Non-contact, label-free monitoring of cells and extracellular matrix using Raman spectroscopy

Non-destructive, non-contact and label-free technologies to monitor cell and tissue cultures are needed in the field of biomedical research. 1-5 However, currently available routine methods require processing steps and alter sample integrity. Raman spectroscopy is a fast method that enables the measurement of biological samples without the need for further processing steps. This laser-based technology detects the inelastic scattering of monochromatic light. 6 As every chemical vibration is assigned to a specific Raman band (wavenumber in cm -1), each biological sample features a typical spectral pattern due to their inherent biochemical composition. 7-9 Within Raman spectra, the peak intensities correlate with the amount of the present molecular bonds. 1 Similarities and differences of the spectral data sets can be detected by employing a multivariate analysis (e.g. principal component analysis (PCA)). 10 Here, we perform Raman spectroscopy of living cells and native ti ssues. Cells are either seeded on glass bottom dishes or kept in suspension under normal cell culture conditions (37 °C, 5% CO 2) before measurement. Native tissues are dissected and stored in phosphate buffered saline (PBS) at 4 °C prior measurements. Depending on our experimental set up, we then either focused on the cell nucleus or extracellular matrix (ECM) proteins such as elastin and collagen. For all studies, a minimum of 30 cells or 30 random points of interest within the ECM are measured. Data processing steps included background subtraction and normalization