Scientists from Saudi Arabia's King Abdulla University of Science and Technology (KAUST) developed a new kind of microscope with an optical lens inspired by the design of a lighthouse lens. The optical device can observe molecular processes such as cell growth within a Petri dish.

The findings were published in the Journal of Biophotonics. Biophotonics combines photonics and biology by using light to interact with molecules, cells, and living tissue.

Other bioimaging techniques use fluorescent dyes for specific cells to be targeted. The new device uses stimulated Raman scattering (SRS) microscopy.

Developing a New Kind of Microscope

SRS turns optical fibers into amplifiers and tunable lasers. As a result, the STS microscopes produce high-resolution and noninvasive images at real-time speeds. The microscope can be used for researchers studying diseases or such as diagnostic studies on organoid tissue or testing antibacterial compounds.

However, the SRS microscope is limited since it is affected by background fluorescence or noise - a signal that appears in view but should not be seen. The background noise, also known as cross-phase modulation, occurs as the laser light interacts with the samples, explained the authors.

New Microscope Design Inspired by Lighthouse Lenses
(Photo: A 3D-printed lens developed at KAUST uses optical features inspired by lighthouse beams to collect laser signals for bioimaging. © 2020 Andrea Bertoncini/KAUST)

Professor Carlo Liberale explained that the background signal appears everywhere and "reduces the contrast during microscopic observation of complex samples" like the live growth of cells. The noise also makes it more difficult for researchers to identify specific targeted molecules.

To eliminate cross-phase modulation or artifacts, a particular type of glass would be needed for the microscopes to collect wide angles of light. However, the glass lenses are too bulky and large to fit into the incubator platform used to grow live cells for bioimaging.

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Inspiration from Lighthouse Lenses

Andrea Bertoncini, from the university's Biological and Environmental Science and Engineering Division, lead the team to develop an ultrathin SRS lens using three-dimensional (3D) printing. The lens was designed after lighthouse lenses using a transparent polymer similar to glass mirrors.

A lighthouse lens or a Fresnel lens creates bright beams of light from a glass lens with multiple prisms. The prisms change the direction that light travels, so it reflects from the lens into one direction. Fresnel lenses can focus up to 98% of light rays from its source for light to be seen up to 20 miles out into open waters.

The catadioptric lens "is a very efficient way to collect and redirect light coming from wide-angle sources right to our laser detector," explained Bertoncini. "And since it's so thin, it easily fits into the closed chambers of an incubator."

It took the team several calibration trials to confirm that the ultrathin lens would not have background noise. The team then started observing cultured cancer cells using the new device. Observations proved the lens's ability to capture the interior of cells with high resolution similar to traditional SRS microscopes. The unique optical devices are also more cost-effective.

Bertoncini explained that traditional SRS microscopes cost a few thousand dollars. In comparison, the new microscope has a lens that produces similar results at less than 10% of that price.

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