Raman imaging of biology and soft matter samples: a few examples

Abstract

Electron microscopy (SEM, TEM) is widely used to characterize the internal structures with micrometer spatial resolution. AFM is also commonly employed for analyzing the surface topography with a superior spatial resolution. However, confocal Raman microspectrometry is a unique way to complete such structural investigation by knowledge on chemical information. Raman imaging combines the spatial resolution of optical microscopy with the molecular analysis capabilities of Raman scattering. Then, it is very well adapted to provide direct information about conformation, structure and behavior of lipids and biopolymers (proteins, polysaccharides) from micronsized zones of interest. Also, the mainly structure‐sensitive bands in protein and lipid spectra makes them suitable for multivariate analysis techniques such as principal component analysis (PCA) to deduce structural relationships. Raman microspectrometry is then a method of choice for the compositional investigation with a high spectral resolution of hydrated biological systems of food interest along with the structural investigation performed conjointly with laser scanning confocal microscopy, AFM or electron microscopy with a superior spatial resolution. We aim here to review few examples of Raman imaging performed on different biological systems (algae, plant and animal tissues) and on soft‐matter based systems (highly diluted gels, dispersions) relevant in food industry, see Figures 1 and 2. We will focus on the complementarity with the other types of microscopy, and on the practical details concerning the sample preparation (choice of objectives, choice and influence of supports, smoothing or not of the surfaces,…).