Electrofluorochromic Detection of Cyanide Anions Using a Nanoporous Polymer Electrode and the Detection Mechanism

Abstract

An electrofluorochromic (EFC) conjugated copolymer (PEFC) containing carbazole and benzothiadiazole (BTD) moieties is synthesized through Suzuki coupling followed by electrochemical polymerization, resulting in a nanoporous EFC polymer electrode. The electrode exhibits high sensitivity and selectivity in the EFC detection of cyanide anions (CN(-)) in largely aqueous electrolyte (67 vol % water) because electrochemical oxidation of PEFC leads to significant fluorescence quenching, and the presence of different concentrations (1 to 100 μM) of CN(-) in the electrolyte can weaken the oxidative quenching to substantially different extents. Although PEFC is hydrophobic in the neutral state, it is converted to radical cation/dication states upon oxidation, rendering the PEFC some hydrophilicity. Moreover, its nanoporous morphology provides a large surface area and short diffusion distance, facilitating the movement of CN(-) in the electrolyte into the PEFC film to interact with receptors. Density functional theory calculations show that the noncovalent interaction between electron-deficient BTD and nucleophilic CN(-) is energy favorable in the oxidized states in both aqueous and organic media, suggesting that the specific π(-)-π(+) interaction plays the main role in the CN(-) detection.

Electroluminochromic Materials: From Molecules to Polymers

“…Electrochemical oxidation, however, changed the film colour to black and quenched the fluorescence due to the formation of radical cations (polarons) and dications (bipolarons) along the conjugated polymer backbone [67]. Xu et al separately reported two carbazole-benzothiadiazole co-polymers P18a and 18b with both EC and EFC properties that were found useful for the detection of cyanide anions [68,69]. Nanoporous copolymer P18a exhibited an oxidative quenching with a high contrast ratio of 19.2 in the absence of cyanide anions [69].…”

“…Xu et al separately reported two carbazole-benzothiadiazole co-polymers P18a and 18b with both EC and EFC properties that were found useful for the detection of cyanide anions [68,69]. Nanoporous copolymer P18a exhibited an oxidative quenching with a high contrast ratio of 19.2 in the absence of cyanide anions [69]. Similarly, a thin film device of P18b spin-coated on ITO/poly(ethylene terephthalate) experienced up to 80% quenching of fluorescence upon undergoing electrochemical oxidation, due to the formation of carbazole radical cation and dications [68].…”

Electroluminochromic Materials and Devices

“…The ELC layer can be deposited onto substrates by electropolymerization in a bath of electrolyte solution. For instance, X. Lu et al successfully prepared a nanoporous EFC copolymer film via electropolymerization . As shown in Figure a, in consecutive cyclic voltammograms, the oxidation and reduction current densities increased and their onsets decreased gradually with increasing cycle number.…”

“…(a) Chemical structure of electropolymerized EFC copolymer, consecutive cyclic voltammograms for the electropolymerization and SEM images with different magnifications showing the surface morphology of the electropolymerized EFC film. Reproduced with permission . Copyright 2014, WILEY‐VCH.…”

Ratiometric and colorimetric near-infrared sensors for multi-channel detection of cyanide ion and their application to measure β-glucosidase

“…For example, ingested amygdalin, which is one of the most typical cyanogenic glycosides found in kernels such as peach, apricot, cherry and almond, would be hydrolysed by the widely distributed natural β-glucosidase and generated hydrogen cyanide (HCN) in living organisms, leading to disruption of normal physiological activities and may result in death caused by rapid suffocation 5 . Therefore, CN − monitoring has attracted much attention, and many techniques such as voltammetry, titrimetry, electrochemical and chromatography have been developed 6 7 8 9 10 . Unfortunately, most of these methods require expensive equipment and are complicated for real-time analyses.…”