Watching proteins in motion, as they orchestrate the chemical processes essential to life, represents one of biology’s most formidable challenges. Capturing these fleeting transformations requires technology capable of freezing time on the atomic scale, allowing scientists to observe molecular shifts that occur in mere femtoseconds—a quadrillionth of a second. In recent years, X-ray free-electron lasers (XFELs) have emerged as revolutionary instruments, enabling researchers to create “molecular slow-motion movies” by firing ultrashort, intensely bright X-ray pulses at tiny protein crystals. These snapshots reveal proteins in action, providing unprecedented insights into how these biomolecules fold, bind, and react during biological processes.
Despite their promise, XFEL experiments have been notoriously sample-hungry, requiring vast amounts of precious protein material. Traditional methods inject a continuous stream of protein crystals into the beam, but most are wasted since only a fraction aligns with the pulsed laser at any given time. This inefficiency restricts dynamic structural studies to abundant proteins and excludes many that are rare, fragile, or difficult to produce at scale. Addressing this bottleneck, a team led by Alexandra Ros at Arizona State University, along with international collaborators including the Consejo Superior de Investigaciones Científicas (CSIC), has engineered a breakthrough microfluidic device that slashes sample consumption by as much as 97% without sacrificing data quality.
The innovation centers on a microfluidic droplet injector, an elegantly designed system that dispenses protein crystals not in a continuous stream but as precisely timed micrometer-scale droplets. These droplets are synchronized perfectly with XFEL pulses, ensuring protein crystals are introduced exactly when the X-ray beam probes their structure. This targeted delivery maximizes the utility of every protein crystal, fundamentally transforming how time-resolved serial crystallography experiments are conducted. The device incorporates advanced 3D printing techniques to fabricate intricate fluid channels that mix solutions and generate droplets on demand—compatible with the lightning-fast repetition rates of modern XFELs.
This technology sets the stage for dynamic studies of medically important proteins that were previously inaccessible due to sample volume constraints. Researchers demonstrated the device’s capabilities at the European XFEL facility by resolving the early redox cycle of human NAD(P)H:quinone oxidoreductase 1 (NQO1), a key enzyme involved in cellular detoxification and oxidative stress defense. By capturing snapshots of NQO1 binding its cofactor NADH in real time, they revealed critical details about molecular interactions driving enzymatic activity. The insight into cofactor dynamics provided by time-resolved crystallography could shed light on disease mechanisms and inform precision drug design.
The impact of such minimal sample consumption extends far beyond this one enzyme. Many proteins implicated in disease pathways or industrial biocatalysis are challenging or costly to produce in high yield. This microfluidic injector lowers the barrier for structural investigations of these elusive molecules’ timed behavior. Facilities equipped with XFELs can now expand their scope to encompass fragile and low-abundance proteins without prohibitive protein waste, democratizing access to dynamic structural biology experiments across the scientific community. Scientists anticipate that this method will accelerate both fundamental research and therapeutic innovation.
Technically, the microfluidic injection system operates by generating a stable “train” of droplets approximately tens of microns in diameter. Each droplet encapsulates a microcrystal slurry and travels through microscale channels etched into the device before arriving at the intercept point with the XFEL beam. The droplet timing is meticulously adjusted and synchronized with pulse sequences typically in the kilohertz to megahertz range of modern X-ray lasers, ensuring maximal hit rates with minimal idle exposure. This mode of sample delivery contrasts sharply with traditional continuous liquid jets, which squander up to 99% of protein samples.
By enabling time-resolved serial femtosecond crystallography with greatly reduced sample volumes, this technology also helps unlock the full potential of next-generation X-ray laser facilities. Upcoming XFELs promise higher repetition rates and brighter pulses, but such improvements come with challenges of sample delivery and data acquisition. The droplet injector design is well suited to meet these demands, offering scalable throughput and compatibility with compact, laboratory-scale XFEL sources under development, such as the Biodesign Institute’s compact X-ray free-electron laser (CXFEL).
The conceptual advance embodied by this work not only solves a major practical impediment but also enriches the study of conformational heterogeneity and reaction intermediates in proteins. By capturing transient states during enzymatic cycles or ligand binding events with unprecedented precision and minimal resource use, it paves the way for discoveries in molecular mechanisms that underlie health and disease. This could facilitate the design of drugs targeting fleeting but functionally critical protein states, a frontier in rational drug development. Moreover, the method’s compatibility with automated workflows promises to speed up data throughput while reducing experimental costs.
Lead researcher Alexandra Ros underscores the transformative potential of this approach: “Seeing proteins react in real time is incredibly powerful, but the sample demands to unravel dynamic protein behavior with X-ray crystallography have been a major limitation. Our droplet approach dramatically reduces that burden, which is exciting because many more labs can now ask dynamic questions that were previously too costly or impractical.” Her team’s work represents a milestone in structural biology, enabling real-time visualization of biochemical pathways at atomic resolution with extraordinary sample efficiency.
In summary, the microfluidic droplet injector designed by ASU researchers addresses one of the physics and biology communities’ key challenges by marrying cutting-edge fluidics with ultrafast X-ray science. It sharply reduces protein consumption in XFEL experiments, unlocks access to rare and valuable proteins, and expands the horizon for time-resolved molecular studies. This technological leap not only enriches our fundamental comprehension of protein dynamics but also holds promise to accelerate drug discovery and biotechnological innovation by providing a clearer window into the molecular machinery of life. As XFEL technology continues to evolve, such innovations in sample delivery will be indispensable for maximizing scientific returns from these colossal instruments.
Subject of Research: Time-resolved serial crystallography of human enzyme NQO1 using microfluidic droplet injector technology
Article Title: Minimized sample consumption for time-resolved serial crystallography applied to the redox cycle of human NQO1
News Publication Date: 29-Jan-2026
Web References:
http://dx.doi.org/10.1038/s42004-026-01908-9
Image Credits: The Biodesign Institute at ASU
Keywords
Applied sciences and engineering, Life sciences, Biochemistry, Biomolecules, Protein crystals, Protein structure, Protein subunits, Protein interactions, Applied physics, Accelerator physics
