Discipline: Technology and Engineering
Subcategory: Materials Science
Jomary Mercado Montijo - University of Puerto Rico Mayaguez
Co-Author(s): Travis W. Nelson and Nicholas Abbott, University of Wisconsin–Madison, Madison, WI
Lipopolysaccharide (LPS), also known as endotoxin, is a component of the outer membrane of gram-negative bacteria. The presence of endotoxin can generate an immune system response including: hemorrhagic shock, severe diarrhea, fever, and other biological effects. Some cases can result in death. There are many contexts where it is important to be able to detect the presence of endotoxin. In previous work, it has been shown that common biological lipids and synthetic surfactants, at concentrations above 1-100 μg/ml, decorate the surfaces of liquid crystal (LC) droplets and induce a transition from the bipolar to the radial configuration. In comparison, endotoxin causes the bipolar to radial ordering transition at concentrations at least six orders of magnitude lower (pg/ml). It has been hypothesized that an endotoxin assembly stabilizes the radial configuration of a LC droplet by decorating the droplet defect. In this study, we explore how changes in solution conditions impact the response of the LC droplets to endotoxin. Liquid crystal droplets were generated by vortexing 4′-pentyl-4-cyanobiphenyl (5CB; a nematic LC) in water to form an oil-in-water emulsion. Bipolar and radial 5CB droplets scatter light in distinct way, thus allowing LC droplet configurations to be determined by flow cytometry. Several systems were explored in order to identify the dependence of the LC droplet response to endotoxin as a function of buffer composition and pH. The number of droplets per microliter was set to 500, 1500, and 5000 for each system. Endotoxin was added to phosphate buffer saline (PBS) and citrate buffer saline (CBS) at pH 5 and 7.4. Additionally, the impact of adding ethylenediaminetetraacetic acid (EDTA), which acts as a strong chelating agent, to PBS was explored. Overall, our results hint that LC droplets offer the basis of a promising method to detect changes in the state of aggregation of endotoxin in the pg/ml range.
References: Gupta et al., Size-dependent ordering of liquid crystals observed in polymeric capsules with micrometer and smaller diameters. Angew. Chem. Int. 48 (2009) 1652-1655.
I-Hsin Lin et al., Endotoxin-induced structural transformations in liquid crystalline droplets. Science 332, (2011) 1297.
Funder Acknowledgement(s): EFRI-REM grant for the REU summer program 2016; University of Wisconsin-Madison Materials Research Science and Engineering Center (DMR-0520527) for funding my REU program.
Faculty Advisor: Nicholas L. Abbott, nlabbott@wisc.edu
Role: During my summer research, I worked directly on the detection of endotoxin by studying the structural transitions in liquid crystalline droplets. The first step of the process was the preparation of liquid crystal droplets by water-in-oil emulsions. Then, endotoxin dilutions were performed in PBS and CBS buffers at different chelating and pH conditions. The structures of the LC droplets were analyzed by flow cytometry. After data collection, I determined the LPS response towards LC droplets and studied the state of aggregation of the endotoxin.