Positive-contrast mid-infrared excitation and optoacoustic/optothermal detection enables label-free live-cell chemical microscopy and non-invasive biosensing in vivo

Mid-infrared (mid-IR) excitation and optoacoustic/optothermal (OA/OT) sensing are perfectly complementary technologies. Mid-IR absorption excites molecular-specific vibrational-transitions that are deexcited in the form of heat, generating OA and OT signal which intensity primarily depends on efficient heat deposition. This chemical-bond specific combination is highly sensitive and we apply it for longitudinal lable-free metabolic imaging in living cells and tissues. Here, we present two different methods harvesting from mid-IR OA/OT sensing: I) Mid-infraRed Optoacoustic Microscopy (MiROM) and II) Phase-Shifting Mid-IR Optothermal Microscopy (PSOM). MiROM uses tightly focused optical excitation with coaxially focused ultrasound detection and Chemical-contrast imaging is obtained at specific molecular vibrations excited by pulsed mid-IR radiation. PSOM is a widefield chemical-contrast imaging method using pump-probe detection of OT signals by optical phase change due to mid-IR irradiation. Chemical-contrast imaging is obtained in large-field-of-views and high cell confluency by taking the difference between Phase Contrast images of the sample with and without Mid-IR illuminati