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Sondhi, P.;  Lingden, D.;  Bhattarai, J.K.;  Demchenko, A.V.;  Stine, K.J. Nanoporous Gold in Therapy, Drug Delivery, and Diagnostics. Encyclopedia. Available online: https://encyclopedia.pub/entry/40257 (accessed on 31 August 2024).
Sondhi P,  Lingden D,  Bhattarai JK,  Demchenko AV,  Stine KJ. Nanoporous Gold in Therapy, Drug Delivery, and Diagnostics. Encyclopedia. Available at: https://encyclopedia.pub/entry/40257. Accessed August 31, 2024.
Sondhi, Palak, Dhanbir Lingden, Jay K. Bhattarai, Alexei V. Demchenko, Keith J. Stine. "Nanoporous Gold in Therapy, Drug Delivery, and Diagnostics" Encyclopedia, https://encyclopedia.pub/entry/40257 (accessed August 31, 2024).
Sondhi, P.,  Lingden, D.,  Bhattarai, J.K.,  Demchenko, A.V., & Stine, K.J. (2023, January 17). Nanoporous Gold in Therapy, Drug Delivery, and Diagnostics. In Encyclopedia. https://encyclopedia.pub/entry/40257
Sondhi, Palak, et al. "Nanoporous Gold in Therapy, Drug Delivery, and Diagnostics." Encyclopedia. Web. 17 January, 2023.
Nanoporous Gold in Therapy, Drug Delivery, and Diagnostics
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This entry is adapted from the peer-reviewed paper 10.3390/met13010078

Nanoporous gold (np-Au) has promising applications in therapeutic delivery. The promises arise from its high surface area-to-volume ratio, ease of tuning shape and size, ability to be modified by organic molecules including drugs, and biocompatibility. For the demands of a real patient, light-triggered on-demand pulsatile release from a reservoir containing highly enriched medicines has been demonstrated to be provided by versatile drug delivery devices using nanoporous membranes made of gold nanorods and dendrimers.

nanotechnology emerging technologies parenteral delivery

1. Introduction

Nanoporous gold (np-Au) obtained by dealloying is a widely researched material and has found use in a diverse range of research areas including catalysis, energy storage, biomedical, and bioanalytical applications including biosensors [1], electrodes for use as neural probes [2], and coatings for applications in drug release [3] as shown in Figure 1. The tremendous interest in the usage of np-Au arose due to its many desirable properties including high effective surface area, interconnected network of nanoscale ligaments, tunable pore volume, good electrical conductivity, and ease of surface modification [4][5]. The rapidly advancing area of np-Au research is a part of the broader effort to fabricate various nanostructured forms of gold. Over the past few decades, there has been a major focus on the controlled preparation of gold nanostructures in numerous geometrical forms [6][7].
Figure 1: Application of np-Au
Nanostructured materials have shown substantial promise as multifunctional coatings from orthopedic implants to neural electrodes. The nanostructured architecture produces a large effective surface area that can improve the quality of the signal from neural electrodes by reducing the impedance at the cell-electrode interface. Nanoscale topographical features determine cell growth and differentiation for different cell types [8][9]. Astrogliosis was reduced when using nanoporous gold as a coating on neural electrodes. Np-Au suppressed the formation of scar tissue and was found to selectively decrease astrocyte coverage while maintaining high neuronal coverage in an in vitro neuron-glia co-culture model. The np-Au surface topographic features are the driving force majorly responsible for a noncytotoxic decrease in the ability of astrocytes to cover the surface of np-Au [10].
The surface nanotopography of np-Au is important for its use as an effective substrate for use in biosensors, as an interface with cells, and as a material for drug delivery. One such area of use of np-Au has been as a cell culture platform for microglia cells. Interactions between neurons, astrocytes, and microglial cells play a critical role in understanding the propagation of neuroinflammatory conditions in the central nervous system. The culture consisting of neurons, astrocytes, and microglia can be a useful tool to study neuroinflammatory pathways [11]. In a recent study, gold substrates with different porosities were evaluated for their ability to support microglial growth, and as a platform to study the morphological changes in microglial cells upon lipopolysaccharide stimulation. Microglial proliferation was hindered when np-Au monolith was used [12]. Morphologically different gold nanostructures support localized surface plasmon resonance [13].
Porous structures have a large surface-to-volume ratio and have been used for drug delivery and release applications in the pharmaceutical industry [14]. There has been a surge of interest in the fabrication of nanostructured materials and their use in cancer therapeutics, as vascular stents, and in neurological applications. The use of np-Au as a drug delivery platform has attracted growing attention recently due to the scope of tuning the pore/ligament sizes and morphology for controlling release kinetics [15]. Biomedical device coatings made up of np-Au have shown significant promise in delivery of therapeutics wherein the porous structure of np-Au has enhanced the loading capacity of small-molecule drugs, proteins with a sustained release kinetics in physiological conditions. The release kinetics have been recently monitored on a np-Au microfluidic platform with a solution flowing at a fixed rate, to attempt to model the situation of a drug eluting stent [16]. Monolithic np-Au rod has been explored for being used as an implant for delivering doxorubicin, an anticancer drug. The encapsulation efficiency was greater than 98% without any chemical modification on the electrode or the drug. The fabricated implant has shown a sustained release of the drug for 26 days in different pH conditions [17]. Drug loading and controlled release systems have been recognized as one of the main approaches to enhance drug delivery. For this application, np-Au has been widely studied as a drug delivery agent due to its excellent corrosion resistance and providing a large surface for the formation of stable self-assembled monolayers (SAMs). In an effort to generate an implantable and biocompatible drug delivery system, the usage of thiolated β-cyclodextrin (HS-β-CD) modified np-Au monolith for pH-sensitive delivery of doxorubicin (DOX) was reported. The drug release from the HS-β-CD modified np-Au was found to be pH dependent. In this investigation, encapsulated DOX with the HS-β-CD was evaluated for its release kinetics for more than 48 h in phosphate-buffered solution (PBS, pH 7.4), acetate buffer solution (pH 5.5), and bovine calf serum (pH 7.4). The release rate clearly increased when the pH was changed from physiological pH (7.4) to more acidic (pH 5.5). This resulted from the DOX’s release from inclusion complexes and an increase in solubility brought on by the protonation of the DOX’s amino group. The use of this kind of NPG implant should take into account the lower pH values, which are generally reported to be 6.84 but lower for particular tumor forms, in the extracellular tumor environment [18].
Modern medicine is taking advantage of the conventional np-Au by functionalizing its surface with drugs and targeting molecules and modifying its shape, size, and charge for selective targeting [19]. The wearable on-demand painless drug delivery system to improve therapeutic efficacy and to better manage chronic diseases like diabetes has been realized by the innovative nano-heater integrated transdermal patch that is filled with insulin. For electrothermal transdermal therapy, the patch’s design is based on the incorporation of nano-engineered heating elements on polyimide substrates. According to the study’s findings, post-coating with reduced graphene oxide allows for the encapsulation of drugs like insulin and allows for the quick response of an electrothermal skin patch made of a pattern of gold nanoholes on polyimide [20]. For the demands of a real patient, light-triggered on-demand pulsatile release from a reservoir containing highly enriched medicines has been demonstrated to be provided by versatile drug delivery devices using nanoporous membranes made of gold nanorods and dendrimers. In both static and fluidic systems, the rate of drug release was seen to be closely proportional to the rise in temperature and the amount of energy provided from a near-IR laser [21]. The long-term effectiveness of implantable drug-delivery devices depends on sustained release of the medicine and replenishment of the drug depot. An investigation was done to show how the ionic environment affected the in-plane movement of fluorescein ions through np-Au thin films (sputtering was used to deposit an Au0.36Ag0.64 (atomic%) alloy over an 80 nm thick Au seed layer and a 160 nm thick Cr adhesion layer. After dealloying the alloy-coated coverslips in nitric acid (70%) at 55 °C for 15 min [22], the np-Au film was created of various morphologies and thicknesses. The presence of halides facilitated molecular movement by lowering non-specific fluorescein (a small-molecule drug surrogate) adsorption onto the pore walls [23].

2. Nanoporous Gold-Based Platforms as Future Drug Reservoirs

2.1. Factors Affecting the Therapeutic Efficacy

Nanoparticles’ size distribution, charge, and surface features are all predominantly involved in influencing their role in drug loading, release, toxicity, in vivo distribution, and stability. Pharmacokinetic and biodistribution properties are impacted by the nanoparticle size in which the particles with sizes exceeding 100 nm have shown limited clearance by the reticuloendothelial system [24]. Additionally, nanoparticle shape is an essential feature in the development of nanocarriers. The synthetic approach and the parameters involved can greatly influence the size and shape of the nanoporous structure. Different parameters including the choice of capping ligand, the solvent used, precursor concentration, reaction temperature and reaction time can all be adjusted to generate nanoporous material of ideal size and shape, meeting the biomedical demands [25]. The delivery of nanoparticles to the desired therapeutic location, in vivo stability in blood and other body fluids, attachment with target cells, and protein corona formation in vivo all depend on the nanoparticle characteristics [26]. The variable aspect ratio of gold nanorods allows the absorption wavelength to be tuned in the near-IR region and facilitates their use in imaging and potentially in the photothermal treatment of cancer. They are biocompatible, optically active absorbers and scatterers and of significant potential in the field of photodiagnostics and therapy [27]. Another interesting material comprising of gold nanoparticle-assembled capsules (GNACs) with controllable size and tunable morphology has been fabricated and applied as a hydrogen peroxide biosensor based on hemoglobin. A tandem self-assembly strategy incorporating a simple two-step mixing procedure of polyelectrolyte aggregates, formed from cationic polymers and multivalent anions into the colloidal gold solution has been used for the fabrication of GNACs with a subsequent combination of hemoglobin to form the bioconjugate, hemoglobin (Hb)-GNACs. The glassy carbon electrode modified with Hb-GNACs showed a high affinity and significant catalytic activity towards H2O2 [28]
Porous nanomaterials have gained significant momentum in their usage as agents for diagnosis and targeted therapy for cancer treatment. Further research on the influence of change in the characteristics of porous particles on their biological fate will be essential for the development of better drug delivery systems [29].

2.2. Mechanism of Targeting

The np-Au can be designed in zero-dimensional to three-dimensional nanostructures [30]. The delivery of the therapeutics to the desired location is based on the size of np-Au. The np-Au structures larger than a few hundred nanometers can be directly implanted near the desired location for sustained/controlled release of the drug. A submicron-thick np-Au coating was used to study the effect of halides on the release of fluorescein, employed as a surrogate for small drug molecules [15]. It was found that the interaction between halide ion and gold surface dictates the loading capacity and release kinetics. This is one of the early works marking the beginning of research on np-Au as a potential drug carrier. Exploiting the effect of the protein corona around np-Au and np-Au@poly (D, L-lactide-co-glycolide) (PLGA)/rapamycin (RAPA) has given an insight into the release kinetics of DOX which was found to be zero-order. This work proved that the np-Au-based implant has the potential to be used as a drug carrier of potential use in cancer treatment [17].
Nanostructures of np-Au smaller than 200 nm can circulate in the bloodstream for a few hours to days depending on size and surface modification. These circulating np-Au nanostructures are more likely to extravasate into the tumor region non-specifically via the leaky vessels due to the enhanced permeability and retention (EPR) effect [31]. This strategy of delivering drug molecules is more prominent for treating tumors that are not easily accessible. However, the EPR effect by itself may not be sufficient for treating most cancers due to the low accumulation of the drug. The low accumulation in the tumor could be because of clearance of nanostructures by the mononuclear phagocyte system, filtration in the kidney, or slow extravasation into normal tissues [31]. Additionally, the aberrant vasculature, increased interstitial fluid pressure, and deregulated extracellular matrix components in the tumor microenvironment work against the EPR effect. These characteristics make it difficult to deliver nanomedicines throughout the tumor in adequate numbers and uniformly, which affects sensitivity and specificity as well as treatment efficacy [32]. For the therapeutic or diagnostic substance to be delivered effectively to the tumor using the EPR effect, several things must be considered. They include blood pressure, fluid and solid stresses, nanoparticle size and shape, tumor perfusion, vascular permeability, interstitial penetration, cancer type, mononuclear phagocyte system (MPS) activity, retention of the diagnostic and therapeutic agent in tumor tissue, tumor tissue lymphatic drainage function, and others [33]. Different strategies have been employed to overcome this problem so that following extravasation, they aggressively bind to particular cells. This can be done by using a variety of conjugation chemistries to attach targeting agents, such as ligands—molecules that can bind to particular receptors on the cell surface—to the surface of the nanocarrier [34]. The use of certain ligands (antibodies or peptides) that can be grafted on the surface of a nanomedicine and precisely bind to overexpressed receptors at the target site is necessary for active drug targeting [35]. In comparison to normal organs, the EPR effect offers only modestly increased specificity and less than a 2-fold increase in nanodrug delivery. There have been reported on several interesting strategies for improving the EPR effect by getting around various obstacles to nanodrug delivery into tumors. These include actions to manage cancer-associated fibroblasts in the tumor microenvironment as well as efforts to control vasculature, regulate permeability, physically disrupt vessels, and act on the tumor microenvironment [31].
Another strategy includes guiding the drug load np-Au nanowire to the target location using ultrasound [14]. Once the drug-loaded nanostructures enter the local environment of the tumor the release of the payload can be controlled by NIR irradiation [14]. The temperature of the tumor environment can also be raised to heat-kill tumor cells by irradiating np-Au nanoparticles with a powerful NIR laser. It was shown in a mouse model that simply modifying the np-Au surface with mercaptosuccinic acid (MSA) can significantly increase the release of doxorubicin under the irradiation of light. The repetitive Ag-AgAu nano-segments and subsequent selective Ag phase etching was used to generate the np-Au NPs (gold nanoparticles ) using templated pulsed electrochemical deposition. The final np-Au NPs had a typical interior porous structure with a gap size of approximately 15 nm. To modulate the chemical binding force at the interface, mercaptosuccinic acid (MSA) and mercaptopropionic acid (MPA) were added to the surface of np-Au NPs. Among the MPA modified and bare np-Au NPs, the MSA modified np-Au NPs demonstrated the superior light-triggered drug release performance for doxorubicin [36]. Lee et al. introduced the facile synthesis of mono-disperse, mesoporous gold nanoparticles (MPGNs) using acidic emulsion method. Hydrochloric acid was dissolved in an aqueous solution with aniline monomers. By injecting an aqueous HAuCl4 solution while the emulsion was still in motion, the metastable aniline emulsion was fixed. After the reaction was finished, a 1 M NaOH solution was used to clean the produced nanoparticles. Three rounds of centrifugation with 1-methylpyrrolidone were performed on the MPGNs (NMP). The surface of as-prepared np-Au was modified with a therapeutic antibody, cetuximab, and loaded it with gadolinium, an MRI contrast agent, for the simultaneous diagnosis by magnetic resonance (MR) imaging and treatment by photo-thermal ablation [36].

2.3. Application to Neurological Conditions and Mental Health

In the United States, Alzheimer’s disease (AD), a neurological illness, is now the fifth-leading cause of death for the elderly. The pathologic characteristics of AD include Aβ-fibrils and neurofibrillary tangles. The development of neurofibrillary tangles, which are composed of misfolded aggregates of tau proteins connected with internal microtubules, and senile plaques, which are composed of external amyloid-(Aβ) peptides, is supported by increasing amounts of data. Preventing the buildup of amyloid beta (Aβ) peptides is one potential strategy for treating AD, and gold nanoparticles have been researched as potential anti-Aβ therapeutics [37]. Due to their excellent biocompatibility, simple functionalization, and possible capacity to traverse the blood–brain barrier, gold (Au) NPs are among the NPs that are thought to be useful nano-chaperones to inhibit and redirect Aβ fibrillization [38]. According to studies, the size, surface chemistry, and electric charge of Au NPs can all affect their capacity to prevent Aβ-aggregation. The degree of inhibition is influenced by NP surface chemistry and size, but NP ability to change aggregate morphology is defined by electric charge [39][40]. In vitro, compounds with surface chirality and helix shape can prevent Aβ aggregation in an enantioselective manner. Therefore, it is anticipated that adding chiral D-glutathione (GSH) ligands to gold NPs will provide them exceptional stability and chiral recognition of Aβ along with enantioselective suppression of Aβ fibrillation in one of the recent studies [38]. Okadaic acid (OA) produced an AD model that resulted in neuroinflammation and oxidative stress. It was interesting to note in another study that the anti-inflammatory and antioxidant qualities of AuNPs have lessened the oxidative stress (sulfhydryl and nitrite levels) brought on by OA in some brain regions. As long-term AuNP treatment reduced the neuroinflammation, control of mitochondrial function, and poor cognition generated by an AD model, AuNPs may be a viable treatment for neurodisease brought on by these variables [41]. In response to the pressing need, a label-free ultrasensitive clinical lab test for AD has been developed. This test is crucial for the current drug regimens. Using a monoclonal anti-tau antibody coated gold nanomaterial for the ultrasensitive and selective detection of tau protein AD biomarker at a 1 pg/mL level, a two-photon Rayleigh scattering (TPRS) assay has been developed. Two-photon scattering properties have been tracked using the hyperRayleigh scattering (HRS) method. It was shown that when anti-tau antibody coated gold nanoparticles (gold nanoparticles were prepared by adjusting the proportions of HAuCl4. 3H2O and sodium citrate, using sodium borohydride approach. The produced gold nanoparticles were spherical and had a diameter of 4 nm) were coupled with tau protein concentrations of 20 pg/mL, the two-photon scattering intensity increased by almost 16 times. The bioassay has proven to have a short response time from protein binding through detection and analysis [42]. The efficiency of the dot-blot immunoassay is combined with the high affinity of biotin and streptavidin in the creation of an Au NP-based dot-blot immunoassay for the detection of Aβ in complex biological materials. When compared to the well-established Aβ detection methods, this technology offers a wide dynamic range and reasonable sensitivity [43]. A dual-readout (colorimetric and fluorometric) test for acetylcholinesterase (AChE) has been discovered utilizing gold nanoparticles coated with Rhodamine B. The assay has been used to monitor AChE levels in the cerebral fluid of transgenic mice with Alzheimer’s disease due to its high sensitivity and specificity [44]. A role for np-Au nanoparticles in the future seems highly probable.
Schizophrenia is another neuropsychiatric condition that affects the central nervous system (CNS), and it is characterized by aberrant fluctuations in dopamine levels. Nanotherapeutic strategies have aided in addressing the issues with CNS medication delivery. In the past, ethyl cellulose microcapsules containing thioridazine were made using gold nanoparticles [45]. The surface modification of the Au NPs can increase their bioavailability. Iswarya et al. created a dopamine detection technique employing gold capped with L-histidine (AuNP). A change in the nanoparticles’ surface plasmon resonance (SPR) was used to track how the surface-modified Au NPs interacted with dopamine [46]. By 2030, depression is expected to afflict more than 300 million people worldwide, making it the most common debilitating ailment. Variations in the expression of glucocorticoid receptors (GRs) can be used to forecast specific cognitive abilities. GRs are also an important marker for assessing the efficacy of various treatments. A cutting-edge electrochemical biosensing technology has been created that allows for the precise and sensitive detection of depression biomarkers. By combining amino-ion graphene oxide (IL-rGO) and amino acid-coated gold nanoparticles (AA-AuNPs) using a green production method, electrochemical signals are noticeably amplified [47]. The use of gold nanoparticles as an antidepressant therapy strategy has been studied. Because they require less frequent administration and are more effective, nano-based formulations are becoming more popular [48].

3. Emerging Biomedical Applications of Nanoporous Gold-based Structures

Nanoporous gold (np-Au) is a metallic structure with pores and ligaments on the nanoscale. Since these particles can be considered as a combination of nanomaterials, inert metals, and nanoporous framework, np-Au provides a wide range of applicability to the field of biomedicine [49]. Due to quantum mechanical principles, nanoparticles with diameters between 1 and 10 nm (between the size of molecules and that of bulk metal properties) exhibit electronic band structure. Nanoparticles can engage in quantum tunneling in this small size range. The physical characteristics that result rely significantly on the particle size, interparticle spacing, kind of organic shell that surrounds them, and shape of the nanoparticles. They are neither those of bulk metal nor those of molecular compounds. A few “last metallic electrons” are employed in nearby particle tunneling [50]. Tunneling effects start to interfere with the interaction between the surface plasmons when the interparticle distance is less than 1 nm, according to theoretical research by Nordlander and colleagues. The interaction between surface plasmons is disrupted by a quantum tunneling phenomenon when the interparticle distance (d) is smaller than 1 nm, which results in the red shift absorption. Tunneling of electrons to and from immobilized biomolecules may enhance the efficiency of biosensors if the biomolecule interacts with gold nanoparticles or structural features in this size range.

There is additional research being done using gold nanoparticles as biological probes. It can be mixed with a variety of biological macromolecules, including nucleic acids, heavy metal ions, and protein, thanks to its unique optical features, macroscopic quantum tunneling effect, surface effect, and strong biocompatibility [51][52]. Nanoscale pores and framework provides enhanced physical, chemical, and biological activities due to their nano-size, enhanced surface, and quantum tunneling effects. The increased surface area also works for the betterment of the adsorption capacity of np-Au by providing more binding surfaces of biomolecules. The porous structures also play a vital role in the transfer of biomolecules through their increased permeability which can catalytically help to increase the reaction rates too [53]. Better electrical conductivity and the energy absorption capacity of np-Au is another main characteristic that facilitates the transfer of electrons which makes it more important for biomedical applications. In addition, the tunability of np-Au in case of size, shape, and pore, makes np-Au more practical in this applied field [54]. Due to these special characteristics, applications of np-Au have been increasing in recent years in the field of biomedicine, such as biosensing, drug delivery, and catalysis. Biosensing has become an important part of research for the analysis and detection of biomedical elements due to its necessity-driven demand. The challenges in the biomedical field due to the surge of known and unknown biological elements are growing continuously thereby increasing the demand for diverse types of biosensors [55]. Researchers in recent years are focusing on the development of simple, low-cost, real-time, and efficient biosensors. For these purposes, np-Au has proven its standing as a promising tool with its unique and excellent characteristics. Different studies have been done to fabricate np-Au-based biosensors using its various forms such as bare np-Au, surface-functionalized np-Au, shape-controlled np-Au, and other np-Au with hybrid structures [56].

3.1. Plasmonics-Based Applications

Plasmonic metal nanostructures have numerous uses in fields including optics, medicine, and catalysis. Their composition, configuration, environment around nanostructures, shape, and size have a major impact on their plasmonic characteristics, such as surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR). Due to the distinctive 3-dimensional bicontinuous nanostructure with a significant surface area, strong catalytic activity, and tunable plasmonic resonance, nanoporous gold (NPG) has recently received a lot of attention [57]. It is believed that a key factor in LSPR sensing and surface-enhanced optical phenomena like surface-enhanced Raman scattering surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence is the enhanced electromagnetic (EM) fields of LSPR excited in the ligaments. By changing the morphology of porous nanostructures such the pore and ligament size by dealloying time and thermal annealing, it is possible to achieve limited tunability in plasmonic resonance [58][59]. By dealloying ultra-dilute Au-Ag alloys with a low gold content of 1–5% at.%, an ultralow density nanoporous gold (ULDNPG) with better plasmonic photocatalytic SERS performances was created. To achieve the dealloying of such diluted solid solutions, a sandwich dealloying strategy was developed. Excellent SERS characteristics of these ULDNPG structures include high sensitivity, good repeatability, and low cost [60]. Small molecule label-free sensing has been accomplished using the morphological characteristics of NPG as a capturing scaffold. Recently, DNA topologically functionalized plasmonic nanostructures were used in SERS sensing systems. Target molecules, such as malachite green, can be attracted to NPG disks (NPGD) surfaces by stacking and electrostatic forces by using guanine quadruplex (G4) moieties. The collected molecules generated a remarkable SERS signal because of the high-density plasmonic hot-spots on NPG disks [61][62]. A microfluidic device with NPGD monolithically embedded inside has been used to produce a microfluidic SERS sensor. The three-dimensionally distributed nanoscale pores and ligaments in the NPGD, which appear as high-density SERS hot-spots, are what contributed to the enhanced surface area. Further ensuring extensive coverage of these hotspots on the microchannel floor are high-density NPGD arrays [63][64]. 

3.2. Hybrid Structures Involving np-Au

Electrochemical biosensors have been widely used in clinical research for recognizing biological analytes through a catalytic or binding event occurring at the electrode’s interface [65][66]. Tremendous demand for enhancing charge transport in the biosensors to significantly increase its sensitivity and reliability along with faster response times have stimulated intensive research on developing versatile materials with ultrahigh activities towards catalysis. For this reason, composite materials are being designed to combine highly electrocatalytic materials with a conductive material [67]. Recently, a hybrid electrode with ultra-thin, ultra-light, and flexible characteristics was created with graphitic carbon nitride (g-C3N4) nanosheets that have been electrochemically deposited on the surface of nanoporous gold film (NPGF). The hybrid electrode has shown a striking enhancement of supercapacitive performance (specific capacitance of 440 F g−1 at 2A g−1 in 0.5 M Na2SO4 solution). The superior property has been attributed to the strong interfacial effect between the defected gold atoms of np-Au and g-C3N4 [68]. Metal oxides supported three-dimensional (3D) hierarchical porous np-Au/Ni foam electrode has shown exceptionally high catalytic activity resulting mainly from its open and porous structure facilitating the mass transport and charge transfer [69]. Np-Au-modified biosensors with hybrid structures have been found more promising for meeting the demands of a highly sensitive and reliable biosensor with rapid response and better selectivity. Many related studies have mentioned the synergistic effect of hybrid structures behind this enhanced sensitivity and selectivity. X. Y. Lang et al. (2013) have reported a flexible and self-supported microelectrode having np-Au/cobalt oxide hybrid structure for electrochemical detection of glucose [67]. As per the study, the synergistic approach of gold skeleton, np-Au and cobalt oxide nanoparticles leads to the enhanced oxidation of glucose and thereby resulting in ultrahigh sensitivity. The sensitivity of up to 12.5 mA mM−1 cm−2 at a very short response time of less than a second was reported by the researchers with a very low detection limit of 5nM. A study performed by Y. Pei et al. (2018) used a hybrid structure of highly surface-roughened np-Au/Au-Sn alloy to increase the performance of a glucose biosensor [70]. 

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Subjects: Nanoscience & Nanotechnology
Contributors MDPI registered users' name will be linked to their SciProfiles pages. To register with us, please refer to https://encyclopedia.pub/register :
Palak Sondhi
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Dhanbir Lingden
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Jay K. Bhattarai
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Alexei V. Demchenko
,
Keith J. Stine
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Update Date: 29 Jan 2023
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