Researchers from Ecole Polytechnique Fédérale de Lausanne (EPFL) and the University of Manchester have used two-dimensional materials and light to unlock the secrets of nanofluids. A breakthrough in nanofluids technology will revolutionize our understanding of molecular dynamics at tiny scales. Scientists from the Ecole Polytechnique Fédérale de Lausanne (EPFL) and the University of Manchester have collaborated to reveal a previously unknown world using the newly discovered fluorescent properties of boron nitride, a two-dimensional graphene-like material.
This innovative approach allows scientists to track individual molecules within nanofluid structures, revealing their behavior in ways never before possible. The findings were recently published in the journal Nature Materials.
Nanofluidics is the study of fluids enclosed in ultra-small spaces, providing insights into the behavior of liquids at the nanoscale. However, exploring the motion of individual molecules in such a closed environment has been a challenge due to the limitations of traditional microscopy techniques. This barrier hinders real-time sensing and imaging, leaving a huge gap in our understanding of molecular properties in closed environments.
Overcoming microscope limitations
Thanks to the unexpected properties of boron nitride, EPFL researchers have achieved what was once thought to be impossible. This two-dimensional material has the extraordinary ability to emit light when in contact with liquids. Taking advantage of this property, scientists at EPFL's Laboratory of Nanobiology have succeeded in directly observing and tracking the motion of individual molecules in nanofluid structures. This discovery opens the door to insights into how ions and molecules behave under conditions that mimic biological systems.
Professor Aleksandra Radenovic, Director of LBEN, explains: "Advances in manufacturing and materials science have given us the ability to control fluid and ion transport at the nanoscale. However, our knowledge of nanofluidic systems is still limited because conventional optical microscopy cannot penetrate structures below the diffraction limit. Our research now shines a bright light on nanofluidic technology and gives us insights into this hitherto largely unknown area."
Applications and future potential
This new discovery of molecular properties has exciting application prospects, including the potential to directly image emerging nanofluidic systems, in which liquids exhibit unconventional behavior when stimulated by pressure or voltage. At the heart of the research is the fluorescence produced by single-photon emitters on the surface of hexagonal boron nitride. "This fluorescence activation was unexpected, as neither hexagonal boron nitride nor the liquid itself shows fluorescence in the visible range. It is most likely generated by the interaction of the molecule with defects on the crystal surface, but we are still not sure of its exact mechanism," says PhD student Nathan Ronceray from LBEN.
Surface defects may be atoms missing from the crystal structure that have different properties than the original material and emit light when they interact with certain molecules. The researchers further observed that when a defect went off, one of its neighbors lit up because the molecule bound to the first site jumped to the second site. This allows the entire molecular trajectory to be reconstructed step by step.
Using a combination of microscopy techniques, the team monitored the color changes and demonstrated that these luminophores emit one photon at a time, providing precise information about their surroundings within about a nanometer. This breakthrough allows these luminophores to be used as nanoscale probes, revealing the arrangement of molecules within confined spaces at the nanoscale.
Collaboration and visualization technology
Professor Radha Boya's research group at Manchester's Department of Physics created nanochannels using two-dimensional materials to confine the liquid to just one nanometer from the boron hydride surface. This partnership enabled optical probing of these systems, uncovering clues of confinement-induced ordering in liquids. "Seeing is believing, but it's not easy to see the effect of confinement at this scale." RadhaBoya said: "We made these extremely thin slit-like channels, and the current study shows an elegant way to observe them through super-resolution microscopy."
The potential of this discovery is profound. Nathan-Lancere envisions applications beyond passive sensing: "We are primarily using boron hydride to observe the behavior of molecules without actively interacting with it, but we think it could be used to observe nanoscale flows caused by pressure or electric fields." This may lead to more dynamic applications for optical imaging and sensing in the future, providing unprecedented insights into the complex behavior of molecules within these confined spaces.