New Ultrasmall, Light-Sensitive Nanoparticles Could Serve as Contrast Agents

Medical imaging technologies face ongoing challenges in capturing accurate, detailed views of internal processes, especially in conditions like cancer, where tracking disease development and treatment response is critical. Current contrast agents often lack the sensitivity and precision needed for advanced diagnostic tools. Now, scientists have created a new class of light-sensitive nanoparticles that respond to light by altering their structure, offering a potential breakthrough in imaging applications.

These light-sensitive single-chain nanoparticles (SCNPs) were made by researchers at Martin Luther University Halle-Wittenberg (MLU, Halle, Germany) from folded polymer chains embedded with polypyrrole molecules, which absorb near-infrared light and convert it into heat. When exposed to laser light, the particles heat up and transform into compact spherical structures only a few nanometers wide, enabling targeted concentration at specific sites in the body.

The particles display remarkable thermoresponsivity thanks to their molecular design, which allows efficient conversion of light into heat. Laboratory experiments showed that even weak laser beams and small amounts of nanoparticles could generate high local temperatures of up to 85 degrees Celsius. This heating effect produces sound waves detectable by photoacoustic imaging, a method that can reconstruct 3D models of tissue.

In their research published in Communications Chemistry, the team demonstrated that these nanoparticles can provide detailed imaging by amplifying signals within tissues during photoacoustic scans. By enhancing visibility inside the body, they could help track tumor growth or monitor responses to therapy. Importantly, their sensitivity and efficiency mean fewer particles and lower laser power are needed, reducing potential risks compared to conventional imaging agents.

Going forward, the researchers see broad applications for their technology. The nanoparticles could be adapted to deliver drugs directly to targeted tissues, where light and heat would activate the compounds. They may also serve in cancer hyperthermia therapies by selectively heating and destroying tumor cells. Further studies will explore their therapeutic potential, scalability, and integration into clinical settings.

“When exposed to light, each individual nanoparticle clumps together to form a spherical structure that is only a few nanometers in diameter. This opens up the possibility of concentrating them in specific areas of the body – precisely where there is light,” said MLU-chemist Professor Wolfgang Binder, who led the study. “In the future, we want to use the nanoparticles to transport an active ingredient into the body in a targeted manner and activate it there using light and heat.”

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