Selective heating of multiple nanoparticles as a new strategy for controlled release applications

Abstract

Utilization of nanoparticle heating for controlled release application was proposed and its feasibility was explored. The proposed method was formulated by realizing that biomolecule - nanoparticle conjugation is heat sensitive and both their dimensions are in the same length scale. This exploration centered on showing the proof of concept that conjugated biomolecules can be released from the nanoparticle surface in a controlled manner by heating the nanoparticles via external energy sources. The selectivity of the multiple releases was also investigated. Two mechanisms of nanoparticle heating were explored. The AC magnetic heating of magnetic nanoparticles has limitation due to its low-power energy delivered to nanoparticles. The irradiation of femtosecond laser pulses on the absorbing gold nanorods provides the answer to this limitation due to the very high-power of energy delivery through these ultrashort pulses. We developed gold nanorod surface customization technique to enable DNA - nanorod conjugation, thus turning gold nanorods into nanoscale carriers. Pulsed laser excitation in resonance with their absorption peaks can heat and melt the nanorods. This is exploitable for controlling the release of DNA oligonucleotides conjugated onto the nanorod surface. Nanorods with different aspect ratios absorb light at different wavelengths and thus can be excited independently. We have successfully demonstrated the selective releases of two distinct DNA oligonucleotides, where each is released from a different type of nanorod.

This was accomplished by the laser excitation at two different wavelengths corresponding to both of the nanorods' absorption peaks. The releases were very selective, efficient, and externally tunable by adjusting the laser fluence. The released DNA oligos were still functional. This concept is expandable to beyond two species. Its thiol conjugation chemistry is versatile and capable of high loading. With these advantageous factors, this proof of concept of selective multiple triggered releases from gold nanorods have a great potential as a new strategy for multiple controlled released application.