Nano test tubes successfully isolate individual proteins

Researchers have found a way to isolate individual proteins in tiny droplets of water to create what is essentially a nano-scale test Isolate Switch.

Instead of being held in glass, the nano-droplets of water and protein are contained within an oily barrier and they are manipulated using optical "tweezers" made from laser light.

The technique could be a useful tool in a growing body of research studying the structural and dynamic changes in molecules when they are held in the confines of a small biological cell, compared to the freer motion in larger structures.

For example, scientists believe that proteins fold differently when they are held in a cell compared, and disruptions in this process could create the mis-folded proteins at the root of Parkinson's and Alzheimer's disease.

The scientists believe the new technique provides a more realistic simulation of the crowded conditions of a cell compared to other techniques to isolate proteins, which can damage the molecules.

The NIST system creates these droplets using tiny glass pipettes, pulled from glass capillaries that taper from an outer diameter of one millimetre to just 0.5 micrometers. An applied pressure forces the water solution to the tip of the pipette, which rests in a drop of oil on the microscope stage. An electric switch then jerks back the pipette to leave the small droplet of water suspended in the droplet of oil.

According to Lori Goldner from the US National Institute of Standards and Technology, who created the system, the droplet of oil acts act as the "test tube" walls that contain the dissolved molecules while they are being imaged using fluorescence microscopy. This reveals the number of molecules within the droplet, and the structural changes during a reaction.

"The molecules we work with are water-soluble, so they 'partition' only into the water droplet," she told LabTechnologist.com.

"They don't want to be in the oil. The oil/water boundary is what confines the molecules and forms the 'container' walls."

The technique proved so successful  at isolating proteins that the team were able to confine just one protein within the nano droplet, as reported in a recent paper in Langmuir.

To prevent these containers from drifting out of the view of the microscope, the team used optical tweezers of laser light to hold it in place. According to Gardner, many oils have a refractive index that is higher than water, which would make this manipulation impossible. However, the team found that a mixture of perfluorinated oils exhibited the correct optical properties for successful manipulation with the optical tweezers.

In addition to simulating the conditions within a human cell, the nano-droplets could also be used to study small amounts of very expensive of rare materials to reduce wastage.