Chang Yu-Chung, Huang Bo-Han, Lin Tsung-Hsien
Department of Electrical Engineering, National Changhua University of Education, Changhua 500, Taiwan.
Nanomaterials (Basel). 2020 Apr 17;10(4):776. doi: 10.3390/nano10040776.
Surface-enhanced Raman scattering (SERS) spectroscopy is a sensitive sensing technique. It is desirable to have an easy method to produce SERS-active substrate with reproducible and robust signals. We propose a simple method to fabricate SERS-active substrates with high structural homogeneity and signal reproducibility using electron beam (E-beam) lithography without the problematic photoresist (PR) lift-off process. The substrate was fabricated by using E-beam to define nanograting patterns on the photoresist and subsequently coat a layer of gold thin film on top of it. Efficient and stable SERS signals were observed on the substrates. In order to investigate the enhancement mechanism, we compared the signals from this substrate with those with photoresist lifted-off, which are essentially discontinuous gold stripes. While both structures showed significant grating-period-dependent fluorescence enhancement, no SERS signal was observed on the photoresist lifted-off gratings. Only transverse magnetic (TM)-polarized excitation exhibited strong enhancement, which revealed its plasmonic attribution. The fluorescence enhancement showed distinct periodic dependence for the two structures, which is due to the different enhancement mechanism. We demonstrate using this substrate for specific protein binding detection. Similar periodicity dependence was observed. Detailed theoretical and experimental studies were performed to investigate the observed phenomena. We conclude that the excitation of surface plasmon polaritons on the continuous gold thin film is essential for the stable and efficient SERS effects.
表面增强拉曼散射（SERS）光谱是一种灵敏的传感技术。期望有一种简便方法来制备具有可重现且稳定信号的SERS活性基底。我们提出一种简单方法，利用电子束光刻技术制备具有高结构均匀性和信号可重复性的SERS活性基底，且无需有问题的光刻胶（PR）剥离工艺。通过使用电子束在光刻胶上定义纳米光栅图案，随后在其顶部涂覆一层金薄膜来制备基底。在这些基底上观察到了高效且稳定的SERS信号。为了研究增强机制，我们将该基底的信号与光刻胶已剥离的基底（本质上是不连续的金条纹）的信号进行了比较。虽然两种结构都显示出显著的与光栅周期相关的荧光增强，但在光刻胶已剥离的光栅上未观察到SERS信号。只有横向磁（TM）极化激发表现出强烈增强，这揭示了其等离子体特性。两种结构的荧光增强显示出不同的周期依赖性，这是由于增强机制不同所致。我们展示了使用该基底进行特定蛋白质结合检测。观察到了类似的周期依赖性。进行了详细的理论和实验研究以探究所观察到的现象。我们得出结论，连续金薄膜上表面等离激元极化子的激发对于稳定且高效的SERS效应至关重要。
