The novel device’s tip measures a mere 200 microns across.

Researchers have developed a new self-calibrating endoscope that produces 3D images of objects smaller than a single cell. Without a lens or any optical, electrical or mechanical components, the tip of the endoscope measures just 200 microns across, about the width of a few human hairs twisted together.

As a minimally invasive tool for imaging features inside living tissues, the extremely thin endoscope could enable a variety of research and medical applications. The research will be presented at the Frontiers in Optics + Laser Science (FIO + LS) conference, held September 15–19 in Washington, D.C., U.S.A.

A lensless endoscope

“The lensless fiber endoscope is approximately the size of a needle, allowing it to have minimally invasive access and high-contrast imaging as well as stimulation with a robust calibration against bending or twisting of the fiber,” said Juergen W. Czarske, Director and C4-Professor at TU Dresden, Germany and lead author on the paper.

Unlike conventional endoscopes that use cameras and lights to capture images inside the body, alternative devices have surfaced in recent years that capture images through optical fibers. This has resulted in thinner endoscopes.

Despite their promise, however, these technologies have their limitations. One such severe limitation is that they require complicated calibration processes.

A thin glass plate

“To address this, the researchers added a thin glass plate, just 150 microns thick, to the tip of a coherent fiber bundle, a type of optical fiber that is commonly used in endoscopy applications. The coherent fiber bundle used in the experiment was about 350 microns wide and consisted of 10,000 cores.

When the central fiber core is illuminated, it emits a beam that is reflected back into the fiber bundle and serves as a virtual guide star for measuring how the light is being transmitted, known as the optical transfer function. The optical transfer function provides crucial data the system uses to calibrate itself on the fly,” said the study’s press release. 

The researchers tested their device by employing it to image a 3D specimen under a 140-micron thick cover slip. Impressively, the device was successful at imaging particles at the top and bottom of the 3D specimen. 

“The novel approach enables both real-time calibration and imaging with minimal invasiveness, important for in-situ 3D imaging, lab-on-a-chip-based mechanical cell manipulation, deep tissue in vivo optogenetics, and key-hole technical inspections,” said Czarske.

The invention is likely to be used in optogenetics or in monitoring cells and tissues during medical procedures.