Abstract
Bacterial lipopolysaccharides (LPSs) are important indicators of a bacteria presence in any samples. They can therefore be used for the detection of microbiological contamination in food and dairy products. We performed a comparative analysis of different bacterial models by the application of liposomes containing LPS from Salmonella enterica serotype typhimurium on the surface of an 11-mercaptoundecanoic acid (MUA) monolayer chemisorbed on the gold surface of quartz crystal. Using quartz crystal microbalance with dissipation monitoring (QCM-D), we were able to monitor the formation of the lectin, concanavalin A (ConA), layer on the MUA surface. We determined the optimal concentration of the ConA for the layer formation. ConA of 0.3 mg/mL was selected as the most suitable adsorption of liposomes containing LPS. Using the Sauerbrey equation, we calculated that approximately 1.13 × 1012 ConA molecules per cm2 was adsorbed on the MUA surface, which closely corresponds to the 1.19 × 1012 molecules per cm2 by theoretical models. Later, mixed LPS liposomes containing dipalmitoyl phosphatidyl choline (DPPC), dipalmitoyl phosphatidyl ethanolamine (DPPE) and cholesterol successfully interacted with the ConA layer, which resulted in a decrease in the resonant frequency and an increase in dissipation. We compared the adsorption of liposomes with different fractions of LPS and containing LPS from different bacteria. Lack of any LPS in liposomes caused weaker adsorption on the ConA layer. Liposomes containing 50% LPS caused the most prominent adsorption and were suitable for interaction with DNA aptamers specific to certain LPS. The addition of the aptamers to the surface of ConA covered by LPS-containing liposomes resulted in a decrease in resonant frequency and an increase in the dissipation. Using the Kelvin–Voigt viscoelastic model and multiharmonic response of acoustic sensors, we also determined changes in viscoelastic values of the molecular films during interaction with liposomes and the ConA layer.
Author Contributions
Conceptualization, T.H.; methodology, T.H. and M.T.; validation, M.T.; formal analysis, M.T.; investigation, M.T.; resources, T.H.; data curation, M.T.; writing—original draft preparation, T.H. and M.T.; writing—review and editing, T.H.; supervision, T.H.; project administration, T.H.; funding acquisition, T.H. All authors have read and agreed to the published version of the manuscript.
Funding
This research was funded by European Union’s Horizon 2020 research and innovation program through the Marie Skłodowska-Curie grant agreement No 101007299, by Science Agency VEGA, project No. 1/0445/23 and by the Slovak Academic Information Agency, project No. 2022-10-15-003.
Institutional Review Board Statement
Not applicable.
Informed Consent Statement
Not applicable.
Data Availability Statement
Not applicable.
Conflicts of Interest
The authors declare no conflict of interest.
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