A Hydrogen Sulfide‐Activated NIR‐II Fluorescence/NIR‐I Photoacoustic Dual‐Ratiometric Nanoprobe With Unique Recognition Reaction for Precise Visual Diagnosis of Hepatitis Disease

Abstract

Hydrogen sulfide (H 2 S) is a vital gaseous signaling molecule that plays a central role in various physiological and pathological processes. Given the complementary advantages of fluorescence (FL) and photoacoustic (PA) imaging, there is a growing demand for dual‐ratiometric probes that enable precise in vivo monitoring of H 2 S levels. In this study, the use of 2‐mercapto‐1,3,4‐thiadiazole (MTD) as a novel recognition group of H 2 S is presented for the first time, following conjugation with cyanine dyes to obtain a new PA probe Cy‐MTD. To achieve dual‐ratiometric imaging, Cy‐MTD is incorporated into down‐conversion nanoparticle (DCNP), resulting in the creation of a pioneering NIR‐II FL/NIR‐I PA dual‐ratiometric nanoprobe DCNP@Cy‐MTD. Cy‐MTD undergoes the blueshift in absorption from 840 to 670 nm after reaction with H 2 S, enabling NIR‐I ratiometric PA imaging of H 2 S by measuring the ratio of PA signal at 670 and 840 nm (PA 670/PA 840). In addition, due to the strong absorption of Cy‐MTD ≈840 nm and the overlapping between the absorption spectrum of Cy‐MTD and 808 nm excitation band of DCNP, the 808 nm‐excited FL emission (F 1550 nm,808Ex) of DCNP in DCNP@Cy‐MTD nanoprobe is quenched through the competitive absorption, while it is restored upon the interaction with H 2 S because of the blueshift in absorption of Cy‐MTD. Using the stable FL emission of DCNP under 980 nm excitation (F 1550 nm,980Ex) as the reference signal, NIR‐II ratiometric FL imaging (F 1550 nm,808Ex/F 1550 nm,980Ex) of H 2 S is achieved. The dual‐ratiometric response features of the DCNP@Cy‐MTD nanoprobe offer a significant advancement over traditional single‐signal or single‐modality imaging techniques. By providing enhanced accuracy and reliability, this probe allows for the diagnosis of hepatitis by monitoring the H 2 S, surpassing the capabilities of conventional histopathological methods, which provides a new way for more effective diagnostic strategies for liver diseases.