Citrate-stabilized AuNPs Research Articles

Citrate gold nanoparticle exposure in the marine bivalve Ruditapes philippinarum: uptake, elimination and oxidative stress response.

Gold nanoparticles (AuNPs) are considered an important nano-sized component of the twenty-first century. Due to their unique physical and chemical properties, they are being used and developed for a wide range of promising applications in medicine, biology and chemistry. Notwithstanding their useful aspects, in recent years concern has been raised over their ability to enter cells, organelles and nuclei and provoke oxidative stress. In a laboratory-based experiment, the non-target marine bivalve Ruditapes philippinarum was used as a model organism. Uptake, elimination and molecular effects under short-term and sub-chronic exposure conditions to an environmental relevant concentration (0.75 μg L(-1)) of weakly agglomerating citrate AuNPs (∼20 nm) were studied. Our results demonstrate that at the tested concentration, the particles are readily taken up into the digestive gland > gills and can produce significant changes (p < 0.05) in oxidative stress and inflammatory response markers, as measured by phase II antioxidant enzymes and q-PCR gene expression analysis. However, the overall magnitude of responses was low, and oxidative damage was not provoked. Further, a significant elimination of Au from the digestive tract within a 7-day purification period was observed, with excretion being an important pathway. In conclusion, short-term and sub-chronic exposure to an environmental relevant concentration of citrate-stabilized AuNPs cannot be considered toxic to our model organism, while some further consideration should be given to chronic exposure effects.

Size-controlled preparation of monodisperse gold nanoparticles for detection of cardiac troponin I by immunochromatography assay

Objective To prepare the monodisperse, colloidal gold nanoparticles (AuNPs) with controllable sizes (50 nm, 65 nm, 79 nm and 102 nm) for the qualitative detection of cardiac troponin I (cTnI) by immunochromatography assay, and to evaluate the effectiveness of the detection. Methods Four kinds of monodisperse citrate-stabilized AuNPs were prepared using small AuNPs as growth centers (seeds) by a seeded growth-thermal aging protocol. As controls, two conventional AuNPs (20 nm, 40 nm) were prepared by the traditional citrate-reduction method. The mouse monoclonal antibody against cTnI -labeled AuNPs were dropped on polyester mat to make AuNPs conjugate pad. The detection line and quality control line of immunochromatography assay kits for detection of cTnI were coated by mouse anti-human cTnI monoclonal antibody paired with antibody in AuNPs and goat anti-mouse polyclonal antiboy respectively. The six kinds of AuNPs were employed as color-labels in immunochromatography assay kits for detecting cTnI, and the corresponding detection effects were evaluated in signal intensity, sensitivity, specificity and stability. The assay kit with the best performance was chosen and compared with the commercialized kits for the detection of cTnI in clinical samples. Results Four kinds of monodisperse AuNPs with large sizes of 50 nm, 65 nm, 79 nm, 102 nm respectively were successfully synthesized by the seeded growth-thermal aging method. The signal strength of four kinds of kits produced by the four large-sized AuNPs was superior to the kits produced by 20 nm AuNPs in detecting cTnI(all P<0.01). The signal strength of the kits produced by 65nm AuNPs showed the best performance among the six kinds of AuNPs(all P<0.01). The lowest detectable limit was 0.50 ng/ml. To compare the agreement of results from chemiluminescent immunoassay versus the results from kits produced by 65nm AuNPs, 100 serum samples have been used for detecting cTnI.Their positive coincidence rate was 97.30% and negative coincidence rate was 100%, the sensitivity and signal strength of the kits produced by 65nm AuNPs was superior to similar products which produced by ABON and Bottests company(all P<0.01). Conclusions Monodisperse, large-sized, citrate-stabilized AuNPs are controllably prepared by a seeded growth-thermal aging method. The development of large-size AuNPs-based immunochromatography assay kits is feasible. 65 nm AuNPs can be a suitable candidate for cTnI immunochromatography assay kit. Our findings provides a new idea for the current immunochromatography assay kits which still adopt small-sized AuNPs as color labels. Key words: Gold; Nanoparticles; Particle size; Immunoassay; Troponin I

Stability and Catalytic Activity of PEG-b-PS-Capped Gold Nanoparticles: A Matter of PS Chain Length

Gold nanoparticles (AuNPs) covered with a series of well-defined poly(ethylene glycol)-b-polystyrene (PEG-b-PS) amphiphilic diblock copolymers containing a thiol group at the end of PS block were prepared to explore the influence of chain length of PS segment on the colloidal stability and catalytic activity of AuNPs. PEG-b-PS amphiphilic diblock copolymers with different PS chain lengths and narrow molecular distributions (Mw/Mn ≤ 1.15) were synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization employing a PEG-based macromolecular chain transfer agent (Mn ≈ 2000 g/mol), followed by transforming the thiocarbonate end functionality into a thiol group in the presence of 2-aminoethanol and tributylphosphane. PEG-b-PS-stabilized gold nanoparticles (Au@PEG-b-PS) were prepared by ligand exchange reaction between citrate-stabilized AuNPs and the thiol end group of PEG-b-PS diblock copolymer. The presence of the hydrophobic PS layer not only improved the stability of Au@PEG-b-PS against electrolyte-induced aggregation but also greatly promoted the resistance of Au@PEG-b-PS against competitive displacement of dithiothreitol. Au@PEG-b-PS showed excellent catalytic activity in the reduction reaction of 4-nitrophenol into 4-aminophenol, and the catalytic activity increased with the decrease in the chain length of PS block. In addition, the high stability imparted by the PS layer endowed Au@PEG-b-PS with good reusability in catalysis without the loss of catalytic activity.

Fabrication of nanopatterned poly(ethylene glycol) brushes by molecular transfer printing from poly(styrene-block-methyl methacrylate) films to generate arrays of Au nanoparticles.

This article presents a soft lithographic approach using block copolymer (BCP) films to fabricate functional chemically patterned polymer brushes on the nanoscale. Hydroxyl-terminated poly(ethylene glycol) (PEG-OH) was transfer printed from the poly(methyl methacrylate) (PMMA) domains of self-assembled poly(styrene-block-methyl methacrylate) films to a substrate in conformal contact with the film to generate patterned PEG brushes mirroring the pattern of BCP domains. A key point in the study is that the chemistry of the functional transferred brushes is different from the chemistry of either block of the copolymer; PEG-OH is miscible only in the PMMA block and therefore transferred only from PMMA domains. The functionality of the PEG brushes was demonstrated by the selective immobilization of citrate-stabilized Au NPs (15 nm) and validated the generation of high-quality chemical patterns with sub-30-nm feature sizes.

Citrate-stabilized gold nanoparticles as negative controls for measurements of neurite outgrowth

Gold nanoparticles (AuNPs) are promising candidates for medical diagnostics and therapeutics, due to their chemical stability, optical properties, and ease of functionalization. Citrate-stabilized reference materials also have potential as negative controls in toxicology studies of other nanoparticles. Here we examine the impact of 30nm particles on the in vitro development of rat-cortex neural progenitor cells (NPCs), which mimic aspects of the developing neurological environment. AuNPs dispersed in a low-serum culture medium initially agglomerated, but then remained stable during a three day incubation period, and agglomerated only slightly during a ten day incubation period, as determined by dynamic light scattering. Transmission electron microscopy indicated the presence of individual nanoparticles at all timepoints examined. Fixed cells were cross-sectioned by ion milling and imaged by scanning electron microscopy and helium-ion microscopy to evaluate particle incorporation. Individual nanoparticles could be resolved inside cross-sectioned cells. AuNPs were incubated with developing NPCs for ten days at concentrations of 0.5μg/mL Au, 0.1μg/mL Au, or 0.05μg/mL Au. Adenosine triphosphate levels, as determined by bioluminescence measurements sensitive to low cell numbers, were not affected by AuNPs and the particles did not interfere with the assay. Multiple endpoints of neurite outgrowth were not altered by AuNPs, in particular, total neurite outgrowth per cell, a sensitive measure of neuronal development. Slide-level comparisons demonstrated the consistent response of NPCs to gold nanoparticles and a positive control chemical, neuroactive lithium. These results indicate that 30nm citrate-stabilized AuNPs could serve as negative-control reference materials for in vitro measurements of neurite outgrowth.

Carboxylated pillar[5]arene-coated gold nanoparticles with chemical stability and enzyme-like activity.

A facile synthesis of gold nanoparticles (AuNPs) covered with a multidentate macrocycle, carboxylated pillar[5]arene (CP), via a one-pot hydrothermal process is reported. The resulting AuNPs are highly stable against salts and pH variations, while their traditional counterparts are not stable at the same conditions. For the stabilization, multiple carboxylate groups of CP might contribute to electrostatic or steric stabilization. In addition, we found that CP-coated AuNPs exhibit greater peroxidase-like activity than citrate-stabilized AuNPs in the presence of silver cations. The system presented herein would provide a new scheme to fabricate unique sensory systems in combination with enzymes, which can bind to the pocket of CP.

Colorimetric protease assay by using gold nanoparticles and oligopeptides

A colorimetric protease assay based on the cleavage of gold nanoparticles (AuNPs) aggregates cross-linked with oligopeptides is developed. In this assay, when oligopeptide YHPQMNPYTKAGGGC is added to a solution containing citrate-stabilized AuNPs, cysteine and lysine on the oligopeptide causes rapid aggregation of AuNPs, resulting in color change from red to blue. However, in the presence of a model protease trypsin, the oligopeptide is cleaved by trypsin into two fragments. As a result, AuNPs do not aggregate and no color change can be observed. By using this principle, trypsin can be detected with the naked eye at a concentration as low as 0.5nM. This assay can also be applied to detect trypsin inhibitors such as benzamidine hydrochloride.

Highly Sensitive and Naked Eye Dual-readout Method for ʟ-Cysteine Detection Based on the NSET of Fluorophore Functionalized Gold Nanoparticles

A simple, highly sensitive and selective method based on the rhodamine B-covered gold nanoparticle with dual-readout (colorimetric and fluorometric) detection for <TEX>$\small{L}$</TEX>-cysteine is proposed. A mechanism is that citrate-stabilized AuNPs were modified with RB by electrostatic interaction, which enables the nanometal surface energy transfer (NSET) from the RB to the AuNPs, quenching the fluorescence. In the presence of <TEX>$\small{L}$</TEX>-cysteine, it was used as a competitor in the NSET by the strongly Au-S bonding to release RB from the Au surface and recover the fluorescence, and the red-to-purple color change quickly, which was monitored simply by the naked eye. Under the optimum conditions, the detection limit is as low as 10 nM. The method possessed the advantages of simplicity, rapidity and sensitivity at the same time. The method was also successfully applied to the determination of <TEX>$\small{L}$</TEX>-cysteine in human urine samples, and the results were satisfying.

Au/montmorillonite/polyaniline nanoflakes: facile fabrication by self-assembly and application as catalyst

Hydrogen bonding between citrate-stabilized Au NPs and the PANI backbone is proposed to play a pivotal role in driving the self-assembly between Au NPs and dedoped PANI, from which a highly catalytic Au NP/PANI/MMT nanocomposite was then synthesized.

Colorimetric detection of quaternary ammonium surfactants using citrate-stabilized gold nanoparticles (Au NPs)

Based on the hydrophobic effect inducing the aggregation of Au NPs, a rapid and low-cost colorimetric method for detection of quaternary ammonium surfactants using citrate-stabilized AuNPs was developed.

Fabrication of gold nanoparticle–polymer composite particles with raspberry, core–shell and amorphous morphologies at room temperature via electrostatic interactions and diffusion

Composite particles with varying morphologies composed of gold nanoparticles (Au NPs) and polymers were fabricated based on a combination of electrostatic interactions between the polymer particles and Au NPs and diffusion processes. The positively charged polymer particles were prepared from amino-terminated polystyrene (PS-NH2) and amino-terminated 1,2-polybutadiene (PB-NH2). Adsorption of citrate-stabilized Au NPs resulted in three different distribution states of Au NPs in the polymer particles, depending on the glass transition temperature (Tg) and molecular weight of the polymer. The adsorption of Au NPs onto PS-NH2 particles produced raspberry-like composite particle morphologies, while the NPs instead diffused into the PB-NH2 particles, since the Tg of PB-NH2 is below room temperature. The diffusion of Au NPs could be controlled by varying the molecular weight of the PB-NH2 and the diameter of the NPs, and both core-shell and amorphous distributions were successfully achieved.

Aggregation-Induced Enhancement Effect of Gold Nanoparticles on Triplet Excited State

Remarkable optical properties are posed with gold nanoparticles (AuNPs) due to the excitation of localized surface plasmon resonances, which makes AuNPs affect strongly both the ground state and the excited state of adjacent organic molecules. Compared with the ground state, the effect of AuNPs on excited state of organic molecules is not always fully understood. Here, we performed transient UV–vis absorption experiments to monitor the triplet excited state formation of three cationic dyes and one anionic dye in the presence of two types of gold nanoparticles: the citrate-stabilized AuNPs and ATP-protected AuNPs. It is found that the three cationic dyes can cause efficient aggregation of citrate-stabilized AuNPs, leading to AuNPs aggregates with varied size, whereas the ATP-protected AuNPs can be sustained in the monodispersed state. By comparing the circumstances of aggregated AuNPs and monodispersed AuNPs, we demonstrate that the enhancement effect on triplet excited state formation results from the agg...

Poly(N-isopropylacrylamide)-Stabilized Gold Nanoparticles in Combination with Tricationic Branched Phenylene-Ethynylene Fluorophore for Protein Identification

Gold nanoparticles stabilized by thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAM-AuNPs) were prepared by surface grafting of thiol-terminated PNIPAM onto citrate-stabilized AuNPs. The color change of the PNIPAM-AuNPs solution from red to blue-purple without precipitation when the solution was heated to 40 °C, above the lower critical solution temperature (LCST) of PNIPAM, indicated the thermoresponsive property of the synthesized AuNPs. PNIPAM-AuNPs were used to detect proteins by chemical nose approach based on fluorescence quenching of fluorophore by AuNPs. An array-based sensing platform for detection of six proteins, namely bovine serum albumin, lysozyme, fibrinogen, concanavalin A, hemoglobin, holo-transferrin human can be successfully developed from the PNIPAM-AuNPs having different molecular weights (4 and 8 kDa) and conformation (varied heat treatment from 25 to 40 °C) in combination with a tricationic branched phenylene-ethynylene fluorophore. From principal component analysis (PCA) followed by linear discriminant analysis (LDA), 100% accuracy of protein classification using a leave-one-out (LOO) approach can be achieved by using only two types of PNIPAM-AuNPs.

Colloidal Stability of Gold Nanoparticles Coated with Multithiol-Poly(ethylene glycol) Ligands: Importance of Structural Constraints of the Sulfur Anchoring Groups

Gold nanoparticles (AuNPs) coated with a series of poly(ethylene glycol) (PEG) ligands appended with four different sulfur-based terminal anchoring groups (monothiol, flexible dithiol, constrained dithiol, disulfide) were prepared to explore how the structures of the sulfur-based anchoring groups affect the colloidal stability in aqueous media. The PEG-coated AuNPs were prepared by ligand exchange of citrate-stabilized AuNPs with each ligand. The colloidal stability of the AuNPs in different harsh environmental conditions was monitored visually and spectroscopically. The AuNPs coated with dithiol- or disulfide-PEG exhibited improved stability under high salt concentration and against ligand replacement competition with dithiothreitol compared with those coated with their monothiol counterpart. Importantly, the ligands with structurally constrained dithiol or disulfide showed better colloidal stability and higher sulfur coverage on the Au surface compared to the ligands with more flexible dithiol and monot...

A Rapid Colorimetric Detection of Melamine in Raw Milk by Unmodified Gold Nanoparticles

We report a rapid, visual, facile colorimetric detection of melamine in raw milk by unmodified gold nanoparticles (AuNPs). AuNPs can be induced by melamine from dispersion to aggregation rapidly, along with the color change from red to blue (or purple). After the optimization of reaction conditions, the whole analysis only needs about 20 min including the simple pretreatment we designed. The analysis can be observed by the naked eye and simple to operate without sophisticated instruments. In the raw milk, the present limit of detection for melamine is down to ∼70 ppb. Furthermore, we explore the interaction principle between melamine and citrate-stabilized AuNPs in this work and establish the foundation for modifying the AuNPs and optimizing the system of AuNPs–melamine in the future.

Covalent Coupling of Nanoparticles with Low-Density Functional Ligands to Surfaces via Click Chemistry

We demonstrate the application of the 1,3-dipolar cycloaddition (“click” reaction) to couple gold nanoparticles (Au NPs) functionalized with low densities of functional ligands. The ligand coverage on the citrate-stabilized Au NPs was adjusted by the ligand:Au surface atom ratio, while maintaining the colloidal stability of the Au NPs in aqueous solution. A procedure was developed to determine the driving forces governing the selectivity and reactivity of citrate-stabilized and ligand-functionalized Au NPs on patterned self-assembled monolayers. We observed selective and remarkably stable chemical bonding of the Au NPs to the complimentarily functionalized substrate areas, even when estimating that only 1–2 chemical bonds are formed between the particles and the substrate.

Mercuric ions induced aggregation of gold nanoparticles as investigated by localized surface plasmon resonance light scattering and dynamic light scattering techniques

With the development of nanosciences, both localized surface plasmon resonance light scattering (LSPR-LS) and dynamic light scattering (DLS) techniques have been widely used for quantitative purposes with high sensitivity. In this contribution, we make a comparison of the two light scattering techniques by employing gold nanoparticles (AuNPs) aggregation induced by mercuric ions. It was found that citrate-stabilized AuNPs got aggregated in aqueous medium in the presence of mercuric ions through a chelation process, resulting in greatly enhanced LSPR-LS signals and increased hydrodynamic diameter. The enhanced LSPR-LS intensity (ΔI) is proportional to the concentration of mercuric ions in the range of 0.4–2.5 μM following the linear regression equation of ΔI = −84.7+516.4c, with the correlation coefficient of 0.983 (n = 6) and the limit of determination (3σ) about 0.10 μM. On the other hand, the increased hydrodynamic diameter can be identified by the DLS signals only with a concentration of Hg2+ in the range of 1.0–2.5 μM, and a linear relationship between the average hydrodynamic diameters of the resulted aggregates and the concentration of Hg2+ can be expressed as d = −6.16 + 45.9c with the correlation coefficient of 0.994. In such case, LSPR-LS signals were further applied to the selective determination of mercuric ions in lake water samples with high sensitivity and simple operation.

Highly efficient "theranostics" system based on surface-modified gold nanocarriers for imaging and photodynamic therapy of cancer.

Nanoparticle technologies are significantly impacting the development of both therapeutic and diagnostic agents. At the intersection between treatment and diagnosis, interest has grown for combining both paradigms into clinically effective formulations. In this study we describe a highly efficient drug vector for photodynamic therapy (PDT) and cell imaging developed by designing multifunctional and biodegradable block copolymer-gold nanoparticle (AuNP) conjugates. These conjugates act as water-soluble and biocompatible carriers that allow the delivery of a hydrophobic photosensitizer to a tumor site for PDT action. The 17.6 nm citrate-stabilized AuNPs used herein were modified with folic acid (FA)-conjugated biocompatible block copolymers through a bidentate dihydrolipoic acid (DHLA) linker. The FA-PEG-P(Asp-Hyd)-DHLA-modified AuNPs (FA-PEG-P(Asp-Hyd)-DHLA-AuNPs) were sufficiently stable that their optical properties were not changed under very harsh conditions. Then, the hydrophobic photosensitizer, pheophorbide a (Pheo), was conjugated to the stable vectors through a pH-sensitive linkage. The synthesis and composition of all copolymers were confirmed by 1H NMR measurement. The size of Pheo-conjugated FA-PEG-P(Asp-Hyd)-DHLA-AuNPs-Pheo determined by light-scattering measurements was about 54.7 nm. FE-SEM and FE-TEM images showed that these nanoparticles have a spherical shape and adequate dispersivity after modification. Confocal microscopy, flow cytometry assay, and bio-TEM measurements were used for determining the cellular uptake of Pheo and AuNPs in HeLa cells. The FA-PEG-P(Asp-Hyd)-DHLA-AuNPs-Pheo showed 99.16% cellular uptake and exhibited an excellent phototoxicity compared to free Pheo and FA-unconjugated nanoparticles at pH 6.4.

Amphiphilic gold nanoparticles formed at a liquid–liquid interface and fabrication of hybrid nanocapsules based on interfacial UV photodimerization

In this paper a novel method for fabrication of hybrid hollow capsules based on interface-directed self-assembly of gold nanoparticles (AuNPs) and interfacial photodimerization of anthracene is reported. A hydrophobic random copolymer with a disulfide group at the midpoint and pendant anthracene groups on the repeating units was synthesized by atom transfer radical polymerization. The hydrophobic random copolymer was dissolved in toluene and hydrophilic citrate-stabilized AuNPs were dispersed in water. An emulsion was obtained upon mixing of the two solutions. In the emulsion, hydrophilic AuNPs were able to undergo interface-directed self-assembly and amphiphilic AuNPs were produced at the liquid–liquid interface via ligand exchange. Hybrid nanocapsules with AuNPs on the surfaces were prepared after anthracene photodimerization at the liquid–liquid interface. Transmission electron microscopy, dynamic light scattering, UV-vis and scanning electron microscopy were used to characterize the structure of the hybrid nanocapsules. In the fabrication of the hybrid nanocapsules, the addition of small molecular surfactant has an important effect on the structures. The average size and size distribution of the hybrid nanocapsules can be controlled by controlling the concentration of the small molecular surfactant in the solution, and in the meanwhile the use of the small molecular surfactant will not reduce the surface density of AuNPs on the hybrid nanocapsules. The hybrid nanocapsules display effective catalytic activity in the reduction of 4-nitrophenol by NaBH4.

Highly selective and sensitive gold nanoparticle-based colorimetric assay for PO43− in aqueous solution

A rapid, simple and real-time colorimetric assay for detecting phosphate anions (PO43−) in aqueous solution was developed. The method was based on a novel functionalized gold nanoparticles (MPTP-Zn-AuNPs), which was synthesized by the ligand-exchange reaction of 4′-(4-mercaptophenyl)-2,2′:6′,2″-terpyridine zinc(II) complex (MPTP-Zn) with citrate-stabilized aqueous AuNPs. The strong coordination between MPTP-Zn-AuNPs and PO43− anion gave rise to a color change from wine-red to blue-gray that was discernible by the naked eye and an easily measurable alteration in the absorption spectrum of the particles in aqueous solution. And the new technique exhibited the high selectivity for PO43− over 11 other anions and could be used to determine PO43− with a detection limit of 11ppm.