Nanoporous Gold Nanoparticles Research Articles

A portable micro-nanochannel bio-3D printed liver microtissue biosensor for DON detection

We investigated a portable micro-nanochannel biosensor 3D-printed liver microtissues for rapid and sensitive deoxynivalenol (DON) detection. The screen-printed carbon electrode (SPCE) was modified with nanoporous anodic aluminum oxide (AAO), gold nanoparticles (AuNPs), and cytochrome C oxidase (COx) to enhance sensor performance. Gelatin methacrylate hydrogel, combined with hepatocellular carcinoma cells, formed the bioink for 3D printing. Liver microtissues were prepared through standardized and high-throughput techniques via bio-3D printing technology. These microtissues were immobilized onto modified electrodes to fabricate liver microtissue sensors. The peak current of this biosensor was positively correlated with DON concentration, as determined by cyclic voltammetry (CV), within a linear detection range of 2∼40 μg/mL. The standard curve equation is denoted by ICV(μA)= =18.76956+0.03107CDON(μg/mL), with a correlation coefficient R2 was 0.99471(n＝3). A minimum detection limit of 1.229 μg/mL was calculated from the formula, indicating the successful construction of a portable micro-nanochannel bio-3D printed liver microtissue biosensor. It provides innovative ideas for developing rapid and convenient instrumentation to detect mycotoxin hazards after grain production. It also holds significant potential for application in the prediction and assessment of post-production quality changes in grain.

Three-dimensional hotspot structures constructed from nanoporous gold with a V-cavity and gold nanoparticles for surface-enhanced Raman scattering.

The intensity and sensitivity of surface-enhanced Raman scattering (SERS) spectra are highly dependent on the consistency and homogeneity of the nanomaterials. In this study, we developed a large-area three-dimensional (3D) hotspot substrate with good homogeneity and reproducibility in SERS signals. The substrate is based on the synergistic structures of nanoporous gold (NPG) and gold nanoparticles (AuNPs). NPG was combined with a periodic V-shaped nanocavity array to create nanoporous gold with a V-cavity (NPGVC) array featuring uniform hotspots. A nanoporous gold V-shaped resonant cavity (NPGVRC) structure was developed by incorporating AuNPs into the NPGVC array. The coupling action between the AuNPs and NPGVC resulted in a SERS-enhanced electromagnetic field with 3D hotspot distribution. The strategic incorporation of NPG and V-cavity array significantly expanded the surface area available for analyte adsorption and interaction with AuNPs. Using rhodamine 6G (R6G) and malachite green (MG) as probe molecules, the SERS performance was investigated, and the NPGVRC substrate not only showed excellent enhancement with the limit of detection as low as 10-11 M, but also presented good homogeneity. NPGVRC was then used for biological detection of the influenza A virus, where we acquired and examined the characteristic SERS spectra of two spike proteins. It is demonstrated that there is significant potential for our proposed SERS platform to be used in biosensors.

Novel nanostructure-coupled biosensor platform for one-step high-throughput quantification of serum neutralizing antibody after COVID-19 vaccination

COVID-19 vaccination efficacy depends on serum levels of the neutralizing antibodies (NAs) specific to the receptor-binding domain of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein. Therefore, a high-throughput rapid assay capable of measuring the total SARS-CoV-2 NA level is urgently needed for COVID-19 serodiagnosis, convalescent plasma therapy, vaccine development, and assessment. Here, we developed a novel nanoplasmonic immunosorbent assay (NanoPISA) platform for one-step rapid quantification of SARS-CoV-2 NAs in clinical serum samples for high-throughput evaluation of COVID-19 vaccine effectiveness. The NanoPISA platform enhanced by the use of nanoporous hollow gold nanoparticle coupling was able to detect SARS-CoV-2 NAs with a limit of detection of 0.2 pM within 15 min without washing steps. The one-step NanoPISA for SARS-CoV-2 NA detection in clinical specimens yielded good results, comparable with those obtained in the gold-standard seroneutralization test and the surrogate virus-neutralizing enzyme-linked immunosorbent assay. Collectively, the one-step NanoPISA might be a rapid and high-throughput NA-quantification platform for evaluating the effectiveness of COVID-19 vaccines.

Quantitative 3D Characterization of Nanoporous Gold Nanoparticles by Transmission Electron Microscopy.

Quantitative structural characterization of nanomaterials is important to tailor their functional properties. Corrosion of AgAu-alloy nanoparticles (NPs) results in porous structures, making them interesting for applications especially in the fields of catalysis and surface-enhanced Raman spectroscopy. For the present report, structures of dealloyed NPs were reconstructed three-dimensionally using scanning transmission electron microscopy tomography. These reconstructions were evaluated quantitatively, revealing structural information such as pore size, porosity, specific surface area, and tortuosity. Results show significant differences compared to the structure of dealloyed bulk samples and can be used as input for simulations of diffusion or mass transport processes, for example, in catalytic applications.

Enantiospecific Molecular Fingerprinting Using Potential-Modulated Surface-Enhanced Raman Scattering to Achieve Label-Free Chiral Differentiation.

Chiral differentiation is critical in diverse fields ranging from pharmaceutics to chiral synthesis. While surface-enhanced Raman scattering (SERS) offers molecule-specific vibrational information with high detection sensitivity, current strategies rely on indirect detection using additional selectors and cannot exploit SERS' key advantages for univocal and generic chiral differentiation. Here, we achieve direct, label-free SERS sensing of biologically important enantiomers by synergizing asymmetric nanoporous gold (NPG) nanoparticles with electrochemical-SERS to generate enantiospecific molecular fingerprints. Experimental and in silico studies reveal that chiral recognition is two pronged. First, the numerous surface atomic defects in NPG provide the necessary localized asymmetric environment to induce enantiospecific molecular adsorptions and interaction affinities. Concurrently, the applied potential drives and orients the enantiomers close to the NPG surface for maximal analyte-surface interactions. Notably, our strategy is versatile and can be readily extended to detect various enantiomers. Furthermore, we can achieve multiplex quantification of enantiomeric ratios with excellent predictive performance. Our combinatorial approach thus offers an important paradigm shift from current approaches to achieve label-free chiral SERS sensing of various enantiomers.

Surface-engineered nanoporous gold nanoparticles for light-triggered drug release

We studied light-triggered drug releasing performance using surface-engineered nanoporous gold nanoparticles (np-Au NPs). The np-Au NPs were prepared by applying templated pulsed electrochemical deposition for repeated Ag–AgAu nano-segments and subsequent selective Ag phase etching. The resulting np-Au NPs showed characteristic internal porous structure with a gap size of ~15 nm. The surface of the np-Au NPs was rationally modified with mercaptosuccinic acid (MSA) and mercaptopropionic acid (MPA) to control chemical binding force at interface. The MSA modified np-Au NPs showed the best light-triggered drug releasing performance for doxorubicin compared to those of the MPA modified np-Au and the bare np-Au NPs. From in vivo fluorescence imaging study, we found that the MSA modified np-Au NPs efficiently worked for controlled release of doxorubicin with light initiation in a mouse.

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.

High-performance non-enzymatic biofuel cells based on an organic copper complex cathode and a nanoporous gold nanoparticle anode.

We developed efficient compartment-less non-enzymatic biofuel cells (NEFCs) with an electrografted copper complex of 3,5-diamino-1,2,4-triazole and nanoporous gold nanoparticles as catalysts, which could not only work in a neutral solution, but also drive the self-powered sensing of pyrophosphate via the stronger coordination of Cu2+ with O than N at the cathode.

A green synthetic approach for size tunable nanoporous gold nanoparticles and its glucose sensing application

A novel approach for environmentally benign green synthesis of zero-dimensional monodispersed nanoporous gold nanoparticles (npGNPs) with tunable size has been developed. It involves the use of Oryza sativa seeds (Asian rice) extract as a reducing agent for the simultaneous bio-reduction of gold (Au3+) and silver (Ag+) ions to form alloys nanoprecursor that led to the formation of npGNPs using Au (I) as an oxidative etchant in galvanic replacement reaction. In comparison to conventional methods, no harsh reaction conditions were used during the synthesis to comply with the green chemistry. The synthesized npGNPs were characterized using transmission electron microscopy (TEM), field emission-scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and UV–visible spectroscopy. Monodispersed nanoporous gold nanoparticles in the size range of 80–150 nm were obtained as confirmed by electron microscopy. The size can easily be tuned by varying the concentration of silver precursor. The synthesized nanoporous gold nanoparticles were then evaluated for their electrocatalytic activity toward non-enzymatic glucose sensing by cyclic voltammetry (CV) and linear scan voltammetry (LSV). In a comparative study with bare Au electrode and Au-Ag nanoparticles modified electrode, the resulting npGNPs modified sensor exhibited a better response toward glucose in the linear range from 1 to 50 μM with a sensitivity of 6.67 µA µM−1 cm2.

TEMPO-Functionalized Nanoporous Au Nanocomposite for the Electrochemical Detection of H2O2.

A novel nanocomposite of nanoporous gold nanoparticles (np-AuNPs) functionalized with 2,2,6,6-tetramethyl-1-piperidinyloxy radical (TEMPO) was prepared; assembled carboxyl groups on gold nanoporous nanoparticles surface were combined with TEMPO by the “bridge” of carboxylate-zirconium-carboxylate chemistry. SEM images and UV-Vis spectroscopies of np-AuNPs indicated that a safe, sustainable, and simplified one-step dealloying synthesis approach is successful. The TEMPO-np-AuNPs exhibited a good performance for the electrochemical detection of H2O2 due to its higher number of electrochemical activity sites and surface area of 7.49 m2g−1 for load bigger amount of TEMPO radicals. The TEMPO-functionalized np-AuNPs have a broad pH range and shorter response time for H2O2 catalysis verified by the response of amperometric signal under different pH and time interval. A wide linear range with a detection limit of 7.8 × 10−7 M and a higher sensitivity of 110.403 μA mM−1cm−2 were obtained for detecting H2O2 at optimal conditions.

Towards Optimal Disorder in Gold Nanosponges for Long‐Lived Localized Plasmonic Modes

AbstractThe potential of disorder to confine and enhance electromagnetic fields is well known and localized fields in turn can be used for non‐linear optical sensing and for studying quantum optics. Recently, nanoporous gold nanoparticles (nanosponges) were shown to support highly localized long‐lived plasmonic modes in the infrared spectral range. In this paper, we take first steps towards tailoring the disorder for optimal field localization and enhancement by calculating extinction and near‐field properties for different filling fractions and correlation lengths. We find that the filling fraction has not only a large effect on the fundamental dipolar surface‐plasmon resonance of the nanoparticle, but also on the frequency range in which localized modes of plasmonic nature occur. The influence of the correlation length is more subtle but is seen to influence the coupling between localized and far‐field modes as well. We briefly discuss first results on details of the localization process, which takes place on the same length scale as the typical structure size, so a simple cavity‐resonance picture cannot account for the relatively low frequency of the modes.

EBL-Based Fabrication and Different Modeling Approaches for Nanoporous Gold Nanodisks

We report electron beam lithography (EBL) based fabrication and different modeling techniques for disk-shaped nanoporous gold nanoparticles (NPG disk). The EBL technique can provide large area 2D patterns of regularly or randomly distributed nanodisks with narrow size distribution and flexible interdisk (center to center) distance. Such flexibility is essential to obtain quasi-single NPG disk response, which typically peaks in the near-infrared (NIR) spectrum beyond 1 μm, from ensemble measurements by common UV/vis/NIR spectrometers instead of a specialized NIR spectroscopic microscope. NPG disks of 200 to 500 nm diameter and 50 nm thickness have been fabricated and characterized. To model the NPG disk and calculate its plasmonic properties, two different modeling approaches have been developed. A model based on the Bruggeman effective medium theory (B-EMT model) requires little information about the nanoporous structure. In contrast, the nanoporous model (NP model) retains the essential nanoporous structural features of NPG disk. To evaluate the performance of these models, simulated extinction spectra have been compared to the experimental data. Both the B-EMT and NP models perform well to estimate the far-field plasmon resonance peak position. However, to obtain the accurate information about the plasmon peak width/plasmon lifetime and near-field plasmonic hot-spots formation within the nanopores, the NP model is essential since the B-EMT model lacks the nanoporous network.

Long-lived electron emission reveals localized plasmon modes in disordered nanosponge antennas

We report long-lived, highly spatially localized plasmon states on the surface of nanoporous gold nanoparticles—nanosponges—with high excitation efficiency. It is well known that disorder on the nanometer scale, particularly in two-dimensional systems, can lead to plasmon localization and large field enhancements, which can, in turn, be used to enhance nonlinear optical effects and to study and exploit quantum optical processes. Here, we introduce promising, three-dimensional model systems for light capture and plasmon localization as gold nanosponges that are formed by the dewetting of gold/silver bilayers and dealloying. We study light-induced electron emission from single nanosponges, a nonlinear process with exponents of n≈5...7, using ultrashort laser pulse excitation to achieve femtosecond time resolution. The long-lived electron emission process proves, in combination with optical extinction measurements and finite-difference time-domain calculations, the existence of localized modes with lifetimes of more than 20 fs. These electrons couple efficiently to the dipole antenna mode of each individual nanosponge, which in turn couples to the far-field. Thus, individual gold nanosponges are cheap and robust disordered nanoantennas with strong local resonances, and an ensemble of nanosponges constitutes a meta material with a strong polarization independent, nonlinear response over a wide frequency range.

Nanoporous Gold Nanoparticles and Au/Al2O3 Hybrid Nanoparticles with Large Tunability of Plasmonic Properties.

Nanoporous gold nanoparticles (NPG-NPs) with controlled particle size and pore size are fabricated via a combination of solid-state dewetting and a subsequent dealloying process. Because of the combined effects of size and porosity, the NPG-NPs exhibit greater plasmonic tunability and significantly higher local field enhancement as compared to solid NPs. The effects of the nanoscale porosity and pore size on the optical extinction are investigated for the NPG-NPs with different particle sizes experimentally and theoretically. The influences of both porosity and pore size on the plasmonic properties are very complicated and clearly different for small particles with dominated dipole mode and large particles with dominated quadrupole mode. Au/Al2O3 hybrid porous NPs with controlled porosity and composition ratio are fabricated through plasma-enhanced atomic layer deposition of Al2O3 into the porous structure. In the Au/Al2O3 hybrid porous NPs, both Au and Al2O3 components are bicontinuously percolated over the entire structure. A further red shift of the plasmon peak is observed in the hybrid NPs due to the change of the environmental refractive index. The high tunability of the plasmonic resonances in the NPG-NPs and the hybrid porous NPs can be very useful for many applications in sensing biological and organic molecules.

Selective epoxidation of cyclohexene with molecular oxygen on catalyst of nanoporous Au integrated with MoO3 nanoparticles

Selective oxidation of olefins to desired products such as epoxides is highly demanded in chemical industry. It remains challenging to achieve high selectivity for production of epoxides over heterogeneous catalysts through using molecular oxygen as the oxidant. Nanoporous reverse catalysts (MoO3@np-Au) consisting of pure nanoporous gold (np-Au) and MoO3 nanoparticles anchored on Au ligaments were synthesized for selective oxidation of cyclohexene with molecular oxygen. By controlling the loading of molybdenum and thermal treatment condition, MoO3 nanoparticles with size of ∼5nm were uniformly anchored on the surface of gold ligaments (30–50nm) of pure nanoporous gold (np-Au). These synthesized MoO3@np-Au catalysts exhibited high selectivity of 58%–73% for production of cyclohexene oxide at conversion of 4%–11% of cyclohexene by using molecular oxygen as the oxidant. Compared to MoO3@np-Au, the selectivity for the production of cyclohexene oxide on pure np-Au catalyst is only 6% under the same catalytic condition as that on MoO3@np-Au. The observed high selectivity for production of cyclohexene oxide on MoO3@np-Au can be rationalized with a bi-functional mechanism of a reverse metal/oxide catalyst. The in-situ formed surface molybdenum oxo-peroxo species are suggested to be responsible for selective oxidation of cyclohexene to cyclohexene oxide, while the MoO3/Au interface activates molecular oxygen to regenerate the molybdenum oxo-peroxo active centers.

Molecularly imprinted electrochemical sensor based on the synergic effect of nanoporous gold and copper nanoparticles for the determination of cysteine

A sensitive molecularly imprinted sensor for L-cysteine (Cys) determination was designed and fabricated by electrodeposition method. The molecularly imprinted polymer (MIP) film was prepared by electrodeposition chitosan (CS) in the presence of Cys after depositing nanoporous gold (np-Au) and copper nanoparticles (CuNPs) onto a glassy carbon electrode (GCE) surface. The morphology and composition of CuNPs/np-Au/GCE were characterized by SEM and energy dispersive spectroscopy (EDS). The MIP/CuNPs/np-Au/GCE sensor was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The sensor displayed an excellent recognition to Cys upon measuring the variation of the oxidation current of Cys. The current response was linear to the logarithm concentration of the analyte in the range of 0.5 nM–10 μM, with a detection limit of 0.7 × 10−10 mol⋅L−1. The sensor showed good selectivity and reproducibility. The prepared sensor was successfully applied to the determination of Cys in bovine serum and sauce of instant noodle samples with satisfactory recoveries ranging from 93.0 to 110.0 %. The desirable performances may be attributed to the synergic catalytic effect and large surface area of CuNPs/np-Au nanocomposites.

Nanoporous Au-based chronocoulometric aptasensor for amplified detection of Pb2+ using DNAzyme modified with Au nanoparticles

The authors herein described an amplified detection strategy employing nanoporous Au (NPG) and gold nanoparticles (AuNPs) to detect Pb2+ ions in aqueous solution. The thiol modified Pb2+-specific DNAzyme was self-assembled onto the surface of the NPG modified electrode for hybridizing with the AuNPs labeled oligonucleotide and for forming the DNA double helix structure. Electrochemical signal, redox charge of hexaammineruthenium(III) chloride (RuHex), was measured by chronocoulometry. Taking advantage of amplification effects of the NPG electrode for increasing the reaction sites of capture probe and DNA-AuNPs complexes for bringing about the adsorption of large numbers of RuHex molecules, this electrochemical sensor could detect Pb2+ quantitatively, in the range of 0.05–100nM, with a limit of detection as low as 0.012nM. Selectivity measurements revealed that the sensor was specific for Pb2+ even with interference by high concentrations of other metal ions. This sensor was also used to detect Pb2+ ions from samples of tap water, river water, and landfill leachate samples spiked with Pb2+ ions, and the results showed good agreement with the found values determined by an atomic fluorescence spectrometer. This simple aptasensor represented a promising potential for on-site detecting Pb2+ in drinking water.

The creation of microscopic surface structures by interfacial diffusion of Au and Ag on Ag(110): A XPS and STM study

Experiments on single crystal Au/Ag alloy surfaces may provide insight into the physical and chemical phenomena that determine the reactivity of complex alloy surfaces such as nanoporous gold or bimetallic nanoparticles. In this study, we report the highly unexpected observation that as soon as interfacial diffusion is feasible (400K) thin gold films drastically restructure Ag(110) surfaces on the micrometer scale and create regular islands in a pattern which resembles the result of a sputter-etching process; bulk diffusion plays apparently no role during this phenomenon. Scanning tunneling microscopy (STM) reveals that the deposition of monolayer quantities of gold on the surface creates elongated islands, typically with a length of 1000nm, a width of ~50nm, and a height of ~30 lattice planes. The islands are predominantly elongated along the [1–10] direction and have a mutual distance of about 50nm. Approximately, one monolayer of gold causes the relocation of ~11ML of material. The islands are thermally unstable as further heating between 450K and 600K reduces the island structure significantly. The ‘etching’ of gold into the Ag(110) bulk material and the associated island formation can be rationalized with a simple kinetic model involving the diffusion of surface atoms only, illustrated with Monte Carlo simulations. A kinetic interpretation is also supported by the fact that those structures diminish after further annealing to higher temperatures. The observed large-scale reorganization underlines that even seemingly simple and well-defined surfaces may evolve in complex ways and that massive restructuring of surfaces can occur at temperatures well below the onset of bulk diffusion.

Electrochemical detection of Hg(II) ions based on nanoporous gold nanoparticles modified indium tin oxide electrode

Nanoporous gold nanoparticles (np-Au NPs), dispersed on the indium tin oxide film coated glass, were firstly employed to fabricate Hg(II) sensing platform in differential pulse anodic stripping voltammetry (DPASV). The np-Au NPs integrated the features of highly porous nanoparticles and the high affinity of gold nanomaterials for mercury, which endowed the sensing platform with high sensitivity and good reproducibility. Following optimization of the method, a calibration curve from 0.1 to 10μg/L Hg(II) was obtained in HCl solution. The detection limit was 0.03μg/L (0.15nM) at a signal-to noise ratio of 3. The interference from other heavy metal ions associated with Hg(II) detection could be effectively avoided. The performance of the proposed electrode was also applied in the detection of trace Hg(II) in different real samples with satisfactory results.

Label-free, zeptomole cancer biomarker detection by surface-enhanced fluorescence on nanoporous gold disk plasmonic nanoparticles.

We experimentally demonstrate a label-free biosensor for the ERBB2 cancer gene DNA target based on the distance-dependent detection of surface-enhanced fluorescence (SEF) on nanoporous gold disk (NPGD) plasmonic nanoparticles. We achieve detection of 2.4 zeptomole of DNA target on the NPGD substrate with an upper concentration detection limit of 1 nM. Without the use of molecular spacers, the NPGD substrate as an SEF platform was shown to provide higher net fluorescence for visible and NIR fluorophores compared to glass and non-porous gold substrates. The enhanced fluorescence signals in patterned nanoporous gold nanoparticles make NPGD a viable material for further reducing detection limits for biomolecular targets used in clinical assays. With patterned nanoporous gold disk (NPGD) plasmonic nanoparticles, a label-free biosensor that makes use of distance-dependent detection of surface-enhanced fluorescence (SEF) is constructed and tested for zeptomole detection of ERBB2 cancer gene DNA targets.