Label-Free Biomedical Imaging with High Sensitivity by Stimulated Raman Scattering Microscopy
Christian W. Freudiger,1,2*
Wei Min,1*
Brian G. Saar,1
Sijia Lu,1
Gary R. Holtom,1
Chengwei He,3
Jason C. Tsai,4
Jing X. Kang,3
X. Sunney Xie1
Label-free chemical contrast is highly desirable in biomedical
imaging. Spontaneous Raman microscopy provides specific vibrational
signatures of chemical bonds, but is often hindered by low sensitivity.
Here we report a three-dimensional multiphoton vibrational imaging
technique based on stimulated Raman scattering (SRS). The sensitivity
of SRS imaging is significantly greater than that of spontaneous
Raman microscopy, which is achieved by implementing high-frequency
(megahertz) phase-sensitive detection. SRS microscopy has a
major advantage over previous coherent Raman techniques in that
it offers background-free and readily interpretable chemical
contrast. We show a variety of biomedical applications, such
as differentiating distributions of omega-3 fatty acids and
saturated lipids in living cells, imaging of brain and skin
tissues based on intrinsic lipid contrast, and monitoring drug
delivery through the epidermis.
2 Department of Physics, Harvard University, Cambridge, MA 02138, USA.
3 Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA.
4 Pfizer Global Medical, 685 3rd Avenue, MS 1325, New York, NY 10017, USA.
* These authors contributed equally to this work.
To whom correspondence should be addressed. E-mail: xie{at}chemistry.harvard.edu
