Infrared‐Responsive Colloidal Silver Nanorods for Surface‐Enhanced Infrared Absorption

Abstract

Surface‐enhanced infrared absorption (SEIRA) spectroscopy, the enhancement of molecular vibrational signals using resonant metal nanostructures, has recently attracted much attention owing to its potential use in molecular detection in chemistry, biology, and medicine. This study reports on the growth of high‐aspect‐ratio metal nanocrystals and their application for SEIRA. Highly uniform Ag nanorods are synthesized through Au nanobipyramid‐directed Ag overgrowth, and Au nanotubes are further prepared through the galvanic replacement reaction from the Ag nanorods. Both Ag nanorods and Au nanotubes possess narrow distributions in diameter and length and exhibit highly tunable plasmon wavelengths in the near and mid‐infrared regions. The Ag nanorods are employed as plasmonic nanoantennas to enhance the molecular vibration signals of cetyltrimethylammonium bromide molecules that are embedded in a mesostructured silica layer coated on the Ag nanorods. The dimension‐dependent SEIRA performances are carefully investigated both experimentally and numerically. The experimental and simulated SEIRA enhancement factors are in good agreement and both determined to be of the order ≈103. The results point out a promising route to the utilization of chemically synthesized, colloidal metal nanostructures as SEIRA platforms. The synthesis method also provides high‐quality metal nanostructures for exploring various plasmon‐based optical and sensing applications in the infrared region.

Shielded Silver Nanorods for Bioapplications

“… 9 , 46 Our results and discrepancies with other reports can be explained by taking into account the similar dielectric functions of Au and Ag in the NIR range, resulting in an equally similar local field and SERS enhancements for both metals, as has been shown by numerical simulations. 9 , 47 Since we used Au and Ag NRs not only with similar size and LSPR wavelength but also with comparable quality in size uniformity and LSPR line width, potential effects derived from these factors can be excluded, which may not have been strictly observed in previous comparisons. Nevertheless, it remains challenging to ensure the same coverage degree with thiolated RaR molecules in our comparison, since the Ag–S bonding strength is generally weaker than that of Au–S bonding.…”

Surface-enhanced infrared absorption

“…这些 需借助电子束、激光、光束或电极的方法都可以归类 为物理方法. 此外, 近年来湿化学合成法(Wet-Chemistry Synthesis Methods)逐渐兴起 [25] . [14,25] .…”

“…图 5 (网络版彩图)可实现表面增强红外吸收的湿化学法合成的纳米晶体. (a) 金纳米壳层(SiO 2 @Au)颗粒的SEM图 [15] ; (b) 金 纳米壳层的孤立颗粒(虚线)和密堆积排列(实线)的红外消光光谱, 插图是金纳米壳层颗粒的核壳结构的示意图 [15] ; (c) 氟和锡 共掺杂的氧化铟(F,Sn:In 2 O 3 )纳米立方体的SEM图 [50] ; (d) 表面修饰了油酸分子的氟和锡共掺杂氧化铟纳米立方体的红外消光 光谱, 插图是耦合区域的放大 [50] ; (e) 银纳米线的SEM图 [25] ; (f) 表面修饰了CTAB分子的银纳米线的红外透射光谱, 插图是耦合 区域的放大 [25] Figure 5 (Color online) Nanocrystals synthesized by wet-chemistry methods for SEIRA. (a) SEM image of an array of SiO 2 @Au nanoshells [15]; (b) infrared extinction spectra of the array (solid line) and that of an isolated nanoshell (dashed line).…”

“…The inset is the schematic of the core@shell nanostructure [15]; (c) SEM image of F-and Sn-codoped In 2 O 3 nanocubes [50]; (d) infrared extinction spectra of oleate-decorated F-and Sn-codoped In 2 O 3 nanocubes. The inset is the zoom-in on the coupling region [50]; (e) SEM image of Ag nanowires [25]; (f) infrared transmittance spectra of CTAB-capped Ag nanowires. The inset is the zoom-in on the coupling region [25].…”

“…The inset is the zoom-in on the coupling region [50]; (e) SEM image of Ag nanowires [25]; (f) infrared transmittance spectra of CTAB-capped Ag nanowires. The inset is the zoom-in on the coupling region [25]. [16] .…”