Understanding Electronic Properties of Gold and Streptavidin-Conjugated Gold Nanoparticles for Use in Photothermal Cancer Medicine

T. Nguyen, T.L. Sung, W.L. Yu, A. Ashcroft, M. Ashcroft, J. Ashcroft
Pasadena City College,
United States

Keywords: gold nanoparticles, streptavidin, photothermal cancer therapy, UV-Vis spectroscopy, femtosecond laser


Nanotechnology has emerged as one of the most instrumental and innovative research fields in the biomedical research community for the past few years. An important focus of this hot topic, gold (Au) nanoparticle, has been widely utilized as an excellent nanomaterial candidate in multiple biomedical applications and cancer treatments including drug delivery, biomedical imaging and photothermal cancer therapy due to its unique properties and non-cytotoxic effects on human bodies. AuNPs and modified AuNPs are great for this purpose because of their absorbance of light and efficient conversion to heat, which simulates the same conditions used in cancer photothermal therapy (PPT). Additionally, protein-functionalized AuNPs, such as Streptavidin-conjugated AuNPs, can facilitate the delivery of AuNPs into specific cells. However, the electronic properties of the Au nanoparticles and Streptavidin-conjugated Au nanoparticles on an atomic level are not well understood. In this study, we examined how the conjugation with Streptavidin antibody alters the electron energy profile of the Au nanoparticles through the electron excitation and relaxation process for analytical comparisons. We synthesized Au nanoparticles at Yin lab at UC Riverside, conjugated them to Streptavidin through EDC/NHS reaction, and measured the absorbance values of Au nanoparticles and Streptavidin-conjugated Au nanoparticles at different wavelengths from 400 to 650 nm using the UV-Vis Spectroscopy technique at Pasadena City College. We then conducted the Ultrafast Femtosecond Laser experiment at Cal State Northridge to capture the electron kinetics of Au and Strep-conjugated Au nanoparticles after 1,2,3,4, and 5 picoseconds of excitation at different intensities. We found that there is little discrepancy between the peaks of Au and Streptavidin-conjugated Au nanoparticles in terms of absorbance, and electrons in the Strep-conjugated Au nanoparticles were excited and returned to the ground state faster than the non-conjugated Au nanoparticles. These results suggested that the conjugation with the Streptavidin protein allows Au nanoparticles to retain their original electronic properties while gaining the ability to target the cancer sites more easily. Additional analysis of Au nanoparticles alone also revealed several electronic mechanisms regarding the excited state and ground state energy peaks at different timepoints and wavelengths. Future directions will be aimed at establishing the therapeutic profile of the Au nanoparticles and their protein-conjugated nanoparticles both in-vitro and in-vivo, especially in mammalian model systems and cancer cells. Generating a hybrid model of gold and silver nanoparticles combined could also offer some interesting insights into an alternative and more efficient cancer treatment when treated with proteins such as Streptavidin, particularly when this version has both metallic properties. The preliminary results, along with the next steps of the experiment, will provide a much-needed understanding of how electrons interact with each other in unconjugated and conjugated nanoparticles, aiding scientists to further optimize these useful nanoparticles for photothermal cancer therapy treatment and medical imaging.