High-speed molecular spectral imaging of tissue with stimulated Raman scattering

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Label-free DNA imaging is highly desirable in biology and medicine to perform live imaging without affecting cell function and to obtain instant histological tissue examination during surgical procedures. Here we show a label-free DNA imaging method with stimulated Raman scattering (SRS) microscopy for visualization of the cell nuclei in live animals and intact fresh human tissues with subcellular resolution. Relying on the distinct Raman spectral features of the carbon-hydrogen bonds in DNA, the distribution of DNA is retrieved from the strong background of proteins and lipids by linear decomposition of SRS images at three optimally selected Raman shifts. Based on changes on DNA condensation in the nucleus, we were able to capture chromosome dynamics during cell division both in vitro and in vivo. We tracked mouse skin cell proliferation, induced by drug treatment, through in vivo counting of the mitotic rate. Furthermore, we demonstrated a label-free histology method for human skin cancer diagnosis that provides comparable results to other conventional tissue staining methods such as H&E. Our approach exhibits higher sensitivity than SRS imaging of DNA in the fingerprint spectral region. Compared with spontaneous Raman imaging of DNA, our approach is three orders of magnitude faster, allowing both chromatin dynamic studies and label-free optical histology in real time.

mentioning

confidence: 99%

Label-free DNA imaging in vivo with stimulated Raman scattering microscopy

Lü

Basu

Igras

et al. 2015

255

213

“…diagnosis would require several days, making conventional infrared and Raman microscopy impractical for use during cancer surgery. Although coherent Raman spectroscopy has demonstrated faster tissue imaging at high spatial resolution (26,27), the ability of these techniques to build classification models that can be used for objective diagnosis of the presence or absence of tumors in independent tissue samples has not been established.…”

Section: Significancementioning

confidence: 99%

Diagnosis of tumors during tissue-conserving surgery with integrated autofluorescence and Raman scattering microscopy

Kong

Rowlands

Varma

et al. 2013

225

223

Tissue-conserving surgery is used increasingly in cancer treatment. However, one of the main challenges in this type of surgery is the detection of tumor margins. Histopathology based on tissue sectioning and staining has been the gold standard for cancer diagnosis for more than a century. However, its use during tissue-conserving surgery is limited by time-consuming tissue preparation steps (1-2 h) and the diagnostic variability inherent in subjective image interpretation. Here, we demonstrate an integrated optical technique based on tissue autofluorescence imaging (high sensitivity and high speed but low specificity) and Raman scattering (high sensitivity and high specificity but low speed) that can overcome these limitations. Automated segmentation of autofluorescence images was used to select and prioritize the sampling points for Raman spectroscopy, which then was used to establish the diagnosis based on a spectral classification model (100% sensitivity, 92% specificity per spectrum). This automated sampling strategy allowed objective diagnosis of basal cell carcinoma in skin tissue samples excised during Mohs micrographic surgery faster than frozen section histopathology, and one or two orders of magnitude faster than previous techniques based on infrared or Raman microscopy. We also show that this technique can diagnose the presence or absence of tumors in unsectioned tissue layers, thus eliminating the need for tissue sectioning. This study demonstrates the potential of this technique to provide a rapid and objective intraoperative method to spare healthy tissue and reduce unnecessary surgery by determining whether tumor cells have been removed.

“…Unfortunately, CARS suffers from spectral distortion, unwanted nonresonant background, nonstraightforward concentration dependence, and coherent image artifact (25). Most recently, SRS microscopy has emerged to supersede CARS microscopy in almost all aspects (29)(30)(31)(32)(33)(34)(35)(36)(37)(38). Using Einstein's stimulated emission principle (39,40), SRS has achieved unprecedented sensitivity down to ∼1,000 retinoic acid molecules and up to video rate imaging speed in vivo (30,33).…”

mentioning

confidence: 99%

Vibrational imaging of newly synthesized proteins in live cells by stimulated Raman scattering microscopy

Lu¹,

Shen³

et al. 2013

211

223

Synthesis of new proteins, a key step in the central dogma of molecular biology, has been a major biological process by which cells respond rapidly to environmental cues in both physiological and pathological conditions. However, the selective visualization of a newly synthesized proteome in living systems with subcellular resolution has proven to be rather challenging, despite the extensive efforts along the lines of fluorescence staining, autoradiography, and mass spectrometry. Herein, we report an imaging technique to visualize nascent proteins by harnessing the emerging stimulated Raman scattering (SRS) microscopy coupled with metabolic incorporation of deuterium-labeled amino acids. As a first demonstration, we imaged newly synthesized proteins in live mammalian cells with high spatial-temporal resolution without fixation or staining. Subcellular compartments with fast protein turnover in HeLa and HEK293T cells, and newly grown neurites in differentiating neuron-like N2A cells, are clearly identified via this imaging technique. Technically, incorporation of deuterium-labeled amino acids is minimally perturbative to live cells, whereas SRS imaging of exogenous carbon-deuterium bonds (C-D) in the cell-silent Raman region is highly sensitive, specific, and compatible with living systems. Moreover, coupled with label-free SRS imaging of the total proteome, our method can readily generate spatial maps of the quantitative ratio between new and total proteomes. Thus, this technique of nonlinear vibrational imaging of stable isotope incorporation will be a valuable tool to advance our understanding of the complex spatial and temporal dynamics of newly synthesized proteome in vivo.stable isotope labeling | stimulated Raman microscopy | protein synthesis