Photo-activated raster scanning thermal imaging at sub-diffraction resolution

Abstract

Active thermal imaging is a valuable tool for the nondestructive characterization of the morphological properties and the functional state of biological tissues and synthetic materials. However, state-of-the-art techniques do not typically combine the required high spatial resolution over extended fields of view with the quantification of temperature variations. Here, we demonstrate quantitative far-infrared photo-thermal imaging at sub-diffraction resolution over millimeter-sized fields of view. Our approach combines the sample absorption of modulated raster-scanned laser light with the automated localization of the laser-induced temperature variations imaged by a thermal camera. With temperature increments ∼0.5–5 °C, we achieve a six-time gain with respect to our 350-μm diffraction-limited resolution with proof-of-principle experiments on synthetic samples. We finally demonstrate the biological relevance of sub-diffraction thermal imaging by retrieving temperature-based super-resolution maps of the distribution of Prussian blue nanocubes across explanted murine skin biopsies.

Focal dynamic thermal imaging for label-free high-resolution characterization of materials and tissue heterogeneity

“…Both of these techniques apply stimulus over a large area and the subsequent thermal response becomes blurred due to thermal conductivity, significantly reducing the spatial resolution. A recent article achieved sub-diffraction limited thermal imaging of tissue slides stained with exogenous methylene blue nanoparticles for contrast enhancement by irradiating the sample using a scanning focal light beam to prevent thermal blurring 11 . This technique tracked optical absorption induced heating, but did not track heat dissipation over time, confining its sensitivity to optical absorption and specific heat capacity rather than thermal conductivity.…”

“…Furthermore, the extraction of FDTI features is straightforward and can be performed in real time. Indeed, the specifications of FDTI equipment will affect the resolution and sensitivity of the system, but these simple requirements are in stark contrast to high-resolution thermal techniques which utilize expensive laser systems 24 , lock-in detection schemes, fragile alignment systems 15 , 19 – 21 , 23 , or which rely on exogenous contrast 11 which limits in vivo application. In addition, some of the lasers used are medical grade therapeutic lasers that cause pain 24 , which highly differ from the painless and low power irradiation used for FDTI.…”

“…In existing implementations of DTI, a thermal stimulus is applied over a large area of tissue, which blurs the detection of unique thermal properties of small areas within the thermally perturbed region. Super-resolution DTI rasters focal excitation of visible light across the sample, followed by image reconstruction that determines the centroid of absorptive agents well beyond the diffraction limit to improve spatial resolution 11 . For biological samples, exogenous contrast agents such as dyes or nanoparticles are used to generate sufficient contrast.…”

Multiphoton Laser Fabrication of Hybrid Photo-Activable Biomaterials

“…For this purpose, it was essential to adopt Rose Bengal as the PI in TPL writing at 800 nm (average power 100 mW, 10 writing speed) for obtaining photothermal microstructures. The resulting 1.5–2 temperature increase, likely underestimated by the average due to the large point spread function width of the Germanium optics of the thermal camera, was measured at high spatial resolution, , by means of photo-activated subdiffraction thermal imaging [ 143 ].…”

Methodologies for Large-Size Pouch Lithium-Ion Batteries End-of-Life Gateway Detection in the Second-Life Application

“…[9][10][11] The underlying degradation mechanisms of LiB include loss of active material (LAM), loss of lithium inventory (LLI), accelerated growth of surface electrolyte interphase (SEI), alteration of the surface areas of the electrodes especially on the anode, https://mc04.manuscriptcentral.com/jes-ecs Infrared (IR) thermography could be a useful NDT for temperature field measurements over the battery surface. [15][16][17][18][19] For LiBs, IR thermography was mostly used to validate calculated temperature over the LiBs surface obtained using electrochemical-thermal or electro-thermal coupled models with experimental measurements on the pristine LiBs. [20][21][22][23] During the cycling of large-size LiBs, there could be variations of voltage, transverse current density and local SoC over LiB's surface even for a brand-new battery.…”