ABSTRACT
Embryonic Stem Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219 8.4.3 Cell Sorting Potential of Raman Spectroscopy . . . . . . . . . . . . . . . . . . . . 222 8.4.4 Extracellular Matrix Characterization Using Raman Spectroscopy . . . . 224 8.4.5 3D Scaffold Characterization Using Raman Spectroscopy . . . . . . . . . . 226 8.4.6 Bioprocesses and Bioreactor Monitoring Using Raman Sensors . . . . 227 8.4.7 Applications of CARS Microscopy in Regenerative Medicine . . . . . . . . 228
8.5 Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
8.1.1 The Raman Effect e Raman eect belongs to the class of light-matter interaction mechanisms. While infrared spectroscopy is based on the absorption of light, the Raman eect is attributed to the inelastic scattering of light. If the photons that make up the light interact with molecules inside the specimen in such a way that distorts its electron cloud (i.e., inducing a polarizability change), then the Raman eect can be observed. In contrast to ultraviolet light, photons in the visible and near-infrared part of the spectrum do not have enough energy to activate the electronic transition of the molecules but will create an unstable and short-lived state called “virtual state.” As the molecules reach the thermal equilibrium, following photon interaction, three distinctive wavelengths will be observed. Quantum mechanics dictates that a photon is born with a specic energy that cannot be modied during its life. Hence, during scattering processes, it is assumed that the incident photon is absorbed and then reemitted with either (1) almost the same energy Rayleigh scattering, (2) less energy (Raman-Stokes generating a spectrum on the longer wavelengths compared to incident light), or (3) higher energy (Raman antiStokes generating spectrum on the shorter wavelengths compared to incident light). An illustration of the three processes is shown in Figure 8.1, together with the process for coherent anti-Stokes Raman scattering (CARS).
