Researchers at New York University, led by Professor Stefano Sacanna, have demonstrated a way to use light to trigger, shape, and reverse crystal formation in a suspension of microscopic particles. The study, published in the Cell Press journal Chem, describes a reversible method for directing colloidal crystallization without mechanically altering the system or repeatedly changing the chemistry of the system. By treating light as an adjustable external input, the team shows that crystal assembly can be controlled in real time rather than left to proceed under fixed conditions.
Professor Stefano Sacanna from New York University stated,
“Our approach brings us closer to dynamic, programmable colloidal materials that can be reconfigured on demand . This system also allows us to test a number of predictions on how self-assembly should behave when interactions between particles or molecules are changing across space or time.”
van Kesteren, S., Smina, N., Zang, S., Leung, C. W., Hocky, G. M., & Sacanna, S. (2026). Light-controlled colloidal crystallization. Chem, 102917. https://doi.org/10.1016/j.chempr.2025.102917
Crystals form when particles arrange into repeating, ordered structures. At the atomic scale, this process underpins semiconductor devices, catalysts, and pharmaceutical solids. To better understand and manipulate crystallization, scientists often turn to colloids, which are micrometer sized particles dispersed in a liquid. These systems act as accessible models because their behavior can be observed directly under a microscope. However, even in colloidal suspensions, nucleation and growth are sensitive to parameters such as ionic strength, particle surface chemistry, and temperature. Once those conditions are set, the pathway to crystallization is usually difficult to adjust.
Sacanna and his colleagues approached this limitation by introducing light responsive molecules known as photoacids into the colloidal mixture. When exposed to light, these molecules temporarily increase the acidity of their surroundings. That change modifies the surface charge of the colloidal particles, which directly affects how strongly they attract or repel one another. By adjusting the intensity and spatial pattern of illumination, the researchers were able to tune interparticle forces and determine whether particles assembled into ordered crystals or dispersed back into a fluid like state.
Experiments combined with computational modeling showed that crystals could be formed at specific locations, reshaped under focused illumination, or dissolved when the light conditions changed. The response was reversible, meaning the same sample could cycle between ordered and disordered states multiple times. Because light can be delivered with fine spatial resolution, the team could effectively sculpt microscopic crystalline regions inside a single droplet without disturbing the rest of the system.
A practical aspect of the work is that it operates as a one pot system. The particles and photoacids remain in the same solution throughout the experiment, and no additional chemical adjustments are required once the mixture is prepared. Traditional methods for tuning colloidal interactions often involve adding salts, modifying particle coatings, or rebuilding the suspension. In this case, control is achieved by varying illumination alone, which simplifies both experimentation and potential future applications.
The findings suggest a path toward materials whose internal structure can be rewritten after fabrication. Colloidal crystals are known for their optical properties, including their ability to reflect specific wavelengths of light depending on particle spacing. If such structures can be assembled and erased using patterned illumination, materials could be reconfigured on demand. Possible applications include adaptive optical coatings, tunable photonic elements, and sensors whose response depends on dynamically defined microstructures.
Beyond applications, the system also offers a controlled platform for studying self assembly under changing conditions. By altering particle interactions across space and time, researchers can test theoretical predictions about how ordered structures emerge in non equilibrium environments. In that sense, the work provides both a practical technique and a research tool for exploring how matter organizes itself when external fields are used as active design parameters rather than fixed boundary conditions.
The study represents a shift from viewing crystallization as a process that must be carefully set up in advance to one that can be adjusted as it unfolds. By using light as a controllable input, Sacanna and his team have added a flexible method to the toolkit of materials science, one that could support the development of programmable and reconfigurable soft matter systems.
Adrian graduated with a Masters Degree (1st Class Honours) in Chemical Engineering from Chester University along with Harris. His master’s research aimed to develop a standardadised clean water oxygenation transfer procedure to test bubble diffusers that are currently used in the wastewater industry commercial market. He has also undergone placments in both US and China primarely focused within the R&D department and is an associate member of the Institute of Chemical Engineers (IChemE).
