ABSTRACT
Femtosecond (fs) laser pulsed excitation of plasmonic nanoparticle (NP)-biomolecule conjugates is a promising method to locally heat biological materials. Studies have demonstrated that fs pulses of light can modulate the activity of DNA or proteins when attached to plasmonic NPs; however, the precision over subsequent biological function remains largely undetermined. Specifically, the temperature the localized biomolecules "experience" remains unknown. We used 55 nm gold nanoparticles (AuNPs) displaying double-stranded (ds) DNA to examine how, for dsDNA with different melting temperatures, the laser pulse energy fluence and bulk solution temperature affect the rate of local DNA denaturation. A universal "template" single-stranded DNA was attached to the AuNP surface, and three dye-labeled probe strands, distinct in length and melting temperature, were hybridized to it creating three individual dsDNA-AuNP bioconjugates. The dye-labeled probe strands were used to quantify the rate and amount of DNA release after a given number of light pulses, which was then correlated to the dsDNA denaturation temperature, resulting in a quantitative nanothermometer. The localized DNA denaturation rate could be modulated by more than threefold over the biologically relevant range of 8-53 °C by varying pulse energy fluence, DNA melting temperature, and surrounding bath temperature. With a modified dissociation equation tailored for this system, a "sensed" temperature parameter was extracted and compared to simulated AuNP temperature profiles. Determining actual biological responses in such systems can allow researchers to design precision nanoscale photothermal heating sources.
Subject(s)
Gold , Metal Nanoparticles , DNA , Lasers , TemperatureABSTRACT
In-plane, or azimuthal, photo-reorientation of azodye films using polarized exposure makes them promising alignment layers for a host of liquid crystal (LC) applications beyond displays including beam steering, q-plates, liquid crystal elastomer origami, and control of active matter. Out-of-plane, or polar, reorientation of azodye films, which dictates the liquid crystal pretilt, has received far less attention. Spatial control over the full polar and azimuthal orientation enables the generation of complex patterns that have broad interests and applications. In this paper, we describe an enhanced out-of-plane reorientation in Brilliant Yellow films utilizing a two-step exposure and demonstrate a liquid crystal pretilt angle that is tunable over a range of 0-33° with the associated anchoring strength of the alignment layer being unaffected by the inclusion of a pretilt. We report an order of magnitude increase in both amplitude and tunability of the pretilt angle in terms of previous results for single photoalignment films. This is a significant result for liquid crystal applications because it offers a simple, scalable, single-component solution with the potential to provide three-dimensional (3-D) patternability of the LC director at the surface.
