Huang Po-Jung, Marks Haley L, Coté Gerard L, Kameoka Jun
Department of Materials Science and Engineering, College Station, Texas 77840, USA.
Department of Biomedical Engineering, College Station, Texas 77840, USA.
Biomicrofluidics. 2017 Jun 7;11(3):034116. doi: 10.1063/1.4985071. eCollection 2017 May.
A microfluidic device utilizing magnetically activated nickel (Ni) micropads has been developed for controlled localization of plasmonic core-shell magnetic nanoparticles, specifically for surface enhanced Raman spectroscopy (SERS) applications. Magnetic microfluidics allows for automated washing steps, provides a means for easy reagent packaging, allows for chip reusability, and can even be used to facilitate on-chip mixing and filtration towards full automation of biological sample processing and analysis. Milliliter volumes of gold-coated 175-nm silica encapsulated iron oxide nanoparticles were pumped into a microchannel and allowed to magnetically concentrate down into 7.5 nl volumes over nano-thick lithographically defined Ni micropads. This controlled aggregation of core-shell magnetic nanoparticles by an externally applied magnetic field not only enhances the SERS detection limit within the newly defined nanowells but also generates a more uniform (∼92%) distribution of the SERS signal when compared to random mechanical aggregation. The microfluidic flow rate and the direction and strength of the magnetic field determined the overall capture efficiency of the magneto-fluidic nanoparticle trapping platform. It was found that a 5 l/min flow rate using an attractive magnetic field provided by 1 × 2 cm neodymium permanent magnets could capture over 90% of the magnetic core-shell nanoparticles across five Ni micropads. It was also observed that the intensity of the SERS signal for this setup was 10-fold higher than any other flow rate and magnetic field configurations tested. The magnetic concentration of the ferric core-shell nanoparticles causes the SERS signal to reach the steady state within 30 min can be reversed by simply removing the chip from the magnet housing and sonicating the retained particles from the outlet channel. Additionally, each magneto-fluidic can be reused without noticeable damage to the micropads up to three times.
一种利用磁激活镍（Ni）微垫的微流控装置已被开发出来，用于等离激元核壳磁性纳米颗粒的可控定位，特别是用于表面增强拉曼光谱（SERS）应用。磁性微流控技术允许进行自动洗涤步骤，提供了一种简便的试剂封装方式，允许芯片重复使用，甚至可用于促进芯片上的混合和过滤，以实现生物样品处理和分析的完全自动化。将数毫升体积的金包覆的175纳米二氧化硅包裹的氧化铁纳米颗粒泵入微通道，并通过磁场使其在纳米级厚的光刻定义的镍微垫上磁浓缩至7.5纳升体积。通过外部施加磁场对核壳磁性纳米颗粒进行这种可控聚集，不仅提高了新定义的纳米阱内的SERS检测限，而且与随机机械聚集相比，还产生了更均匀（约92%）的SERS信号分布。微流控流速以及磁场的方向和强度决定了磁流体纳米颗粒捕获平台的整体捕获效率。研究发现，使用由1×2厘米钕永磁体提供吸引力磁场、流速为5微升/分钟时，可在五个镍微垫上捕获超过90%的磁性核壳纳米颗粒。还观察到，这种设置下的SERS信号强度比测试的任何其他流速和磁场配置高10倍。铁核壳纳米颗粒的磁浓缩使SERS信号在30分钟内达到稳态，只需将芯片从磁体外壳中取出并对出口通道中保留的颗粒进行超声处理，即可使信号反转。此外，每个磁流体装置可重复使用三次，且对微垫无明显损坏。
