Label-free biochemical quantitative phase imaging with mid-infrared photothermal effect

Label-free optical imaging is valuable in biology and medicine because of its non-destructive nature. Quantitative phase imaging (QPI) and molecular vibrational imaging (MVI) are the two most successful label-free methods, providing morphological and biochemical information, respectively. These techniques have enabled numerous applications as they have matured over the past few decades; however, their label-free contrasts are inherently complementary and difficult to integrate due to their reliance on different light–matter interactions. Here we present a unified imaging scheme with simultaneous and in situ acquisition of quantitative phase and molecular vibrational contrasts of single cells in the QPI framework using the mid-infrared photothermal effect. The robust integration of subcellular morphological and biochemical label-free measurements may enable new analyses, especially for studying complex and fragile biological phenomena such as drug delivery, cellular disease, and stem cell development, where long-time observation of unperturbed cells is needed under low phototoxicity.