Ag-Nanoparticle-Decorated Ge Nanocap Arrays Protruding from Porous Anodic Aluminum Oxide as Sensitive and Reproducible Surface-Enhanced Raman Scattering Substrates

Abstract

We report on the fabrication of Ag nanoparticle (Ag NP) decorated germanium (Ge) nanocap (Ag-NPs@Ge-nanocap) arrays protruding from highly ordered porous anodic aluminum oxide (AAO) template as highly sensitive and uniform surface-enhanced Raman scattering (SERS) substrates. The hybrid SERS substrates are fabricated via a combinatorial process of AAO template-assisted growth of Ge nanotubes with each tube having a hemispherical nanocap on the AAO pore bottom, wet chemical etching of the remaining aluminum and the AAO barrier layer to expose the Ge nanocaps, and sputtering Ag NPs on the Ge nanocap arrays. Because sufficient SERS "hot spots" are created from the electromagnetic coupling among the Ag NPs on the Ge nanocap and the highly ordered Ge nanocap arrays also have semiconducting chemical supporting enhancement, the hybrid SERS substrates have high SERS sensitivity and good signal reproducibility. Using the hybrid SERS substrates, Rhodamine 6G with a concentration down to 10(-11) M is identified, and one congener of highly toxic polychlorinated biphenyls with a concentration as low as 10(-6) M is also recognized, showing great potential for SERS-based rapid detection of organic pollutants in the environment.

Three‐Dimensional TiO2−Ag Nanopore Arrays for Powerful Photoinduced Enhanced Raman Spectroscopy (PIERS) and Versatile Detection of Toxic Organics

“…On the other hand, chemical enhancement accounts for a smaller enhancement, which results from the charge transfer between the molecules and the substrate. Recently, extensive investigations have demonstrated that additional Raman scattering enhancement arise from semiconductor (TiO 2 , ZnO, CdTe, Ge)‐Au (Ag) hybrid nanostructures, in which charge transfer occurs efficiently among them. The chemical mechanism is believed to contribute majorly to the observed large enhancement signals in these cases.…”

Gallium/gold composite microspheres fixed on a silicon substrate for surface enhanced Raman scattering

“…[20] However, the HSCH 2 COOoccupied the active sites on the surface of the Ag particles, thereby weakening the SERS effect. Several kinds of nanomaterials including ZnO nanorod arrays, [21] carbon nanosheets, [22] germanium nanocap arrays, [23] ZnGa 2 O 4 nanoarrays, [24] SiO 2 nanofibers or nanospheres, [25][26] silicon nanowires, [27] TiO 2 nanoarrays, [28] vanadate microspheres, [29][30] polymer spheres and arrays, [31][32] graphitic petal arrays [33] have been used as templates to fabricate such hybrid nanostructures. [21][22][23][24][25][26][27][28][29][30][31][32][33] The hybrid nanostructure has advantages over the conventional pure bimetallic noble metal nanostructures, such as higher SERS activity, batter reproducibility and lower cost when used as SERS substrate.…”

Advanced Nanoporous Anodic Alumina-Based Optical Sensors for Biomedical Applications

“…FIGURE 4 | (A)Schematic for the fabrication of Ag-NPs @ Ge-nanocap arrays protruding from AAO template(Liu et al, 2014a); (B) Schematic illustration of nanoporous AAO-based multiplex vertical flow assay (VFA) for the detection of four inflammatory biomarkers with Raman dyes encoded core-shell SERS nanotags. Characteristic Raman peaks of NBA at 593 cm −1 , 4-MBA at 1,075 cm −1 , DNTB at 1,341 cm −1 , and MB at 1,621 cm −1 , are used to encode CRP, IL-6, SAA, and PCT, respectively(Chen et al, 2020).…”