基于超疏水高黏附结构的痕量农药分子现场检测SERS基底研究

多种农药，包括孔雀石绿（MG）作为禁用兽药，存在食用致癌的风险。由于MG低廉的价格和极好的药效，在渔业养殖中一直被不法商贩非法使用，使得鱼类生鲜中时有MG残留检出。针对MG分子痕量残留的检测，目前一般是抽取少量养殖水样，再利用高效液相色谱柱、液相色谱-光谱等方法来评估其是否超标。这类传统的检测方法一般需要依赖价格昂贵的大型设备，且检测过程操作繁琐复杂，单次检测耗时长、价格高，因而与农贸市场中商品流通量大、速度快、价格需亲民低廉等特点和要求不相符合。近年来，表面增强拉曼散射（SERS）检测技术以及便携式拉曼光谱仪的出现，有望实现对痕量农药分子的现场快速检测，进而很好地解决这一问题。SERS检测技术利用金属纳米结构的表面等离激元效应感应位于其结构表面附近的分子，得到分子种类和浓度信息。为了降低可检测的浓度极限，一般会在SERS基底上利用咖啡环效应或其他手段将待测分子蒸发富集，以获得足够高的信号强度。针对亲水基底，液滴与基底相接触后，会在基底表面摊开，使其分布面积扩大，导致其咖啡环周长变长，分子分布浓度随之降低。而当采用疏水基底富集时，由于常规的疏水基底表面黏附性小，液滴在其表面处于随处滚动无法抓取的状态，极大增加了操作的难度。以MG分子痕量残留的检测为例，由于农贸市场人员众多、无专业实验平台，磕碰撞击时有发生，在此环境下采用疏水SERS基底对农药分子进行检测显然是不可取的。该研究提出一种基于超疏水高黏附纳米森林结构的SERS基底用于痕量MG分子的快速现场检测。相比于超疏水SERS基底，所提出的超疏水高黏附基底利用其高黏附性可牢固抓取待测液滴，解决了以往超疏水基底在实际现场检测中存在液滴滚动无法操作的问题。此外，与亲水基底相比，超疏水高黏附基底由于接触角大，可将咖啡环面积缩小5.73倍，继而使分子的富集浓度提高5.73倍，最终使检测极限浓度降低了至少两个数量级。研究所提出的超疏水高黏附SERS基底有望在痕量农药分子快速现场检测中得到应用。

A SERS Substrate for On-Site Detection of Trace Pesticide Molecules Based on Parahydrophobic Nanostructures

As banned veterinary drugs, many pesticides, including malachite green (MG), pose a risk of carcinogenesis. Due to its low price and strong antiseptic qualities, MG has been used illegally in fisheries. As a result, MG residues are usually detected in fresh fish. To evaluate MG residues, currently, approaches include high-performance liquid chromatography (HPLC), liquid chromatography-mass spectrometry (LC-MS) and other methods are used, and the detections are performed using a small volume of aquaculture water. However, such traditional detections rely on large and expensive equipment, which are cumbersome, and their processes are complicated, time-consuming and expensive. Consequently, these traditional methods cannot meet the needs of on-site detection of pesticides in markets, which are with features of large circulation, fast speed and low price. In recent years, with the emergence of surface-enhanced Raman scattering (SERS) and portable Raman spectrometers, a rapid on-site detection method for trace pesticide molecules becomes possible. Herein, the SERS technology uses surface plasmon of metallic nanostructures to sense molecules located nearby, thus obtaining information of molecular species and concentrations. In order to achieve an extremely low limit of detection(LOD), generally, the coffee ring effect or other means are used on SERS substrates to enrich molecules into a certain region sufficiently. When a droplet contact the substrate for a hydrophilic substrate, the liquid spreads on the surface, leading to a long perimeter of its coffee ring and a decrease in molecular distribution concentration. While when a superhydrophobic substrate is used for molecule enrichment, due to its small surface adhesion, droplets are unable to be fixed and would roll on the surface, thus shall significantly increase the difficulty of operation. Taking detection of trace residues of MG molecule as an example, due to the noisy environment caused by people in the market, collisions occur from time to time, and due to the lack of professional experiment platforms in the market, it is not desirable to use a superhydrophobic SERS substrate to detect pesticide molecules under this condition. A SERS substrate based on parahydrophobic nanostructures is proposed for rapid on-site trace detection of MG molecules in this work. Compared with previous superhydrophobic substrates, parahydrophobic substrates presented herein is able to firmly grasp droplets to be measured, which perfectly solves the problem that in on-site detections, droplets roll on conventional supehydrophobic substrates. In addition, compared with the hydrophilic substrates, due to a large contact angle of the parahydrophobic substrate, the area of the coffee ring can be reduced by 5.73 times, thus enriching concentration of the molecules can be largely increased, which as a result, can ultimately reduce LOD by at least two orders of magnitude. In short, the parahydrophobic SERS substrate proposed in this work is expected to be applied in rapid on-site detections of trace pesticide molecules.