Laser-Driven Platform Spins Single Cells Along Any Axis in Real Time

One of the most fundamental limitations in modern microscopy is that a cell, once it settles onto a glass slide, tends to sit still. Biologists who want to see a cell from every side must either physically reorient the sample, rely on fluorescent labels that can perturb delicate biology, or reconstruct three-dimensional structure computationally from limited viewing angles. A team at The University of Texas at Austin, led by Prof. Yuebing Zheng, now reports a platform that changes this picture dramatically. Writing in Light: Science & Applications, the researchers describe an opto-thermo-osmotic system that can rotate individual cells around essentially any chosen axis and, remarkably, can switch between different rotational modes in less than a second, all without touching the cell or altering it in any way.

The significance of controlled single-cell rotation extends well beyond a clever laboratory demonstration. When a cell can be turned at will, researchers can perform true three-dimensional imaging with conventional microscopes, capturing morphology and internal architecture from multiple viewing angles. Rotation also matters for mechanobiology, the study of how cells sense and respond to mechanical forces, because orientation relative to a substrate or a neighboring cell influences how forces are transmitted and interpreted. Controlled rotation can further support investigations of cell-cell interactions, intracellular dynamics, and developmental processes in which the spatial arrangement of cellular components is central to function.

Yet programmable rotation has long been an elusive goal. Optical tweezers, magnetic manipulation, electric fields, and acoustic techniques have each made substantial contributions to single-cell control, but most existing approaches depend on specially engineered beam structures, microfabricated mechanical components, or intrinsic asymmetries in the objects being manipulated. Spherical particles and many living cells present a particular difficulty: because they are geometrically symmetric, there is no natural feature that defines a rotation axis. Dynamically switching between different rotation modes within a single platform has remained largely unexplored, which has limited the flexibility of previous systems and confined many of them to narrow, pre-set operating regimes.

The new platform is built on a plasmonic substrate composed of gold nano-islands functionalized with bovine serum albumin, or BSA. When laser light illuminates these nanostructures, they generate localized temperature gradients that drive strong thermo-osmotic flows along the solid-liquid interface. Thermo-osmotic flow is a well-characterized phenomenon in which a temperature gradient at a boundary produces directed fluid motion, and plasmonic substrates are especially effective at creating steep, highly localized gradients because the nanostructures concentrate optical energy into nanoscale volumes. The BSA functionalization plays a complementary role in stabilizing cells at the interface, while polyethylene glycol molecules in the surrounding solution generate depletion forces that gently confine cells near the substrate surface, precisely where the thermo-osmotic flow is strongest.

Control over the flow field comes from a spatial light modulator, a device that can dynamically project programmable laser patterns onto the substrate. By reshaping these patterns in real time, the researchers tailor both the temperature distribution and the resulting flow field, and with them the forces and torques acting on individual cells. This is the conceptual heart of the platform: the rotation axis is not dictated by the geometry of the object but is instead written into the engineered flow field itself. The same cell, sitting in the same spot, can be made to spin in entirely different ways depending only on how the laser light is patterned.

The team first validated the concept using spherical polydimethylsiloxane particles, an ideal test case precisely because a sphere possesses complete geometric symmetry and its rotation axes cannot be defined by shape. Numerical simulations revealed that a single Gaussian laser spot positioned asymmetrically relative to a particle creates a highly non-uniform thermo-osmotic flow field around it. That asymmetry in the flow produces a hydrodynamic torque of sufficient magnitude to drive stable rotation. Crucially, by simply moving the position of the laser spot, the direction of the torque can be tuned continuously, allowing the particle to rotate about different axes. Experimental observations confirmed the theoretical predictions and demonstrated arbitrary-axis rotation of spherical particles, establishing that the axis of rotation is defined entirely by the engineered flow field rather than by particle geometry.

With the principle demonstrated on synthetic spheres, the researchers extended the approach to biological cells, using yeast as a model system. They showed that two distinct rotational modes can be selectively activated through optical pattern engineering. Under a single Gaussian laser spot, the induced thermo-osmotic torque drives the cell to rotate around its major axis, the long axis of the cell body. When the laser pattern is reconfigured into a half-ring shape, an optical torque joins the thermo-osmotic torque, and the combined action reorients the cell and drives continuous rotation around its minor axis. The two modes are therefore not separate operating regimes requiring different hardware; they are two settings of the same optical interface.

Perhaps the most striking capability of the platform is the speed and cleanliness of the switching between these modes. In the reported experiments, the team maintained stable major-axis rotation with a Gaussian beam, then changed the illumination pattern to a half-ring configuration. The cell transitioned into minor-axis rotation in less than one second. The entire process occurred without mechanical movement, sample repositioning, or physical contact, relying solely on optical reconfiguration. For live-cell imaging, this matters enormously: cells are fragile, and any approach that avoids contact, labeling, or chemical modification preserves the native state of the specimen while it is being manipulated.

To understand why the system works so well, the researchers combined multiphysics simulations with electromagnetic calculations. Their analysis showed that major-axis rotation is predominantly driven by thermo-osmotic torque, whereas minor-axis rotation arises from the synergistic coupling of thermo-osmotic and optical torques. Together, these torques create a continuous torque landscape that sustains rotation throughout the entire cycle without trapping the cell in stable equilibrium states. In other words, the optical patterns are designed so that at no point in the rotational cycle does the cell find a configuration where the torques vanish and motion stops; the driving torque persists around the full revolution, which is what enables continuous, stable spinning.

The practical advantages of the platform are considerable. It operates at relatively low optical power, which reduces the risk of photothermal damage to living specimens. It requires no labeling or modification of cells, making it a genuinely label-free technique. It offers exceptional programmability through dynamic optical pattern generation, and unlike many conventional rotational manipulation techniques, it does not depend on complex beam shaping or specialized particle geometries. The researchers believe the technique could become a powerful tool across a broad range of biological and biomedical applications. By integrating with confocal microscopy and other advanced imaging modalities, the platform may enable label-free three-dimensional cellular imaging and reconstruction. It could also facilitate studies of cell mechanics, cellular interactions, developmental biology, and drug screening, where observing a cell from multiple orientations under controlled conditions would add a valuable new dimension to existing assays.

Looking forward, the team envisions combining opto-thermo-osmotic manipulation with emerging metasurface and integrated photonic technologies. Metasurfaces, which are engineered planar optical structures capable of shaping light with subwavelength precision, could replace bulky spatial light modulators with compact, chip-scale pattern generators. Such integration could lead to miniature platforms capable of high-throughput cellular manipulation and analysis, opening new opportunities for next-generation bioanalytical systems in which individual cells are imaged, rotated, and characterized automatically. If that vision is realized, the ability to spin a single cell along any axis with nothing more than a reconfigured beam of light may become as routine a capability in the biology laboratory as focusing the objective lens is today.

Subject of Research: Programmable opto-thermo-osmotic rotation of single cells along arbitrary axes

Article Title: Programmable rotation of single cells along arbitrary axes via opto-thermo-osmotic torque

Article References: Programmable rotation of single cells along arbitrary axes via opto-thermo-osmotic torque. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: cell rotation, opto-thermo-osmotic torque, plasmonic substrate, gold nano-islands, thermo-osmotic flow, spatial light modulator, yeast cells, three-dimensional imaging, mechanobiology, optical manipulation, label-free imaging, Light Science & Applications