Near-Infrared II Nanohybrid Enables Single-Excitation, Fully Ratiometric Imaging of Hydrogen Sulfide In Vivo.

As a crucial endogenous gasotransmitter, the precise in vivo monitoring of hydrogen sulfide (H2S) is of fundamental importance for elucidating its associated physiological and pathological processes. However, current fluorescence imaging systems for H2S critically lack ratiometric probes that simultaneously feature a single excitation wavelength alongside both working and reference emission bands operating entirely within the second near-infrared (NIR-II) window. To address this gap, we present a NIR-II ratiometric nanohybrid, ErNPs@mSiO2-Cy-NO2, that integrates Er3+-doped lanthanide downconversion nanoparticles encapsulated by mesoporous silica loading with NIR II cyanine dye (Cy-NO2). In the presence of H2S, Cy-NO2 is converted to Cy-NH2, regulating an intramolecular photoinduced electron-transfer (PET) process. Under single 980 nm excitation, this reaction selectively modulates the ∼1026 nm emission (located in NIR II), while the Er3+ emission at 1550 nm (located in NIR II) remains invariant and serves as an internal reference. The resulting fully NIR II ratiometric readout (I1026/I1550) enables real-time visualization of H2S in vitro and in vivo. Overall, ErNPs@mSiO2-Cy-NO2 establishes a robust platform for monitoring of H2S and holds broad potential for advanced biosensing and diagnostic applications.