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On-site detection of chlorpyrifos, the most commonly used insecticide, is still a challenge for food safety concerns. So far, different chromatographic methods and immunological methods have been used for chlorpyrifos assays due to their reliability and sensitivity, yet they have been time-consuming, depended too much on expensive facilities and needed a lot of technical skills, making them unsuitable for on-site screening. In this study, a plastic lab-on-a-chip was developed to rapidly detect chlorpyrifos residue. The 1.8x5.3 cm. acrylic chip was fabricated using an engraving machine. It had two parts, a sample socket for sample application and a reaction part for chlorpyrifos signal detection. The simple and rapid chlorpyrifos assay combining a chlorpyrifos specific aptamer and colorimetric detection using gold nanoparticle was in its entirety operated on the acrylic plastic chip. The sample was just applied to the chip via a sample socket, then the chip was sealed with a sticker and flicked forward to get the gold nanoparticles/aptamer solution mixed and flicked backward to see the result. When chlorpyrifos was present in a sample, a binding between chlorpyrifos and aptamer protected the gold nanoparticles from salt induced aggregation, leaving a distinct ruby red color on the chip, whereas when chlorpyrifos was absent, the aptamer would induce particle aggregation leaving only purple color. The assay completion requires less than 10 minutes, has a limit of detection (LOD) of 10 ppb, and has high specificity (100%) and sensitivity (100%). When this was used to identify chlorpyrifos residue in commercial samples, residue contamination was identified in 6 of 30 samples tested (20.00%). This work demonstrates the fabrication of a simple, low-cost, paper-based lab-on-a-chip platform suitable for rapid-detection applications.
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