A Combined Raman Spectroscopy and Chemometrics Study of the Interaction of Water-Soluble Polymers with Microorganisms

Optical spectroscopic methods such as Raman spectroscopy offer several advantages for the analysis of water-soluble polymers (WSPs). There is often no need for complex sample preparation, and measurements are usually rapid, mostly non-destructive and no harmful chemicals are required. In this work, we investigated WSPs and their interaction with bacteria using Raman spectroscopic methods. We analyzed four different WSPs, each with three different molar masses, in solid form using Raman microscopy, and in aqueous solutions using another Raman system designed for measurements in cuvettes, to train predictive models for concentration determination. Thus, we were able to show both the high potential of these approaches, especially for fast and easy investigations both qualitatively and quantitatively, as well as their limitations. Furthermore, we chose one of the molar masses of each tested polymer to carry out extensive Raman spectroscopic investigations with Escherichia coli and Enterococcus faecium, and revealed that bacterial cells exposed to polymers exhibited distinguishable spectral characteristics compared to those not in contact with polymers. Using Raman microscopy combined with partial least squares discriminant analysis (PLS-DA), we effectively distinguished between these groups. Further chemometric analysis indicated potential polymer-induced modifications to the bacterial cell membranes. While this differentiation may partly reflect polymer interactions at the membrane level, it could also correspond to shifts in bacterial growth phases. Together, these findings suggest a complex interplay between polymer exposure and bacterial physiological states.