Controlled Linking and Photothermal Release of Small Molecules from Gold Nanorod

Gold nanoparticles such as gold nanospheres and gold nanorods have been extensively studied for various applications---catalysis, electronics, sensing, drug delivery and therapeutics. Gold nanorods are particularly important than gold nanospheres because gold nanorods have two-dimensions for tuning particle properties---the length and the width of the nanorods. The length of the nanorods determine the Longitudinal Surface Plasmon Resonance (LSPR) and the Transverse Plasmon Resonance (TSPR) is determined by the width of the nanorods. LSPR is particularly important for engineering purposes such as the length of the nanorods allow the arrangement of complex structures which can be used for various functions. It has been studied extensively in tumor therapy through photothermal ablation, comprising an important example of LSPR use. On exposure to electromagnetic waves the incident energy is converted to localized heat and this can be used for killing tumor cells.;We have extended the basic physics of this light-matter interaction to de- velop sophisticated biosensing and engineering approaches. Our objective in this study is to demonstrate (i) the plasmon coupling of gold nanorods by selectively binding molecules to the nanorods, leading to a desired LSPR and (ii) the abil- ity to trigger the release of the molecules on demand, under the influence of an electromagnetic field.;To achieve this objective, we designed nanorods of aspect ratios varying from 2-4 that were coupled to 4 different thiol-terminated organic compounds via the gold-thiol bond. We were able to control the LSPR, based on the type of linker and the distance between the gold nanorods. Simulations were performed using Finite-Difference Time-Domain (FDTD) techniques to validate the experimental results.;To study the controlled release of molecules, peptides were designed such that they were labeled with a fluorophore on one end and a cysteine on the other. On exposure to light of specific wavelength (at 808 nm), we demonstrated the selective release of the target biomolecules in an LSPR-dependent fashion. The amount of peptide released from the nanorods was quantified using (Ultravio- let) UV and fluorescent spectrophotometry. The amount released was a strong function of the LSPR and time of exposure.;Results from these studies can be further extended for use in photother- mal ablation. Depending on the LSPR which, can be controlled with precision, deeper penetration of light can be achieved. It can also be used for the detection and quantification of a large number of proteins in biological samples of clinical relevance. These studies are also promising for the detection of protein variants in developing analytical techniques in downstream bioprocessing applications.