Researchers use nontoxic silicon nanocrystals to convert low-energy photons into high-energy ones, bringing scientists closer to developing photodynamic treatments for cancer.
Materials scientists at the University of California, Riverside and The University of Texas at Austin have demonstrated that it is possible to achieve photon up-conversion, the emission of light with energy higher than the one that excites the material, when using carefully designed structures containing silicon nanocrystals and specialized organic molecules.
The accomplishment, published in Nature Chemistry, brings scientists one step closer to developing minimally invasive photodynamic treatments for cancer. The advance could also hasten new technologies for solar-energy conversion, quantum information, and near-infrared driven photocatalysis.
High energy light, such as ultraviolet laser light, can form free radicals able to attack cancer tissue. Ultraviolet light, however, doesn’t travel far enough into tissues to generate therapeutic radicals close to the tumor site. On the other hand, near-infrared light penetrates deeply but doesn’t have enough energy to generate the radicals.
While photon up-conversion can overcome this limitation, up-converted materials have either low efficiency or are based on toxic materials. Silicon is well-known for being nontoxic, but until now, researchers have not been able to demonstrate that silicon nanocrystals can up-convert photons, leaving this promising cancer treatment tantalizingly out of reach.
The research group learned how to attach ligands, which help bind molecules together, to the nanoparticle that are specifically designed to transfer the energy from the nanocrystals to surrounding molecules.
The team then shined laser light into the solution. They found silicon nanocrystals with appropriate surface ligands can rapidly transfer the energy to the triplet state of surrounding molecules. A process called triplet-triplet fusion then converts the low-energy excitation to a high energy one, resulting in the emission of a photon at shorter wavelength, or higher energy, than the one originally absorbed by the nanoparticle.
This discovery could also lead to improved photocatalysis, which uses light to drive chemical reactions.
The environmentally sustainable silicon-centered approach is also relevant for quantum information science and singlet fission-driven solar cells.
News Source: UCR
