Encapsulation of metal nanoclusters into hydrogen-bonded organic frameworks for double-response-reverse ammonia fluorescence sensing

Ammonia (NH₃) is considered a biomarker of liver and kidney diseases; sensitive and visible fluorescence sensors are expected to achieve quantitative detection of breath NH₃, although low accuracy makes them difficult to apply in breath tests. Herein, we adopted a “double-response-reverse fluorescence” strategy via in situ encapsulation of a metal nanocluster (MNC) into a hydrogen-bonded organic framework, successfully constructing an ultra-accurate ratiometric fluorescence sensor (Pt₂Cu₄@HOF-101). With a combination of π-conjugated HOF and luminescent MNC, two kinds of NH₃ recognition sites were preciously assembled and raised significant orbital energy changes, thus realizing a strong response to trace NH₃. The precision-assembled Pt₂Cu₄@HOF-101 has been eloquently inspected by three-dimensional electron diffraction, which comprehensively uncovered the structure-induced double-response-reverse sensing mechanism. Notably, Pt₂Cu₄@HOF-101 enabled exact quantification of the NH₃ exhaled, and the measured expiratory concentration was highly positively correlated with the blood test, which offers a new approach for the painless diagnosis of liver and kidney diseases.