Metal‐Dielectric Nanocavity for Real‐Time Tracing Molecular Events with Temperature Feedback

Abstract

Plasmonic nanoparticles coupled with metallic films forming nanometer scale cavities have recently emerged as a powerful tool for enhancement of light-matter interaction. Despite high efficiency for sensing and light emission, such nanocavities exhibit harmful and uncontrolled optical heating which limits the ranges of light intensities and working temperature. In contrast to plasmonic nanoparticles, all-dielectric counterparts possess low Ohmic losses, high temperature stability along with a strong temperature-dependent Raman response. Here, we demonstrate that a silicon nanoparticle coupled with a thin gold film can serve as a multifunctional metal-dielectric (hybrid) nanocavity operating up to 1200 K. Resonant interaction of light with such nanocavity enables molecular sensing, heat-induced molecular events (protein unfolding), and their real-time tracing with a nanoscale thermometry through the monitoring enhanced Raman scattering both from the nanoparticle and analyzed molecules. We model numerically the thermo-optical properties of the hybrid nanocavity and reveal two alternative regimes of operation -with and without strong optical heating while other functionalities are preserved. We believe that the concept of the multifunctional hybrid nanocavities holds great potential for diverse photochemical and photophysical applications.

The conformation of bovine serum albumin adsorbed to the surface of single all‐dielectric nanoparticles following light‐induced heating

“…Direct assessment of the local temperature and heat‐induced changes in the conformation of BSA on the surface of c‐Si and c‐Ge NPs via confocal Raman spectroscopy revealed the following: Within the experimental error, there was no significant shift (Figure B) or noticeable change in the FWHM (Figure E) of the vibrational modes of BSA upon heating to 640 K, a good agreement with experimental findings on the heat‐induced unfolding of the same protein in a solid state or in solution . In contrast, both c‐Si and c‐Ge NPs (Figure A,E) showed significant temperature‐dependent Raman shifts and increases in the FWHM that corresponded to the appearance of anharmonic terms in the vibrational potential energy . The latter provided information concerning the local temperature, that is, the temperature to which the protein adsorbed on the NP surface was exposed. The dependency of the intensities of the SS and amide I modes on local temperature (dashed lines in Figure C) was similar to that for the protein unfolding in heated solution .…”

“…All‐dielectric NPs and nanostructures promote optical field localization near the surface and redirection of light to biomolecules that interact poorly with light. It also should be noted that such NPs are promising candidates for bioimaging , biosensing and heat therapy . In addition, most all‐dielectric NPs are rapidly bio‐degradable and relatively non‐toxic .…”

“…In addition, most all‐dielectric NPs are rapidly bio‐degradable and relatively non‐toxic . However, few available reports on biophotonic applications of such NPs have not addressed potential conformational changes in biomolecules adsorbed on their surface.…”

“…For light‐induced heating of NP‐biomolecule complexes, we followed a recently developed strategy to heat all‐dielectric NPs by light involving a regime with temperature feedback . As has been shown, the specific sizes of our NPs allowed resonant interaction with light, while the non‐zero imaginary part of its permittivity promoted light absorption and conversion of photon energy to heating up to 1200 K . Since heat influences the lattice dynamics of solids, the local temperature ( T ) of the NP‐biomolecule complex can be determined from the Raman shift ( Ω ) .…”

“…Irradiation of single c‐Si and c‐Ge NPs with a cw He‐Ne laser (632.8 nm) resulted in heating to 640 K (Figure ) with temperature feedback as showed by the relationship T ( Ω ). The latter can be approximated as T = 140(525 − Ω ) 0.65 for c‐Si and T = 17 943 – 58.6 Ω for c‐Ge NPs providing the temperature in K when Ω is expressed in cm −1 (dashed lines in Figure ). In contrast, light‐induced heating of plasmonic NPs to such temperatures usually damages them, and the temperature is measured by additional techniques (for a review, see Reference ).…”