Plasmonic nanostructures exhibit intriguing optical properties due to spectrally selective plasmon resonance and thus have broad applications, including biochemical sensing and photoelectric detections. However, excited plasmons are often strongly influenced by the substrates supporting the metallic nanostructures, which not only weakens the intrinsic plasmon coupling effect, but also results in a great reduction of optical near‐field enhancement. Here, a plasmonic nanostructure combining collapsible Au‐nanofingers with selective‐etching that enables Au to be suspended is demonstrated, thus avoiding the undesirable influence of the substrates on the local near‐field distribution and forming symmetric electromagnetic‐field enhancements at both the top and bottom surfaces. The polymer support of the Au‐nanofingers is selectively etched by oxygen plasma, while the Au‐cap retains its original size. After an ultrathin dielectric coating is applied on the Au‐nanofingers, suspended Au‐caps with extremely small dielectric gaps are formed via the collapse of neighboring Au‐nanofingers by exposing them to ethanol. These nanostructures can provide a surface‐enhanced Raman scattering (SERS) enhancement of up to ≈10⁹, which is nearly twice that in the nonsuspended system. As a highly active SERS substrate, the label‐free detection of low‐concentration harmful plastic phthalates in a child's urine without any pretreatment is successfully demonstrated, which suggests that this method is suitable for medical prediagnosis.

中文翻译：

---

儿童尿液中悬浮的金属/介电/金属纳米结构和塑料邻苯二甲酸盐检测增强了双电磁场

等离子体纳米结构由于光谱选择性等离子体激元共振而表现出令人感兴趣的光学性质，因此具有广泛的应用，包括生化传感和光电检测。但是，激发的等离子体激元通常会受到支撑金属纳米结构的基底的强烈影响，这不仅削弱了固有的等离子体激元耦合效应，而且导致光学近场增强的极大降低。在这里，展示了结合可折叠金纳米指和选择性蚀刻的等离子纳米结构，该悬浮使Au能够悬浮，从而避免了基板对局部近场分布的不良影响，并在顶部和顶部形成对称的电磁场增强底面。金纳米指的聚合物载体被氧等离子体选择性蚀刻，而金帽保留其原始尺寸。将超薄介电涂层涂在金纳米指上后，通过将相邻的金纳米指暴露于乙醇中而坍塌，形成了具有极小的介电间隙的悬浮金盖。这些纳米结构可提供高达≈10的表面增强拉曼散射（SERS）增强⁹，几乎是非暂停系统的两倍。作为一种高活性SERS底物，已成功证明了无需任何预处理即可对儿童尿液中的低浓度有害塑料邻苯二甲酸酯进行无标签检测，这表明该方法适用于医学预诊断。