D.A. Hastman, E. Oh, P. Chaturvedi, J.S. Melinger, P.D. Cunningham, M.C. Chiriboga, D. Mathur, I.L. Medintz, L. Vuković, S.A. Díaz
U.S. Naval Research Lab,
Keywords: photothermal, thermoplasmonics, gold nanoparticles, femtosecond laser, nucleic acids, denaturation, controlled release
Summary:Photothermal heating systems can be engineered to generate nanoscale temperature increases for modulating the activity of highly local biological materials without causing off-target heating effects. When properly designed, a system utilizing femtosecond (fs)-pulsed laser excitation of gold nanoparticles (AuNPs) can realize biologically relevant temperature increases that are confined to the local environment around each AuNP. While the magnitude of the temperature increase can easily exceed 100 °C, the nanosecond heating duration and the steep temperature gradient extending from the AuNP surface make these temperature profiles highly dynamic, and as a consequence the response of biological materials in these non-equilibrium temperature profiles is currently unpredictable. To this end, we have designed a quantitative local “nanothermometer” using a 55 nm AuNP functionalized with double-stranded deoxyribonucleic acid (dsDNA) to monitor dsDNA dehybridization rates in the non-equilibrium temperature profiles generated through fs-pulse laser excitation of the AuNP. We find that the dsDNA denaturation rate depends on the pulse energy fluence, bulk solution temperature, dsDNA melting temperature, and dsDNA location with respect to the AuNP surface. The dsDNA denaturation rate could be precisely controlled, and anywhere from 5-95% of the dsDNA could be dehybridized in as little as 100 seconds of irradiation. By fitting the dsDNA denaturation rate to a modified dsDNA dissociation equation, we obtained “sensed” temperature values and compared them with simulated AuNP temperature profiles. In doing so, we found that the high temperatures at the beginning of the heating and nearest to the AuNP surface have significant impact on the dsDNA denaturation rate. Additionally, molecular dynamics (MD) simulations were preformed to replicate the confined heat pulse around the dsDNA in order to better understand the experimental results and the process of dsDNA denaturation in this environment. In summary, this work provides a basis for understanding how dsDNA denatures in non-homogenous temperature increases, which enables researchers to better optimize confined photothermal heating systems for controlled release of nucleic acids and other biological materials.