The paths taken by fluorescent particles as they diffuse through a porous nanoscale structure reveal the arrangement of the pores through a novel technique developed by scientists at Rice University. Image: Landes Research Group/Rice University.Rice University scientists have led a project to ‘see’ and measure the space in porous materials, even if that space is too small or fragile for traditional microscopes.
The Rice lab of chemist Christy Landes invented a new technique to characterize such nanoscale spaces, an important advance toward her group's ongoing project to efficiently separate ‘proteins of interest’ for drug manufacture. It should also benefit the analysis of porous materials of all kinds, including liquid crystals, hydrogels, polymers and even biological substances like cytosol, the compartmentalized fluids in cells.
The Landes lab conducted the research with collaborators at the University of California, Los Angeles (UCLA), and Kansas State University, and has published their findings in ACS Nano.
According to Landes, it's easy to use a fluorescent chemical compound to tag, or ‘label’, a material and take a picture of it. "But what if the thing you want a picture of is mostly nothing? That's the problem we had to solve to understand what was going on in the separation material," she says.
The team aims to improve protein separation by chromatography, in which solutions flow through porous material in a column. Because different materials travel at different speeds, the components separate and can be purified.
"We learned that in agarose, a porous material used to separate proteins, the clustering of charges is very important," Landes says. While the protein project succeeded, "when we matched experimental data to our theory, there was something additional contributing to the separation that we couldn't explain."
The answer appeared to be related to how charged particles like nanoscale ligands arranged themselves in the pores. "It was the only possible explanation," Landes says. "So we needed a way to image the pores." Standard microscopy techniques like atomic force, X-ray and electron microscopy would require samples to be frozen or dried. "That would either shrink or swell or change their structures," she explains.
So the team decided to utilize their experience with both Nobel Prize-winning super-resolution microscopy and fluorescence correlation spectroscopy. Super-resolution microscopy provides a way to see objects at resolutions below the diffraction limit, which normally prevents the imaging of features smaller than the wavelength of light directed at them. Correlation spectroscopy provides a way to measure fluorescent particles as they fluctuate.
The combined technique, termed fcsSOFI (for ‘fluorescence correlation spectroscopy super-resolution optical fluctuation imaging’), measures fluorescent tags as they diffuse in the pores, allowing the researchers to simultaneously characterize dimensions and dynamics within the pores. In this way, they are able to map slices of a porous material to see where charged particles tend to cluster. The lab tested its technique on both soft agarose hydrogels and lyotropic liquid crystals. Next, they plan to extend their mapping to three-dimensional spaces.
"We now have both pieces of our puzzle: We can see our proteins interacting with charges within our porous material, and we can measure the pores," Landes said. "This has direct relevance to the protein separation problem for the $100 billion pharmaceutical industry."
This story is adapted from material from Rice University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.