Twin-focus photothermal correlation spectroscopy

Selmke, Markus; Schachoff, Romy; Braun, Marco; Cichos, Frank

doi:10.1039/c2ra22061j

Cited by 22 publications

(37 citation statements)

References 23 publications

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“…So far, several of the predictions of the theory of hot Brownian motion could be validated experimentally and in numerical simulations [8,23,27,31]. We specifically mention the experimental verification of the translational effective temperature from Eq.…”

Section: Fluctuations: Hot Brownian Motionmentioning

confidence: 96%

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Hot microswimmers

Kroy

Chakraborty

Cichos

2016

Eur. Phys. J. Spec. Top.

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Hot microswimmers are self-propelled Brownian particles that exploit local heating for their directed self-thermophoretic motion. We provide a pedagogical overview of the key physical mechanisms underlying this promising new technology. It covers the hydrodynamics of swimming, thermophoresis and -osmosis, hot Brownian motion, force-free steering, and dedicated experimental and simulation tools to analyze hot Brownian swimmers. a arXiv:1805.07150v1 [cond-mat.soft] 18 May 2018 with self-thermophoresis than with conventional macroscopic thermophoresis. Selfthermophoresis is thus arguably an interesting and technologically promising propulsion mechanism, with some important advantages over other designs. i) Universality, Availability, Biocompatibility: it does not rely on exotic (maybe poisonous) solvents or fuels, but exploits a comparatively "universal" mechanism. It does not run out of fuel and is minimally invasive, since the heating is local and sizable motion can already be achieved with minor heating of the surroundings. ii) Control: the propulsion speed can be regulated continuously and propulsion can instantly be switched on and off, e.g. by using conventional lasers and microscopy equipment. Thanks to emerging efficient cooling mechanisms for colloidal particles [4], one can even imagine fabricating particles with a reverse gear. Besides, efficient force-free steering mechanisms such as photon nudging [5] are already available. iii) Versatility: heating can be realized by a variety of methods, such as the absorption of laser light by metal or carbon parts, or of microwaves by super-paramagnetic parts, which opens up the possibility of combining several independent and independently addressable thermophoretic propulsion mechanisms into one microstructure. A whole community of researchers is moreover interested in micro-and nano-particle heating for its own sake [6]. iv) Scalability: downscaling does not reduce the propulsion speed [5] but increases the efficiency [7]. Synthesis, speed control, and steering [5] of self-thermophoretic swimmers, as well as their photothermal detection [8], are all scalable to nanoscopic dimensions. The remainder of the paper is structured as follows. The next section reviews the distinction between self-phoretic, phoretic, and passive motion and the concomitant flow fields excited in the solvent, on a hydrodynamic level. This means that the physical mechanism that actually drives the motion is confined to such a narrow boundary layer that it is sufficiently well captured by a mere hydrodynamic boundary condition for the solvent flow. On this level, the theory of swimming is universal and independent of the actual propulsion mechanism. The following section provides a closer look at the engine of the swimmer, namely the processes of phoresis and self-phoresis of heated particles. The basic principles of self-thermophoretic propulsion and the underlying osmotic processes are very similar to those in other phoretic phenomena, such as diffusiophoresis and electrophoresis. In fact, ...

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Section: Fluctuations: Hot Brownian Motionmentioning

confidence: 96%

“…The experimental results displayed in the left panel of Fig. 4 have been obtained by a slightly more sophisticated, highly quantitative (twin-focus) implementation of this technique [8].…”

Section: "Hot" Experimental Techniquesmentioning

confidence: 99%

Hot microswimmers

Kroy

Chakraborty

Cichos

2016

Eur. Phys. J. Spec. Top.

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“…So far, a number of predictions of the theory of hot Brownian motion, as sketched above, could be validated with great precision by experiments and non‐equilibrium molecular dynamics simulations . Conversely, after the accuracy of the theory has been established, it can help to develop practically useful innovative experimental applications, such as photothermal microscopy/spectroscopy setups, which employ nano‐particles suspended in water as dynamic tracers . Gold particles can for example be heated by a green laser beam that is well absorbed, and the mirage generated by the emanating heat in the solvent can be detected by another (red) laser beam.…”

Section: Non‐equilibrium Brownian Thermometrymentioning

confidence: 99%

“…So far, a number of predictions of the theory of hot Brownian motion, as sketched above, could be validated with great precision by experiments [73,79,70,77,36] and non-equilibrium molecular dynamics simulations. [16,36] Conversely, after the accuracy of the theory has been established, it can help to develop practically useful innovative experimental applications, such as photothermal microscopy/spectroscopy setups, which employ nano-particles suspended in water as dynamic tracers.…”

Section: A Perfect Paradigm: Hot Brownian Motionmentioning

confidence: 99%

“…[16,36] Conversely, after the accuracy of the theory has been established, it can help to develop practically useful innovative experimental applications, such as photothermal microscopy/spectroscopy setups, which employ nano-particles suspended in water as dynamic tracers. [79,70,11] Gold particles can for example be heated by a green laser beam that is well absorbed, and the mirage generated by the emanating heat in the solvent can be detected by another (red) laser beam. A useful feature of such a setup is that it allows for a highly sensitive back-ground-free lock-in detection, so that it can be recommended as a more robust, sensitive and easily manageable replacement for similar fluorescent tracer techniques.…”

Section: A Perfect Paradigm: Hot Brownian Motionmentioning

confidence: 99%

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Brownian Thermometry Beyond Equilibrium

Geiß

Kroy

2019

ChemSystemsChem

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Since Albert Einstein's seminal 1905‐paper on Brownian motion, the temperature of fluids and gases of known viscosity can be deduced from observations of the fluctuations of small suspended probe particles. We summarize recent generalizations of this standard technique of Brownian thermometry to situations involving spatially heterogeneous temperature fields and other non‐equilibrium conditions in the solvent medium. The notion of effective temperatures is reviewed and its scope critically assessed. Our emphasis is on practically relevant real‐world applications, for which effective temperatures have been explicitly computed and experimentally confirmed. We also elucidate the relation to the more general concept of (effective) temperature spectra and their measurement by Brownian thermospectrometry. Finally, we highlight the conceptual importance of non‐equilibrium thermometry for active and biological matter, such as microswimmer suspensions or biological cells, which often play the role of non‐thermal (“active”) heat baths for embedded Brownian degrees of freedom.

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Introduction

2019

Photothermal Spectroscopy Methods

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Twin-focus photothermal correlation spectroscopy

Cited by 22 publications

References 23 publications

Hot microswimmers

Hot microswimmers

Brownian Thermometry Beyond Equilibrium

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