Supramolecular Host–Guest Strategy for the Accelerating Detection of Nitroreductase

Identifying nitroreductase (NTR) with fluorescent techniques has become a research hotspot, due to its good sensitivity and selectivity toward the early-stage cancer diagnosis and monitoring. Herein, a host–guest reporter (NAQA⊂Zn-MPPB) is successfully achieved by encapsulating the NTR probe NAQA into a new NADH-functioned metal–organic cage Zn-MPPB, which makes the reporter for ultrafast detection of NTR within dozens of seconds in solution. The host–guest strategy fuses the Zn-MPPB and NAQA to form a pseudomolecule material, which changes the reaction process of NTR and NAQA from a double substrates mechanism to a single substrate one, and accelerates the reduction efficiency of NAQA. This advantage make the new host–guest reporter exhibit a linear relationship between emission changes and NTR concentration, and it shows better sensitively toward NTR than that of NAQA. Additionally, the positively charged water-soluble metal–organic cage can encapsulate NAQA in the cavity, promote it to dissolve in an aqueous environment, and facilitate their accumulation into tumor cells. As expected, such host–guest reporter displays a fast and high efficiently imaging capability toward NTR in tumor cells and tumor-bearing mice, and flow cytometry assay is conducted to corroborate the capability as well, implying the considerably potential of host–guest strategy for early tumor diagnosis and treatment.