Fig. 4.

Comparison of cardiac photoactivation using NIR laser via UCNPs and blue laser. (a) Emission spectrum of the 20-mg/ml UCNP film irradiated by a 980-nm laser from 1 to 5 W. (b, c) ECG (black line) triggered by two illumination methods on the right ventricles (b) red line: 980 nm, 20 ms, 8 Hz, 1.54 W; (c) blue line: 473 nm, 20 ms, 8 Hz, 0.19 mW/mm²)). (d, e) Illuminations on the right ventricle with pulse durations of 2, 5, 10, 20, and 50 ms with 980 nm (d) and 473 nm (E) laser. (f, g) Capture rate of the heart with increased power at 980 nm (f) and light intensity at 473 nm (g) with pulse durations of 2, 5, 10, 20, and 50 ms (n = 5; The data are presented as the mean ± SEM. *P < 0.05, ****P < 0.0001; NS P > 0.05; Chi-square test). (h, i) Minimum NIR laser power (h) and blue laser intensity (i) under different durations to achieve capture rate over 90% (n = 5; The data are presented as the mean ± SEM. **P < 0.01, ***P < 0.001, ****P < 0.0001; NS, P > 0.05; one-way ANOVA/Bonferroni)). (j, k) Illuminations of the right ventricle with increasing pulse frequencies from 7 to 13 Hz under 980 (j) and 473 nm (k) laser. (l, m) Capture rates with increased pulse frequencies from 7 to 13 Hz with 980 and 473-nm lasers (l: 980 nm, 20 ms, 2.77 ± 0.79 W; m: 473 nm, 20 ms, 0.72 ± 0.18 mW/mm²; n = 5; The data are presented as the mean ± SEM. *P < 0.05, **P < 0.01; Chi-square test).