Self-Assembled Plasmonic Nanoring Cavity Arrays for SERS and LSPR Biosensing
Self-Assembled Plasmonic Nanoring Cavity Arrays for SERS and LSPR Biosensing
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DOI：
10.1002/adma.201204283
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发表时间：
2013-05-21
影响因子：
29.4
通讯作者：
Oh, Sang-Hyun
中科院分区：
文献类型：
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作者：
Im, Hyungsoon;Bantz, Kyle C.;Oh, Sang-Hyun
近年来，表面增强拉曼散射（Sers）作为表征表面分子结构和取向的方法以及传感器中的分析信号转导机制的应用越来越多。[1-10] Sers的广泛应用的一个主要挑战在于材料设计方面，即，理想地使用廉价的高通量方法，在宽区域上产生具有可再现的和大的拉曼增强的贵金属基底。在用于生产Sers基底的各种纳米纤维技术中，纳米球光刻（NSL）-也称为胶体光刻-已被许多研究人员采用，因为它是一种用于生产大面积有序纳米结构的简便，廉价和可重复的制造方法。[11-17]特别是，纳米球上的Ag膜（AgFON）基底已广泛用于复杂介质中的许多Sers生物传感应用。[6，18，19]坚固的AgFON结构简单地通过在自组装纳米球上沉积光学厚（通常至少是纳米球直径的一半）Ag膜来制造。这些衬底呈现多个尺度上的粗糙度，包括由纳米球光栅产生的粗糙度以及金属沉积产生的粗糙度，与随机粗糙化的金属表面相比，产生具有改进的控制和可调谐性的等离子体特征。然而，先前的研究已经表明，只有少数占主导地位的Sers“热点”对AgFON基底上的整体Sers信号有贡献，[20]因此需要控制这些热点的位置和密度。除了依赖于金属纳米颗粒或粗糙表面之外，还从位于薄金属间隙和空腔内的分子中观察到大的Sers增强。基于纳米薄金属间隙将产生非常大的电磁场的理论预测，[21-24]许多小组已经探索了通过光刻图案化、纳米颗粒聚集、或薄膜处理。[17 23，25-27]虽然已经广泛研究了独立间隙中或粗糙化纳米球光栅上Sers，但是非常期望构建能够将AgFON衬底的廉价、大面积制造与纳米金属间隙中的大场增强联合收割机组合的集成结构。在这项工作中，我们报告了一种新的方法模板，高通量制造周期性阵列的环形纳米腔与10 nm的间隙大小相结合的NSL与简单的批量处理步骤，即原子层沉积（ALD）和离子铣削。在所得的混合纳米结构中，入射光共振激发沿着金属纳米球曲率形成的环形10 nm间隙腔。与传统的AgFON衬底相比，纳米环腔的加入提高了Sers增强因子（EF）至少一个数量级，并且可以通过改变原始模板步骤中使用的纳米球的尺寸来容易地调谐共振波长。纳米环腔基板的光学特性后，我们采用它们检测腺嘌呤，一种常见的检测分子在固有的DNA传感实验，并证明提高检测限，以及使用相同的基板并发LSPR生物传感。
In recent years, surface-enhanced Raman scattering (SERS) has found increased use both as a method to characterize surface molecular structure and orientation and as an analytical signal transduction mechanism in sensors.[1–10] One major challenge in widespread use of SERS lies in the materials design aspect, namely, creating noble metal substrates with reproducible and large Raman enhancements over wide areas, ideally using inexpensive, high-throughput methods. Among the various nanofabrication techniques used to produce SERS substrates, nanosphere lithography (NSL)–also called colloidal lithography–has been adopted by many researchers, because it is a facile, inexpensive, and reproducible fabrication method for the production of large-area ordered nanostructures.[11–17] In particular, Ag film over nanosphere (AgFON) substrates have been widely used in many SERS biosensing applications in complex media.[6, 18, 19] The robust AgFON structures are simply made by depositing optically thick (usually at least half the nanosphere diameter) Ag films over self-assembled nanospheres. These substrates present roughness on multiple scales, including that generated by the nanosphere grating as well as the metal deposition-generated roughness, creating plasmonic features with improved control and tunability compared to randomly roughened metal surfaces. Nevertheless, previous studies have shown that only a few dominant SERS ‘hotspots’ contribute to the overall SERS signal on the AgFON substrate,[20] and thus it is desirable to control the position and density of those hotspots. Alternately to relying on metallic nanoparticles or rough surfaces, large SERS enhancements have also been observed from molecules positioned inside thin metallic gaps and cavities.Based on theoretical predictions that nanometer-thin metallic gaps will generate very large electromagnetic fields,[21–24] many groups have explored the controlled creation of nanometric gaps for SERS via lithographic patterning, aggregation of nanoparticles, or thin-film processing.[17, 23, 25–27] While SERS in standalone gaps or on roughened nanosphere gratings have been widely investigated, it is highly desirable to build integrated structures that can combine inexpensive, large-area fabrication of AgFON substrates with large field enhancements in ultrathin metallic gaps. In this work, we report a novel method for templated, high-throughput fabrication of a periodic array of ringshaped nanocavities with 10 nm gap size by combining NSL with straightforward batch processing steps, namely, atomic layer deposition (ALD) and ion milling. In the resulting hybrid nanostructure, incident light resonantly excites ring-shaped 10-nm-gap cavities formed alongside the curvature of metallic nanospheres. Compared to conventional AgFON substrates, the addition of nanoring cavities improves the SERS enhancement factor (EF) by at least an order of magnitude, and the resonance wavelength can be readily tuned by changing the size of nanospheres used in the original templating step. After optical characterization of the nanoring cavity substrates, we employ them for the detection of adenine, a commonly detected molecule in intrinsic DNA sensing experiments, and demonstrate improved detection limits as well as the use of the same substrate for concurrent LSPR biosensing.