A molecular-size sieve-inspired metal-organic cage-based hydrogen sulfide probe for colon cancer diagnosis

Colon cancer remains the second leading cause of cancer-related deaths, necessitating advanced early diagnostic tools to improve survival outcomes. Leveraging the tumor-specific overexpression of hydrogen sulfide (H 2 S) in colon cancer, various H 2 S-responsive probes have been developed. However, conventional H 2 S fluorescent probes suffer from interference by commonly expressed nitroreductase (NTR) in normal colonic tissues due to shared activation mechanisms. Here, we proposed an innovative size-exclusion strategy utilizing metal-organic cages (MOCs) to engineer a highly-selective H 2 S probe (MOC-HSN1). MOCs was synthesized by coordinating BPAB with palladium ions, and a classic H 2 S-responsive probe HSN1 was concurrently loaded to form MOC-HSN1. With a molecular weight of 10–20 kDa, the MOCs function as a molecular size sieve, which selectively excludes NTR (200–220 kDa) from the outside while permitting H 2 S (34 Da) molecules to enter the inside and activate HSN1, thereby improving the selectivity of H 2 S imaging to achieve precise colon cancer diagnosis. Results showed that MOC-HSN1 had good stability, biocompatibility, and it enabled precise qualitative and quantitative H 2 S detection in vitro, in cells, and in vivo. This size-discrimination strategy effectively circumvents NTR interference, positioning MOC-HSN1 as a translatable platform for integration with fluorescence endoscopy, with potential to augment early colorectal cancer localization and diagnosis in clinical settings.