Anti-Stokes Thermometry in Nanoplasmonics

Abstract

Whereas heating nanoparticles with light is straightforward, measuring the resulting nanoscale temperature increase is intricate, and still a matter of active research in plasmonics, with envisioned applications in nanochemistry, biomedicine, and solar light harvesting, among others. Interestingly, this research line mostly belongs to the optics community today, because light is not only used for heating but also often for temperature probing. In this Perspective, I present and discuss recent advances in the search for efficient and reliable thermometry techniques for nanoplasmonic systems by the nanooptics community. I focus on the recently proposed approach based on the spectral measurement of anti-Stokes emission from the plasmonic nanoparticles themselves.Nanoscale heating is a fundamental concept that offers research opportunities in many scientific fields.The method of choice for achieving nanoscale heating has been the use of light to illuminate molecular dyes or absorbing nanoparticles. Nanoparticles have been the preferred light absorbers over molecules because they neither photo-nor thermo-bleach, and are thus more suited for applications requiring prolonged use. The best photothermal conversion efficiencies are reached using metal nanoparticles.Metals feature large electronic density, in comparison to semiconductors for example, which ensures much stronger interactions with light and subsequent absorption. In addition, metal nanoparticles can exhibit localized plasmonic resonances, which further enhance light absorption by several orders of magnitude, especially with noble metals. This picture led to the field of thermoplasmonics, 1 which is the use of metal nanoparticles under illumination as nanosources of heat. In this field, gold nanoparticles in particular have played a major role for the past two decades because they feature strong plasmonic resonances, are biocompatible, and their resonance can be adjusted from the visible to the infrared range, as a function of their morphology.The challenge in nanoscale heating research and applications is not in achieving nanoscale heating. This achievement is actually trivial, when using nanoparticles. Rather, the difficulty is in measuring the resulting nanoscale temperature increase. 2 After two decades, the lack of efficient and reliable nanoscale thermometry continues to cause problems in some applications of nanoplasmonics. In particular, in plasmonics-assisted chemistry, the possible occurrence of plasmonic heating has been disregarded for a decade, with some work recently questioning the interpretation of data from several impactful publications. 3,4 In this field, heating is not the target, but rather a side effect. Nevertheless, it is crucial to quantify temperature increases properly to ensure correct interpretations of the experimental observations. Thus, thermometry is not only the concern of applications where heating is the target, it is ubiquitous in plasmonics, whether the resultant heating is desired or not.

Real‐Time Interfacial Nanothermometry Using DNA‐PAINT Microscopy

“…The first includes methods that probe the temperature of the metal (inside the NP), most prominently anti-Stokes Raman scattering. [28][29][30][31] Second, methods based on photo thermal microscopy [18,20] or interferometry [32][33][34] probe local refractive index changes induced by heat conduction across several microns into the surrounding medium. In both approaches the interfacial temperature can be extracted using thermodynamic models, [32,33] but these require knowledge of the size and shape of each individual particle and its interfacial thermal resistance.…”

Designing two-dimensional temperature profiles using tunable thermoplasmonics

“…In our experiment, the optical heating of the TiN : Si voxel is measured with the help of Raman thermometry. 52 To avoid unwanted effects related to vibrational (non-Boltzmann) pumping 53 (see details in the ESI, Fig. S1 †), we utilize a Raman shift-based probe (Fig.…”

Optical Hydrogen Nanothermometry of Plasmonic Nanoparticles under Illumination

“… 25 − 30 Focusing on catalysis, several attempts in this direction have been reported. They include anti-Stokes radiation and fluorescence spectroscopy that either require rather complicated equipment or the use of fluorescent labels, 44 − 47 or the application of a specific temperature-sensitive thin film coating to the sample, 48 which renders it a destructive measurement method. These and other thermometry methods for the nano- and microscale can achieve in some cases high temporal resolution of down to 10 –9 s, spatial resolutions of 10 –2 μm, or temperature resolution of 10 –5 K. 49 However, although all of these are impressive achievements, a reasonably simple, noninvasive, and nondestructive means to directly measure the temperature of metal nanoparticles with good resolution in general, and of plasmonic nanoparticles under different levels of illumination in particular, still does not exist.…”