Abstract：
In this work, a microfluidic paper-based analytical device (μPAD) was developed to detect the biopesticide azadirachtin (Aza) through a colorimetric assay. High precision estimation of Aza is classically carried out using high performance liquid chromatography (HPLC), which requires highly skilled personnel. Acidified vanillin is a commonly used colorimetric indicator in thin layer chromatography for detection of various phytochemicals. However, the assay involves concentrated acid, which limits the choice of paper substrates for paper-based sensors and raises safety concerns. In this work, we show how the assay can be extended from the liquid phase to a paper substrate. Glass microfiber (GMF) filter paper was found to be suitable paper as it was acid resistant; besides, its hydrophilicity enabled smooth flow of reagents. A microfluidic paper-based sensor (μPAD) was developed by sandwiching 5 mm sized GMF dots between two parafilm sheets. We demonstrate the use of colorimetric assay on the μPAD for on-site detection of Aza in neem kernels. The magenta color developed upon the reaction of acidified vanillin with Aza was captured using a smart-phone and analysed using RGB levels in the image. Calibration was established using neem kernel extract of known concentration. Linearity was seen in the concentration range of 5 to 25 mg L-1 Aza. A limit of detection of 2.3 mg L-1 was obtained using this method. The colorimetric assay showed a relative recovery of >85% when compared with the values obtained from HPLC. The stability of the reagents on the GMF sensor was investigated to understand the storage conditions and shelf life of the reagents and sensor. The present work demonstrates the development of a portable sensor for on-site detection of phytochemicals that can be an integral part of the agricultural supply chain.
摘要：
在这项工作中,开发了一种微流控纸基分析装置（μPAD），通过比色法检测生物杀虫剂印字素（Aza）。传统上使用高效液相色谱（HPLC）对Aza进行高精度估算，这需要高技能的人才。酸化香兰素是薄层色谱中常用的比色指示剂，用于检测各种植物化学物质。然而,该试验涉及浓酸，这限制了纸基传感器的纸张基材的选择，并引发了安全问题。在这项工作中,我们展示了该测定如何从液相延伸到纸基材。发现玻璃超细纤维（GMF）滤纸是合适的纸，因为它耐酸；此外，它的亲水性使试剂流动顺畅。通过将5mm大小的GMF点夹在两个石蜡片之间来开发微流体纸基传感器(μPAD)。我们证明了在μPAD上使用比色测定法来现场检测印em内核中的Aza。使用智能手机捕获酸化香草醛与Aza反应后产生的品红色，并使用图像中的RGB水平进行分析。使用已知浓度的苦杏仁仁提取物建立校准。在5至25mgL-1Aza的浓度范围内观察到线性。使用该方法获得2.3mgL-1的检出限。当与从HPLC获得的值相比时,比色测定显示>85%的相对回收率。研究了试剂在GMF传感器上的稳定性，以了解试剂和传感器的储存条件和保质期。目前的工作展示了用于现场检测植物化学物质的便携式传感器的开发，该传感器可以成为农业供应链的组成部分。
