Fig. 4. Single-particle upconversion enhancement of DSPE-UCNPs by using sulfo-rhodamine B. (a) Representative single-particle image and corresponding (b) single-particle UCL histogram of DSPE-CSS²⁵-NaLuF₄ under 976 nm excitation (11.6 kW cm⁻²). (c) Representative single-particle image and corresponding (d) single-particle UCL histograms of DSPE-Sulfo-RB-CSS²⁵-NaLuF₄ under 976 nm excitation (11.6 kW cm⁻²). (e) The single-particle intensity of DSPE-CSS²⁵-NaLuF₄ and DSPE-Sulfo-RB-CSS²⁵-NaLuF₄ under 976 nm excitation (11.6 kW cm⁻²). (Left) 750 nm short pass, (right) 607 nm short pass. (f) Time-dependent emission intensity changes of DSPE-Sulfo-RB-CSS²⁵-NaLuF₄ from single-particle measurement under the irradiation of a 976 nm laser (duration: 5 min, irradiance: 11.6 kW cm⁻²). (g) Colocalization of particles using SEM. Corresponding wide-field UCL images at 11.6 kW cm⁻² of (h) DSPE-CSS²⁵-NaLuF₄ and (i) DSPE-Sulfo-RB-CSS²⁵-NaLuF₄. Scale bars, 500 nm.