008, 112, 13320-13323.
*These authors contributed equally to the work.