Manipulation of Energy Migration in Upconversion Nanoparticles for Long-Lived Mn²⁺ Emission and Enhanced Singlet Molecular Oxygen Generation

High Resolution Image Download MS PowerPoint Slide Nanosensitizers having long-lived upconversion emission under near-infrared (NIR) excitation offer unique advantages in terms of reduced background noise and prolonged signal detection for deep tissue therapy of cancer. Herein, we demonstrate a systematic mechanism of energy migration toward achieving long-lived Mn 2+ upconversion emission in the multilayered core–shell–shell lattice of NaGdF 4:Yb 3+,Tm 3+,Ca 2+ /NaGdF 4:Yb 3+,Ca 2+ /NaGdF 4:Mn 2+ upconversion nanoparticles (NPs), following the Yb 3+ → Tm 3+ → Gd 3+ → Mn 2+ intermetal ions energy transfer pathway. Furthermore, a rational design of nanosensitizer was achieved by incorporating Er 3+ ions into the intermediate shell of multishell NPs, which was subsequently conjugated with the Rose Bengal sensitizer to enable the enhancement in singlet molecular oxygen ( 1 O 2 ) generation under excitation of a 980 nm NIR laser. An intense higher-energy emission in the UV–blue visible region from Tm 3+ was achieved by optimizing the amount of Ca 2+ in the core–shell NPs, followed by subsequent energy migration to the Mn 2+ ion incorporated at the outer shell. The Mn 2+ ions were strategically doped in the outer shell of NPs to leverage the catalytic activities of Mn 2+ for H 2 O 2 decomposition and decrease the backward energy transfer to the Tm 3+ ion. Hence, this approach resulted in a long lifetime of Mn 2+ (∼34 ms), attributed to the spin-forbidden 4 T 1g → 6 A 1g transition within 3d 5 configuration. Additionally, the nanosensitizer demonstrated high 1 O 2 (∼0.39 μM) generation even at a very low concentration (5 μg/mL) under a laser power of 2 mW cm –2 . The hydrogenase-like catalytic activities of Mn 2+ exhibited significant oxygen production through decomposition of H 2 O 2 . Hence, these findings might contribute to the development of convenient multifunctional nanosensitizers for multimodal bioimaging and therapeutic features, including efficient 1 O 2 generation and catalytic decomposition of H 2 O 2 (found excessively in a tumor environment) to oxygen for alleviating the hypoxia.