Annihilation upconversion in cells by embedding the dye system in polymeric nanocapsules.

Area of Science:

• Biophotonics
• Nanotechnology
• Photochemistry

Background:

• Photon energy upconversion (UC) is crucial for advanced optical applications.
• Existing UC methods often require high excitation intensities, limiting their use in biological systems.
• Developing biocompatible UC systems for in vivo applications remains a challenge.

Purpose of the Study:

• To describe the first energetically conjoined triplet-triplet annihilation (TTA)-assisted photon energy upconversion system operating in cell tissue.
• To demonstrate efficient UC emission from synthesized nanocapsules under low excitation intensity.
• To explore the potential of this UC system for life-science applications.

Main Methods:

• Synthesis of nanocapsules encapsulating a UC dye system (emitter and sensitizer).
• Investigation of UC emission efficiency in aqueous dispersion.
• Measurement of UC emission under varying excitation intensities, down to 0.05 W·cm⁻².
• Analysis of the intensity dependence of UC emission.

Main Results:

• Achieved highly efficient UC emission from nanocapsules in aqueous dispersion.
• Demonstrated efficient UC under extremely low excitation intensity (0.05 W·cm⁻²), ensuring minimal damage to cells and tissues.
• Observed a sub-linear intensity dependence of the UC emission.

Conclusions:

• The developed nanocapsule-based TTA-UC system is suitable for operation in cell tissue.
• Low excitation intensity operation makes the system safe for biological applications.
• The UC photons can act as localized optical excitation sources for subsequent light-triggered processes in situ.