New Custom-Designed Polymer Shows Promise in Bioimaging Trials

A polymer designed specifically to generate light that can penetrate turbid environments has exhibited the potential for bioimaging trials, where it can identify nano-sized particles present below the surface of realistic tissue models.

Polymers offer an alternative to semiconductor quantum dots or rare-earth-doped nanoparticles that are unsuitable for many specimens because of their toxic side effects. Image Credit: © 2021 KAUST; Anastasia Serin.

New studies have shown that fluorescent probes— light-emitting materials that bind to small targets like cells—are specifically beneficial for bioimaging when they radiate in the optical spectrum’s shortwave infrared (SWIR) region.

This kind of fluorescent light can penetrate deeper into biological objects without scattering or attenuation, and therefore, SWIR probes can be spotted deeper into tissue compared to traditional emitters.

Such aspects have allowed SWIR probes to take high-resolution images of structures that are situated deep inside the body, like brain tissue, without the risks of X-rays.

Satoshi Habuchi and his collaborators have been making efforts to enhance fluorescent imaging by widening the kind of probes that can generate SWIR radiation. At present, a majority of the bright SWIR emitters are either rare-earth-doped nanoparticles or semiconductor quantum dots that are inappropriate for several specimens due to their harmful side effects.

By contrast, highly biocompatible materials, like organic dyes, are often not intense sufficiently to be viewed inside the tissue.

To find a solution to this problem, scientists from KAUST resorted to the use of polymers that have 'donor–acceptor' structures, a layout in which electron-rich components are found alternating with electron-poor portions across a conductive molecular chain.

This distribution promotes charge transfer along the polymer backbone, which is a very effective way to obtain SWIR light.

Hubert Piwoński, Study Lead Author, King Abdullah University of Science and Technology

The researchers selected two donor–acceptor polymers with perfect properties for SWIR emission and further developed a precipitation process that integrated the compounds into small polymer spheres, or 'dots,' with a width of only a few nanometers.

Optical characterizations showed that these materials had remarkably bright SWIR emissions that were spotted easily in biological tissue models.

Per volume, our particles have a brightness value larger than almost all other SWIR emitters reported so far. This enabled detection of nanometer-sized polymer dots in specimens one millimeter thick.

Satoshi Habuchi, King Abdullah University of Science and Technology

The new polymer dots that fluoresce just for a nanosecond can generate low noise images with single-molecule sensitivity thanks to the high throughput detection of the emitted fluorescence. The potential to detect single probes at quick acquisition rates could help scientists seeking to capture the processes in organs and tissues as they occur.

There are huge opportunities for new probes and imaging modalities capable of addressing the dynamics of molecules in living systems, and our polymer dots are a big step toward single-particle tissue imaging.

Hubert Piwoński, Study Lead Author, King Abdullah University of Science and Technology

Ultrabright dots see beyond skin deep

KAUST researchers have developed a custom-designed polymer to produce light that penetrates murky environments, such as inner organs. The light-emitting material has shown promise in bioimaging trials. Video Credit: © 2021 KAUST; Anastasia Serin.

Journal Reference

Piwoński, H., et al. (2020) Millimeter-Deep Detection of Single Shortwave-Infrared-Emitting Polymer Dots through Turbid Media. Nano Letters.


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