Abstract
Herein, a novel configuration for the detection of a chemical warfare agent, namely sulfur mustard (bis(2-chloroethyl)sulphide) was designed to develop a biosensor that can play a relevant role in the monitoring of such a chemical threat in risk and war areas. In detail, a tailor-made heterogeneous oligonucleotide-antibody biosensor was realised, based on the formation of a sulfur mustard-oligonucleotide adduct on the surface of a screen-printed electrode. Thus, the immunoassay was carried out through a sequential immobilisation process, involving a primary antibody, ad hoc synthesised for the selective recognition of the sulfur mustard-oligonucleotide adduct, followed by an alkaline phosphatase-conjugated anti-mouse anti-IgG as secondary antibody. The detection was performed by adding the substrate 1-naphthyl phosphate and measuring the enzymatic product in differential pulse voltammetry. In order to improve the electroanalytical performances of the novel heterogeneous oligonucleotide-antibody sensor, we have explored the advantageous use of carbon black for the detection of alkaline phosphatase by-products. The electrochemical response of graphite-based screen-printed electrodes modified with three types of carbon black (i.e. N220, N115, and HP160) was thoroughly investigated by using cyclic voltammetry and amperometry for the detection of different enzymatic by-products namely 1-naphthol, hydroquinone, 4-nitrophenol, and ascorbic acid. This study allowed to shed light on the capacity of carbon black of remarkably enhancing the measurement of alkaline phosphatase’s products. Particularly, carbon black N220 and 1-naphthol were selected for developing a highly performant heterogeneous oligonucleotide-antibody assay for the detection of sulfur mustard. Under optimized conditions, the carbon black-based biosensor showed a linear range from 20 μM to 80 mM and a LOD of 12 μM in liquid samples, demonstrating high sensitivity as well as selectivity in presence of some possible interfering sources in the war field.
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