Monolithic NPG nanoparticles with large surface area, tunable plasmonics, and high-density internal hot-spots

Abstract

Plasmonic metal nanostructures have shown great potential in sensing, photovoltaics, imaging and biomedicine, principally due to the enhancement of local electric field by light-excited surface plasmons, i.e., collective oscillation of conduction band electrons. Thin films of nanoporous gold have received a great deal of interest due to the unique 3-dimensional bicontinuous nanostructures with high specific surface area. However, in the form of semi-infinite thin films, nanoporous gold exhibits weak plasmonic extinction and little tunability in the plasmon resonance, because the pore size is much smaller than the wavelength of light. Here we show that by making nanoporous gold in the form of disks of sub-wavelength diameter and sub-100 nm thickness, these limitations can be overcome. Nanoporous gold disks not only possess large specific surface area but also high-density, internal plasmonic "hot-spots" with impressive electric field enhancement, which greatly promotes plasmon-matter interactions as evidenced by spectral shifts in the surface plasmon resonance. In addition, the plasmonic resonance of nanoporous gold disks can be easily tuned from 900 to 1850 nm by changing the disk diameter from 300 to 700 nm. Furthermore, nanoporous gold disks can be fabricated as either bound on a surface or as non-aggregating colloidal suspension with high stability.

Plasmonic nanosponges

“…By combining with other synthesis or nanofabrication methods including polyol process, templated process, solid-state dewetting, and different nanolithography techniques, Au-Ag alloys can be formed in many specific forms, and after dealloying, the nanoporous gold can be obtained in the corresponding forms, including the forms of nanotubes [38], nanowires [39], nanoparticles [17,40,41], hollowed nanospheres [42], nanobowls [43], nanodisks [44,45], ordered array of nanoparticles and nanodisks [46][47][48].…”

Noninvasive glucose sensing by transcutaneous Raman spectroscopy

“…[4][5][6][7][8][9][10][11][12][13] The intensity of a Raman signal bears a linear relationship to the analyte concentrations, therefore, Raman spectroscopy can be used as a quantitative tool in concentration measurements as well. 1,4,5,[14][15][16][17] An ultimate goal in this field is to develop Raman spectroscopy-based techniques for biomedical applications through instrumentation, [18][19][20][21][22] plasmonic substrates, [23][24][25][26][27] devices, 28,29 assays, 30,31 and techniques. 32,33 Raman spectroscopic measurements, like other optical techniques, pose minimal danger from exposure to ionizing radiation due to the low-energy optical radiation exposure.…”

3D Plasmonic Nanoarchitecture As an Emerging Biosensing Platform

“…Recently, nanocomposites formed by colloidal AuNP on NPG disks have been shown to form additional hot-spots at the binding sites [19]. NPG arrays have been demonstrated in various plasmonic sensing mechanisms such as refractive index sensing via extinction spectroscopy, as well as spectroscopic fingerprinting by enhanced fluorescence, NIR absorption, and Raman spectroscopy [8][9][10][11]14]. A number of label-free biosensing applications have been developed in the past 4 years for nucleic acids, proteins, enzymes, metabolites, neurotransmitters, polycyclic aromatic hydrocarbons, carcinogenic environmental and food contaminants, and etc [11,[19][20][21][22][23].…”

“…Nanoporous gold (NPG) nanoparticles and arrays can be formed by a hybrid fabrication process combining top-down lithography and bottom-up atomic dealloying [14,15]. The lithography step patterns gold-silver film into nanoparticles of well-defined shape and size, while the dealloying step produces highly porous nanostructures throughout each individual nanoparticles.…”