Electrochemical sensing of sulfate in aqueous solution with a cyclopeptide-dipyrromethene-Cu(II) or Co(II) complex attached to a gold electrode

[Display omitted] •Anion-binding cyclopeptide was immobilized on a gold surface via (bis)dipyrromethene metal complexes.•Anion sensing relies on the combination of a redox center and an anion receptor.•Lack of the necessity of using the external redox marker.•Sensors allow the sensitive detection of SO42– at the pM range. An electrochemical sensor comprising a cyclopeptide connected to the surface of a gold electrode via a bis(dipyrromethene) Cu(II) or Co(II) complex allows detection of sulfate in water. This sensor displays high selectivity and sensitivity at the pM level of the target anion, rendering it potentially useful for environmental monitoring. Importantly, since electrochemical anion sensing relies on the redox properties of the metal centers embedded between the anion-binding cyclopeptide and the electrode surface, no addition of an external redox marker to the sample solution is required. The elimination of the external redox marker improved sensor sensitivity and possibility for its miniaturisation. These parameters are important for possible application in environmental monitoring. The structure and properties of the sensor were characterized by a combination of electrochemical methods, atomic force microscope as well as contact angle measurements. The mechanism of sensing mode was proposed and discussed.