Development of a novel three-dimensional microfluidic paper-based analytical device (3D-μPAD) for chlorpyrifos detection using graphene quantum-dot capped gold nanocomposite for colorimetric assay

This report presents a three-dimensional microfluidic paper-based analytical device (3D-μPAD) with colorimetric assay, for chlorpyrifos organophosphate pesticide detection in vegetable samples. The 3D-µPAD was fabricated by one-step polymer-screen-printing, using rubber latex (RL) waste as a hydrophobic reagent for low-cost and simple manufacture. The 3D-µPAD design comprises two sheets; a testing sheet containing two circular zones, and a sampling sheet in the shape of a dumbbell design. Assay involves the acetylcholinesterase (AChE)-catalysed hydrolysis of an acetylthiocholine (ATCh) substrate to produce thiocholine. Thiocholine causes the aggregation of graphene-quantum-dot capped gold-nanocomposite particles (GQD-AuNPs) to give a purple–blue-coloured solution. Incubation with chlorpyrifos inhibits the hydrolysis reaction, resulting in anti-aggregation of red-coloured GQD-AuNPs. The assay can determine chlorpyrifos by ImageJ detection, over a linear range of 0.001 to 1.0 µg mL⁻¹, with a detection limit of 0.0007 µg mL⁻¹, without sophisticated instrumentation. The developed 3D-µPAD was applied to detect chlorpyrifos in spiked vegetable samples, with per cent recoveries ranging from 93.0% to 104.6%. Our developed device provides good precision (%RSD ranges from 0.3 to 1.6). The calculated relative error comparison with HPLC ranges from 1.0% to 5.2%, indicating a high degree of accuracy. The 3D-µPAD exhibits good sensitivity and selectivity for a low-cost and rapid-screening test for the presence of insecticides, and might be useful for on-site applications.