Nanoporous Gold Disks Research Articles

10×-Enhanced Heterogeneous Nanocatalysis on a Nanoporous Gold Disk Array with High-Density Hot Spots.

Certain noble metal nanostructures as heterogeneous photocatalysts have drawn significant attention in the recent past because of their unique optical properties which lead to the excitation of localized surface plasmon resonance (LSPR). The LSPR concentrates electromagnetic fields to the surfaces and its relaxation processes can convert photon energy to energetic charge carriers or heat, which can be subsequently harvested to enhance surface catalysis. Here, we report the catalytic performance of a novel plasmonic nanostructure, disk-shaped nanoporous gold (NPG) nanoparticles or simply NPG disks, using a well-tested reduction pathway of resazurin to resorufin. We show that the catalytic reaction rate of NPG disks is enhanced by 10-fold upon external light illumination because of the excitation of LSPR. The plasmon-enhanced catalytic reaction follows a linear-to-superlinear transition in the rate dependence on the input light power. In addition, the light input results in a room temperature reaction rate equivalent to that of an ambient temperature of 70 °C. Together, the results support that hot charge carriers play the dominant role in the enhancement.

Nanoporous Gold Nanocomposites as a Versatile Platform for Plasmonic Engineering and Sensing.

Plasmonic metal nanostructures have shown great potential in sensing applications. Among various materials and structures, monolithic nanoporous gold disks (NPGD) have several unique features such as three-dimensional (3D) porous network, large surface area, tunable plasmonic resonance, high-density hot-spots, and excellent architectural integrity and environmental stability. They exhibit a great potential in surface-enhanced spectroscopy, photothermal conversion, and plasmonic sensing. In this work, interactions between smaller colloidal gold nanoparticles (AuNP) and individual NPGDs are studied. Specifically, colloidal gold nanoparticles with different sizes are loaded onto NPGD substrates to form NPG hybrid nanocomposites with tunable plasmonic resonance peaks in the near-infrared spectral range. Newly formed plasmonic hot-spots due to the coupling between individual nanoparticles and NPG disk have been identified in the nanocomposites, which have been experimentally studied using extinction and surface-enhanced Raman scattering. Numerical modeling and simulations have been employed to further unravel various coupling scenarios between AuNP and NPGDs.

Photothermal therapy with gold nanoparticles as an anticancer medication

Over the past few decades, gold nanoparticles and diverse gold nano-forms have been considered for both cancer therapy and bioimaging due to their surface plasmon resonance effect and its capability of loading contrast agent. This effect enables thermal destruction of cells or organs by drastically elevating temperature when exposed to a specific energy of visible light either near infrared light. In addition, chemical modifications of the surfaces of gold nanoparticles or nano-forms are well known. Sulfur-containing functional groups of biomolecules or polymers can be easily conjugated with Aurum atoms on the surface of gold nanoparticles. There are also various nano-forms with different shapes and sizes derived from gold nanoparticles such as the nanosphere, nanorod, nanocage, nanoshell, and nanoporous gold disks. The various forms of nano-scaled gold materials have unique properties that can be used as carrier, simultaneously thermal destruction agent. Its properties of the materials are able to applied to a number of desired purposes. Regardless of the physicochemical properties of gold nanoparticles, they present several challenges, such as the instance energy penetrating depth availability aspect required for gold nanoparticles to enter organs and the cellular toxicity issues of nano-scaled gold particles in the body. The purpose of this review is to introduce the advantages using gold nanoparticles-based materials and its diverse approaches to several types of cancer therapies due to its distinct properties.

Nanoporous Gold Disks Functionalized with Stabilized G-Quadruplex Moieties for Sensing Small Molecules.

We report label-free small molecule sensing on nanoporous gold disks functionalized with stabilized Guanine-quadruplex (G4) moieties using surface-enhanced Raman spectroscopy (SERS). By utilizing the unique G4 topological structure, target molecules can be selectively captured onto nanoporous gold (NPG) disk surfaces via π-π stacking and electrostatic attractions. Together with high-density plasmonic "hot spots" of NPG disks, the captured molecules produce a remarkable SERS signal. Our strategy represents the first example of the detection of foreign molecules conjugated to nondouble helical DNA nanostructures using SERS while providing a new technique for studying the formation and evolution of G4 moieties. The molecular specificity of G4 is known to be controlled by its unit sequence. Without losing generality, we have selected d(GGT)7GG sequence for the sensing of malachite green (MG), a known carcinogen frequently abused illegally in aquaculture. The newly developed technique achieved a lowest detectable concentration at an impressive 50 pM, two orders of magnitude lower than the European Union (EU) regulatory requirement, with high specificity against potential interferents. To demonstrate the translational potential of this technology, we achieved a lowest detectable concentration of 5.0 nM, meeting the EU regulatory requirement, using a portable probe based detection system.

Simultaneous Chemical and Refractive Index Sensing in the 1–2.5 μm Near-Infrared Wavelength Range on Nanoporous Gold Disks

Near-infrared (NIR) absorption spectroscopy provides molecular and chemical information based on overtones and combination bands of the fundamental vibrational modes in the infrared wavelengths. However, the sensitivity of NIR absorption measurement is limited by the generally weak absorption and the relatively poor detector performance compared to other wavelength ranges. To overcome these barriers, we have developed a novel technique to simultaneously obtain chemical and refractive index sensing in 1-2.5 μm NIR wavelength range on nanoporous gold (NPG) disks, which feature high-density plasmonic hot-spots of localized electric field enhancement. For the first time, surface-enhanced near-infrared absorption (SENIRA) spectroscopy has been demonstrated for high sensitivity chemical detection. With a self-assembled monolayer (SAM) of octadecanethiol (ODT), an enhancement factor (EF) of up to ∼10(4) has been demonstrated for the first C-H combination band at 2400 nm using NPG disk with 600 nm diameter. Together with localized surface plasmon resonance (LSPR) extinction spectroscopy, simultaneous sensing of sample refractive index has been achieved for the first time. The performance of this technique has been evaluated using various hydrocarbon compounds and crude oil samples.

Photothermal inactivation of heat-resistant bacteria on nanoporous gold disk arrays

A rapid photothermal bacterial inactivation technique has been developed by irradiating near-infrared (NIR) light onto bacterial cells (Escherichia coli, Bacillus subtilis, Exiguobacterium sp. AT1B) deposited on surfaces coated with a dense, random array of nanoporous gold disks (NPGDs). With the use of cell viability tests and SEM imaging results, the complete inactivation of the pathogenic and heat-resistant bacterial model strains is confirmed within ~25 s of irradiation of the NPGD substrate. In addition to irradiation control experiments to prove the efficacy of the bacterial inactivation, thermographic imaging showed an immediate averaged temperature rise above 200 °C within the irradiation spot of the NPGD substrate. The light-gated photothermal effects on the NPGD substrate offers potential applications for antimicrobial and nanotherapeutic devices due to strong light absorption in the tissue optical window, i.e., the NIR wavelengths, and robust morphological structure that can withstand high instantaneous thermal shocks.

Morphological control and plasmonic tuning of nanoporous gold disks by surface modifications

We report a surface modification protocol to control nanoporous gold (NPG) disk morphology and tune its plasmonic resonance.

In situ patterning of hierarchical nanoporous gold structures by in-plane dealloying

Abstract We report a novel in situ patterning method that generates hierarchical nanoporous gold (NPG) structures such as sub-micron NPG disks and microscale NPG patterns during dealloying for the first time. Our patterning method also enables the quantification of dealloying rate by scanning electron microscopy (SEM) without the need for depth-resolving imaging modalities. As potential applications, we demonstrate that the hierarchical NPG dot arrays are effective for surface-enhanced Raman scattering (SERS) and metal-enhanced fluorescence (MEF), both are highly sensitive molecular sensing techniques.

Characterization of nanoporous gold disks for photothermal light harvesting and light-gated molecular release.

Nanoporous gold disks (NPGDs) with 400 nm diameter, 75 nm thickness, and 13 nm pores exhibit large specific surface area and effective photothermal light harvesting capability with a conversion efficiency of 56%. A potential application is demonstrated by light-gated, multi-step molecular release of the pre-adsorbed R6G fluorescent dye on arrayed NPGDs.

Surface-enhanced Raman spectroscopy with monolithic nanoporous gold disk substrates

Monolithic hierarchical nanoporous gold disks, 500 nm in diameter, 75 nm in thickness and 3.5 nm in pore radius, have been fabricated by hybrid processes. A surface-enhanced Raman scattering enhancement factor of at least 10(8) has been obtained on individual disks using benzenethiol self-assembled monolayer with 785 nm laser excitation.