Photothermal optical microscopy
Photothermal optical microscopy / "photothermal single particle microscopy" is a technique that is based on detection of non-fluorescent labels. It relies on absorption properties of labels (gold nanoparticles, semiconductor nanocrystals, etc.), and can be realized on a conventional microscope using a resonant modulated heating beam, non-resonant probe beam and lock-in detection of photothermal signals from a single nanoparticle. It is the extension of the macroscopic photothermal spectroscopy to the nanoscopic domain. The high sensitivity and selectivity of photothermal microscopy allows even the detection of single molecules by their absorption. Similar to Fluorescence Correlation Spectroscopy (FCS), the photothermal signal may be recorded with respect to time to study the diffusion and advection characteristics of absorbing nanoparticles in a solution. This technique is called photothermal correlation spectroscopy (PhoCS).
Forward detection scheme
In this detection scheme a conventional scanning sample or laser-scanning transmission microscope is employed. Both, the heating and the probing laser beam are coaxially aligned and superimposed using a
Detection mechanism
The physical basis for the photothermal signal in the transmission detection scheme is the lensing action of the refractive index profile that is created upon the absorption of the heating laser power by the nanoparticle. The signal is homodyne in the sense that a steady state difference signal accounts for the mechanism and the forward scattered field's self-interference with the transmitted beam corresponds to an energy redistribution as expected for a simple lens. The lens is a Gadient Refractive INdex (GRIN) particle determined by the 1/r refractive index profile established due to the point-source temperature profile around the nanoparticle. For a nanoparticle of radius embedded in a homogeneous medium of refractive index with a thermorefractive coefficient the refractive index profile reads:
in which the contrast of the thermal lens is determined by the nanoparticle absorption cross-section at the heating beam wavelength, the heating beam intensity at the point of the particle and the embedding medium's
Backwards detection scheme
In this detection scheme a conventional scanning sample or laser-scanning transmission microscope is employed. Both, the heating and the probing laser beam are coaxially aligned and superimposed using a
Detection mechanism
The detection is heterodyne in the sense that the scattered field of the probe beam by the thermal lens interferes in the backwards direction with a well-defined retroreflected part of the incidence probing beam.
References
- Boyer, D. (2002-08-16). "Photothermal Imaging of Nanometer-Sized Metal Particles Among Scatterers". Science. 297 (5584). American Association for the Advancement of Science (AAAS): 1160–1163. S2CID 8758957.
- Cognet, L.; Tardin, C.; Boyer, D.; Choquet, D.; Tamarat, P.; Lounis, B. (2003-09-17). "Single metallic nanoparticle imaging for protein detection in cells". Proceedings of the National Academy of Sciences. 100 (20): 11350–11355. PMID 13679586.
- Gaiduk, Alexander; Ruijgrok, Paul V.; Yorulmaz, Mustafa; Orrit, Michel (2010). "Detection limits in photothermal microscopy". Chemical Science. 1 (3). Royal Society of Chemistry (RSC): 343–350. ISSN 2041-6520.
- Selmke, Markus; Cichos, Frank (2013). "Photonic Rutherford scattering: A classical and quantum mechanical analogy in ray and wave optics". American Journal of Physics. 81 (6). American Association of Physics Teachers (AAPT): 405–413. S2CID 119276853.
- Selmke, Markus; Cichos, Frank (2013-03-06). "Photothermal Single Particle Rutherford Scattering Microscopy". Physical Review Letters. 110 (10). American Physical Society (APS): 103901. PMID 23521256.
- Selmke, Markus; Braun, Marco; Cichos, Frank (2012-02-28). "Photothermal Single-Particle Microscopy: Detection of a Nanolens". ACS Nano. 6 (3). American Chemical Society (ACS): 2741–2749. PMID 22352758.
- Selmke, Markus; Braun, Marco; Cichos, Frank (2012-03-22). "Nano-lens diffraction around a single heated nano particle". Optics Express. 20 (7). The Optical Society: 8055–8070. PMID 22453477.
- Selmke, Markus; Braun, Marco; Cichos, Frank (2012-09-28). "Gaussian beam photothermal single particle microscopy". Journal of the Optical Society of America A. 29 (10). The Optical Society: 2237–41. PMID 23201674.
- Selmke, Markus; Schachoff, Romy; Braun, Marco; Cichos, Frank (2013). "Twin-focus photothermal correlation spectroscopy". RSC Adv. 3 (2). Royal Society of Chemistry (RSC): 394–400. ISSN 2046-2069.
- Selmke, Markus; Braun, Marco; Schachoff, Romy; Cichos, Frank (2013). "Photothermal signal distribution analysis (PhoSDA)". Physical Chemistry Chemical Physics. 15 (12). Royal Society of Chemistry (RSC): 4250–7. PMID 23385281.
- Bialkowski, Stephen (1996). Photothermal spectroscopy methods for chemical analysis. New York: Wiley. OCLC 32819267.
- "Molecular Nanophotonics Group: Photothermal Imaging". Retrieved 2020-03-19.