Structure and Applications of Gold in Nanoporous Form (original) (raw)
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Nanomaterials
Nanoporous gold (np-Au), because of its high surface area-to-volume ratio, excellent conductivity, chemical inertness, physical stability, biocompatibility, easily tunable pores, and plasmonic properties, has attracted much interested in the field of nanotechnology. It has promising applications in the fields of catalysis, bio/chemical sensing, drug delivery, biomolecules separation and purification, fuel cell development, surface-chemistry-driven actuation, and supercapacitor design. Many chemical and electrochemical procedures are known for the preparation of np-Au. Recently, researchers are focusing on easier and controlled ways to tune the pores and ligaments size of np-Au for its use in different applications. Electrochemical methods have good control over fine-tuning pore and ligament sizes. The np-Au electrodes that are prepared using electrochemical techniques are robust and are easier to handle for their use in electrochemical biosensing. Here, we review different electrochemical strategies for the preparation, post-modification, and characterization of np-Au along with the synergistic use of both electrochemistry and np-Au for applications in biosensing.
An overview of dealloyed nanoporous gold in bioelectrochemistry
Nanoporous gold (NPG) obtained via dealloying of Au alloys has potential applications in a range of fields, and in particular in bioelectrochemistry. NPG possesses a three dimensional bicontinuous network of interconnected pores with typical pore diameters of ca. 30-40 nm, features that are useful for the immobilisation of enzymes. This review describes the common routes of fabrication and characterization of NPG, the use of NPG as a support for oxidoreductases for applications in biosensors and biofuel cells together with recent progress in the use of NPG electrodes for applications in bioelectrochemistry.
Gold nanoparticle-based electrochemical biosensors
Electrochimica Acta, 2008
The unique properties of gold nanoparticles to provide a suitable microenvironment for biomolecules immobilization retaining their biological activity, and to facilitate electron transfer between the immobilized proteins and electrode surfaces, have led to an intensive use of this nanomaterial for the construction of electrochemical biosensors with enhanced analytical performance with respect to other biosensor designs. Recent advances in this field are reviewed in this article. The advantageous operational characteristics of the biosensing devices designed making use of gold nanoparticles are highlighted with respect to non-nanostructured biosensors and some illustrative examples are commented. Electrochemical enzyme biosensors including those using hybrid materials with carbon nanotubes and polymers, sol-gel matrices, and layer-by-layer architectures are considered. Moreover, electrochemical immunosensors in which gold nanoparticles play a crucial role in the electrode transduction enhancement of the affinity reaction as well as in the efficiency of immunoreagents immobilization in a stable mode are reviewed. Similarly, recent advances in the development of DNA biosensors using gold nanoparticles to improve DNA immobilization on electrode surfaces and as suitable labels to improve detection of hybridization events are considered. Finally, other biosensors designed with gold nanoparticles oriented to electrically contact redox enzymes to electrodes by a reconstitution process and to the study of direct electron transfer between redox proteins and electrode surfaces have also been treated.
Nanoporous Gold Leaves: preparation, optical characterization and biosensing capabilities
The preparation, optical characterization and plasmonic biosensing properties of self-standing nanoporous gold leaves are presented. Respect to the bulk gold, the material shows metallic behaviour at higher wavelengths and a lower imaginary part of the dielectric constants. The plasmonic properties in the near infrared range have been investigated probing the resonance shift after a self-assembling monolayer functionalization. Due to a great increase of the active surface the presence of an organic molecule adsorbed on its surface leads to important optical responses. This demonstrates how nanoporous gold reveals benefits for better reaction efficiency and detection sensitivity and how plasmonic properties in the near-IR range can assure employment in plasmonic devices.
Gold nanomaterials as key suppliers in biological and chemical sensing, catalysis, and medicine
Biochimica et Biophysica Acta (BBA) - General Subjects, 2019
Background: Gold nanoparticles (AuNPs) with unique physicochemical properties have received a great deal of interest in the field of biological, chemical and biomedical implementations. Despite the widespread use of AuNPs in chemical and biological sensing, catalysis, imaging and diagnosis, and more recently in therapy, no comprehensive summary has been provided to explain how AuNPs could aid in developing improved sensing and catalysts systems as well as medical settings. Scope of review: The chemistry of Au-based nanosystems was followed by reviewing different applications of Au nanomaterials in biological and chemical sensing, catalysis, imaging and diagnosis by a number of approaches, and finally synergistic combination therapy of different cancers. Afterwards, the clinical impacts of AuNPs, future application of AuNPs, and opportunities and challenges of AuNPs application were also discussed. Major conclusions: AuNPs show exclusive colloidal stability and are considered as ideal candidates for colorimetric detection, catalysis, imaging, and photothermal transducers, because their physicochemical properties can be tuned by adjusting their structural dimensions achieved by the different manufacturing methods. General significance: This review provides some details about using AuNPs in sensing and catalysis applications as well as promising theranostic nanoplatforms for cancer imaging and diagnosis, and sensitive, non-invasive, and synergistic methods for cancer treatment in an almost comprehensive manner.
Characterization of Nanoporous Gold Electrodes for Bioelectrochemical Applications
Langmuir, 2012
The high surface areas of nanostructured electrodes can provide for significantly enhanced surface loadings of electroactive materials. The fabrication and characterization of nanoporous gold (np-Au) substrates as electrodes for bioelectrochemical applications is described. Robust np-Au electrodes were prepared by sputtering a goldÀsilver alloy onto a glass support and subsequent dealloying of the silver component. Alloy layers were prepared with either a uniform or nonuniform distribution of silver and, post dealloying, showed clear differences in morphology on characterization with scanning electron microscopy. Redox reactions under kinetic control, in particular measurement of the charge required to strip a gold oxide layer, provided the most accurate measurements of the total electrochemically addressable electrode surface area, A real . Values of A real up to 28 times that of the geometric electrode surface area, A geo , were obtained. For diffusion-controlled reactions, overlapping diffusion zones between adjacent nanopores established limiting semi-infinite linear diffusion fields where the maximum current density was dependent on A geo . The importance of measuring the surface area available for the immobilization was determined using the redox protein, cyt c. The area accessible to modification by a biological macromolecule, A macro , such as cyt c was reduced by up to 40% compared to A real , demonstrating that the confines of some nanopores were inaccessible to large macromolecules due to steric hindrances. Preliminary studies on the preparation of np-Au electrodes modified with osmium redox polymer hydrogels and Myrothecium verrucaria bilirubin oxidase (MvBOD) as a biocathode were performed; current densities of 500 μA cm À2 were obtained in unstirred solutions.
Development of nanoporous gold electrodes for electrochemical applications
Microelectronic Engineering, 2011
In this work we have used simple microfabrication techniques and chemical de-alloying of co-sputtered AgAu alloys to create nanoporous gold (np-Au) electrodes. The physical properties of the np-Au electrodes were investigated using scanning electron microscopy with energy dispersive X-ray analysis, X-ray photo-electron spectroscopy and profilometer. The electrochemical performance of the np-Au electrodes was measured by cyclic voltammetry and electrochemical impedance spectroscopy. We have fabricated np-Au electrodes with pore sizes between 10 nm and 60 nm, directly related to the Ag:Au ratio. The electrochemical results reveal that np-Au electrodes have much lower impedance than the conventional Au electrodes, due to the significantly higher surface area to volume ratio of np-Au. The np-Au electrodes made from Ag 66 Au 34 and Ag 60 Au 40 show more than 10-fold magnitude reduction in impedance compared to conventional Au electrodes. These results show that np-Au electrodes have a great potential for electrochemical applications.
Nanoporous Gold Electrode for Electrochemical Sensors in Biological Environment
Procedia Engineering, 2011
This work describes the use of nanoporous gold as an electrode material for biosensing applications. Nanoporous gold electrodes are fabricated, and their electrochemical performance is compared to plain gold electrodes of similar dimensions. For the detection of potassium ferricyanide, the nanoporous gold electrodes show improved sensitivity and higher currents compared to planar gold electrodes. Furthermore, the nanoporous electrodes show slower adsorption kinetics and maintain a significantly higher active electrochemical surface area in the presence of fragmented amyloid beta proteins.
Small, 2005
Metal nanoparticles (NPs) are employed as versatile labels for the optical or electrical detection of biorecognition events or biocatalytic transformations. [1] For example, the interparticle plasmon-coupling absorbance of Au nanoparticles was employed for the detection of DNA hybridization [2] or DNA cleavage. Also, the coupling of a localized plasmon of Au-nanoparticle labels with the surface plasmon wave on gold surfaces was used for the amplified surfaceplasmon-resonance (SPR) imaging of biological complexes. Amplified detection of biorecognition complexes was achieved by the dissolution of the metal-NP labels and the electrochemical stripping of the dissolved ions. Metal NPs were also employed as "weight units" for the quartzcrystal-microbalance analysis of biomaterial complexes, such as DNA hybridization. The unique catalytic properties of metal NPs to stimulate the enlargement of the NPs by the same metal or another metal were extensively used for the amplified optical or electrical sensing of biomolecular complexes. For example, the generation of conductive networks as a result of the catalytic enlargement of NP labels associated with biorecognition complexes such as DNA, or antigen-antibody complexes was extensively studied. Also, the catalytic enlargement of Au NPs was employed for the amplified microgravimetric quartz-crystal-microbalance detection of DNA or single-base mismatches in nucleic acids. The use of metal nanoparticles in biocatalytic transformations that involve enzymes is, however, an almost unexplored field. Only very recently, the optical detection of NAD(P)H cofactors by the enlargement of Au NPs with gold was reported. Also, the hydrogen-peroxide-mediated growth of Au NPs with gold was explored, and the process was applied for the optical detection of glucose in the presence of glucose oxidase. Here we wish to report on the optical or electrical detection of 1,4-dihydro-b-nicotinamide adenine dinucleotide (NADH) and the sensing of ethanol by the NAD + -dependent alcohol dehydrogenase.