3D Microscopy: Laser Rotates Samples Contact-Free

The laser rotates delicate cell samples under the microscope without physical contact.
Image Credit: Fan Nan, KIT

Scientific Frontline: Extended "At a Glance" Summary: Laser-Driven 3D Micro-Sample Rotation

The Core Concept: A non-contact technique that utilizes laser-induced thermo-viscous fluid flows to rotate delicate microscopic samples in all three spatial dimensions.

Key Distinction/Mechanism: Unlike traditional micromanipulation using physical tools (pipettes or grippers) which risk damaging samples, this method manipulates the surrounding liquid via localized laser heating to induce controlled, gentle rotational flows.

Major Frameworks/Components:

• Localized Laser Heating: Creates temperature gradients within the sample's suspension medium.
• Thermo-viscous Fluid Flows: Laser-generated heat triggers subtle, precise fluid currents.
• Rapid Laser Scanning: Facilitates the generation of spiral flow patterns, enabling full 3D rotation of the specimen.
• Contact-Free Manipulation: Eliminates mechanical force on the sample, preventing structural damage.

Branch of Science: Microscopy, Optical Imaging, Fluid Dynamics, Biophysics, Microrobotics

Future Application: Advanced 3D biological imaging for basic medical research, precise microscopic manufacturing, and non-invasive microrobotics.

Why It Matters: By overcoming the depth-perception limitations of modern 2D optical microscopes, this technology provides the high-fidelity 3D structural data required to analyze complex biological processes while ensuring the integrity of sensitive cell samples.

Gentle Laser-Driven Flows Enable Precise 3D Imaging of Delicate Samples

Until now, it has been technically almost impossible to rotate highly sensitive samples in all directions under a microscope without making physical contact. Researchers at the Karlsruhe Institute of Technology (KIT) have developed a new laser-based technique that allows microscopic samples, such as cells, to be rotated contact-free in all three spatial directions. The laser creates tiny temperature differences in the liquid, which trigger gentle fluid flows that move the sample. This protects delicate samples and enables more accurate three-dimensional images—an important step for basic medical research.

Modern optical microscopes can produce extremely sharp images in a single plane, comparable to a photograph, but depth information is often imprecise. To overcome this limitation, samples must be imaged from multiple viewing angles, and the images must be combined into a three-dimensional model. This requires rotating the object under investigation. The new method makes it possible to accomplish this in an exceptionally gentle manner.

Rotation Without Physical Contact

The research team, led by Professor Moritz Kreysing and Dr. Fan Nan at KIT’s Institute of Biological and Chemical Systems, uses a laser to locally heat the liquid in which the sample is suspended. This creates subtle fluid flows that can be used to precisely move freely floating microscopic objects—entirely without mechanical microtools such as tiny pipettes, needles, or grippers. “We do not manipulate the sample directly,” says Nan. “Instead, we control the movement of the surrounding liquid so that the object aligns itself.”

Laser-driven flows have been known for some time but previously enabled motion only within a single plane. Now, controlled rotation in three-dimensional space is also possible: by rapidly scanning the laser, the researchers generate a spiral flow that gently rotates objects—similar to a small paper boat spinning on its own in a tiny whirlpool.

Benefits for Medicine and Technology

Three-dimensional control allows cellular structures to be captured more effectively from different perspectives. “When samples can be aligned more precisely, we see more details,” says Kreysing. “This is a key prerequisite for better understanding biological structures and processes.” In the long term, the method could also become relevant for contact-free micromanipulation, microscopic robotics, or highly precise manufacturing at the smallest scales, according to Kreysing.

Published in journal: Light: Science & Applications

Title: Helical opto-thermoviscous flows drive out-of-plane rotation and particle spinning in a highly viscous micro-environment

Authors: Fan Nan, Weida Liao, Adrián Puerta, Josephine Spiegelberg, Elena Erben, Ralf Mikut, Stephan Allgeier, Martin Wegener, Eric Lauga, and Moritz Kreysing

Source/Credit: Karlsruhe Institute of Technology

Reference Number: phy051226_01

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