School of Electrical, Computer and Energy Engineering, ‡The Center for Photonics Innovation, and §Biodesign Center for Molecular Design & Biomimetics, Arizona State University , Tempe, Arizona 85287, United States.
ACS Nano. 2017 Aug 22;11(8):8034-8046. doi: 10.1021/acsnano.7b02687. Epub 2017 Jul 17.
Here we report an infrared plasmonic nanosensor for label-free, sensitive, specific, and quantitative identification of nanometer-sized molecules. The device design is based on vertically coupled complementary antennas (VCCAs) with densely patterned hot-spots. The elevated metallic nanobars and complementary nanoslits in the substrate strongly couple at vertical nanogaps between them, resulting in dual-mode sensing dependent on the light polarization parallel or perpendicular to the nanobars. We demonstrate experimentally that a monolayer of octadecanethiol (ODT) molecules (thickness 2.5 nm) leads to significant antenna resonance wavelength shift over 136 nm in the parallel mode, corresponding to 7.5 nm for each carbon atom in the molecular chain or 54 nm for each nanometer in analyte thickness. Additionally, all four characteristic vibrational fingerprint signals, including the weak CH modes, are clearly delineated experimentally in both sensing modes. Such a dual-mode sensing with a broad wavelength design range (2.5 to 4.5 μm) is potentially useful for multianalyte detection. Additionally, we create a mathematical algorithm to design gold nanoparticles on VCCA sensors in simulation with their morphologies statistically identical to those in experiments and systematically investigate the impact of the nanoparticle morphology on the nanosensor performance. The nanoparticles form dense hot-spots, promote molecular adsorption, enhance near-field intensity 10 to 10 times, and improve ODT refractometric and fingerprint sensitivities. Our VCCA sensor structure offers a great design flexibility, dual-mode operation, and high detection sensitivity, making it feasible for broad applications from biomarker detection to environment monitoring and energy harvesting.
在这里，我们报告了一种用于无标记、灵敏、特异和定量识别纳米级分子的红外等离子体纳米传感器。该器件设计基于具有密集图案热点的垂直耦合互补天线（VCCA）。基底中凸起的金属纳米棒和互补纳米狭缝在它们之间的垂直纳米间隙中强烈耦合，导致双模式传感，取决于光偏振平行于或垂直于纳米棒。我们通过实验证明，单层十八硫醇（ODT）分子（厚度 2.5nm）在平行模式下导致天线共振波长显著移动超过 136nm，对应于分子链中每个碳原子的 7.5nm 或分析物厚度中每个纳米的 54nm。此外，所有四个特征振动指纹信号，包括较弱的 CH 模式，在两种传感模式下都在实验中得到了清晰的描绘。这种具有宽波长设计范围（2.5 至 4.5μm）的双模式传感对于多分析物检测可能是有用的。此外，我们创建了一个数学算法，用于在模拟中设计 VCCA 传感器上的金纳米粒子，其形态在统计学上与实验中的相同，并系统地研究了纳米粒子形态对纳米传感器性能的影响。纳米粒子形成密集的热点，促进分子吸附，增强近场强度 10 到 10 倍，并提高 ODT 折光率和指纹灵敏度。我们的 VCCA 传感器结构提供了很大的设计灵活性、双模式操作和高检测灵敏度，使其适用于从生物标志物检测到环境监测和能量收集的广泛应用。
