Gold Nanoparticle Substrates Research Articles

Comparing silver and gold nanoislands’ surface plasmon resonance for bisacodyl and its metabolite quantification in human plasma

Gold and silver nanoparticles have witnessed increased scientific interest due to their colourful colloidal solutions and exceptional applications. Comparing the localized surface plasmon resonance (LSPR) of gold and silver nanoparticles is crucial for understanding and optimizing their optical properties. This comparison informs the design of highly sensitive plasmonic sensors, aids in selecting the most suitable nanoparticles for applications like surface-enhanced infrared spectroscopy (SEIRA) and biomedical imaging, and guides the choice between gold and silver nanoparticles based on their catalytic and photothermal properties. Ultimately, the study of LSPR facilitates the tailored use of these nanoparticles in diverse scientific and technological applications. Two SEIRA methods combined with partial least squares regression (PLSR) chemometric tools were developed. This development is based on the synthesis of homogeneous, high-dense deposited metal nanoparticle islands over the surface of glass substrates to be used as lab-on-chip SEIRA sensors for the determination of bisacodyl (BIS) and its active metabolite in plasma. SEM micrographs revealed the formation of metallic islands of colloidal citrate-capped gold and silver nanoparticles of average sizes of 29.7 and 15 nm, respectively. BIS and its active metabolite were placed on the nanoparticles’ coated substrates to be directly measured, then PLSR chemometric modelling was used for the quantitative determinations. Plasmonic citrate-capped gold nanoparticle substrates showed better performance than those prepared using citrate-capped silver nanoparticles in terms of preparation time, enhancement factor, PLSR model prediction, and quantitative results. This study offers a way to determine BIS and its active metabolite in the concentration range 15–240 ng/mL in human plasma using inexpensive disposable glass-coated substrates that can be prepared in 1 h to get results in seconds with good recovery between 98.77 and 100.64%. The sensors provided fast, simple, selective, molecular-specific and inexpensive procedures to determine molecules in their pure form and biological fluid.

Ultrasensitive Determination of Thiabendazole in Fruit Juice by Surface-Enhanced Raman Scattering (SERS) Using a Covalent Organic Framework (COF) Gold Nanoparticle (Au NP) Substrate

An effective and sensitive SERS substrate (TPDH-COF/Au NPs) on a covalent organic framework (TPDH-COF) decorated with gold nanoparticles (Au NPs) was fabricated via electrostatic self-assembly and successfully applied for the determination of thiabendazole (TBZ) in fruit juice. The “raspberry-like” structure SERS substrate combined the properties of the abundant “hot spots” between the Au NPs and the adsorption performance of TPDH-COFs for trace analytes. Excellent SERS performance was observed, which achieved a high enhancement factor value of 2.01 × 108 for rhodamine 6 G, with considerable reproducibility and excellent long-term stability of at least 28 d. The limit of detection was estimated to be 5 ppb for TBZ in fruit juice. The result demonstrated that the TPDH-COF/Au NPs have great potential for SERS analyses and determination of pesticide residues in foods.

Use of Nanoparticle Decorated Surface-Enhanced Raman Scattering Active Sol-Gel Substrates for SALDI-MS Analysis.

Spectroscopy and mass spectrometry techniques are sometimes combined into the same analytical workflow to leverage each technique's analytical benefits. This combined workflow is especially useful in forensic and medical contexts where samples are often precious in nature. Here, we adopt metal nanoparticle (NP) doped sol-gel substrates, initially developed for surface-enhanced Raman scattering (SERS) analysis, as surface-assisted laser desorption/ionization-mass spectrometry (SALDI-MS) substrates. Using dried blood and sample protocols previously developed for SERS analysis, we observe heme-related spectral features on both silver and gold NP substrates by SALDI-MS, demonstrating dual functionality for these orthogonal techniques. Modifying the dried blood extraction procedures also allows for the observation of blood triacylglycerols by SALDI-MS. This is the first demonstration of a SERS/SALDI-MS substrate based on a sol-gel scaffold and the first demonstration of a gold NP sol-gel substrate for SALDI-MS which features lower substrate-related SALDI-MS background compared to the silver substrate.

Gold Nanoparticles Produced by Low-temperature Heating of the Dry Residue of a Droplet of an HCl Acidic Solution of HAuCl4·4H2O in a Low Vacuum.

An easy method is presented for producing gold nanoparticles. We show that by performing simultaneous low-temperature heating of a quartz glass substrate on which the dry residue of a 10 μL droplet of an HCl acidic solution of HAuCl4·4H2O is deposited and a counter substrate using Peltier devices in a low vacuum produced by a rotary pump, gold nanoparticles with sizes ranging from about twenty to one hundred and several tens of nanometers are produced on the counter substrate. In this study, an application of a gold nanoparticle substrate produced by this method to the sample holder for surface-enhanced Raman scattering analysis is also shown.

Rapid and sensitive label-free SERS determination of fucoxanthin in algae using gold nanoparticles

In this paper, we explored a rapid and ultra-sensitive detection method of fucoxanthin in algae by surface-enhanced Raman scattering. Gold nanoparticles (Au NPs) were prepared by the reduction of chloroauric acid with citric acid. An effective Raman indicator molecule, Rhodamine 6G(R6G) dye molecule, was used to characterize Au NPs that were used in SERS analysis to detect fucoxanthin. It was found that the detection limit of fucoxanthin could reach 10−6 mol·L−1. The characteristic peak of fucoxanthin at a wave number of 1520 cm−1was selected as the working curve, and it presents good linearity of fucoxanthin concentration with R2 = 0.932 in the range from 5×10−4∼1×10−7 M. We first proposed the rapid detection of fucoxanthin by surface-enhanced Raman scattering, which took only one minute to detect. In addition, the Raman strength of the pure algae or kelp and the addition of fucoxanthin was compared under the gold nanoparticle substrate, so as to verify the application value of SERS technology in the rapid determination of fucoxanthin.

Gold-Nanoparticle Layer Substrate Assisted Transmission-Mode Laser Desorption for Atmospheric Pressure Mass Spectrometry Imaging

We demonstrate continuous-wave laser-based ambient mass spectrometry imaging with the use of a gold-nanoparticle layer substrate. When a fresh tissue slice is placed on a gold-nanoparticle layer substrate and irradiated with a 532-nm continuous-wave laser, the transmission-mode laser configuration provides precise desorption performance to facilitate mass spectrometry imaging. The subsequent ionization process with nonthermal atmospheric pressure plasma jets generates sufficient amounts of molecular ions. By using this method, micrometer-spatial-resolution mass spectrometry imaging of humid tissues can be obtained. The gold-nanoparticle layer substrates can be prepared and stored in advance of the experiment, resulting in simplified specimen preparation and an advantage in faster preparing of fresh tissue specimen for analysis.

Enhanced emission of in-situ fabricated perovskite-polymer composite films on gold nanoparticle substrates

We compared the photoluminescence (PL) of perovskite-polymer composite films on gold nanoparticle (AuNPs) substrates without and with a buffer layer of polymethyl methacrylate (PMMA). It is found that a 1.8-fold PL enhancement can be experienced due to surface plasmons with solely AuNPs substrates. With PMMA placed between the emissive layer and AuNPs, the plasmonic effect is reduced while reflectance and interface enhanced emission is increased, which results in a final PL increase of 2-fold. Such enhancements provide potential strategies to enhance the light-emitting properties of in-situ fabricated perovskite quantum dots films for light conversion applications such as LCD backlights, silicon solar cells, and photodetectors.

Enhanced emission of in-situ fabricated perovskite-polymer composite films on gold nanoparticle substrates

We compared the photoluminescence (PL) of perovskite-polymer composite films on gold nanoparticle (AuNPs) substrates without and with a buffer layer of polymethyl methacrylate (PMMA). It is found that a 1.8-fold PL enhancement can be experienced due to surface plasmons with solely AuNPs substrates. With PMMA placed between the emissive layer and AuNPs, the plasmonic effect is reduced while reflectance and interface enhanced emission is increased, which results in a final PL increase of 2-fold. Such enhancements provide potential strategies to enhance the light-emitting properties of in-situ fabricated perovskite quantum dots films for light conversion applications such as LCD backlights, silicon solar cells, and photodetectors.

The influence of gold nanoparticles on the thermal conductivity of water solutions of graphen

The objects of study were water dispersions of raw graphene (hereinafter referred to as graphene-n), higher degree of purification of graphene samples (hereinafter graphene), and nanoparticles of graphene-Au nanoparticles based on them.
 The thermal conductivity of water graphene dispersions and water dispersions of gold graphene nanoparticles nanostructures at different temperatures and component ratios was investigated. The values ​​of effective thermal conductivity of dry nanofillers are calculated. The temperature dependences of the thermal conductivity of the nanofillers were obtained. It is found that the in-thermal conductivity of water dispersions of purified graphene is higher than the thermal conductivity of raw graphene as a result of better packing of nanoparticles in pure graphene nanofillers compared to raw. The effect of enhancement of thermal conductivity of gold nanoparticles, which is accompanied by higher absolute values of thermal conductivity of nanoparticles of graphene-nanoparticles of gold than the corresponding graphene, was revealed. At the same time, there is a significant difference in thermal conductivity between nanoparticles of graphene nanoparticles of gold.
 It is established that higher values of thermal conductivity of graphene-nanoparticles nanostructures of gold are the result of the reinforcing action of a gold nanoparticle substrate, which is formed as a result of joint sedimentation with graphene during the formation of nano-flakes from water solution during evaporation of water.

Ultrathin Homogenous AuNP Monolayers as Tunable Functional Substrates for Surface-Assisted Laser Desorption/Ionization of Small Biomolecules.

A series of ultrathin, homogenous gold nanoparticle (AuNP) substrates for surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) were prepared using a simple air/water interface approach. These SALDI substrates enabled soft ionization and provided significant improvements in terms of signal intensities and reduced background levels in comparison to other AuNP morphologies for different analytes such as fatty acids, peptides, amino acids, saccharides, and drugs. Through different microscopic and spectroscopic methods, we determined that the packing homogeneity of the [AuNP]n substrates played a vital role in the efficiency of the SALDI process. We demonstrated that the signal intensities of the investigated analytes were readily optimized by manipulating the thickness of the [AuNP]n substrates. The desorption/ionization efficiency increased as a function of the number of layers and then reached a saturation point. The optimized [AuNP]n substrates not only exhibited high SALDI-MS desorption/ionization efficiencies but also showed excellent reproducibilities of the analyte signals.

Detection and quantification of carbendazim in Oolong tea by surface-enhanced Raman spectroscopy and gold nanoparticle substrates

The contamination of pesticide residues in Oolong tea has raised much concern in recent years. The objective of this study was to synthesize gold nanoparticles (AuNPs) and develop surface-enhanced Raman spectroscopy (SERS) methods for detection and quantification of pesticides in Oolong tea. Facile synthesis of spherical and monodispersed AuNPs with an average diameter of 15 nm was achieved, which induced strong electromagnetic fields in SERS analysis. AuNP substrates were employed for rapid detection and quantification of carbendazim in Tieguanyin Oolong tea. Partial least squares (PLS) analysis and leave-one-out cross validation were utilized in spectral data analysis. The PLS results for Oolong tea samples were obtained: R value = 0.964; the detection limit = 100 μg/kg. These results demonstrate that SERS coupled with gold nanoparticle substrate is a simple, rapid, and sensitive analytical tool for measurement and quantification of carbendazim residues in Oolong tea.

Protein Labeling and Bioconjugation Using N-Myristoyltransferase.

Methods that allow for labeling of proteins cotranslationally within protein expression systems have had wide-ranging applications in health, engineering, and medicine. Bioorthogonal chemistries that allow for conjugation of proteins or biomolecules of interest to substrates (fluorophores, gold nanoparticles, polymers, etc.) in living cells without prior enrichment or purification have likewise enabled advances in technology to study and engineer cellular and biomolecular systems. At the intersection of these, chemoenzymatic labeling of proteins at specific sites of interest and their subsequent selective bioconjugation to substrates without prior purification has dramatically streamlined workflows that allow proteins to reside in the native expression volumes as long as possible prior to conjugation, be readily isolated upon conjugation, and remain functionally active after conjugation. Here we present methods and protocols to express and label proteins of interest at the N-terminus with azide derivatives of myristic acid, a small, soluble, 14-carbon fatty acid, and conjugate the labeled protein to fluorophores and gold nanoparticle substrates. These methods can be extended to label proteins with other myristoyl derivatives and to conjugation to other solid or polymeric substrates of interest.

Label-Free Detection of Human Serum Using Surface-Enhanced Raman Spectroscopy Based on Highly Branched Gold Nanoparticle Substrates for Discrimination of Non-Small Cell Lung Cancer

Surface-enhanced Raman spectroscopy (SERS) is a good candidate for the development of fast and easy-to-use diagnostic tools, possibly used on serum in screening tests. In this study, a potential label-free serum test based on SERS spectroscopy was developed to analyze human serum for the diagnosis of the non-small cell lung cancer (NSCLC). We firstly synthesized novel highly branched gold nanoparticles (HGNPs) at high yield through a one-step reduction of HAuCl4 with dopamine hydrochloride at 60°C. Then, HGNP substrates with good reproducibility, uniformity, and high SERS effect were fabricated by the electrostatically assisted (3-aminopropyl) triethoxysilane-(APTES-) functionalized silicon wafer surface-sedimentary self-assembly method. Using as-prepared HGNP substrates as a high-performance sensing platform, SERS spectral data of serum obtained from healthy subjects, lung adenocarcinoma patients, lung squamous carcinoma patients, and large cell lung cancer patients were collected. The difference spectra among different types of NSCLC were compared, and analysis result revealed their intrinsic difference in types and contents of nucleic acids, proteins, carbohydrates, amino acids, and lipids. SERS spectra were analyzed by principal component analysis (PCA), which was able to distinguish different types of NSCLC. Considering its time efficiency, being label-free, and sensitivity, SERS based on HGNP substrates is very promising for mass screening NSCLC and plays an important role in the detection and prevention of other diseases.

Excitation wavelength dependent photon anti-bunching/bunching from single quantum dots near gold nanostructures.

In this study, we aim to investigate the change in photon emission statistics of single CdSe/CdS core/shell quantum dots (QDs) on dielectric modified gold nanoparticle (NP) substrates as a function of the excitation wavelength. Photons emitted from single QDs are typically "anti-bunched" and are independent of the excitation wavelength. However, when QDs are coupled to plasmonic substrates, even at the low excitation power regime, we observed a significant change in photoluminescence emission behavior of single QDs; i.e. the emission transformed from incomplete photon anti-bunched to bunched when the excitation was changed from "off" to "on" plasmon resonance. Theoretical studies based on electrodynamics modeling suggested that for the QD-Au NP system, the quantum yield of single excitons decreases while that of biexcitons increases. In addition, when excited at the "on" resonance condition, the absorption is highly enhanced, resulting in an increased population of higher order excitons of the QDs. The higher order exciton emission was directly observed as an additional peak appeared at the blue side of the exciton peak of single QDs. The combined effect of the change in quantum yield and the increase in the absorption cross-section switches the photons emitted by single QDs from anti-bunched to bunched. These results provided direct evidence that not only the plasmonic nanostructures but also the excitation wavelength can effectively control the photon emission statistics of single QDs in the hybrid metal-semiconductor system. Manipulating the multiexciton-plasmon interaction in a hybrid complex like this could possibly open up new doors for applications such as entangled photon pair generation and plasmon-enhanced optoelectronic devices.

Ligand-Mediated Deposition of Noble Metals at Nanoparticle Plasmonic Hotspots.

We report the use of gold nanoparticle surface chemistry as a tool for site-selective noble metal deposition onto colloidal gold nanoparticle substrates. Specifically, we demonstrate that partial passivation of the gold nanoparticle surface using thiolated ligands can induce a transition from linear palladium island deposition to growth of palladium selectively at plasmonic hotspots on the edges or vertices of the underlying particle substrate. Further, we demonstrate the broader applicability of this approach with respect to substrate morphology (e.g., prismatic and rod-shaped nanoparticles), secondary metal (e.g., palladium, gold, and platinum), and surface ligand (e.g., surfactant molecules and n-alkanethiols). Taken together, these results demonstrate the important role of metal-ligand surface chemistry and ligand packing density on the resulting modes of multimetallic nanoparticle growth, and in particular, the ability to direct that growth to particle regions of impact such as plasmonic hotspots.

Fluorogenic Gold Nanoparticle (AuNP) Substrate: A Model for the Controlled Release of Molecules from AuNP Nanocarriers via Interfacial Staudinger-Bertozzi Ligation.

The ability to regulate small-molecule release from metallic nanoparticle substrates offers unprecedented opportunities for nanocarrier-based imaging, sensing, and drug-delivery applications. Herein we report a novel and highly specific release methodology off gold nanoparticle (AuNP) surfaces based on the bioorthogonal Staudinger-Bertozzi ligation. A thiol ligand bearing the molecular cargo, a Rhodamine B dye derivative, was synthesized and used to modify small water-soluble 5 nm AuNPs. Upon incorporation into the AuNP monolayer, we observed efficient quenching of the dye emission, resulting in a very low level of fluorescence emission that provided the baseline from which cargo release was monitored. We examined the ability of these AuNPs to react with azide molecules via Staudinger-Bertozzi ligation on the nanoparticle surface by monitoring the fluorescence emission after the introduction of an organic azide. We observed an immediate increase in emission intensity upon azide addition, which corresponded to the release of the dye into the bulk solution. The 31P NMR spectrum of the AuNP product also agrees with the formation of the ligation product. Thus this system represents a novel and highly specific release methodology off AuNP surfaces that can have potential applications in drug delivery, sensing, and materials science.

Determination of the Valence State of Diruthenium Moiety Using Redox Reactions and Surface-Enhanced Raman Scattering: Application in Heterometal Extended Metal-Atom Chain Diruthenium Nickel Complexes

Redox reaction was photoinduced on metal nanoparticle (NP) with diruthenium complexes absorbing on the surface. Surface enhanced Raman scattering (SERS) was employed to detect the vibrational wavenumber of the Ru–Ru stretching mode νRu–Ru,str. During reaction, the local environment remains roughly unaltered; the variation of bonding strength of Ru–Ru related to its valence state can be measured. The heterometal extended metal atom chain (EMAC) complexes diruthenium nickel dipyridylamide [Ru2Ni(dpa)4Cl2]0,1+ (dpa = dipyridylamide) display the Raman νRu–Ru,str at 327 (broad) and 333 cm–1 in solid form for the neutral and oxidized complexes, respectively, but red-shift to 312 cm–1 on gold NP substrate and to 328 cm–1 on AgNP. According to the oxidation potentials from voltammogram, and the Raman shifts obtained for the model complex Ru2(OAc)4Cl we assign the diruthenium core with charge +5/+4 and +6, respectively for the neutral and oxidized diruthenium nickel dipyridylamide in solid form. On substrate AuNP ...

Disposable Plasmonic Plastic SERS Sensor Using Gold Nanoparticles Arrays

Our ultimate goal of this study is to form a monolayer of plasmonic anisotropic gold nanoparticles on the surface of disposable plastics via chemical processes to use LSPR sensor. The process creates hydroxyl group by method of plasma cleaning or piranha treatment, subsequently substitute hydroxyl groups for Amine functions by using amino silane solution. Then, the surface is coated with the gold nanoparticles. For the plasmonic gold nanoparticles, gold bipyramids (Au BPs) and gold nanorods (Au NRs) with a surfactant, cetyltrimethylammonium bromide (CTAB) bilayer were employed. Then, their surfaces were modified with methoxy polyethylene glycol thiol (mPEG-SH). Based on these plasmonic gold nanoparticle substrates, we have investigated adsorption sensitivity and kinetics of self-assembly of thiolated organic molecules.

Polyelectrolyte Multilayers Assembled Entirely from Immune Signals on Gold Nanoparticle Templates Promote Antigen-Specific T Cell Response.

Materials that allow modular, defined assembly of immune signals could support a new generation of rationally designed vaccines that promote tunable immune responses. Toward this goal, we have developed the first polyelectrolyte multilayer (PEM) coatings built entirely from immune signals. These immune-PEMs (iPEMs) are self-assembled on gold nanoparticle templates through stepwise electrostatic interactions between peptide antigen and polyanionic toll-like receptor (TLR) agonists that serve as molecular adjuvants. iPEMs do not require solvents or mixing, offer direct control over the composition and loading of vaccine components, and can be coated on substrates at any scale. These films also do not require other structural components, eliminating the potentially confounding effects caused by the inherent immune-stimulatory characteristics of many synthetic polymers. iPEM loading on gold nanoparticle substrates is tunable, and cryoTEM reveals iPEM shells coated on gold cores. These nanoparticles are efficiently internalized by primary dendritic cells (DCs), resulting in activation, selective triggering of TLR signaling, and presentation of the antigens used to assemble iPEMs. In coculture, iPEMs drive antigen-specific T cell proliferation and effector cytokines but not cytokines associated with more generalized inflammation. Compared to mice treated with soluble antigen and adjuvant, iPEM immunization promotes high levels of antigen-specific CD8(+) T cells in peripheral blood after 1 week. These enhancements result from increased DC activation and antigen presentation in draining lymph nodes. iPEM-immunized mice also exhibit a potent recall response after boosting, supporting the potential of iPEMs for designing well-defined vaccine coatings that provide high cargo density and eliminate synthetic film components.

Fast detection of paracetamol on a gold nanoparticle–chitosan substrate by SERS

A fast method for detecting pharmaceutical drugs, such as paracetamol, by surface-enhanced Raman spectroscopy (SERS) using a gold nanoparticle substrate was studied.