Raman microscopy and surface-enhanced Raman scattering (SERS) for in situ analysis of biofilms

Biofilms are communities of micro-organisms enclosed in a matrix of extracellular polymeric substances (EPS). They represent a ubiquitous form of microbial life on Earth. Detailed information on chemical composition and structure of the EPS matrix is relevant in medicine, industry and technological processes. Raman microscopy (RM) provides whole-organism fingerprints for biological samples with spatial resolution in the mu m range and enables correlations between optical and chemical images to be made. Low water background makes RM beneficial for in situ studies of biofilms, since water is the major component of the biofilm matrix. In this paper we discuss the feasibility of RM for chemical characterization of different structures in a multispecies biofilm matrix, including microbial constituents and EPS. We show that by improving the sensitivity of RM with surface-enhanced Raman scattering (SERS) one can perform rapid biofilm analysis. In particular, by choosing appropriate SERS substrates and solving the problem of SERS measurement reproducibility one can carry out in situ study of different components in the complex biofilm matrix. [GRAPHICS] Optical image (a), Raman spectra (b) and Raman images of aggregates (c) and protozoa (d) in biofilm matrix.