Gold Nanocolloids Research Articles

Crystallization of Lysozyme Induced by Gap-Mode Surface Plasmon Resonance of Gold Nanocolloids

Crystallization of Lysozyme Induced by Gap-Mode Surface Plasmon Resonance of Gold Nanocolloids

Gold Nano-colloids impregnated in Langmuir-Blodgett Film of MoS2 flakes as SERS active platform: Fabrication and its application in Malathion detection

The current work focuses on fabrication of Langmuir-Blodgett (LB) films of MoS2 flakes with impregnated gold nano particles (AuNPs) as a noble Surface enhanced Raman Scattering (SERS) active hetero structure. The hot spots created over the heterostructures work as a potent agent for localization of electromagnetic field resulting in high enhancement of Raman Signals. The LB film of MoS2 flakes with and without the AuNPs were thoroughly characterized in our present work. The efficacy of Au–MoS2 substrate as a SERS sensing platform was investigated up to ultrasensitive concentrations using Raman probe molecules. Moreover, the reproducibility and homogeneity of the substrate was also tested with Raman mapping. The as prepared SERS sensing platform was engaged further for detection of Malathion at trace concentrations. The tests to check on service time was also performed. In the contemporary exploration the fabricated substrate reveals its accuracy and effectivity as a SERS sensor. Thus, in future this substrate can be a novel “Nano-Lab on Chip” device for ultrasensitive detections of chemical and bio-chemical composites.

Protein Corona Formation and Aggregation of Amyloid β 1-40-Coated Gold Nanocolloids.

Amyloid fibrillogenesis is a pathogenic protein aggregation process that occurs through a highly ordered process of protein-protein interactions. To better understand the protein-protein interactions involved in amyloid fibril formation, we formed nanogold colloid aggregates by stepwise additions of ∼2 nmol of amyloid β 1-40 peptide (Aβ1-40) at pH ∼3.7 and ∼25 °C. The processes of protein corona formation and building of gold colloid [diameters (d) of 20 and 80 nm] aggregates were confirmed by a red-shift of the surface plasmon resonance (SPR) band, λpeak, as the number of Aβ1-40 peptides [N(Aβ1-40)] increased. The normalized red-shift of λpeak, Δλ, was correlated with the degree of protein aggregation, and this process was approximated as the adsorption isotherm explained by the Langmuir-Freundlich model. As the coverage fraction (θ) was analyzed as a function of ϕ, which is the N(Aβ1-40) per total surface area of nanogold colloids available for adsorption, the parameters for explaining the Langmuir-Freundlich model were in good agreement for both 20 and 80 nm gold, indicating that ϕ could define the stage of the aggregation process. Surface-enhanced Raman scattering (SERS) imaging was conducted at designated values of ϕ and suggested that a protein-gold surface interaction during the initial adsorption stage may be dependent on the nanosize. The 20 nm gold case seems to prefer a relatively smaller contacting section, such as a -C-N or C═C bond, but a plane of the benzene ring may play a significant role for 80 nm gold. Regardless of the size of the particles, the β-sheet and random coil conformations were considered to be used to form gold colloid aggregates. The methodology developed in this study allows for new insights into protein-protein interactions at distinct stages of aggregation.

Bioreduction of gold nanocolloids using Quercus infectoria (Oliv): UV-assisted cationic-anionic dye degradation

Bioreduction of gold nanocolloids using Quercus infectoria (Oliv): UV-assisted cationic-anionic dye degradation

Anisotropic nanocluster arrays to a diminished zone: different regimes of surface deposition of gold nanocolloids.

Evaporation-induced assembly of nanoparticles has emerged as a versatile technique for the production of large-scale ordered structures and materials with complex features. In this study, we show that a dried particulate of an anisotropic nanocolloid undergoes non-ubiquitous surface morphological transitions at varying particle concentrations. Below 5 nM, deposits reveal the formation of linear arrays of AuNR clusters outside of the coffee ring and an annular CTAB-rich depletion zone in the inner vicinity of the coffee ring. For nanoparticle concentrations ≥5 nM, the outer cluster deposits disappear and a region of reduced AuNR density, sandwiched between the coffee ring and the depletion zone, analogous to the diminished zone, is observed. Within the coffee-ring deposits, nanoscale smectic AuNR assembly occurs via the expulsion of the cetyltrimethyl ammonium bromide (CTAB) bilayer, which contributes to the inward solutal Marangoni flow. An enhanced inward solutal Marangoni flow at high particle concentrations assists in the formation of a wider depletion zone, the emergence of the diminished zone and suppression of the width of the coffee-ring deposits. Through detailed analysis of data from ex situ (scanning electron microscopy, SEM) and in situ (contact angle and confocal imaging) measurements, we establish a direct correlation between the different evaporation modes and the various deposition regimes. A detailed mechanism for the surface morphology modulation of AuNR deposits by tuning the nanoparticle concentration in the drying sessile drop is discussed.

White-Light Spectral Interferometry for Characterizing Inhomogeneity in Solutions and Nanocolloids.

We demonstrate the use of white-light spectral interferometry as an effective technique involving only linear optical interactions and a partially coherent light source to measure the complex transmission response function of optical resonance and to determine the corresponding variation in the refractive index relative to a reference. We also discuss experimental arrangements to increase the accuracy and sensitivity of the technique. The superiority of the technique over single-beam absorption measurements is demonstrated by the accurate determination of the response function of the chlorophyll-a solution. The technique is then applied to chlorophyll-a solutions of varying concentrations and gold nanocolloids to characterize inhomogeneous broadening. Results on the inhomogeneity of gold nanocolloids are also supported by transmission electron micrographs, showing distributions of the size and shape of the constituent gold nanorods.

Optical Density Optimization of Malaria Pan Rapid Diagnostic Test Strips for Improved Test Zone Band Intensity.

For the last few decades, the immunochromatographic assay has been used for the rapid detection of biological markers in infectious diseases in humans and animals The assay, also known as lateral flow assay, is utilized for the detection of antigen or antibody in human infectious diseases. There are a series of steps involved in the development of these immuno-chromatographic test kits, from gold nano colloids preparation to nitrocellulose membrane coating (NCM). These tests are mostly used for qualitative assays by a visual interpretation of results. For the interpretation of the results, the color intensity of the test zone is therefore very significant. Herein, the study was performed on a malaria antigen test kit. Several studies have reported the use of gold nanoparticles (AuNPs) with varying diameters and its binding with various concentrations of protein in order to optimize tests. However, none of these studies have reported how to fix (improve) test zone band intensity (color), if different sized AuNPs were synthesized during a reaction and when conjugated equally with same amount of protein. Herein, different AuNPs with average diameter ranging from 10 nm to 50 nm were prepared and conjugated equally with protein concentration of 150 µg/mL with KD = 1.0 × 10−3. Afterwards, the developed kits’ test zone band intensity for all different sizes AuNPs was fixed to the same band level (high) by utilization of an ultraviolet-visible spectrophotometer. The study found that the same optical density (OD) has the same test zone band intensity irrespective of AuNP size. This study also illustrates the use of absorption maxima (λ max) techniques to characterize AuNPs and to prevent wastage of protein while developing immunochromatographic test kits.

Rapid Photoligation of Gold Nanocolloids with Lipoic Acid-Based Ligands

An effective and easy to implement ligand exchange strategy is paramount to the design of stable and multifunctional gold and other inorganic nanocolloids. This is also crucial for their use in bio...

Single-Stage Formation of Film Polymer Composites in Supercritical Colloid Solutions of Nanoparticles Obtained by Laser Ablation

Abstract—A review of earlier studies is presented together with new results on the creation of highly concentrated colloid solutions with nanoparticles of noble metals (gold and silver) in a supercritical carbon dioxide (SC–CO2) medium and the development of a single-stage method for the production of polymer nanocomposites. The effect of the SC–CO2 density on the dynamics of the formation and decomposition of supercritical fluids (SCFs) of silver and gold nanocolloids in the process of pulsed laser ablation and after its termination is studied. The possibility of the formation of colloids from bimetallic nanoparticles was considered. The effective dielectric permittivity of a colloid solution of silver nanoparticles in SC–CO2 is calculated by the numerical modeling of extinction spectra in the dipole approximation at various densities, with consideration for the size of nanoparticles and the degree of their asphericity. The formation of various film nanocomposites based on a porous copolymer polytetrafluoroethylene—vinylidenefluoride with ruby nanoparticles and two modifications of pure porous polytetrafluoroethylene with silver nanoparticles in the same SCF reactor and with a single technological process is considered.

Photodriven chiral nanoparticle assembly

Nanomaterials Circularly polarized (CP) light can drive the synthesis of chiral small molecules and polymers. Kim et al. now show that photoreduction of a solution of a gold(III) salt (HAuCl4) and citrate with green CP laser light (543 nanometers) produces chiral gold nanocolloids. Initially, gold nanoparticles (about 3 nanometers in diameter) form and then assemble into chiral clusters. Red solutions had circular dichroism (CD) peak at 550 nanometers (the gold plasmon resonance) that changed sign for assemblies made with left- or right-handed CP light. The CD spectra could be quantitatively modeled on the basis of the irregular shapes revealed by electron tomography of these nanocolloids. J. Am. Chem. Soc. 141 , 11739 (2019).

One-pot synthesis of sugar-decorated gold nanoparticles with reduced cytotoxicity and enhanced cellular uptake

The unique properties of gold nanoparticles (AuNPs) enable their use for instance in medical diagnostics and therapeutic applications. The straightforward applicability of AuNPs requires accordingly the development of facile synthesis approaches towards the manufacturing of ready-to-use biomedical devices. Additionally, the behavior of nano-sized gold colloids in contact with living systems needs further and deeper investigations since nanoparticle-cell interactions, cellular uptake and cytotoxicity, particularly with regard to surface chemistry effects, are still poorly understood. Taken it into account, we herein demonstrate a facile one-pot synthesis of polymer-stabilized gold nanoparticles (AuNPs) using branched polyethyleneimine (BPEI) with primary amine groups substituted by lactose residues. The polymer chains are simultaneously responsible for the Au3+ reduction and stabilization of the produced metallic colloids. The approach enables the manufacturing of highly stable ∼ 20 nm AuNPs with the surface decorated by sugar moieties. The use of sugar substituted polymer chains leads to gold nanocolloids with reduced cytotoxicity and enhanced cellular uptake compared to those stabilized by unmodified polymer chains. These findings can lead to significant advances towards the application of AuNPs-based therapies, diagnostics and imaging.

SERS active substrates of gold nanoparticles embedded in the pool of 5-CB liquid crystal molecules organized in Langmuir–Reverse Schaefer films: A facile fabrication route to make the topological defects useful

This paper reports for the first time, fabrications of SERS active substrates I and II from Langmuir Reverse Schaefer (L-R Sh) films of 5-CB nematic liquid crystal molecules immersed in gold nanocolloids for 36 and 48 h respectively. Under parallel or slightly crossed polarizations, the POM images of these two substrates exhibit micro aggregated textures embedded in the pool of 5-CB molecules. Under crossed polarizations, the aggregated textures disappear with the appearance of bright birefringent defects of various sizes and shapes. The rationale behind the evolution of such micro aggregated textures and spatial locations of birefringent defects in these substrates are suggested. The FESEM images of the substrates exhibit distinctive patterns driven by the birefringent defects and confirm trapping of gold nanoparticles within the defect sites. The instabilities appeared in the patterns are estimated from statistical considerations in terms of Hurst exponent and phase space trajectories. The chaotic domains prevailing in these substrates are confirmed from the Lyapunov exponents. The efficacies of both the substrates as efficient SERS sensing platform have been tested to detect 4-MPy molecules at trace concentration. The as prepared substrates can be used as “lab on a chip” for chemical and biochemical sensing at ultralow concentrations.

Gold nanoparticle-carboxymethyl cellulose nanocolloids for detection of human immunodeficiency virus type-1 (HIV-1) using laser light scattering immunoassay.

It is estimated that over 100 million people have been infected with human immunodeficiency virus (HIV-1) resulting in approximately 30 million deaths globally. Herein, we designed and developed novel nano-immunoconjugates using gold nanoparticles (AuNPs) and carboxymethylcellulose (CMC) biopolymer, which performed simultaneously as an eco-friendly in situ reducing agent and surface stabilizing ligand for the aqueous colloidal process. These AuNPs-CMC nanocolloids were biofunctionalized with the gp41 glycoprotein receptor (AuNPs-CMC-gp41) or HIV monoclonal antibodies (AuNPs-CMC_PolyArg-abHIV) for detection using the laser light scattering immunoassay (LIA). These AuNPs-CMC bioengineered nanoconjugates were extensively characterized by morphological and physicochemical methods, which demonstrated the formation of spherical nanocrystalline colloidal AuNPs with the average size from 12 to 20 nm and surface plasmon resonance peak at 520 nm. Thus, stable nanocolloids were formed with core-shell nanostructures composed of AuNPs and biomacromolecules of CMC-gp41, which were cytocompatible based on in vitro cell viability results. The AuNPs-CMC-gp41 nanoconjugates were tested against HIV monoclonal antibodies conjugates (AuNPs-CMC_PolyArg-abHIV) using the light scattering immunoassay (LIA) where they behaved as active nanoprobes for the detection at nM level of HIV-1 antigenic proteins. This strategy offers a novel nanoplatform for creating bioprobes using green nanotechnology for the detection of HIV-1 and other virus-related diseases.

Gas Chromatography-Mass Spectrometry (GC-MS) Analysis of Essential Oils from AgNPs and AuNPs Elicited Lavandula angustifolia in vitro Cultures.

The aim of this study was to determine how the addition of gold and silver nanoparticles to culture media affects the composition of essential oils extracted from Lavandula angustifolia propagated on MS media with the addition of 10 and 50 mg·dm−3 of gold (24.2 ± 2.4 nm) and silver (27.5 ± 4.8 nm) nanocolloids. The oil extracted from the lavender tissues propagated on the medium with 10 mg·dm−3 AgNPs (silver nanoparticles) differed the most with respect to the control; oil-10 compounds were not found at all, and 13 others were detected which were not present in the control oil. The addition of AuNPs (gold nanoparticles) and AgNPs to the media resulted in a decrease of lower molecular weight compounds (e.g., α- and β-pinene, camphene, δ-3-carene, p-cymene, 1,8-cineole, trans-pinocarveol, camphoriborneol), which were replaced by those of a higher molecular weight (τ- and α-cadinol 9-cedranone, cadalene, α-bisabolol, cis-14-nor-muurol-5-en-4-one, (E,E)-farnesol).

Infused self‐assembly on Langmuir–Blodgett Film: Fabrication of highly efficient SERS active substrates with controlled plasmonic aggregates

AbstractA facile procedure towards the fabrication of highly reproducible, large area surface‐enhanced Raman scattering (SERS) active substrates through integration of Langmuir–Blodgett and self‐assembly technique has been reported. The plasmonic architectures of the substrates can be tuned at will to control the hot spots and hence the overall enhancements of SERS signal. The as‐prepared substrates of classes “A” and “B” incubated in gold nanocolloids show their respective efficacies as efficient SERS sensing scaffolds for detecting 4‐MPy molecule at ultrasensitive concentrations. Moreover, these substrates are unique in their kinds, where explicit or concomitant presence of protonated and deprotonated forms of 4‐MPy can be detected at trace concentrations. The substrates also exhibit remarkable spectral reproducibility and show early promise to overcome the “SERS uncertainty principle”. To our knowledge, this genre of SERS active substrates with facile control over plasmonics, is the first report of its kind and are expected to provide new direction towards successful fabrication of the next generation SERS sensing platforms.

Intracellular Delivery of Gold Nanocolloids Promoted by a Chemically Conjugated Anticancer Peptide.

We report on the ability of a chemically synthesized anticancer peptide, SVS-1, to promote the rapid uptake of gold nanorods (AuNRs) and gold nanoparticles (AuNPs) by live HeLa cells. For this, AuNPs and AuNRs, surface ligated with a multicoordinating polymer that presents several amine groups per ligand, are simultaneously reacted with SVS-1 and Texas-Red dye; the latter allows fluorescence visualization of the nanocrystals. Using epifluorescence microscopy, we find that incubation of the SVS-1-conjugated AuNPs and AuNRs with a model cancer cell line yields extended staining throughout the cell cytoplasm, even at low conjugate concentrations (∼0.1 nM). Furthermore, uptake is specific to the SVS-1-conjugated nanocrystals. Additional endocytosis inhibition experiments, where cells have been incubated with the conjugates at 4 °C or in the presence of endocytic inhibitors, show that significant levels of conjugate uptake persist. These results combined indicate an uptake mechanism that does not necessarily rely on endocytosis, a promising finding with implications for the use of nanomaterials in the field of biology and nanomedicine.

Utilization of Near IR Absorbing Gold Nanocolloids by Green Synthesis

The rapid developments in nanoscience, and its applications on biomedical areas have a large impact on drug delivery, tissue engineering, sensing, and diagnosis. Gold is widely investigated nanomaterial for the last couple of decades, since it has unique surface properties and very low toxicity to biological environment. In this work, we present a novel synthesis of gold nanoparticles (GNPs) exhibiting both visible and near-IR absorbance without agglomeration. The surface of GNPs were analyzed by routine methods and the binding kinetics were investigated by Surface Plasmon Resonance (SPR) Spectroscopy. The unique optical properties of near-IR asorbing GNP colloids hold promise for biological applications.

Role of gold nanocolloids on the photostability of 2-hydroxy-5-methyl benzaldehyde molecule and evidence of excited state intramolecular proton transfer process aided by DFT, non-adiabatic Ab Initio molecular dynamics simulations

The role of gold nanocolloids (AuNCs) on the photostability of 2-hydroxy-5-methyl benzaldehyde (HMBZ) molecule under UV exposures has been investigated using UV–vis absorption and fluorescence spectroscopic techniques. The experimental observations indicate the prominent role of AuNC towards controlling the photoproduct formations and rupture of intramolecular hydrogen bond (IHB) in the ‘CE’ conformeric form of the molecule. The rationale behind the experimental observations has been suggested to be due to the absorption of incident UV radiations by the nanoparticles, leaving behind only insignificant fraction of it for inducing photodegradation of HMBZ molecule. The photophysical behaviors of HMBZ molecule in different solvents and in varied pH media are also explicitly studied for the first time. Evidences of excited state intramolecular proton transfer (ESIPT) species of the molecule are estimated from the experimental observations aided by non-adiabatic Ab Initio molecular dynamics and density functional theory (DFT) calculations.

Numerical simulation of optical dispersion, group velocity, and waveguide properties of gold and silver nanocolloids and hybrids

This work is a numerical study of optical properties of colloids and polymers composed of gold and silver nanoparticles. A numerical method has been used to simulate absorption and dispersion properties of colloids and hybrids composed of gold and silver nanocolloids. For individual nanoparticles, optical susceptibilities and constants are studied considering their limited size effects. A theoretical model is used to relate macroscopic optical behavior of the nanohybrids to the susceptibility of individual particles. Effects of the size and the volume fraction of the particles on the peak and broadening of the absorption and dispersion bands are also discussed. The kind of the solvent in colloids and the host polymer in optical fibers composed of nanoparticles is a key parameter that is investigated. The group velocity of the light propagation in the mentioned hybrids is studied. Subsequently, waveguide properties of optical fibers made of PVA polymer composed of gold and silver nanoparticles are simulated numerically. As the main advantage of this procedure, dispersion and absorption curves of the nanohybrids could be obtained simultaneously. Optical dispersion curves, group velocity curves, and waveguide properties of these nanohybrids are offered for the first time.

Dual-responsive and Multi-functional Plasmonic Hydrogel Valves and Biomimetic Architectures Formed with Hydrogel and Gold Nanocolloids.

We present a straightforward approach with high moldability for producing dual-responsive and multi-functional plasmonic hydrogel valves and biomimetic architectures that reversibly change volumes and colors in response to temperature and ion variations. Heating of a mixture of hybrid colloids (gold nanoparticles assembled on a hydrogel colloid) and hydrogel colloids rapidly induces (within 30 min) the formation of hydrogel architectures resembling mold shapes (cylinder, fish, butterfly). The biomimetic fish and butterfly display reversible changes in volumes and colors with variations of temperature and ionic conditions in aqueous solutions. The cylindrical plasmonic valves installed in flow tubes rapidly control water flow rate in on-off manner by responding to these stimuli. They also report these changes in terms of their colors. Therefore, the approach presented here might be helpful in developing new class of biomimetic and flow control systems where liquid conditions should be visually notified (e.g., glucose or ion concentration changes).