  Label-free optical imaging is valuable in biology and medicine with its
non-destructive property and reduced optical and chemical damages. Quantitative
phase (QPI) and molecular vibrational imaging (MVI) are the two most successful
label-free methods, providing morphology and biochemistry, respectively, that
have pioneered numerous applications along their independent technological
maturity over the past few decades. However, the distinct label-free contrasts
are inherently complementary and difficult to integrate due to the use of
different light-matter interactions. Here, we present a unified imaging scheme
that realizes simultaneous and in-situ acquisition of MV-fingerprint contrasts
of single cells in the framework of QPI utilizing the mid-infrared photothermal
effect. The fully label-free and robust integration of subcellular morphology
and biochemistry would have important implications, especially for studying
complex and fragile biological phenomena such as drug delivery, cellular
diseases and stem cell development, where long-time observation of unperturbed
cells are needed under low phototoxicity.
