Bacterial lipopolysaccharides (LPSs) are important indicators of bacterial infection in organisms or food contamination. They can be therefore used for medical diagnostics as well as for the detection of microbiological contamination in food and dairy products. We performed a comparative analysis of different techniques to isolate LPSs from Salmonella enterica serotype typhimurium (S. typhi). Different stages of the isolation method were applied to receive LPSs and the lipid component responsible for LPS toxicity called Lipid A was separated. As receptors for LPS detection, we used the lectin concanavalin A (ConA) or DNA aptamers immobilized at the gold layers of the quartz crystal modified by 11-mercaptoundecanoic acid. Using carbodiimide chemistry, the covalent immobilization of ConA or amino-modified DNA aptamers was possible. The interaction of LPSs with the sensing surface was studied by quartz crystal microbalance with dissipation monitoring (QCM-D). We have shown that DNA aptamers that specifically bind to lipid A in LPSs from S. typhi more strongly decrease the resonant frequency and increase the dissipation in comparison with ConA layers. Significant changes in the resonant frequency were observed already at 0.3 ng/mL of LPSs. The specificity of the interaction was confirmed by using LPSs isolated from other bacteria such as E. coli. We also used an extract of the bacterial membranes from Gram-positive bacteria Listeria monocytogenes that do not contain LPSs. In this case, no significant changes in frequency and dissipation were observed. Thus, the QCM-D is a sensitive tool for the detection of LPSs using DNA aptamers with high sensitivity and selectivity.

Acknowledgments. This work was funded under the European Union’s Horizon 2020 research and innovation program through the Marie Skłodowska-Curie grant agreement No. 101007299 (T.H.) and the Science Agency VEGA, project No. 1/0445/23 (T.H.).