Super-Resolution Nonlinear Photothermal Microscopy

• Published in: Small (Weinheim an der Bergstrasse, Germany) Vol. 10; no. 1; pp. 135 - 142
• Main Authors: Nedosekin, Dmitry A., Galanzha, Ekaterina I., Dervishi, Enkeleda, Biris, Alexandru S., Zharov, Vladimir P.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 15.01.2014; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: cell imaging; Diffraction; Lasers; Microscopy; Nanoparticles; Nanotechnology; nonlinear effects; photoacoustic microscopy; photothermal microscopy; spatial sharpening; super-resolution; nonlinear effects; cell imaging; photoacoustic microscopy; super-resolution; spatial sharpening; photothermal microscopy
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.201300024

Super‐resolution fluorescence microscopy enables imaging of fluorescent structures beyond the diffraction limit. However, this technique cannot be applied to weakly fluorescent cellular components or labels. As an alternative, photothermal microscopy based on nonradiative transformation of absorbed energy into heat has demonstrated imaging of nonfluorescent structures including single molecules and ~1‐nm gold nanoparticles. However, previously photothermal imaging has been performed with a diffraction‐limited resolution only. Herein, super‐resolution, far‐field photothermal microscopy based on nonlinear signal dependence on the laser energy is introduced. Among various nonlinear phenomena, including absorption saturation, multiphoton absorption, and signal temperature dependence, signal amplification by laser‐induced nanobubbles around overheated nano‐objects is explored. A Gaussian laser beam profile is used to demonstrate the image spatial sharpening for calibrated 260‐nm metal strips, resolving of a plasmonic nanoassembly, visualization of 10‐nm gold nanoparticles in graphene, and hemoglobin nanoclusters in live erythrocytes with resolution down to 50 nm. These nonlinear phenomena can be used for 3D imaging with improved lateral and axial resolution in most photothermal methods, including photoacoustic microscopy. The resolution of photothermal microscopy is enhanced beyond the diffraction limit by exploring nonlinear signal enhancement for nanosized absorbers. Using a Gaussian diffraction‐limited laser beam profile, the imaging of calibrated plasmonic nanostructures at a resolution as low as 50 nm, graphene decorated with gold nanoparticles, and hemoglobin nanoclusters in live erythrocytes is demonstrated.