Surface‐Structured Gold‐Nanotube Mats: Fabrication, Characterization, and Application in Surface‐Enhanced Raman Scattering

Abstract

The fabrication and characterization of nanostructured fibrous gold mats having high specific surface areas is reported. Freestanding porous films of 6-20-μm thickness and density 0.43 ± 0.02 g cm(3) are prepared using e-beam evaporation of gold on an electrospun nanoporous polymer template and subsequent removal of the template polymer in a suitable solvent. Structural characterization using electron microscopy techniques shows a nanofiber diameter in the range of 300-6000 nm, and the size of the nanochannels on the fiber surface is ≈200-350 nm. Such surface structuring is achieved through fast evaporation of organic solvent and phase separation of polymers during the electrospinning process. The wedge thickness varies from a few nanometers to a few tens of nanometers. The freestanding films possess good mechanical integrity and robustness. The calculated Young's modulus based on the slope in the elastic region is ≈114 MPa and gives an ultimate breaking strength of 0.7-0.8 MPa at a percentage elongation of 1.5-2.0%. X-ray diffraction and transmission electron microscopy measurements demonstrate the formation of polycrystalline gold nanostructures. Electrical characterization performed on these gold nanotubes reveals pure metallic behavior. Raman spectroscopic characterization of the fibrous membrane is performed using crystal violet (CV) adsorbed on it. Well-defined spectral peaks are obtainable at concentrations as low as 10(-7) M of CV, which did not give spectral signals at this low concentration on its own.

Nanoporous Gold Electrodes and Their Applications in Analytical Chemistry

“…High surface area nanostructured electrodes have received considerable attention in recent years [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. These materials are conductive, have surface areas that are typically 2-1000 times larger than a planar electrode of similar size, and consist of either oriented, well-defined or random pore morphology.…”

“…This can potentially lead to larger currents, even for diffusing species, because Faradaic current typically scales linearly with electrode area; a significantly larger electrode area can potentially yield better S/N ratios, enhanced sensitivity, and lower detection limits. High surface area noble metal electrodes have been fabricated using a number of different approaches including hard templating of latex spheres or SiO 2 spheres [7,8,19,20], chemical dealloying [9,21], electrochemical dealloying [22,23], H 2 bubble formation [24], electrodeposition in the pores of nanopore membranes [1,2] as well as from ensembles of gold nanoparticles [5,6], gold microparticles [25,26], and electrospun gold nanofibers [3,4]. Each approach has its unique advantages and disadvantages.…”

Thickness of a metallic film, in addition to its roughness, plays a significant role in SERS activity

“…Since the late 1990 s, SERS has particularly benefited from advances in the nanotechnology field, which enabled the development of highly sensitive SERS substrates6789. Currently, significant efforts by the scientific community are dedicated towards applications of SERS to biomedical problems, food industry, material characterization, environment monitoring, or detection of bio-and chemical hazards.…”

The fabrication and surface functionalization of porous metal frameworks – a review

“…These electrodes are of particular interest for chemical, water vapour or gas sensing 265,266 , as lower detection limits can be achieved 10,11,193,264 and for electro-analytical chemistry, where rates of reactions are interface dependant 267,268 . , and electro-spun metal webs 272,273 .…”