Keiichiro Toda

Quantitative phase imaging (QPI) with its high-contrast images of optical phase delay (OPD) maps is often used for label-free single-cell analysis. Contrary to other imaging methods, sensitivity improvement has not been intensively explored because conventional QPI is sensitive enough to observe the surface roughness of a substrate that restricts the minimum measurable OPD. However, emerging QPI techniques that utilize, for example, differential image analysis of consecutive temporal frames, suc

An optical microscope enables image-based findings and diagnosis on microscopic targets, which is indispensable in many scientific, industrial and medical settings. A standard benchtop microscope platform, equipped with e.g., bright-field and phase-contrast modes, is of importance and convenience for various users because the wide-field and label-free properties allow for morphological imaging without the need for specific sample preparation. However, these microscopes never have capability of a

Quantitative phase microscopy (QPM) literally images the quantitative phase shift associated with image contrast, where the phase shift can be altered by laser heating. In this study, the thermal conductivity and thermo-optic coefficient (TOC) of a transparent substrate are simultaneously determined by measuring the phase difference induced by an external heating laser using a QPM setup. The substrates are coated with a 50-nm-thick titanium nitride film to photothermally generate heat. Then, the

Vibrational microscopy provides label-free, bond-selective chemical contrast by detecting molecular vibrations, making it invaluable for biomedical research. While conventional methods rely on the direct detection of Raman scattering or infrared absorption, recently developed vibrational photothermal (ViP) microscopy achieves chemical contrast indirectly through refractive index (RI) changes. This indirect approach enables unique imaging capabilities beyond traditional chemical imaging. Here, we

Acquisition of molecular information is useful in various aspects of science, industry and medicine. Fluorescence imaging is the most widely used molecular imaging technique in biological fields, but is accompanied by chemical alteration of and photodamage to the sample due to the use of fluorescent labelling agents. Alternatively, label-free molecular-vibrational imaging methods, such as mid-infrared (MIR) absorption imaging and spontaneous/coherent Raman scattering (RS) imaging [1], suffer fro

Vibrational microscopy provides label-free, bond-selective chemical contrast by detecting molecular vibrations, making it invaluable for biomedical research. While conventional methods rely on the direct detection of Raman scattering or infrared absorption, recently developed vibrational photothermal (ViP) microscopy achieves chemical contrast indirectly through refractive index (RI) changes. This indirect approach enables unique imaging capabilities beyond traditional chemical imaging. Here, we

Fluorescent thermometry has reported noteworthy intracellular temperature gradients, suggesting the possibility of thermal regulation of cellular functions. However, heat conduction calculations assuming an aqueous intracellular environment contradict these findings. To resolve this contradiction, we visualized intracellular heat conduction using label-free mid-infrared photothermal optical diffraction tomography and obtained thermal diffusivity similar to that of water. Furthermore, we found a

We develop a method for phase retrieval from a single image captured with Zernike phase-contrast microscopy without any hardware modification. We show its performance with a cell’s phase image obtained with digital holographic microscopy.

Fluorescent nanothermometry has revealed pronounced inhomogeneous temperature distributions within cells, establishing the field of single-cell thermal biology. However, this finding has sparked a controversial discussion known as the "10^5 gap issue", stemming from a simple heat conduction calculation suggesting such large temperature distributions should not exist within cells. Here, we address this issue using label-free mid-infrared photothermal microscopy, which enables measurement of heat-

An optical microscope enables image-based findings and diagnosis on microscopic targets, which is indispensable in many scientific, industrial and medical settings. Majority of microscope users are accustomed to standard benchtop microscopes, but it fails to give molecular contrast of the specimen which otherwise requires expensive specialized instruments to measure, accompanied by chemical or optical damages to the sample and/or slow imaging speed. Here, we report on a simple optical instrument

Mid-infrared photothermal (MIP) microscopy can be categorized into point-scanning (PS) and wide-field (WF) configurations, each having independently achieved substantial technical advancements. Because MIP microscopy utilizes thermal effects as a detection signal, the well-known properties of conventional PS and WF microscopy cannot be straightforwardly applied to evaluate MIP imaging performance. In this study, we present comparative analyses of MIP imaging performances between PS and WF config

Coherent Raman scattering (CRS) and mid-infrared photothermal (MIP) microscopy have overcome the limitations of traditional vibrational imaging. MIP microscopy has recently presented high imaging performance comparable to CRS microscopy, including high speed beyond video rate and high spatial resolution below 200 nm. So far, a comparative analysis of imaging performance between CRS and MIP microscopy has not been discussed comprehensively. In this study, we present numerical evaluations of the i