A smart probe for multi-analyte signaling: Cascade detection of HSA mediated by N2H4

Human serum albumin (HSA) and hydrazine (N2H4) are known biomarkers and damage agents of liver function activity, respectively. However, the mechanism of association between HSA and N2H4 in the liver remains unexplored. Herein, we report a naphthalimide-based smart fluorescent probe NI-2 for the N2H4 mediated cascade detection of HSA (N2H4 ∩HSA). Results showed that the levulinate recognition group on NI-2 is ammonolyzed within seconds in response to N2H4, releasing the compound NI-OH, triggering a hypsochromic shift of the emission to 400 nm; while with the coexistence of HSA, the entry of NI-OH into the hydrophobic cavity of HSA, resulting a bathochromic emission shift to 670 nm. We have further revealed the reaction mechanism of NI-2 cascade reacting with N2H4 ∩HSA through HRMS, replacement experiment and molecular docking method. NI-2 has been successfully applied in detecting N2H4 ∩HSA in human urine quantitatively and N2H4 in water samples or plants. A qualitative test paper strip model for quick response of N2H4 and N2H4 ∩HSA has also been established. Moreover, NI-2 can be applied in bioimaging of HepG2 cells and zebrafish, indicating that NI-2 can be a potential tool for the study of liver damage.