Fig. 1. Characterization and sonodynamic performance of BT-based sonosensitizers with different counterions. (a) Molecular structures of BT with corresponding counterions. (b) Molecular volumes of the three counterions (Cl⁻, CF₃SO₃⁻, and F₅-TPB⁻). (c) Normalized absorption spectra of BT-Cl, BT-CF₃SO₃, and BT-F₅-TPB in DMF. (d–f) Fluorescence spectra of DCFH in the presence of BT-Cl (d), BT-CF₃SO₃ (e), and BT-F₅-TPB (f) under ultrasound irradiation. (g) Heatmap summarizing ROS generation efficiency among the three sonosensitizers and DCFH over time. (h) DPBF absorbance changes reflecting ¹O₂ generation capacity of BT-Cl, BT-CF₃SO₃, BT-F₅-TPB, and DPBF alone under ultrasound. (i) ESR measurements of BT-Cl, BT-CF₃SO₃, and BT-F₅-TPB under ultrasound irradiation using TEMP as a ¹O₂ indicator. (j) ROS generation ability on BT-Cl at different penetration depths with ultrasound irradiation (1 W cm⁻², 1.0 MHz, 50% cycle) for 5 min. (k) Sonostability assessment of BT-Cl and ICG for different times (0–30 min). (l) UV-vis absorption spectra of NADPH in the presence of BT-Cl under ultrasound irradiation.