Liquid crystals in your screen can detect bacterial contamination

The technique could lead to faster, more sensitive tests for bacterial contamination in water and injectable medical fluids. And no more horseshoe crabs will need to donate blood.

The lasted on biological sensors...

Droplets of liquid crystals – found in our everyday electronic displays – could be used to detect bacterial contamination in water, a new report finds.

Gram-negative bacteria like E. coli and Salmonella have toxins in their outer membranes. Called endotoxins, they're considered to be key indications of bacterial infection.

A team led by Nicholas Abbott from the University of Wisconsin–Madison found a way to detect these bacterial lipid-polysaccharides using a simple microscope.

Liquid crystals typically flow like liquids, but they have molecules that have a crystalline-like order to them… an orientation that changes in the presence of very low bacterial concentrations.

New Scientist explains:

When suspended in water, the molecules in a liquid crystal droplet normally form chains that wrap around the droplet like the lines of longitude on a globe. But in the presence of endotoxins, disease-causing molecules produced by E. coli bacteria, they rearrange to form a pattern that radiates from the drop's center.

More specifically, endotoxins interact with defects in liquid crystal droplets – the little imperfections in the ordering of their molecules. Endotoxin molecules build up inside the cores of defects and then trigger changes in their molecular orientation.

It only takes about a thousand endotoxin molecules to change the appearance of a single liquid crystal droplet visible in a light microscope. This small scale (in the pictogram/milliliter range) indicates that liquid crystals can detect endotoxins with high sensitivity.

The Food and Drug Administration requires testing for endotoxins on equipment used to make vaccines, drugs, intravenous fluids, and other kinds of devices and materials. The new technique could become improved assays for bacterial contamination of injectable medical fluids.

The current FDA-approved test for endotoxin is based on the blood of horseshoe crabs, which have evolved to combat infection by clotting their blood in the presence of endotoxins. These primitive animals are captured, bled, and then returned to the water.

The horseshoe crab test is the ‘gold standard assay’ for endotoxin, Abbott says, "but our system so far seems a bit more sensitive and does not involve any biological components. The change in optical appearance of the droplets is quite striking, and it occurs within a minute."

If the technique becomes commercialized, it could replace the current standard, and Abbott believes horseshoe crabs would appreciate not having to donate blood quite so often.

The study was published in Science today.

Image: LCD screens prairie by Felix SF via flickr

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