A dual-responsive pH-sensor and its potential as a universal probe for assays of pH-changing enzymes.

We described a dual turn-on probe sensitive to both acidity and basicity, which could be designed by connecting a fluorophore to a quencher via metal-ligand interaction. Atto488-labeled nitrilotriacetic acid and polyhistidine peptide were used as the fluorophore and the quencher, respectively, and linked to each other by coordination with a cobalt(II) ion. After preparation of the probe, the pH-sensitive dual turn-on property of the probe has been successfully observed upon responding to both acidity and basicity of the solution. The probe has been employed as a signal reporter in assays of pH-changing enzymes such as penicillinase generating acidity and adenosine deaminase generating basicity. Furthermore, the practical utility of the probe was also demonstrated by utilizing the probe in the discrimination of β-lactamase-producing bacteria.