Physicists find electronic light opening new pathway for targeted cancer therapy
Researchers at Kazan Federal University have uncovered how electronic light drives photoheating in optically transparent nanoscale materials. New mechanism advances cancer diagnostics and targeted therapy.
The study, published in Laser & Photonics Reviews, explains the mechanism of capturing light by optically transparent heterogeneous systems via a scattering mechanism rather than conventional absorption.
"The term electronic light refers to photons that undergo inelastic scattering by electronic states," commented senior author Sergey Kharintsev. "This effect appears in Raman spectra of spatially confined, heterogeneous media – such as amorphous and porous materials, high-entropy crystals, foams, gels, polymers, cells, and so on, – as a featureless broadband background, known as electronic light scattering (ELS). Sharp molecular peaks associated with specific chemical bonds are superimposed on this background."
As the scientist notes, the physical origin of this background remained unclear for years, leading researchers to routinely subtract it from Raman spectra to improve the performance of molecular peaks. However, earlier works by Prof. Kharintsev's team showed that a spatially confined medium enables light-induced transfer of momentum to electrons – a mechanism analogous to how phonons transfer momentum in bulk crystals.
"A crucial factor lies in the emergence of additional electronic states triggered by spatial symmetry breaking within the material. Thus, it leads to a significant increase in oscillator strength of electronic transitions driven by both indirect optical and resonant transitions," he continued.
Researchers have demonstrated that the broadband electronic light scattering (ELS) signal encodes information about the energy band structure of materials. This distinguishes ELS from molecular peaks, which reveal the chemical identity of a substance.
"What makes our research particularly intriguing is that an optically transparent medium begins to heat up as soon as it transforms to heterogeneous one – revealing a previously unrecognized pathway for light-induced thermal effects in non-absorbing media. This discovery reevaluates well-established therapeutic modalities such as photothermal therapy and photodynamic therapy. Indeed, these methods utilize light-absorbing agents such as photosensitizers, organic dyes, and metallic nanoshells, which are attached to malignant tissues to convert light energy into either heat or chemical energy for destroying cancer cells through their thermal damage or oxygen-triggered immune response. Our approach opens unique opportunities for safely guiding and manipulating light in live systems, without the need for light-harvesting agents," adds the interviewee..
An agent-free strategy makes photothermal therapy a powerful, minimally invasive tool for treating cancer cells without harming healthy tissue. It is important to notice that the earliest attempts to use light alone for therapeutic purposes relied on resonant absorption of high-power laser radiation (exceeding TW/cm2), which caused ablation of both benign and malignant tissues. This is the reason why this approach has not found widespread use in cancer therapy. Moreover, the standard photothermal therapy methods lack the ability to detect cancer cells.
"To demonstrate the principle, we deliberately employed a simplified chemical system – a water-in-decane microemulsion stabilized with a surfactant," noted first author Elina Battalova.
A discrete droplet microemulsion is optically transparent, and can be heated up under illumination at the percolation threshold, the point where electrical conductivity rises sharply. Conceptually, the percolating medium serves as a model for a malignant tumor, which can be selectively destroyed using non-resonant, sub-bandgap light excitation, bypassing the need for direct optical absorption.
"This means that the incident radiation at a specific wavelength is literally "blind" to healthy cells across a broad spectral range, yet selectively targets and thermally destroys cancer cells via ELS. We established that this system can be heated by several tens of degrees upon illumination with the intensity of about kW/cm2. We attribute this counterintuitive behavior to energy band bending within the transparent system, where electronic light scattering supersedes conventional light absorption. By directing non-resonant light onto malignant tissue, targeted therapeutic effects can be achieved by selecting a proper excitation wavelength and pump power," explained Battalova.
Despite the fact that the results obtained in this work pertain to a model chemical system, they may be potentially scalable to living systems, thereby expanding the scope of thermo-optical technology and applications. A strategy based on photoheating of optically transparent, spatially dispersive media via light scattering rather than absorption, offers a promising pathway toward non-invasive, targeted ablation of highly heterogeneous cancer cells while leaving surrounding healthy tissue entirely unharmed.
More information:
Optically Transparent Percolating Colloids Heated by Electronic Light Scattering
onlinelibrary.wiley.com/doi/ep … .1002/lpor.202502239
Provided by Kazan Federal University
