Liao Qing, Mu Cheng, Xu Dong-Sheng, Ai Xi-Cheng, Yao Jian-Nian, Zhang Jian-Ping
Department of Chemistry, Renmin University of China, Beijing 100872, China.
Langmuir. 2009 Apr 21;25(8):4708-14. doi: 10.1021/la8036555.
We have attempted to develop surface-enhanced Raman scattering (SERS) substrates by the use of two-dimensional (2D) Au nanorod arrays and to characterize the SERS-active sites of the Au nanostructures. We prepared two different types of 2D Au nanorod arrays by means of the anodic aluminum oxide (AAO) template-assisted nanofabrication. In the template-embedded array (type I) an Au nanorod fills up the AAO pore, while in the annularly spaced array (type II) an Au nanorod keeps approximately 20 nm away from the pore wall. The strongest SERS effect was observed for both types of substrates with an Au nanorod diameter of approximately 66 nm. With respect to the bare AAO template, the NaOH-etched (unetched) type I substrate with the 66 nm Au nanorod showed 115-fold (63-fold) enhancement in Raman scattering, corresponding to a SERS enhancement factor of 10(7)-10(9). For the unetched and ordered Au naonorod arrays, the SERS-active sites localized around the rod end, whereas for the NaOH-etched and partially aggregated Au nanorods, hot spots for SERS were found in the interstices between rod tips. The type II substrate allowed the effect of rod length on the SERS response to be investigated, and the SERS response was observed to vary very little with the rod length increase (250-1000 nm), indicating that majority of the signal originates at the rod end. A comparison between the analytes all-trans-beta-carotene and pyridine suggests that, for both types of substrates, the electromagnetic enhancement is predominant over the chemical enhancement. This work demonstrates that the unetched type I substrate is highly SERS effective, for which the fabrication protocol is advantageous in its simplicity and reproducibility.
我们尝试通过使用二维（2D）金纳米棒阵列来开发表面增强拉曼散射（SERS）基底，并对金纳米结构的SERS活性位点进行表征。我们借助阳极氧化铝（AAO）模板辅助纳米制造制备了两种不同类型的二维金纳米棒阵列。在模板嵌入阵列（I型）中，金纳米棒填充AAO孔，而在环形间隔阵列（II型）中，金纳米棒与孔壁保持约20 nm的距离。对于两种类型的基底，当金纳米棒直径约为66 nm时，观察到最强的SERS效应。相对于裸露的AAO模板，具有66 nm金纳米棒的NaOH蚀刻（未蚀刻）I型基底在拉曼散射中显示出115倍（63倍）的增强，对应于10（7）-10（9）的SERS增强因子。对于未蚀刻且有序的金纳米棒阵列，SERS活性位点位于棒端周围，而对于NaOH蚀刻且部分聚集的金纳米棒，在棒尖之间的间隙中发现了SERS热点。II型基底使得能够研究棒长度对SERS响应的影响，并且观察到随着棒长度增加（250 - 1000 nm）SERS响应变化很小，这表明大部分信号源自棒端。对分析物全反式β-胡萝卜素和吡啶的比较表明，对于两种类型的基底，电磁增强比化学增强更占主导。这项工作表明未蚀刻的I型基底具有高度的SERS有效性，其制造方案在简单性和可重复性方面具有优势。
