电热诱导抓捕分析物的高灵敏度复合纳米结构表面增强拉曼散射系统

Surface-enhanced Raman scattering (SERS) effect based technique has promising potential in rapid identification of analytes with high sensitivity and fingerprint characteristics. The key issues for SERS-based analysis is to build substrates with not only high SERS-activity but also good ability to capture the target analytes, however it is difficult to simultaneously achieve these two goals using the current synthetic approaches. From the view point of high SERS activity, it has been reported that nanostructures of noble metals have electromagnetic coupling induced SERS enhancement, and semiconductor nanoscale-frameworks have chemical supporting SERS enhancement. From the view point of capturing the target analyte molecules, chemical modification and mechanical trapping have been used. In order to achieve SERS system with both high SERS-activity and ability to capture target analyte molecules, in this project we will design and build a small battery (electric heating) controlled composite SERS system with much higher SERS-activity and ability to capture the analyte molecules for rapid trace analysis of highly toxic pollutants in aqueous solution. Firstly, arrays of radial semiconductor ZnO nanotapers are electrodeposited on an electric heating constantan wire, then high density of Ag-nanoparticles are decorated onto each ZnO-nanotaper, next the above-built electric heating constantan with ZnO-nanotapers and Ag-nanoparticles is inserted into a glass capillary, and finally the analyte solution and Au-nanorods colloids as well as thermo-responsive pNIPAM microgels are mixed and injected into the remnant empty room of the capillary. The compact composite microfluidic SERS system will have much higher SERS-activity as the electromagnetic enhancement of neighboring Au-nanorods, the Au-nanorods and their nearby Ag-nanoparticles decorated on ZnO-nanotapers, and the chemical supporting enhancement of ZnO-nanotapers all have contributions to the SERS activity. Furthermore if the circuit is switched on and the system is heated up to about 32oC, the thermo-responsive pNIPAM microgels will shrink, leading to not only trapping (capturing) the analyte molecules closer to the plasmonic Au-nanorods and Ag-nanoparticles decorated on ZnO-nanotapers but also abridging the spacing of the neighboring Au-nanorods, and that of the Au-nanorods and their nearby Ag-nanoparticles decorated on ZnO-nanotapers, thus the SERS-sensitivity is much improved. As such, multiple noble metal electromagnetic enhancement, semiconductor chemical supporting enhancement and effective trapping of the analyte are realized in a simple battery-powered (electric heating) controlled compact microfluidic system, and the composite SERS system has promising potentials in SERS-based rapid trace analysis of highly toxic pollutants in aqueous solution samples.

表面增强拉曼散射(SERS)可望用于痕量物质的快速鉴别。该技术要求衬底既具有高的活性、又能抓捕待检物。SERS来源于贵金属的电磁增强和半导体的化学增强作用。本项目首先在电热丝上生长ZnO纳米锥阵列；再在纳米锥上生长高密度Ag纳米颗粒；然后将其置入毛细管内，在电热丝与毛细管间，充填温敏水凝胶、Au纳米棒和待检物的混合体，形成既能抓捕待检物、又具有高SERS活性的复合系统。其中，ZnO具有化学增强作用；Ag颗粒之间、Au棒之间以及Ag颗粒与Au棒之间，均具有电磁增强作用。尤为重要的是，当电热丝加热时，温敏水凝胶收缩，不仅使Au棒之间相互靠拢，提高SERS活性；而且也使Au棒与Ag颗粒靠近，提高SERS活性。同时，伴随水凝胶分子链的收缩，将待检物拉近Au颗粒和Ag棒，起到了抓捕待检物的作用。因此，系统不仅具有很高的SERS敏感性，而且能有效抓捕待检物。对高毒性污染物的快速痕量检测具有重要的意义。

基于表面增强拉曼散射(SERS)效应对物质的检测方法，可望用于痕量物质的快速识别。构筑SERS活性高且能够有效抓捕待检物的基底，是实现这种检测方法的关键与难点。本项目利用了贵金属的电磁增强和半导体的化学增强的作用，构筑了系列高活性的贵金属/半导体复合纳米结构SERS基底。进一步，构建了两种能够有效抓捕待检物的高灵敏SERS系统。(1)与温敏水凝胶结合，构建了电热诱导抓捕待检物的SERS系统。首先在康铜丝上生长ZnO纳米锥阵列，并在ZnO纳米锥表面生长高密度的Ag纳米颗粒，构筑了高活性的Ag纳米颗粒@ZnO纳米锥@康铜丝基底；接着将其置入毛细玻璃(或石英)管内，在毛细管内的剩余空间填充温敏水凝胶、Au纳米棒和待检物的混合体。当康铜丝通电加热系统时，温敏水凝胶受热发生相变收缩，将待检分子拉到SERS热点范围，实现了对待检物的有效抓捕。此外，水凝胶收缩还可使Au纳米棒之间相互靠拢，Au纳米棒与Ag纳米颗粒靠近，产生更多的SERS热点，进一步增强了系统的SERS活性，大幅度提高了检测灵敏度。利用该系统实现了对模拟湖水中痕量(10^-7 M)农药甲基对硫磷的快速识别。(2)与静电场结合，构建了电场力驱动抓捕待检物的高活性SERS系统。首先在透射电镜制样用的铜网表面生长Ge纳米线，并在Ge纳米线表面生长高密度Ag纳米颗粒，构筑了高活性的Ag纳米颗粒@Ge纳米线@铜网基底。在检测液体样品时，将该基底作为电极紧贴液面，另一电极置于液体下方。在两个电极间施加电压后使待检液体处于电场中，极性的待检分子在电场力的驱动下聚集在SERS基底表面，起到了有效抓捕和富集待检物的作用。利用该系统实现了对常见抗生素(6-氨基青霉烷酸和青霉素G钠)的有效捕获与快速痕量检测。这两种SERS检测系统不但具有很高的活性，还能有效抓捕待检物，在环境、食品和生物检测分析方面具有很好的应用前景。