Optofluidic force induction allows for real-time nanoparticle characterization

A team of researchers at Brave Analytics GmbH, working with a colleague from the Gottfried Schatz Research Center and another from the Institute of Physics, all in Austria, has developed a device that is capable of conducting real-time nanoparticle characterization. The group published their work in the journal Physical Review Applied.

Over the past several decades, product engineers have increasingly added nanoparticles to products to give them desired qualities—to thicken or color paints, for example. The types of nanoparticles used depend on many factors, such as their composition and shape, which are generally easily determined. The size of the nanoparticles is also important to ensure consistency, but figuring out how big they are has proven to be more challenging. One approach called dynamic light scattering has been found to work well, but only with tiny nanoparticles. In this new effort, the researchers created a device that can be used to determine the size of larger nanoparticles.

The new device is based on optofluidic force induction (OF2i). It consists of a clear cylinder and a laser beam. In use, the cylinder is filled with water into which sample nanoparticles have been added—in this case, tiny bits of polystyrene. The laser is fired in a way that allows the light to travel in a spiral through the water, forming a water vortex.

The laser light is used in two ways: to push the nanoparticles through the water and to track their motion. In such a setup, the amount of acceleration experienced by a given nanoparticle will depend on its size. The researchers suggest it is similar to a sailboat. Two boats of the same size experiencing the same force of wind will be pushed at different speeds if they have differently sized sails. And because the laser forms a vortex, the nanoparticles travel in a spiral, making collisions less likely.

The light scattered after bouncing off of the nanoparticle can then be viewed with a time-lapse microscope, which can reveal the paths taken by the individual nanoparticles. Analysis of the shape of such trajectories can be used to determine changes in velocity due to the force exerted by the laser and in so doing reveal the size of the nanoparticles. Testing showed the device capable of measuring nanoparticles in the range of 200 to 900 nm.

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