Chlorophyll based biosensor for sulfur mustard - a chemical warfare agent

Sulfur mustard (SM), a chemical warfare agent (CWA) is a bifunctional blistering and alkylating agent used in military warfare having antimitotic, mutagenic, carcinogenic, teratogenic and cytotoxic effects. Conventional techniques used for the detection of CWAs are complex, expensive and require sophisticated analytical procedures thus entailing the development of alternative analytical tools. Biosensors offer an alternative analytical approach with a promise of selectivity in addition to sensitivity, ease of use, rapid response and negligible sample pre-treatment. Furthermore, biomolecules have the ability to detect toxicity in addition to concentration. This work reports the development of a fluorescence based biosensor for detection of SM. 2-chloroethyl ethyl sulfide (2-CEES), a sulfur mustard mimic which is structurally similar to it but not as lethal was used for the study, utilizing the ability of chlorophyll to detect the said compound owing to fluorescence. For this, chlorophyll extract from a plant source was immobilized on fibre glass discs of 5mm diameter, and its fluorescence was studied by excitation at 437 nm and emission at 667 nm. The exposure of the biocomponent to 2-CEES led to quenching of fluorescence, which varied linearly with increasing concentration of 2-CEES with a detection limit of 7.68 × 10⁻¹⁰ M. The fluorescence drop mechanism was characterized by HPLC studies which confirmed the conversion of chlorophyll, upon exposure to the analyte, to non-fluorescing catabolic products. The low detection limit was a promising feature of the biosensor.