Song Junyeob, Cheng Weifeng, Nie Meitong, He Xukun, Nam Wonil, Cheng Jiangtao, Zhou Wei
Department of Electrical and Computer Engineering, Virginia Tech, Blacksburg, Virginia 24061, United States.
Department of Mechanical Engineering, Virginia Tech, Blacksburg, Virginia 24061, United States.
ACS Nano. 2020 Aug 25;14(8):9521-9531. doi: 10.1021/acsnano.0c04239. Epub 2020 Jul 6.
The conventional methods of creating superhydrophobic surface-enhanced Raman spectroscopy (SERS) devices are by conformally coating a nanolayer of hydrophobic materials on micro-/nanostructured plasmonic substrates. However, the hydrophobic coating may partially block hot spots and therefore compromise Raman signals of analytes. In this paper, we report a partial Leidenfrost evaporation-assisted approach for ultrasensitive SERS detection of low-concentration analytes in water droplets on hierarchical plasmonic micro-/nanostructures, which are fabricated by integrating nanolaminated metal nanoantennas on carbon nanotube (CNT)-decorated Si micropillar arrays. In comparison with natural evaporation, partial Leidenfrost-assisted evaporation on the hierarchical surfaces can provide a levitating force to maintain the water-based analyte droplet in the Cassie-Wenzel hybrid state, , a Janus droplet. By overcoming the diffusion limit in SERS measurements, the continuous shrinking circumferential rim of the droplet, which is in the Cassie state, toward the pinned central region of the droplet, which is in the Wenzel state, results in a fast concentration of dilute analyte molecules on a significantly reduced footprint within several minutes. Here, we demonstrate that a partial Leidenfrost droplet on the hierarchical plasmonic surfaces can reduce the final deposition footprint of analytes by 3-4 orders of magnitude and enable SERS detection of nanomolar analytes (10 M) in an aqueous solution. In particular, this type of hierarchical plasmonic surface has densely packed plasmonic hot spots with SERS enhancement factors (EFs) exceeding 10. Partial Leidenfrost evaporation-assisted SERS sensing on hierarchical plasmonic micro-/nanostructures provides a fast and ultrasensitive biochemical detection strategy without the need for additional surface modifications and chemical treatments.
传统的制备超疏水表面增强拉曼光谱（SERS）器件的方法是在微/纳米结构的等离子体基底上保形涂覆一层疏水材料纳米层。然而，疏水涂层可能会部分阻挡热点，从而影响分析物的拉曼信号。在本文中，我们报道了一种部分莱顿弗罗斯特蒸发辅助方法，用于在分级等离子体微/纳米结构上对水滴中的低浓度分析物进行超灵敏SERS检测，该结构是通过将纳米层状金属纳米天线集成在碳纳米管（CNT）修饰的硅微柱阵列上制备的。与自然蒸发相比，分级表面上的部分莱顿弗罗斯特辅助蒸发可以提供一个悬浮力，以将水基分析物液滴维持在卡西-文策尔混合状态，即一种双面液滴。通过克服SERS测量中的扩散限制，处于卡西状态的液滴连续收缩的圆周边缘向处于文策尔状态的液滴固定中心区域移动，导致稀释的分析物分子在几分钟内在显著减小的面积上快速浓缩。在这里，我们证明分级等离子体表面上的部分莱顿弗罗斯特液滴可以将分析物的最终沉积面积减少3 - 4个数量级，并能够对水溶液中的纳摩尔分析物（10⁻⁹ M）进行SERS检测。特别是，这种类型的分级等离子体表面具有密集排列的等离子体热点，其SERS增强因子（EFs）超过10⁷。分级等离子体微/纳米结构上的部分莱顿弗罗斯特蒸发辅助SERS传感提供了一种快速且超灵敏的生化检测策略，无需额外的表面修饰和化学处理。
