Figure 3. Micro⁵⁴⁰-UCPs show significant particle-to-particle energy transfer.

(A) Schematic representation of the experimental setup to test the NIR laser spreading profile and inter-particle energy transfer of micro⁵⁴⁰-UCPs. To test the NIR laser spreading, a single micro⁵⁴⁰-UCP (blue) was irradiated by the NIR beam and imaged while moving the microscope stage in ~1 µm increments away from the NIR beam per acquisition interval. To test inter-particle energy transfer, the NIR laser was used to irradiate either all particles in a chain of five (1°–5°) or just the primary particle (1°) in the chain. (C) Representative images of a chain of 5 micro⁵⁴⁰-UCPs where either all 5 (left panels) or just the 1° particle (right panels) are excited by the NIR laser. White dashed lines represent the edges of individual microparticles in the chain as seen in the transmitted light image used for the ROI for quantification in (B, D). FIRE LUT used to indicate emission intensity. Scale bars = 5 µm (B) Scatter plot of sum projected average particle intensity within an ROI roughly equal to the area of individual micro⁵⁴⁰-UCPs particles within either a single particle (blue) or chains of 5 particles (green) versus distance from the edge of the NIR beam, n = 10 individual and chains of particles. Curve fitting was done using a one phase decay equation (D) Quantification of sum projected average particle intensity within an ROI roughly equal to the area of individual micro⁵⁴⁰-UCPs normalized to 1° particle for each of the 5 microparticles in a chain when either all 5 particles or just the 1° particle are/is excited by the NIR laser, n = 10 chains of particles.