Fluorescent nanochemosensor for direct optosensing of butachlor based on l-cysteine-capped ZnS quantum dots

Abstract

Butachlor is a systemic herbicide greatly applied on rice, wheat, tea, beans and other nontarget animals including humans. The content of this paper includes the exploitation of dominant optical properties of the quantum dots ZnS capped by l-cysteine. A nanochemosensor was fabricated in aqueous solution at room temperature through a straightforward one-pot process by using safe and low-cost inorganic salts as precursors and was used as a novel fluorescent sensor for herbicide butachlor recognition. Preliminarily studies showed that fluorescence enhancement of the l-cysteine-capped ZnS nanoparticles depends on the concentration of butachlor solution and any change in fluorescence intensity was directly proportional to the concentration of butachlor. Fluorescence enhancement was observed at pH 4.4 with the excitation and emission wavelengths of 265 nm and 359 nm, respectively. Under optimum conditions, the linear range for the detection of butachlor was 3.4 × 10−7–1.7 × 10−5 mg L−1 with a detection limit of 1.4 × 10−7 mg L−1. Enhancement of its fluorescence due to butachlor at 3.5 × 10−6 mg L−1 level was unaffected by the presence of excesses amounts of other common agricultural pesticides and ion metals. For describing the relationship between butachlor concentration and fluorescence intensity of the l-cysteine-capped ZnS QDs, a Langmuir-type binding model was highly effective. The mechanism of this enhancement was discussed. The proposed fluorescent sensor was successfully used for the determination of butachlor in natural water.