Trying to pick up faint microscopic signals is no easy task. As a result, researchers find it difficult to catch small things happening in cells or other materials. Boston University is creating advanced techniques to make microscopes better at seeing tiny sample details without needing special dyes. Results of the study are published in Nature Communications and Science Advances.
The primary findings of the two papers focus on a fundamental challenge in the rising field of vibrational imaging—how to push the detection limit so that vibrational imaging is as sensitive as fluorescence imaging in a dye-free manner. The researchers deploy photothermal microscopy to detect the chemical bonds, and after excitation of chemical bond vibration, energy dissipates into heat, causing a rise in temperature.
This represents a new class of chemical imaging toolbox called vibrational photothermal microscopy (VIP) microscopy. Developments include a wide-field mid-infrared photothermal microscope to visualize the chemical content of a signal viral particle and a novel vibrational photothermal microscope based on the stimulated Raman process.
The development of SRP microscopy was unexpected. After running a calculation of temperature rise in the focus of an SRS (stimulated Raman scattering) microscope, the team found a strong stimulated Raman photothermal (SRP) effect. With SRP microscopy, each beam can have absorption, causing a weak non-Raman background in the SRP image. Methods reported in these two papers are complimentary. The WIDE-MIP method is good for detecting IR-active bonds, while the SRP method is sensitive to Raman-active bonds.
Together, the two papers indicate a novel chemical microscopy class termed vibrational photothermal microscopy or VIP microscopy. This offers a very sensitive way to probe specific chemical bonds that can be used to map molecules of very low concentrations without dye labeling.