Highly Sensitive Electrochemical Sensor for the Detection of Anions in Water Based on a Redox-Active Monolayer Incorporating an Anion Receptor

Abstract

In the present work, gold electrodes were modified using a redox-active layer based on dipyrromethene complexes with Cu(II) or Co(II) and a dipodal anion receptor functionalized with dipyrromethene. These modified gold electrodes were then applied for the electrochemical detection of anions (Cl, SO, and Br) in a highly diluted water solution (in the picomolar range). The results showed that both systems, incorporating Cu(II) as well as Co(II) redox centers, exhibited highest sensitivity toward Cl. The selectivity sequence found for both systems was Cl > SO > Br. The high selectivity of Cl anions can be attributed to the higher binding constant of Cl with the anion receptor and the stronger electronic effect between the central metal and anion in the complex. The detection limit for the determination of Cl was found at the 1.0 pM level for both sensing systems. The electrodes based on Co(II) redox centers displayed better selectivity toward Cl anion detection than those based on Cu(II) centers which can be attributed to the stronger electronic interaction between the receptor-target anion complex and the Co(II)/Co(III) redox centers in comparison to the Cu(II)/Cu(I) system. Applicability of gold electrodes modified with DPM-Co(II)-DPM-AR for the electrochemical determination of Cl anions was demonstrated using the artificial matrix mimicking human serum.

Redox-active Monolayers Deposited on Gold Electrode Surface–Universal Platforms for Electrochemical Sensing

“…(15) The sensing platform incorporating DPM-Co(II)-DPM centers poses a higher selectivity than the platform incorporating DPM-Cu(II)-DPM. This phenomenon was observed for chloride (14) and phosphate (15) sensors.…”

“…Both sensing systems were able to detect chloride anions in a highly diluted water medium (in the picomolar range). (14) The decrease in redox current and the shift in redox peak potential after the complexation of anions by the anion receptor are consequences of the changes in the accessibility of counterions from the supporting electrolyte to the redox center, in electron transfer efficiency to/from the underlying electrode, and in electrostatic interaction through space between the central metal and target anion in the complex. (7,10) Gold electrodes modified with a unique cyclopeptide effective for anion recognition via the creation of hydrogen bonds have been used for sulphate sensing (Fig.…”

“…This strongly facilitates their complexation by the receptors attached to the electrodes. (14)(15)(16)(17)(18) 3. Electrochemical Genosensors…”

Enhanced voltammetric anion sensing at halogen and hydrogen bonding ferrocenyl SAMs

“…5,6 This has also been exploited in electrochemical anion sensors in solution, [7][8][9][10][11] and, very recently, at receptive interfaces. [12][13][14] The surface-immobilisation of (redox-active) receptors is relevant to the development of real-life relevant sensors, [15][16][17][18] enabling facile sensor reuse, and sensing both under flow and in (aqueous) solvent media in which many synthetic receptors are not natively soluble. 1,19 Our quantitative understanding of anion sensing at redox-active interfaces, does, however, remain underdeveloped.…”

Enhanced Voltammetric Anion Sensing at Halogen and Hydrogen Bonding Ferrocenyl SAMs

“…The surface-immobilisation of (redox-active) receptors is relevant to the development of real-life relevant sensors, [15][16][17][18] enabling facile sensor reuse, and sensing both under flow and in (aqueous) solvent media in which many synthetic receptors are not natively soluble. 1,19 Our quantitative understanding of anion sensing at redox-active interfaces, does, however, remain underdeveloped.…”