Observing suppression of microbial growth with surface-enhanced raman scattering

Microorganisms can be both harmful and beneficial for human depending on their nature. If the mechanisms that make them harmful are known, their detrimental effects can be minimized, which makes the study of microbial growth crucial. The amount of nutrients plays an important role on the growth as well as presence of different chemicals that are toxic to them. Observation of microbial growth in different environmental conditions is important in terms of understanding the growth mechanisms of microorganisms. Among many analytical and spectroscopic methods, Surface-Enhanced Raman Scattering (SERS) is a promising technique to work with biological samples. It gives valuable information about molecular structures based on their vibrational modes. While working with biological samples, it has many advantages such as simple sample preparation, no interference from water and achieving low limits of detection. In the thesis presented below, microbial growth of bacteria and yeast cells in the presence of a biocidal agent were investigated with SERS. Maltose-reduced silver nanoparticles (mAgNPs) were used as biocidal agent. Escherichia coli (E.coli) and Saccharomyces cerevisiae (S.cerevisiae) were selected as model organisms for bacteria and yeast, respectively. The effect of three different concentrations (5, 10, and 20 ppm) of m-AgNPs were tested on the mentioned microorganisms. Their microbial growth was monitored by both measuring optical density (OD) and collecting their Raman scattering under a laser beam. The spectral changes with respect to time were analyzed and the bands related to certain metabolites of microorganisms such as amino acids, carbohydrates, proteins and genetic material were used to monitor the changes in the chemical composition of cell cultures. Results of both analysis revealed that microbial growth of E.coli is suppressed when the cells are treated with 5 and 10 ppm m-AgNPs, and is inhibited in the presence of 20 ppm m-AgNPs. The results obtained from S.cerevisiae demonstrates suppression of its growth increses with the increasing concentration of m-AgNPs as well.