Nanofluidic scattering microscopy offers new view of molecular behavior

21 Jun 2022

Chalmers University label-free technique uses diffusion within nanofluidic channel.

Label-free microscopy of single biomolecules is inherently attractive as a complement to established fluorescence methods, where a marker label is attached to the molecules of interest.

At present several label-free modalities are available, but often require a surface-enhanced operation, with the target molecule binding to a surface or substrate in order to become visible. A technique able to image them directly in solution instead would be preferable.

A project at Chalmers University of Technology has now developed an alternative approach, potentially able to monitor conformational changes and interactions of single biomolecules inside a nanofluidic channel.

As described in Nature Methods, nanofluidic scattering microscopy (NSM) works by imaging the nanofluidic channels nanofabricated into an optically transparent matrix such as silicon dioxide, using dark-field light-scattering microscopy.

"With current methods you can never quite be sure that the labeling or the surface to which the molecule is attached does not affect the molecule's properties," commented Christoph Langhammer of Chalmers University. "With the aid of our technology, which does not require anything like that, it shows its completely natural silhouette or optical signature, which means that we can analyse the molecule just as it is."

The technique, developed at Chalmers and the University of Gothenburg, is being commercialized by Langhammer and colleagues via the spin-out company Envue Technologies.

In NSM the molecules or particles of interest are flushed through the channels of a nanofluidic chip, channels tens to hundreds of nanometers in diameter. A test fluid is added and the chip illuminated with visible light.

The light scattered from the chip is collected in dark-field configuration, with the nanochannels ensuring that the molecules are localized within the microscope focal plane. The NSM principle involves subtracting the scattering pattern of the empty nanochannel from that of the channel containing a biomolecule, to give a differential dark-field image of just the molecule.

Development of medicines and vaccines

The smaller the nanochannel, the greater the amplification effect and the smaller the molecules that can be seen, with the nanochannels improving the optical contrast of the imaged nano-object by several orders of magnitude according to the project.

"The interaction that occurs between the light, the molecule and the small fluid-filled channels makes the molecule inside show up as a dark shadow, and it can be seen on the screen connected to the microscope," commented the Chalmers project. "By studying it, researchers can not only see but also determine the mass and size of the biomolecule, and obtain indirect information about its shape, something that was not previously possible with a single technique."

Envue Technologies expects to address markets in industrial quality control as well as research and development, saving time and money in development of medicines and vaccines.

"The aim is to further hone our technique so that it can help to increase our basic understanding of how life works, and contribute to making the development of the next generation medicines more efficient," said Langhammer.