Self-assembly Of Gold Nanoparticles Research Articles

Surface lattice resonance in three-dimensional plasmonic arrays fabricated via self-assembly of silica-coated gold nanoparticles

HypothesisThree-dimensional plasmonic nanoparticle arrays in which the nanoparticles are assembled with a certain distance apart are expected to exhibit unique optical properties attributed to surface lattice resonances because of the interactions between the nanoparticle layers. ExperimentsMulti-layered gold nanoparticle arrays were created to experimentally prove surface lattice resonances from three-dimensional arrays. Silica-coated gold nanoparticles were employed as building blocks for the array because the distance between the nanoparticles can be tuned by adjusting the thickness of the silica coating. Employing highly monodisperse building blocks enabled to fabricate both single-layered and multi-layered plasmonic arrays via a confined convective assembly method. FindingsMulti-layering of monodisperse building blocks brought about some additional peaks corresponded to Bragg diffraction of gold nanoparticle periodic array and the interactions between layers in a hexagonal close-packed structure of the nanoparticles, respectively. Most importantly, the multi-layered arrays exhibited a distinctive extinction peak at the same wavelength as that observed from the single-layered array, proving the realization of surface lattice resonances from the three-dimensional plasmonic array.

Large-scale assembly and pattern transfer of SERS-active nanoparticles for application in drug monitoring of methotrexate in blood serum

Self-assembly of plasmonic gold nanoparticles (AuNPs) in periodic arrays with nanometric gaps results in the optimization of near- and far-field effects, which provides excellent surface-enhanced Raman spectroscopy (SERS) sensitivity. Herein, we report the assembly of ∼30 nm AuNPs on electron beam lithography (EBL) substrates using an inexpensive and simple method of stamping. This method yields a highly regular arrangement of AuNPs in the nanochannels of EBL substrates. An experimental approach reveals that, when using the stamping method, the groove width of the gratings plays an important role in linearly arranging the AuNPs on the EBL substrates and is a result of unidirectional flow of AuNPs due to the capillary effect. For assessment of the substrate’s SERS efficiency, rhodamine 6 G and brilliant blue were tested with a limit of detection (LOD) of 10.2 nM. To practically test the clinical-based translation of SERS substrates, detection of the chemotherapy drug methotrexate (MTX) was performed with an LOD of 13.7 nM in human blood serum to illustrate its potential in therapeutic drug monitoring (TDM) and its translation into clinics.

Fabrication of gold nanoparticles tethered in heat-cooled calf thymus-deoxyribonucleic acid Langmuir-Blodgett film as effective surface-enhanced Raman scattering sensing platform

SERS active substrate fabricated through self-assembly of Gold nanoparticles on the disjointed networks of Heat-cooled Calf Thymus DNA (HC-Ct DNA) Langmuir-Blodgett (LB) film has been reported. Adsorption kinetics of HC-Ct DNA molecules at the air-water interface has been studied explicitly. The UV-Vis electronic absorption spectra in conjunction with the FESEM images collectively suggest the presence of H- type aggregated domains most likely owing to plane-to-plane self-association of the HC-Ct DNA molecules aligned vertically on the surface of the LB film. Elemental composition and the morphological features of the as-prepared substrate (APS) are explored from XPS analysis and the FESEM, AFM images respectively. The SERS efficacy of the APS has been tested with trace concentrations of 4-Mercaptopyridine molecule. Finally, this SERS active substrate has also been used for the detection of malathion at ultrasensitive concentrations.

Self-assembly of polysarcosine amphiphilic polymers-tethered gold nanoparticles for precise photo-controlled synergistic therapy

Self-assembly of polysarcosine amphiphilic polymers-tethered gold nanoparticles for precise photo-controlled synergistic therapy

Thermal-annealing-regulated plasmonic enhanced fluorescence platform enables accurate detection of antigen/antibody against infectious diseases.

Plasmonic enhanced fluorescence (PEF) technology is a powerful strategy to improve the sensitivity of immunofluorescence microarrays (IFMA), however, current approaches to constructing PEF platforms are either expensive/time-consuming or reliant on specialized instruments. Here, we develop a completely alternative approach relying on a two-step protocol that includes the self-assembly of gold nanoparticles (GNPs) at the water—oil interface and subsequent annealing-assisted regulation of gold nanogap. Our optimized thermal-annealing GNPs (TA-GNP) platform generates adequate hot spots, and thus produces high-density electromagnetic coupling, eventually enabling 240-fold fluorescence enhancement of probed dyes in the near-infrared region. For clinical detection of human samples, TA-GNP provides super-high sensitivity and low detection limits for both hepatitis B surface antigen and SARS-CoV-2 binding antibody, coupled with a much-improved detection dynamic range up to six orders of magnitude. With fast detection, high sensitivity, and low detection limit, TA-GNP could not only substantially improve the outcomes of IFMA-based precision medicine but also find applications in fields of proteomic research and clinical pathology.Electronic Supplementary MaterialSupplementary material (UV—Vis absorption and transmission spectra of GNPs, SEM, microscopy and digital images of PEF platforms, and fluorescence images of IFMA on PEF platforms) is available in the online version of this article at 10.1007/s12274-022-5035-6.

Properties of SiC and Si3N4 Thin Films Containing Self-Assembled Gold Nanoparticles

The properties of semiconductor materials can be strongly affected by the addition of metallic nanoparticles. Here we investigate the properties of SiC + Au and Si3N4 + Au thin films prepared by magnetron sputtering deposition followed by thermal annealing. The influence of gold addition on the optical and electrical properties is explored. We show the formation of self-assembled Au nanoparticles in SiC and Si3N4, with the size and arrangement properties determined by the deposition and annealing conditions. Both SiC- and Si3N4-based films show an increase in the overall absorption with increasing Au content, and its decrease with increasing annealing temperature. All films show the presence of surface plasmon resonance, whose peaks shift toward larger wavelengths with increasing Au nanoparticle size. The resistivity significantly drops with the Au content increase for both types of matrices, although the resistivity of Si3N4-based films is much higher. The incorporated quantity of Au in the host matrix was chosen in such a way to demonstrate that a huge range of optical and electrical characteristics is achievable. The materials are very interesting for application in opto-electronic devices.

Solvent Effect on the Synthesis of Oleylamine Modified Au Nanoparticles and Their Self-Assembled Film for SERS Substrate

The preparation and self-assembling of monodisperse gold nanoparticles (Au NPs) is of great significance for its SERS application. According to the oleylamine-reduced method, oleylamine (OAm) serves as the reducing agent and stabilizing agent, and the effects of different reaction parameters such as solvent and temperature on the size and dispersity of Au NPs have been evaluated. The Au NPs synthesized with toluene as the solvent have the best dispersity and narrowest particle size distribution with adjustable sizes. The particle size gradually increases with the increase in reaction temperature. The highly ordered self-assembly film of Au NPs was employed as surface-enhanced Raman scattering (SERS) substrate for the probing molecule of rhodamine 6G. The Au substrate exhibits excellent spatial uniformity and SERS reproducibility, which indicates its practicability as a substrate. This study provides a simple synthesis strategy of highly ordered monodispersed Au NPs, which can serve as a SERS substrate with excellent spatial uniformity and SERS re-producibility.

A Novel Fabrication of Single Electron Transistor from Patterned Gold Nanoparticle Array Template-Prepared by Polystyrene Nanospheres.

In this paper, polystyrene microspheres were firstly prepared by seeded emulsion polymerization, and the uniform monolayer of polystyrene microspheres was prepared on the substrate by the dipping method. Then, polystyrene monolayer film was used as a mask and a low dimensional array structure of gold was prepared by bottom-up self-assembly process. After that, the method of solution etching and annealing was used, and the gold nanoparticle array was post-processed. As a result, gold nanoparticles were recrystallized, with an average diameter of about 50 nm. Subsequently, the semiconductor process was adopted, with focused ion beams induced deposition and electron beam evaporation, and single electron transistors were fabricated, based on self-assembled gold nanoparticles. Finally, the devices were fixed in a liquid helium cryostat and Coulomb blockade was observed at 320 mK. It is a novel fabrication of a single electron transistor based on gold nanoparticle array template and prepared with polystyrene nanospheres.

Gold Nanoparticle-Bridge Array to Improve DNA Hybridization Efficiency of SERS Sensors.

The interfacial mass transfer rate of a target has a significant impact on the sensing performance. The surface reaction forms a concentration gradient perpendicular to the surface, wherein a slow mass transfer process decreases the interfacial reaction rate. In this work, we self-assembled gold nanoparticles (AuNPs) in the gap of a SiO2 opal array to form a AuNP-bridge array. The diffusion paths of vertical permeability and a microvortex effect provided by the AuNP-bridge array synergistically improved the target mass transfer efficiency. As a proof of concept, we used DNA hybridization efficiency as a research model, and the surface-enhanced Raman spectroscopy (SERS) signal acted as a readout index. The experimental verification and theoretical simulation show that the AuNP-bridge array exhibited rapid mass transfer and high sensitivity. The DNA hybridization efficiency of the AuNP-bridge array was 15-fold higher than that of the AuNP-planar array. We believe that AuNP-bridge arrays can be potentially applied for screening drug candidates, genetic variations, and disease biomarkers.

Two-Dimensional Janus Film with Au Nanoparticles Assembled on Trinuclear Gold(I) Pyrazolate Coordination Nanosheets for Photocatalytic H2 Evolution.

A two-dimensional (2D) Janus film with self-assembled gold nanoparticles (AuNPs) is a class of fascinating materials that may offer unprecedented opportunities to realize diverse applications due to their two distinct faces with anisotropic properties. In this work, we report a novel, straightforward strategy for the preparation of a bilayer coordination nanosheet (CONASH)/AuNP Janus film, where the CONASH features infinite trinuclear gold(I) pyrazolate cyclic complexes with electron-accepting viologen as bridges. The bilayer film has visible light absorption and redox properties and showcased promising photocatalytic H2 evolution activity by virtue of the formed unique heterojunction structure between AuNPs and CONASH. The current study opens a novel pathway for controlled fabrication of the 2D Janus film with assembled AuNPs for photocatalytic applications.

Self-Assembled Au Nanoparticle Monolayers on Silicon in Two- and Three-Dimensions for Surface-Enhanced Raman Scattering Sensing.

Gold nanoparticle/silicon composites are canonical substrates for sensing applications because of their geometry-dependent physicochemical properties and high sensing activity via surface-enhanced Raman spectroscopy (SERS). The self-assembly of gold nanoparticles (AuNPs) synthesized via wet-chemistry on functionalized flat silicon (Si) and vertically aligned Si nanowire (VA-SiNW) arrays is a simple and cost-effective approach to prepare such substrates. Herein, we report on the critical parameters that influence nanoparticle coverage, aggregation, and assembly sites in two- and three-dimensions to prepare substrates with homogeneous optical properties and SERS activity. We show that the degree of AuNP aggregation on flat Si depends on the silane used for the Si functionalization, while the AuNP coverage can be adjusted by the incubation time in the AuNP solution, both of which directly affect the substrate properties. In particular, we report the reproducible synthesis of nearly touching AuNP chain monolayers where the AuNPs are separated by nanoscale gaps, likely to be formed due to the capillary forces generated during the drying process. Such substrates, when used for SERS sensing, produce a uniform and large enhancement of the Raman signal due to the high density of hot spots that they provide. We also report the controlled self-assembly of AuNPs on VA-SiNW arrays, which can provide even higher Raman signal enhancement. The directed assembly of the AuNPs in specific regions of the SiNWs with a control over NP density and monolayer morphology (i.e., isolated vs nearly touching NPs) is demonstrated, together with its influence on the resulting SERS activity.

Ratiometric Fluorescent Biosensor Based on Self-Assembled Fluorescent Gold Nanoparticles and Duplex-Specific Nuclease-Assisted Signal Amplification for Sensitive Detection of Exosomal miRNA.

The sensitive detection of cancer-associated exosomal microRNAs shows enormous potential in cancer diagnosis. Herein, a ratiometric fluorescent biosensor based on self-assembled fluorescent gold nanoparticles (Au NPs) and duplex-specific nuclease (DSN)-assisted signal amplification was fabricated for sensitive detection of colorectal cancer (CRC)-associated exosomal miR-92a-3p. In this biosensing system, the hairpin DNA modified with sulfhydryl and fluorescent dye Atto-425 at both ends is conjugated to fluorescent Au NPs through Au-S bonds, resulting in the quenching of Atto-425. The miR-92a-3p can open the hairpin of DNA and forms an miR-92a-3p/DNA heteroduplex, triggering the specific cleavage of DSN for the DNA in the heteroduplex. As a result, Atto-425 leaves the fluorescent Au NPs and recovers the fluorescence emission. The released miR-92a-3p can hybridize with another hairpin DNA and lead to a stronger fluorescence recovery of Atto-425 to form a signal amplification cycle. The stable fluorescence of Au NPs and the changing fluorescence of Atto-425 constitute a ratiometric fluorescent system reflecting the concentration of miR-92a-3p. This biosensor exhibits excellent specificity and can distinguish CRC patients from healthy individuals by detecting miR-92a-3p extracted from clinical exosome samples, showing the potential in CRC diagnosis.

Self-assembly of gold nanoparticles by chitosan for improved epinephrine detection using a portable surface enhanced Raman scattering device

Surface enhanced Raman scattering (SERS) has become widely used for identification, quantification and providing structural information about molecular structure in low concentrations as it allows signal Raman enhancement using metallic nanoparticles (NPs). Controlling interaction between analyte and NPs is a major point for the optimization of signal exaltation in SERS analysis. The objective of this study is the improvement and the control of SERS analysis by aggregation/self-assembly optimization of AuNPs using quaternized chitosan. The interest of this approach is to allow stable and reliable measurements with a simple and low cost approach compatible with a massive use in the field. In this work, we used design of experiments by Box-Behnken design to fix optimized conditions to increase signal sensibility of epinephrine water solutions. We also tested SERS signal stability in isotonic sodium chloride 0.9% and glucose 5% matrices.Our results demonstrate that globally neutral AuNPs aggregates were stabilized at a nanometric size by the subsequent addition of polyelectrolyte chains and allows for significant Raman signal enhancement of epinephrine. We succeed to prepare the SERS active material and measure a stable signal of epinephrine at a concentration as down as 0.1 μg mL−1 in less than 5 min. The signal remained stable and exploitable for at least 2 h. Our results reveal a strong correlation between intensity and logarithm of the concentration (concentration before dilution from 0.1 to 10 μg mL−1) suggesting a possible quantification. Furthermore, the signal of epinephrine at 10 μg mL−1 were also exploitable and stable in complex media as isotonic sodium chloride 0.9% and glucose 5%. This represents a particularly interesting application that would allow direct analysis of drugs complex media and open the way to analysis in biological samples.

Formation of Stable Cruciform Assembly of Gold Nanoparticles from Cannabis indica Leaves

Gold nanoparticles have been increasingly used in several electronic, material fabrication, and biomedical applications. Several methods have been reported to prepare gold nanoparticles of various shapes and sizes with different photophysical properties. Although useful to prepare gold nanoparticles, most of the methods are not stable enough, which leads to the degradation of the nanoparticles, if they are stored at room temperatures (up to 30 °C) for a few days. In this paper, we report a novel and environmentally friendly method to synthesize self-assembled gold nanoparticles in cruciform shapes by using leaf extract of Cannabis indica as a reducing agent without the aid of any polymers or additional chemicals. The nanoparticles are found to be stable for more than a month (45 days) when stored at room temperature (up to 30 °C). They were able to form stable conjugates with bovine α-lactalbumin protein that may possess anti-cancerous properties.

Enhanced immunoassay in a nanofluidic preconcentrator utilizing nano-interstices among self-assembled gold nanoparticles.

In this study, we developed a microfluidic device for a dual work of protein preconcentration and subsequent capture by an immunoassay system. The fabrication of nano-interstices (nanochannels) to generate ion concentration polarization effect (ICP) for the preconcentration was simply performed by exploiting the loose association of glass-on-modified AuNPs to the polydimethylsiloxane (PDMS) channel pads as well as spaces between the substrate and the PDMS pad caused by these AuNPs. As a result, 65-fold concentration enhancement was achieved when performed on a sample of fluorescein isothiocyanate-labeled bovine serum albumin (FITC-BSA). Furthermore, a modification procedure of antibodies responsible for capturing target proteins was performed on gold electrodes integrated into the proposed chip. After preconcentration, the immunoassay system was worked, and showed a good performance in capturing targets. Through this study, we demonstrated that the device can work efficiently for the dual purpose, has the potential to apply widely for the analysis and capture of various targets.

Self-assembly of gold nanoparticles grafted with amphiphilic supramolecular block copolymers

Design of polymer grafted plasmonic metal nanoparticles (PGNPs) has received continuous interest due to polymer-driven self-assembly of plasmonic nanoparticles (NPs) as a means to control interparticle plasmon coupling in ensembles. We report the use of supramolecular “V-shaped” block copolymers (VBCPs) as surface ligands of PGNPs to study their hydrophobicity-driven self-assembly. The amphiphilic VBCPs are prepared from two homopolymers, namely dipicolyamine (DPA)-terminated polystyrene (PS) and pyridine (Py)-terminated poly(N,N-dimethylacrylamide) (PDMA) where the two polymers are bridged with Cu2+ ions. Those supramolecular VBCPs formed spherical micelles in the range of 100–300 nm, much larger than those of linear BCPs with similar chemical composition as a result of Cu2+ ions at the hydrophobic/hydrophilic interface. Thioester-containing supramolecular polymers can modify plasmonic AuNPs through ligand exchange even in the presence of Cu2+ ions. Those supramolecular polymers can drive PGNPs to form giant vesicles and two-dimensional (2-D) layered nanosheets. Using in situ light scattering, the supramolecular dynamics is found to allow maximum chain reconformation of polymer ligands where the interparticle distance of PGNPs grafted with VBCPs is smaller compared to that of PGNPs with linear BCPs. The assembled nanostructures with VBCPs also showed similar stimuli-responsive properties where the dissociation of DPA-Cu2+-Py coordination results in the disruption of assembled nanostructures. The supramolecular approaches potentially provide a new toolbox to design PGNP assemblies with tunable nanostructures and interesting dynamic properties enabled by non-covalent interaction.

Donor–Acceptor Stenhouse Adducts for Stimuli-Responsive Self-Assembly of Gold Nanoparticles into Semiconducting Thin Films

Donor–Acceptor Stenhouse Adducts for Stimuli-Responsive Self-Assembly of Gold Nanoparticles into Semiconducting Thin Films

Electrochemical Self-Assembled Gold Nanoparticle SERS Substrate Coupled with Diazotization for Sensitive Detection of Nitrite.

The accurate determination of nitrite in food samples is of great significance for ensuring people’s health and safety. Herein, a rapid and low-cost detection method was developed for highly sensitive and selective detection of nitrite based on a surface-enhanced Raman scattering (SERS) sensor combined with electrochemical technology and diazo reaction. In this work, a gold nanoparticle (AuNP)/indium tin oxide (ITO) chip as a superior SERS substrate was obtained by electrochemical self-assembled AuNPs on ITO with the advantages of good uniformity, high reproducibility, and long-time stability. The azo compounds generated from the diazotization-coupling reaction between nitrite, 4-aminothiophenol (4-ATP), and N-(1-naphthyl) ethylenediamine dihydrochloride (NED) in acid condition were further assembled on the surface of AuNP/ITO. The detection of nitrite was realized using a portable Raman spectrometer based on the significant SERS enhancement of azo compounds assembled on the AuNP/ITO chip. Many experimental conditions were optimized such as the time of electrochemical self-assembly and the concentration of HAuCl4. Under the optimal conditions, the designed SERS sensor could detect nitride in a large linear range from 1.0 × 10−6 to 1.0 × 10−3 mol L−1 with a low limit of detection of 0.33 μmol L−1. Additionally, nitrite in real samples was further analyzed with a recovery of 95.1−109.7%. Therefore, the proposed SERS method has shown potential application in the detection of nitrite in complex food samples.

Merging Porphyrins with Gold Nanorods: Self Assembly Construct to High Fluorescent Polyelectrolyte Microcapsules.

Dual probe porphyrin-gold nanorod polyelectrolyte microcapsules were developed to explore the enhancing effects of a plasmonic interface of self-assembled gold nanoparticles in the fluorescence emission from porphyrins loaded into the capsules’ core. An analysis of fluorescence lifetime imaging microscopy (FLIM) data reports a notable 105–106-fold increase in the maximum detected photon rates from diffraction-limited spots and an overall six-fold increase in fluorescence as averaged over the whole microcapsule area. Large emission enhancements were correlated with decreases in fluorescence lifetimes. The microcapsule’s design proved effective in achieving high fluorescent hybrids and may shed light on new possibilities for advanced materials imaging applications.

The self-assembly of gold nanoparticles in large-pore ordered mesoporous carbons

Simple encapsulation of 3 nm gold nanoparticles in ordered mesoporous carbon with large pores of 17 nm and thick pore walls of 16 nm was achieved by a metal–ligand coordination assisted-self-assembly approach. Polystyrene-block-polyethylene-oxide (PS-b-PEO) diblock copolymer with a large molecular weight of the PS chain and mercaptopropyltrimethoxysilane were used as the template and the metal ligand, respectively. Small-angle X-ray scattering, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy showed that monodispersed aggregation-free gold nanoparticles approximately 3 nm in size were partially embedded in the large open pore structure of the ordered mesoporous carbon. The strong coordination between the gold species and the mercapto groups and the thick porous walls increased the dispersion of the gold nanoparticles and essentially inhibited particle aggregation at 600 °C. The gold nanoparticles in the ordered mesoporous carbon are active and stable in the reduction of nitroarenes involving bulky molecules using sodium borohydride as a reducing agent under ambient conditions (30 °C) in water. The large interconnected pore structure facilitates the mass transfer of bulky molecules.