Electric fields direct nanoparticles through a liquid-filled maze – this new method could improve drug delivery and purification systems
In the home, laboratory, and factory, electric fields control technologies such as Kindle screens, medical diagnostic tests, and devices that purify cancer drugs. In an electric field, anything with an electric charge – from an individual atom to a large particle – experiences a force that can be used to push it in a desired direction.
When an electric field pushes charged particles in a fluid, the process is called electrophoresis. Our research team is studying how to harness electrophoresis to move tiny particles – called nanoparticles – in porous and spongy materials. Many emerging technologies, including those used in DNA analysis and medical diagnostics, use these porous materials.
Understanding how to control tiny charged particles as they move through these environments can make them faster and more efficient in existing technologies. It can also enable entirely new smart functions.
Ultimately, scientists aim to make such particles serve as tiny nanorobots. These could carry out complex tasks in our body or in our environment. They could search for tumors and administer treatments or look for sources of toxic chemicals in the soil and convert them into harmless compounds.
To achieve this progress, we need to understand how charged nanoparticles move through porous and sponge materials under the influence of an electric field. In a new study, published November 10, 2025 in the Proceedings of the National Academy of Sciences, our team of engineering researchers led by Anni Shi and Siamak Mirfendereski sought to do just that.
Weak and strong electric fields
Imagine a nanoparticle as a tiny submarine navigating a complex, interconnected, liquid-filled maze while simultaneously experiencing random movements. By observing nanoparticles moving through a porous material, we observed surprising behavior linked to the intensity of the applied electric field.
A weak electric field acts only as an accelerator, increasing the particle’s speed and greatly improving its chances of finding an exit from a cavity, but offering no directional guidance – it’s fast, but random.
In contrast, a strong electric field provides the necessary “GPS coordinates,” forcing the particle to move quickly in a specific, predictable direction through the array.
This discovery was puzzling but exciting, because it suggested that we could control the movement of nanoparticles. We could choose to have them move quickly and randomly with a weak field or directionally with a strong field.
The former allows them to efficiently search the environment while the latter is ideal for delivering goods. This puzzling behavior prompted us to take a closer look at the effect of the weak field on the surrounding fluid.
This diagram shows how a particle moves through a porous material over time in a weak or strong electric field. The darkest color indicates the starting point of the particle, and successively lighter colors represent the position of the particle after a certain time. The particle in a weak field moves randomly, while the particle in a strong field moves gradually in the direction determined by the electric field. Anni Shi
By studying the phenomenon more closely, we discovered the reasons for these behaviors. A weak field causes stagnant liquid to circulate in random swirling motions through the tiny cavities of the material. This random flow enhances the natural movement of a particle and pushes it toward the cavity walls. By moving along the walls, the particle significantly increases its probability of finding a random escape route, compared to searching the entire cavity space.
However, a strong field provides a powerful directional push to the particle. This thrust overcomes the natural shaking of the particle as well as the random flow of the surrounding liquid. This ensures that the particle migrates predictably in the direction of the electric field. This discovery opens the door to new, efficient strategies for moving, sorting and separating particles.
Nanoparticle tracking
To conduct this research, we integrated laboratory observation with computer modeling. Experimentally, we used an advanced microscope to meticulously track how individual nanoparticles moved inside a perfectly structured porous material called silica inverse opal.
A scanning electron micrograph of a silica inverse opal, showing a cross section of the engineered porous material with cavities 500 nanometers in diameter, placed in small holes 90 nanometers in diameter. Anni Shi
We then used computer simulations to model the underlying physics. We modeled the random motion of the particle, the electric driving force and the flow of the fluid near the walls.
By combining this precise visualization with theoretical modeling, we deconstructed the overall behavior of the nanoparticles. We could quantify the effect of each individual physical process, from tremor to electrical surge.
This high-resolution fluorescence microscope, housed in the University of Colorado Boulder’s Advanced Optical Microscopy Facility, obtained three-dimensional traces of nanoparticles moving in porous materials. Joseph Dragavon
Devices that move particles
This research could have major implications for technologies requiring precise microscopic transport. In these areas, the goal is rapid, precise and differential movement of particles. Examples include drug delivery, which requires guiding “nanocargo” to specific tissue targets, or industrial separation, which involves purifying chemicals and filtering contaminants.
Our discovery – the ability to separately control a particle’s speed using weak fields and its direction using strong fields – acts as a two-lever control tool.
This control can allow engineers to design devices applying weak or strong fields to move different types of particles in customized ways. Ultimately, this tool could improve diagnostic tools and faster, more efficient purification systems.
What’s next
We established independent control over finding particles using velocity and their migration using direction. But we still do not know all the limits of the phenomenon.
Key questions remain: What are the upper and lower particle sizes that can be controlled in this way? Can this method be reliably applied in complex and dynamic biological environments?
More fundamentally, we will need to study the exact mechanism behind the spectacular acceleration of these particles under a weak electric field. Answering these questions is essential to unlocking the full precision of this particle control method.
Our work is part of a larger scientific effort to understand how confinement and boundaries influence the movement of objects at the nanoscale. As technology shrinks, understanding how these particles interact with neighboring surfaces will help design small, efficient devices. And as they move through spongy and porous materials, nanoparticles constantly encounter surfaces and boundaries.
The collective goal of our research and that of others is to transform the control of tiny particles from a process of trial and error into a reliable and predictable science.
This article is republished from The Conversation, an independent, nonprofit news organization that brings you trusted facts and analysis to help you make sense of our complex world. It was written by: Daniel K. Schwartz, University of Colorado Boulder and Ankur Gupta, University of Colorado Boulder
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Daniel K. Schwartz receives funding from the U.S. Department of Energy, the National Science Foundation, and the National Institutes of Health.
Ankur Gupta receives funding from the National Science Foundation and the Air Force Office of Scientific Research.
