在全球大健康时代，人们对生命安全健康的关注日益提升，特别是在健康安全饮食方面展现出多样化和个性化的需求，其中“药食同源”类产品深受国内外追捧。在此背景下，“十四ž五”规划强调了“加速中医药事业发展”的重要性，认为这是应对健康挑战、满足人们健康需求的关键路径之一，并设定了完善中医药高质量发展政策和体系的目标。实现中医药的高质量发展，关键在于确保中药材的质量和安全，尤其是兼具食用价值和药用功能的“药食同源”中药材，如薄荷和麦芽。

这些“药食同源”中药材在种植、采收及贮藏过程中普遍使用农药来防治病虫草害，进而导致农药通过土壤、空气和水源等多种途径残留于中药材中，不仅会影响药材的质量和安全，也会降低其药效和治疗效果，更会威胁使用者的身体健康，损害中国中药材产品的全球形象与信誉。建立高效灵敏的技术手段准确检测“药食同源”中药材中农药残留水平，以对保障药材的质量和安全、提高中药材的国际竞争力具有重要意义。现有技术如高效液相色谱（HPLC）和气相色谱串联质谱联法（GC-MS/MS）等已展示出高灵敏度和准确性的优势，但往往面临前处理复杂、成本高等限制。因此，亟需开发设备便携、操作简单、灵敏度高、定量精准的“药食同源”中药材中农药残留检测新方法。本研究以农药检出率较高的常用“药食同源”中药材麦芽、薄荷为研究对象，百草枯农药为靶标，结合电化学传感平台的操作简单、响应快速、灵敏度高的优势，适配体的高特异识别能力、MXene的优异电化学性能，基于两种策略构建了高灵敏的电化学适配体传感器，可实现大批量麦芽、薄荷中百草枯的高效快速检测，为更多“药食同源”中药材农药残留提供了技术参考和数据支撑。

一、构建基于3D纳米蛋糕状Au-MXene/AuP结构的电化学适配体传感器快速检测百草枯农药残留

本研究于丝网印刷碳电极（SPCE）上，基于“信号关闭（Signal off）”策略构建了一种新型3D纳米蛋糕状Au-MXene/AuP结构的电化学适配体传感器，并用于实际样品“药食同源”麦芽和薄荷中百草枯残留检测。首先，通过原位生长的方式获得Au-MXene复合纳米材料，并与电沉积在SPCE电极表面的金盘Au Pallet（AuP）层复合形成3D纳米蛋糕状Au-MXene/AuP结构，用于适配体的固定以特异性识别和捕获百草枯农药分子。当待测样品中存在靶标百草枯农药时，它会被适配体捕获并在电极表面形成复合体，从而产生较大的空间位阻，阻碍电子转移，导致电信号响应（电流，I）降低。所以，通过记录由于靶标存在导致的电流信号变化值（ΔI，与百草枯含量呈正相关），可实现百草枯农药的准确定量。实验过程中，采用SEM、TEM、XPS、EDS等手段对纳米材料及电极自组装过程进行表征，结果表明Au-MXene/AuP/SPCE形貌符合预期且表现出高导电性能。利用循环伏安法(CV)、差分脉冲伏安法（DPV）对Au-MXene浓度、适配体浓度等因素进行优化。在最佳条件下，该3D纳米蛋糕状Au-MXene/AuP双信号放大的适配体传感器对百草枯农药表现出宽线性检测范围（0.05-1000 ng/mL）、低检测限（LOD）为0.028 ng/mL、高特异性、良好的重现性和稳定性，在麦芽和薄荷实际样品中的加标回收率分别为95.20%-100.40%和96.6%-104.00%，均符合要求。该电化学适配体传感器具有构建简单、省时、仪器小巧、成本低、适合大规模生产的优势，在食品安全、环境监测和更多痕量污染物的即时检测中具有广阔的应用前景。

二、建立基于风筝型MXene-Ag的比率电化学适配体传感器高灵敏检测百草枯农药残留

本研究采用“信号开启（Signal on）”策略构建了一种基于风筝型MXene-Ag复合纳米材料的比率电化学适配体传感器，检测“药食同源”麦芽和薄荷样品中百草枯农药残留。首先，在MXene的层间原位生长银粒子（Ag）以获得MXene-Ag复合纳米材料，再与互补DNA序列（cDNA）偶联形成cDNA-MXene-Ag信号探针。然后，在玻碳电极（GCE）表面通过电沉积HAuCl₄形成金Au薄层（Au/GCE），滴加捕获DNA（Capture DNA, CapDNA）探针后通过Au-S键固定，再滴加巯基己醇（MCH）以封闭电极表面多余的位点。随后，适配体通过碱基互补配对与CapDNA结合形成双链。当样品液中存在靶标百草枯农药分子时，优先与适配体形成“适配体-百草枯”复合体，释放CapDNA单链并使其暴露。随着cDNA-MXene-Ag信号探针的引入，cDNA会与CapDNA结合形成双链结构，以在GCE电极表面固定该信号探针，导致电流的变化。为了消除背景干扰及不同电极之间可能存在的差异影响，本研究通过在电解质溶液中加入 [Ru(NH₃)₆]^3+/2+作为参比探针以对MXene-Ag产生的信号进行校正。这两种信号探针在不同电压下产生各自的电流信号（探针信号I_Ag，参比信号I_Ru），通过计算I_Ag/I_Ru比值从而实现信号校正和精确检测。实验过程中，采用SEM、TEM、EDS、XPS、CV、电化学阻抗谱（EIS）等手段对MXene-Ag复合纳米材料及自组装过程进行表征的结果佐证了该比率传感器构建的可行性。利用DPV、SEM对纳米材料复合比例、缓冲液pH值等因素进行优化。在最佳条件下，该风筝型MXene-Ag的比率电化学适配体传感器对百草枯农药的线性检测范围为0.01-1000 ng/mL，LOD为5.154 pg/mL，在麦芽和薄荷实际样品中的加标回收率分别为95.20%-97.29%和79.40%-105.00%，均符合要求。该比率电化学适配体传感器具有操作简单、信号响应直观、无背景干扰、高灵敏度等优势，适用于复杂基质中痕量农药残留的高精准检测。本研究致力于“药食同源”中药材中（以麦芽、薄荷为例）百草枯残留检测方法的探索。

从选定高性能纳米材料MXene出发，确定两种检测策略，分别构建基于3D纳米蛋糕状Au-MXene/AuP结构的电化学适配体传感器及基于风筝型MXene-Ag的比率电化学适配体传感器，用于检测百草枯残留，为麦芽和薄荷的农药残留防控提供方法参考，为“药食同源”中药材的质量安全控制提供技术支撑，对保障人们的生命健康建立“保护线”具有重要意义。

In the era of global health consciousness, the public's concern on safety and health is increasing, especially in terms of healthy and safe diets, showcasing diverse and personalized demands. Of these, the edible and medicinal products are in high interests at home and abroad. In this context, the "14^th Five-Year Plan" underscores the importance of accelerating the development of traditional Chinese Medicine, which is considered as a crucial pathway to address health challenges and meet the people’s health requirements with setting the objectives to improve the policies and systems for the high-quality development of traditional Chinese Medicine. For achieving these, the key is to ensure the quality and safety of Chinese medicinal materials (CMMs), especially those with both edible and medicinal values, such as mint and malt.

Pesticides are widely used during the cultivation, harvesting, and storage processes of these edible and medicinal CMMs to prevent diseases, pests, and weeds. This practice will lead to pesticide residues in the CMMs through soil, air, water, and other pathways to not only affect the quality and safety of them and reduce their medicinal efficacy and therapeutic effects, but also potentially threaten the users’ health and thereby damage the global image and reputation of the CMMs and their relevant products. The establishment of efficient and sensitive techniques for the accurate detection of pesticide residues in the edible and medicinal CMMs is of great significance to warrant their quality and safety for enhancing their international competitiveness. The existing technologies, such as high-performance liquid chromatography (HPLC) and gas chromatography tandem mass spectrometry (GC-MS/MS) methods, have demonstrated high sensitivity and accuracy, but often face limitations like complex pretreatment and high cost. Therefore, it is urgent to develop new techniques with portable devices, easy operation, high sensitivity and accurate quantification for the pesticide detection in the edible and medicinal CMMs. In this research, with  malt and mint that are commonly used and reported with a high rate of pesticide residue as the examples, and paraquat as the target pesticide, in combination with the electrochemical sensor showing advantages of simple operation, rapid response, and high sensitivity, the aptamers regarding highly-special recognition ability, and MXene nanomaterials with excellent electrochemical performance, two highly-sensitive electrochemical aptasensors were constructed based on two strategies. The developed aptasensing platforms could achieve efficient and rapid detection of paraquat in a large quantity of malt and mint samples, providing powerful technical references and data supports for pesticide detection in more edible and medicinal CMMs.

1. Establishment of a “signal off” strategy-based 3D nanocake-like Au-MXene/AuP electrochemical aptasensor for rapid detection of paraquat

This study developed a novel electrochemical aptasensor based on a 3D nanocake-like Au-MXene/AuP structure on a screen-printed carbon electrode (SPCE) through employing a "signal off" strategy for rapid paraquat detection in edible and medicinal malt and mint samples. Initially, Au-MXene composite nanomaterials were synthesized through in-situ growth, which were then integrated with gold pallet (AuP) layers that were electrodeposited on the SPCE surface to form the 3D nanocake-like Au-MXene/AuP structure. This structure served to immobilize aptamers for the specific recognition and capture of target paraquat molecules. In the presence of target paraquat in a sample, it was captured by the corresponding aptamer to obtain the paraquat-aptamer complex on the electrode surface, resulting in large spatial hindrance that impeded the electron transfer and thus reduced the electrical signal intensity (I). Therefore, by measuring the change in current signal intensity (ΔI) caused by the addition of paraquat, which was positively correlated with the concentration of paraquat, this pesticide could achieve accurate quantification. Characterization of the nanomaterials and electrode assembly process through SEM, TEM, XPS, and EDS tools revealed that the morphology of Au-MXene/AuP/SPCE was good with high electrical conductivity. The concentrations of Au-MXene and aptamer, as well as other crucial factors was optimized by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods. Under optimal conditions, this dual signal-amplified 3D nanocake-like Au-MXene/AuP aptasensor demonstrated a wide linear detection range (0.05-1000 ng/mL) and a low limit of detection (LOD, 0.028 ng/mL) for paraquat, as well as high specificity, good reproducibility, and excellent stability. The average recovery rates in the spiked malt and mint samples were in the ranges of 95.20%-100.40% and 96.6%-104.00%, respectively, meeting the official requirements. This proposed electrochemical aptasensing platform offered fascinating advantages of simple construction, short time, compact instrumentation, low cost, and good suitability for mass production, holding broad application prospects in food safety, environmental monitoring, and the real-time detection of trace contaminants.

2. Development of a “signal-on” strategy-based kite-shaped MXene-Ag ratiometric electrochemical aptasensor for the highly sensitive measurement of paraquat

This study introduced a ratiometric electrochemical aptasensor based on kite-shaped MXene-Ag composite nanomaterials through adopting a "signal on" strategy for the highly sensitive detection of paraquat in the edible and medicinal malt and mint samples. At first, silver particles (Ag NPs) were in-situ grown between MXene layers to create the MXene-Ag composite nanomaterials, which were then coupled with complementary DNA sequences (cDNA) to form the cDNA-MXene-Ag signal probes. Subsequently, HAuCl₄ solution was electrodeposited on the surface of a glassy carbon electrode (GCE) by using to form the Au/GCE layer, followed by the addition of capture DNA (CapDNA) probes that were anchored via the Au-S bonds, with the addition of mercaptohexanol (MCH) to block excess sites on the electrode surface. The aptamer was introduced to bind to CapDNA through base pairing to form the aptamer-CapDNA double-stranded structure. Upon the addition of target paraquat, it would be preferentially captured by the aptamers to form the paraquat-aptamer complexes, leading to the release and exposure of CapDNA strands. Then, the introduced cDNA-MXene-Ag signal probes would bind with CapDNA strands to form the double-stranded structures on the GCE surface, causing a change in the current intensity (I). Aiming to eliminate the background interferences and potential differences between electrodes, the [Ru (NH₃)₆]^3+/2+ solutions were added into the electrolyte solution to be used as the reference probes for calibrating the signal produced by MXene-Ag signal probes. These two kinds of probes generated their respective current signals at different voltages (signal probe I_Ag, reference probe I_Ru), and the signal calibration and precise detection of paraquat were achieved by calculating the I_Ag/I_Ru ratio. Characterization of the MXene-Ag composite nanomaterials and the self-assembly process on the surface of GCE using SEM, TEM, EDS, XPS, CV, and electrochemical impedance spectroscopy (EIS) techniques validated the feasibility of this constructed ratiometric aptasensor. Optimization of the composite ratio of nanomaterials, buffer pH, and other factors was performed through the DPV and SEM methods. Under optimal conditions, the kite-shaped MXene-Ag ratiometric electrochemical aptasensor allowed a linear concentration range of 0.01-1000 ng/mL and a low LOD of 5.154 pg/mL for paraquat. The average recovery rates in the spiked malt and mint samples were 95.20%-97.29% and 79.40%-105.00%, respectively. This newly-developed ratiometric electrochemical aptasensor provided advantages regarding simple operation, intuitive signal response, low background interference, and high sensitivity, which was suitable for highly accurate detection of trace paraquat and other pesticide residues in complex CMM matrices.

With MXenes as the high-performance nanomaterials and based on two detection strategies or principles, an electrochemical aptasensor based on a 3D nanocake-like Au-MXene/AuP structure, and a ratiometric electrochemical aptasensor based on a kite-shaped MXene-Ag nanocomposite were constructed for the sensitive detection of paraquat residues. The developed aptasensing platforms provided methodological references for the prevention and control of pesticide residues in malt and mint, as well as technical supports for quality and safety control of edible and medicinal CMMs, playing a significant role in establishing a "protective line" to safeguard public health.