Citrate-stabilized AuNPs Research Articles

Rapid Size Determination of Quasispherical Gold Nanoparticles by Electrocatalysis Efficiency-Regulated Electrochemiluminescence.

The size of gold nanoparticles (AuNPs) largely decides their properties and applications, making the rapid screening of AuNP size important. Despite the fact that AuNP-amplified electrochemiluminescence (ECL) is widely used in various ECL sensing applications, the mechanism of ECL enhancement remains elusive, especially the quantitative relationship between the enhanced ECL intensity and the size of AuNPs. In this work, taking quasispherical and citrate-stabilized AuNPs as model nanoparticles, we have reported that the ECL intensity of the S2O82--O2 system enhanced significantly with the increasing AuNP size. AuNPs acted as bielectrocatalysts for reducing the S2O82- and O2. The further study of enhancement mechanism demonstrates that AuNPs with increasing size facilitate the electron transfer and promote the generation of radicals required for the ECL emission, which produces more emitters-singlet oxygen. Meanwhile, the high surface density of citrate on small AuNPs suppresses the ECL signal by forming an electrostatic barrier. On the basis of the above phenomena, an ECL-based rapid AuNP size screening approach has been established. The accuracy of this platform is verified by the consistent results in comparison to transmission electron microscopy (TEM) measurements. This work not only provides deep insight into the correlation between the AuNP size and the ECL enhancement but also contributes an alternative to the TEM technique for the rapid AuNP size screening. Additionally, this study also extends the exploration of ECL-based structure analysis techniques toward nanomaterials through clarifying the structure-electrocatalytic activity correlation.

Copolymer-Coated Gold Nanoparticles: Enhanced Stability and Customizable Functionalization for Biological Assays.

Gold nanoparticles (AuNPs) play a vital role in biotechnology, medicine, and diagnostics due to their unique optical properties. Their conjugation with antibodies, antigens, proteins, or nucleic acids enables precise targeting and enhances biosensing capabilities. Functionalized AuNPs, however, may experience reduced stability, leading to aggregation or loss of functionality, especially in complex biological environments. Additionally, they can show non-specific binding to unintended targets, impairing assay specificity. Within this work, citrate-stabilized and silica-coated AuNPs (GNPs and SiGNPs, respectively) have been coated using N,N-dimethylacrylamide-based copolymers to increase their stability and enable their functionalization with biomolecules. AuNP stability after modification has been assessed by a combination of techniques including spectrophotometric characterization, nanoparticle tracking analysis, transmission electron microscopy and functional microarray tests. Two different copolymers were identified to provide a stable coating of AuNPs while enabling further modification through click chemistry reactions, due to the presence of azide groups in the polymers. Following this experimental design, AuNPs decorated with ssDNA and streptavidin were synthesized and successfully used in a biological assay. In conclusion, a functionalization scheme for AuNPs has been developed that offers ease of modification, often requiring single steps and short incubation time. The obtained functionalized AuNPs offer considerable flexibility, as the functionalization protocol can be personalized to match requirements of multiple assays.

The Brown Sugar Mediated Carbon Quantum Dots as a Novel Fluorescence Sensor for Sensitive Detection of Gentamicin and Its Application in Foods.

In this work, a novel fluorescence sensing strategy was proposed for the detection of gentamicin based on fluorescent carbon quantum dots (CQDs) and gold nanoparticles (AuNPs). Herein, the CQDs were green-synthesized for the first time via a one-step hydrothermal method utilizing brown sugar as the precursor. In the presence of citrate-stabilized AuNPs, the fluorescence of CQDs was quenched efficiently. Gentamicin, on the other hand, had a higher affinity for AuNPs and was able to compete with CQDs for a preferential binding to AuNPs, which ultimately led to the aggregation of AuNPs and freeing of CQDs in solution, causing the fluorescence recovery of CQDs. Based on the above phenomenon, the concentrations of gentamicin could be ascertained by detecting the variations in fluorescence intensity of CQDs. This sensing strategy exhibited excellent selectivity in various antibiotics. At the same time, the method displayed outstanding sensitivity for gentamicin, which was successfully applied to real samples detection.

Synergistic Bonding of Poly(N-isopropylacrylamide)-Based Hybrid Microgels and Gold Nanoparticles Used for Temperature-Responsive Controllable Catalysis of p-Nitrophenol Reduction

Stimuli-responsive hybrid nanoparticles used for controllable catalysis have been attracting increasing attention. This study aims to prepare hybrid microgels with excellent temperature-sensitive colorimetric and catalytic properties through combining the surface plasmon resonance properties of gold nanoparticles (AuNPs) with the temperature-sensitive properties of poly(N-isopropylacrylamide) (PNIPAM)-based microgels. Microgels with hydroxy groups (MG-OH) were prepared by soap-free emulsion polymerization, using N-isopropylacrylamide as the main monomer, hydroxyethyl methylacrylate as the functional monomer, N,N'-methylene bisacrylamide as the crosslinker, and 2,2'-azobis(2-methylpropionamidine) dihydrochloride as an initiator to ensure the microgels are positively charged. Furthermore, chemical modification on the surface of MG-OH was carried out by 3-mercaptopropyltriethoxysilane to obtain thiolated microgels (MG-SH). Two kinds of hybrid nanoparticles, AuNPs@MG-OH and AuNPs@MG-SH, were self-assembled, through electrostatic interaction between positive MG-OH and negative citrate-stabilized AuNPs as well as through synergistic bonding of electrostatic interaction and Au-S bonding between positive MG-SH and negative AuNPs. The morphology, stability, temperature-sensitive colorimetric properties, and catalytic properties of hybrid microgels were systematically investigated. Results showed that although both AuNPs@MG-OH and AuNPs@MG-SH exhibit good temperature-sensitive colorimetric properties and controllable catalytic properties for the reduction reaction of p-nitrophenol, AuNPs@MG-SH with synergistic bonding has better stability and higher catalytic performance than AuNPs@MG-OH. This work has good competitiveness against known PNIPAM-based materials and may provide an effective method for preparing smart catalysts by self-assembly with stimuli-responsive polymers, which has a great potential application for catalyzing a variety of reactions.

In vitro toxicity and internalization of gold nanoparticles (AuNPs) in human epithelial colorectal adenocarcinoma (Caco-2) cells and the human skin keratinocyte (HaCaT) cells

Ingestion and transdermal delivery are two common routes of nanoparticle (NP) exposure. In this study, the intracellular uptake, cytotoxicity and genotoxicity of 14 nm and 20 nm citrate-stabilized gold nanoparticles (AuNPs), 14 nm polyethylene glycol (PEG)-liganded carboxyl AuNPs, 14 nm PEG-liganded hydroxyl AuNPs and 14 nm PEG-liganded amine AuNPs were assessed on human epithelial colorectal adenocarcinoma (Caco-2) cells and the human skin keratinocyte (HaCaT) cells. The uptake of AuNPs in the cells was confirmed through darkfield microscopy and hyperspectral imaging followed by spectral angle mapping (SAM). A high level of citrate AuNPs was found in both cell lines whilst uptake of PEGylated AuNPs was low, irrespective of their functional groups. Cytotoxicity assessed by cell impedance was only observed for the 14 nm citrate-stabilized AuNPs. Enhanced cell proliferation was also observed in 14 nm PEG-liganded hydroxyl and 14 nm PEG-liganded amine AuNP-treated Caco-2 and HaCaT cells. For the assessment of genotoxicity, the in vitro micronucleus assay was used. Dose-dependent genotoxicity was observed in both Caco-2 and HaCaT cells, with all the AuNPs inducing genotoxicity. In conclusion, the entry of NPs into the cells as well as toxicity was dependent on their physicochemical properties such as surface coating and different chemical functional groups.

Influence of the synthesis route on the electrocatalytic performance for ORR of citrate-stabilized gold nanoparticles

Citrate-stabilized gold nanoparticles (AuNPs) were synthesized by two different citrate-based reduction methods, namely a one-pot wet chemical synthesis (Turkevich method) and seed-mediated growth (Bastús method). Although both types of AuNPs produce similar surface plasmon resonance bands and have a similar particle size and shape, the NPs obtained by the Turkevich method show significantly higher crystallinity. Static and dynamic electrochemical analysis using both types of AuNPs for the oxygen reduction reaction (ORR), under alkaline conditions, confirmed the significant influence of the synthesis route on the resulting onset potentials and maximum intensities in ORR electrocatalysis. These results were attributed to the higher percentage of Au(100) facets and the greater number of active sites on citrate-stabilized AuNPs obtained by the Turkevich method. Underpotential deposition of lead and electrochemical active surface area (ECSA) analysis further confirmed the importance of the crystalline facets in the performance of the AuNPs as electrocatalysts. This study demonstrates the influence of the synthesis route on the electrocatalytic activity of AuNPs, despite using the same starting reagents.

Interaction of Metallic Nanoparticles With Biomimetic Lipid Liquid Crystalline Cubic Interfaces.

In the past decades, events occurring at the nano-bio interface (i.e., where engineered nanoparticles (NPs) meet biological interfaces such as biomembranes) have been intensively investigated, to address the cytotoxicity of nanomaterials and boost their clinical translation. In this field, lamellar synthetic model membranes have been instrumental to disentangle non-specific interactions between NPs and planar biological interfaces. Much less is known on nano-biointeractions occurring at highly curved biological interfaces, such as cubic membranes. These non-lamellar architectures play a crucial -but far from understood-role in several biological processes and occur in cells as a defence mechanism against bacterial and viral pathologies, including coronaviruses infections. Despite its relevance, the interaction of cubic membranes with nano-sized objects (such as viral pathogens, biological macromolecules and synthetic NPs) remains largely unexplored to date. Here, we address the interaction of model lipid cubic phase membranes with two prototypical classes of NPs for Nanomedicine, i.e., gold (AuNPs) and silver NPs (AgNPs). To this purpose, we challenged lipid cubic phase membranes, either in the form of dispersed nanoparticles (i.e., cubosomes) or solid-supported layers of nanometric thickness, with citrate-stabilized AuNPs and AgNPs and monitored the interaction combining bulk techniques (UV-visible spectroscopy, Light and Synchrotron Small-Angle X-ray Scattering) with surface methods (Quartz Crystal Microbalance and Confocal Laser Scanning Microscopy). We show that the composition of the metal core of NPs (i.e., Au vs Ag) modulates their adsorption and self-assembly at cubic interfaces, leading to an extensive membrane-induced clustering of AuNPs, while only to a mild adsorption of isolated AgNPs. Such differences mirror opposite effects at the membrane level, where AuNPs induce lipid extraction followed by a fast disruption of the cubic assembly, while AgNPs do not affect the membrane morphology. Finally, we propose an interaction mechanism accounting for the different behaviour of AuNPs and AgNPs at the cubic interface, highlighting a prominent role of NPs’ composition and surface chemistry in the overall interaction mechanism.

Kinetic and Mechanistic Insight into the Surfactant-Induced Aggregation of Gold Nanoparticles and Their Catalytic Efficacy: Importance of Surface Restructuring.

Understanding the fundamental interactions between plasmonic metal nanoparticles (MNPs) and small molecules is of utmost importance in various applications such as catalysis, sensing, drug delivery, optoelectronics, and surface-enhanced Raman spectroscopy. Herein, we have investigated the early stage of the aggregation pathway of citrate-stabilized Au NPs with surfactants and explored their catalytic efficacy. Our findings reveal that (17 ± 2)-nm-sized citrate-stabilized Au NPs undergo concentration and time-dependent aggregation with positively charged cetyltrimethylammonium bromide (CTAB). Kinetic analyses revealed the presence of two distinct kinds of aggregates, namely, smaller clusters and a larger branched network of Au nanochains. At longer times and in the presence of higher concentrations of CTAB, these branched networks of Au nanochains transform into dense compact globular aggregates. The catalytic efficacy of Au NPs, branched Au nanochains, and dense compact aggregates has been explored with respect to the reductive hydrogenation of 4-nitophenol in the presence of excess NaBH4. Our study revealed that the catalytic rate decreases in the order of Au NPs > branched Au nanochains > compact aggregates. Interestingly, pre-equilibrating different Au NP samples with excess NaBH4 prior to the onset of the reaction results in similar catalytic activity irrespective of the aggregation state of Au NPs. This observation has been explained by considering efficient surface restructuring via ligand exchange with H- ions and the subsequent disruption of CTAB-induced aggregates of Au NPs. Moreover, the aggregated Au NPs can be recycled over several consecutive cycles for the reductive hydrogenation of 4-NP upon ligand exchange with H- ions. Taken together, our present study highlights the early-stage aggregation kinetics of Au NPs with CTAB surfactants and demonstrates the importance of the surface restructuring of Au NPs on their catalytic efficacy.

Finite-difference time-domain to screen Au NPs as SERS active substrate for the sensitive determination of prohibited drugs in fish via solvent cleaning.

Surface enhanced Raman spectroscopy (SERS), as a molecule-specific method using plasmonic nanostructures to significantly enhance signal intensity, has been employed in various fields. In our study, we investigated the size effect of gold nanoparticles (Au NPs) on surface plasmon response by finite-difference time-domain (FDTD) simulation. In addition, SERS experiments, using the same concentrations of crystal violet (CV), were also carried out to confirm the simulation results. On this basis, the size of citrate-stabilized Au NPs (∼100 nm) was controlled by a seed-mediated growth, thus providing great electromagnetic field enhancement for SERS detection of CV in fish. Methanol solvent cleaning along with high speed centrifugal separation was developed, which could not only remove lipids in fish, but also produce hot spots via induced aggregation of Au NPs. The SERS detection limit of CV in fish could be less than 1 ppb. Such cost-effective and facile routes will be attractive for the trace detection of various analytes in complex matrices.

Lysozyme-AuNPs Interactions: Determination of Binding Free Energy.

Investigation and optimization of lysozyme (Lys) adsorption onto gold nanoparticles, AuNPs, were carried out. The purpose of this study is to determine the magnitude of the AuNPs–lysozyme interaction in aqueous media by simple spectrophotometric means, and to obtain the free energy of binding of the system for the first time. In order to explore the possibilities of gold nanoparticles for sensing lysozyme in aqueous media, the stability of the samples and the influence of the gold and nanoparticle concentrations in the detection limit were studied. ζ potential measurements and the shift of the surface plasmon band showed a state of saturation with an average number of 55 Lys per gold nanoparticle. Lysozyme–AuNPs interactions induce aggregation of citrate-stabilized AuNPs at low concentrations by neutering the negative charges of citrate anions; from those aggregation data, the magnitude of the interactions has been measured by using Benesi–Hildebrand plots. However, at higher protein concentrations aggregation has been found to decrease. Although the nanocluster morphology remains unchanged in the presence of Lys, slight conformational changes of the protein occur. The influence of the size of the nanoclusters was also investigated for 5, 10, and 20 nm AuNPs, and 10 nm AuNPs was found the most appropriate.

Effect of Metal Nanoparticle Aggregate Structure on the Thermodynamics of Oxidative Dissolution.

Here, we compare the electrochemical oxidation potential of 15 nm diameter citrate-stabilized Au NPs aggregated by acid (low pH) to those aggregated by tetrakis(hydroxymethyl) phosphonium chloride (THPC). For acid-induced aggregation, the solution changes to a blue-violet color, the localized surface plasmon resonance (LSPR) band of Au NPs at 520 nm decreases along with an increase in absorbance at higher wavelengths (600-800 nm), and the peak oxidation potential (Ep) in anodic stripping voltammetry (ASV) obtained in bromide has a positive shift by as large as 200 mV. For THPC-induced aggregation (Au/THPC mole ratio = 62.5), the solution changes to a blue color as the LSPR band at 520 nm decreases and a new distinct peak at 700 nm appears, but the Ep does not exhibit a positive shift. Scanning transmission electron microscopy (STEM) images reveal that acid-induced aggregates are three-dimensional with strongly fused Au NP-Au NP contacts, while THPC-induced aggregates are linear or two-dimensional with ∼1 nm separation between Au NPs. The surface area-to-volume ratio (SA/V) decreases for acid-aggregated Au NPs due to strong Au NP-Au NP contacts, which leads to lower surface free energy and a higher Ep. The SA/V does not change for THPC-aggregated Au NPs since space remains between them and their SA is fully accessible. These findings show that metal NP oxidative stability, as determined by ASV, is highly sensitive to the details of the aggregate structure.

Factors Influencing the Surface Functionalization of Citrate Stabilized Gold Nanoparticles with Cysteamine, 3-Mercaptopropionic Acid or l-Selenocystine for Sensor Applications

Thiols and selenides bind to the surface of gold nanoparticles (AuNPs) and thus provide suitable platforms for the fabrication of sensors. However, the co-existence of adsorbed citrate on the surface of the nanoparticles can influence their functionalization behavior and potentially their sensing performance measured by the extent of particle aggregation. In this study, the functionalization of purchased (7.3 ± 1.2 nm) and in-house prepared AuNPs (13.8 ± 1.2 nm), under the same experimental conditions with either cysteamine (Cys), 3-mercaptopropionic acid (3-MPA), or l-selenocystine (SeCyst) was investigated. 1H-NMR measurements showed distinct citrate signatures on the in-house synthesized citrate-stabilized AuNPs, while no citrate signals were detected on the purchased AuNPs other than evidence of the presence of α-ketoglutaric acid. Carboxylate-containing species attributed to either citrate or α-ketoglutaric acid were identified in all functionalized AuNPs. ATR-FTIR spectroscopy confirmed the functionalization of AuNPs with Cys and 3-MPA, and energy dispersive X-ray (EDX) spectroscopy measurements suggested the formation of SeCyst functionalized AuNPs. Co-adsorption rather than displacement by the functionalizing agents and carboxylate-containing molecules was indicated, which for Cys and SeCyst functionalized AuNPs was also the aggregation limiting factor. In contrast, the behavior of 3-MPA functionalized AuNPs could be attributed to electrostatic repulsions between the functionalized groups.

Ingenious aspartic acid-functionalized gold nanoparticles by one-pot protocol for the sensitive detection of chromium (III) ions

In this work, we report an effective one-pot strategy for synthesizing aspartic acid-functionalized gold nanoparticles (Asp-AuNPs) and constructing chromium (III) ion (Cr3+) colorimetric sensing system. Aspartic acid, acting as a reductant and stabilizer, was used directly to synthesize functionalized AuNPs without additional surface modification procedure. The Asp-AuNPs possesses the same good stability and optical properties as citrate-stabilized AuNPs, which become a new option for preparing AuNPs. More importantly, aspartic acid exhibits superior performance than citrate and other succinic acid derivatives because of its Cr3+identifying property. The Asp-AuNPs was used for the sensitive and selective detection of Cr3+ based on the aggregation-induced color change of AuNPs from wine red to blue-gray. Under optimal conditions, the absorbance ratios (A660 nm/A520 nm) show good linearity with Cr3+ concentrations with a limit of detection of 0.6 nM. Furthermore, the proposed method was applied for the analysis of Cr3+ in environmental water samples successfully with a reliable recovery of 95.4%-105.1%. Besides, the scanometric analysis model based on three primary colors change was established to deal with the requirement for the rapid quantitative determination of Cr3+ inenvironmental emergencies.

RNAi in Spodoptera frugiperda Sf9 Cells via Nanomaterial Mediated Delivery of dsRNA: A Comparison of Poly-l-arginine Polyplexes and Poly-l-arginine-Functionalized Au Nanoparticles.

This work focused on the delivery of dsRNA either complexed with poly-l-arginine (PLR-polyplex) or loaded onto poly-l-arginine functionalized 20 nm Au nanoparticles (PLR/Au NPs). RNA interference (RNAi) of a luciferase gene expressed in Spodopteria frugiperda Sf9 stable cell line (Sf9_LUC) was used as a model system. The binding affinity of dsRNA with two modes of functionalization of Au NPs was investigated: the electrostatic binding of PLR on citrate stabilized Au NPs (e-PLR/Au NPs) via the layer-by-layer method or the covalent-linking reaction of the polymer with NHS groups on the Au NPs surface (c-PLR/Au NPs) with excess groups quenched with either hydroxylamine (c-PLR/Au/Hyd NPs) or bovine serum albumin (c-PLR/Au/BSA NPs). The formation of PLR-polyplex particles resulting from the complexation of PLR and dsRNA were revealed by transmission electron microscope (TEM), scanning transmission electron microscope (STEM), and elemental mapping by energy dispersive X-ray spectroscopy (EDS). Luciferase gene knockdown was evaluated after exposure of Sf9 cells for 72 h to 600 ng of dsRNA. Gene knockdown (GK) was found to be more efficient by exposing Sf9 cells to nanoscaled (size <100 nm) PLR-polyplex (58% GK), in contrast to microscaled (size >1 μm) PLR-polyplex (20% GK) or covalent PLR/Au/Hyd (7% GK) particles. The replacement of hydroxylamine by bovine serum albumin as ligand has significantly enhanced the efficiency of GK (31% GK). Investigation of endosomal escape, a key physiological barrier for dsRNA delivery, with CypHer5E labeled dsRNA showed the good ability for the dsRNA conjugated to the different nanosystems to enter the cells compared to the unconjugated one. This study provides valuable information concerning the required properties of materials used for dsRNA delivery in lepidopteran cells such as nanoparticle size, stability in the cell culture media, the polymer molecular weight and binding strength to the nanoparticle, and the nature of ligands on the surface.

Self-Assembled Gold Nanoparticle Cluster Array Onto Seeded Optical Fiber for Chemical Sensors

IntroductionGold nanoparticles (Au NP) exhibit interesting optical, physical and chemical features that can be tuned by modifying their morphology or by functionalizing them [1]. Therefore, a wide variety of sensing applications based on optical fiber have been developed using them, such as the colorimetric detection of toxic metal ions, cysteine or hydrogen peroxide. For those purposes, Au NP are typically embedded into polyelectrolyte multilayers or polymeric matrices, in order to be deposited onto optical fibers. Recent studies showed the possibility of depositing Au NP onto substrates seeded with block copolymers forming nanoparticle clusters [2]. The resulting array gave rise to a localized surface plasmon resonance, whose wavelength can be tailored, for instance, by modifying the amount of nanoparticles of each cluster or the distribution of the clusters. In order to check out the feasibility of the array as sensing structure, citrate-stabilized Au NPs have been self-assembled onto a polymeric template deposited along an optical fiber. The utilization of this device as a pH sensor opens the doors for the fabrication of sensors for different applications by controlling the seeding process and the morphology of Au NP clusters onto the surface of the optical fiber. Self-assembly of patterned gold nanoparticle cluster array along the optical fiber Au NP clusters were self-assembled by electrostatic interactions with a polymeric template [2] along the core of a 200 μm-core optical fiber. The optical fiber was first cleaned and activated by immersing it for 20 minutes in each one of the following solutions: soap, ultrapure water, potassium hydroxide (KOH) and ultrapure water. Subsequently, in order to build the template and so seeding the substrate, the fiber was dipped for 30 seconds in a 5 mg/mL solution of the cationic copolymer poly(styrene-b-2-vinylpyridine) in o-xylene. Finally, gold nanoparticles were self-assembled onto the template by immersing the fiber for 60 minutes into the anionic citrate-stabilized gold nanoparticles solution. The resulting coating was analyzed with images obtained by a Scanning Electronic Microscope (SEM).The deposition of the Au NP cluster array along the fiber was controlled by analyzing the absorption spectra during the different steps of the process explained above. The experimental set up used to study the processes consisted of the connection of the optical fiber between a white light source in the Visible Spectra (VIS) and a spectrometer (see Figure 1). Results The averaged diameter of the clusters is 120nm whereas the distance between the centers is 140nm (see Figure 2). Due to their formation on the seeded surface of the optical fiber, an absorption peak was observed in the transmitted spectra: as the formation of the cluster array moved forward, the absorption peak broadened and red-shifted from 630 nm up to 700 nm, while the absorbance increased, as it is shown in Figure 3. These changes in the absorption spectra are characteristic of the formation of the cluster array along the surface of the optical fiber.In order to evaluate the utilization of this Au NP cluster array as a possible sensing structure, the as-patterned optical fiber was exposed to different pH values ranging from 2 to 6. For each distinct pH value, the absorption peak was located at a different wavelength: as it can be observed in Figure 4, the absorption peak was red-shifted as the pH value decreased, showing a repetitive and reversible response. Conclusions The results exposed previously showed how the formation of a patterned gold nanoparticle cluster array yield to a localized surface plasmon resonance that could be used for measuring pH variations. The utilization of this array as sensing structure opens the possibility of utilizing this pattern for other sensing purposes by employing modified of functionalized Au NP. These parameters are currently been studied, together with different modifications of the patterned array, such as the distribution of the clusters and the amount of gold nanoparticles adsorbed in each cluster. Acknowledgements This research was supported by the Spanish State Research Agency (AEI) through the TEC2016-79367-C2-2-R project.

Rapid determination of the pesticide ametryn based on a colorimetric aptasensor of gold nanoparticles

A new, simple colorimetric aptasensor based on the aggregation-induced color change of citrate-stabilized AuNPs was designed for the specific and sensitive determination of ametryn.

Colloidal Capsules Assembled from Gold Nanoparticles Using Small-Molecule Hydrophobic Cross-linkers.

Colloidal capsules (or colloidosomes) have been studied for various applications such as therapeutic agent encapsulation, photothermal therapy, imaging, and energy storage. Emulsion-based synthesis is the most common approach for preparing colloidal capsules as it is relatively straightforward and scalable. However, while the initial formation requires only introducing the colloidal subunits into an emulsion and letting them assemble at the interface, a second step is required in order to prepare stable, covalently linked colloidal capsules, and preparing submicron colloidal capsules is quite challenging. Here, we describe a simple and quick one-step method to synthesize covalently linked, stable nanoscale colloidal capsules consisting of gold nanoparticles (NPs) (AuNP) and thiol-containing cross-linkers. Gold nanoparticle capsules (AuNCs) were formed by coating emulsion droplets containing thiol-containing cross-linkers with citrate-stabilized AuNPs. The physicochemical properties of the colloidal capsules can be tailored by changing the building blocks. In order to demonstrate this, colloidal capsules were assembled from AuNPs ranging from 5 to 20 nm in size. The use of the larger 20 nm starting particles resulted in AuNCs with a sufficiently pronounced red shift for λmax to be suitable for biological photothermal applications, where use of a near-infrared laser is strongly preferred. The AuNCs were found to be biocompatible and stable in cell culture conditions and to provide moderate heating. This demonstrates the modularity of the synthesis and the potential advantages of a one-step synthesis to prepare nanoscale gold colloidal capsules.

Selective and sensitive detection of L-Cysteine via fluorometric assay using gold nanoparticles and Rhodamine B in aqueous medium

An assay method based on fluorometric and colorimetric change was developed for selective sensing of important thiol containing amino acid L-Cysteine (L-Cys) by using gold nanoparticles (Au NPs) and Rhodamine B (RhB) in aqueous environment. This fluorometric assay is basically relies on the competitive binding between RhB and Au NPs via electrostatic interaction as well as strong thiol(-SH)-Au NPs bonding via chemisorption. Citrate stabilized Au NPs (diameter ∼27 nm) was synthesized by soft chemical method and characterized by UV–Vis absorption spectroscopy and Transmission electron microscopic (TEM) techniques. The change in non-radiative energy transfer between RhB and Au NPs are responsible for the observed drastic fluorescence quenching of RhB via FRET process. The recovery of fluorescence from the assay solution of RhB/Au NPs after addition of L-Cys was found linear over the concentration range 0.01 μM–1000 μM with experimental limit of detection (LOD) of 0.01 μM. The selective interaction of L-Cys with the mixed solution of RhB/Au NPs was reflected by the color change from wine to bluish-black of the final solution. The proposed fluorometric assay method accompanied with the observed colorimetric change could successfully differentiate other interfering amino acids including thiol (-SH) containing compounds namely L-Methionine, L-Homocysteine and antioxidant glutathione with the high degree of accuracy. Also the LOD is comparable to the concentration of L-Cys present in the blood plasma. The proposed sensing mechanism is also confirmed with pure human urine sample to detect the response of L-Cys in the urine. Therefore, this fluorometric assay technique for detection of L-Cys has great potential with the diagnostic impact for biomedical interest.

A simple colorimetric probe based on anti-aggregation of AuNPs for rapid and sensitive detection of malathion in environmental samples.

In this study, a simple colorimetric probe was developed for rapid and highly sensitive detection of malathion based on gold nanoparticles (AuNPs) anti-aggregation mechanism. A certain amount of NaOH can cause the aggregation of citrate-stabilized AuNPs due to the electrostatic interactions, and the color of AuNP solution changes from wine-red to gray. While in the presence of malathion, malathion is easily hydrolyzed in a strong alkali environment (pH > 9), followed by the production of a mass of negative charges, and thus the aggregated AuNPs turns to well-dispersed and the color of AuNP solution changes from gray to wine-red. This characteristic change can be visualized with the naked eye and quantitatively detected by an ultraviolet-visible (UV-Vis) spectrometer. Under optimized conditions, this probe exhibited a linear response to malathion in the concentration range of 0.05-0.8μM with a limit of detection (LOD) down to 11.8nM. The probe also showed good specificity for malathion detection in the presence of other interfering pesticide residues. Furthermore, the probe was successfully employed to detect malathion in environmental samples, with a recovery of 94-107% and a relative standard deviation (RSD) less than 8%. The results demonstrated that the proposed colorimetric probe based on anti-aggregation of AuNPs could be used for quantitative analysis of malathion and provided great potential for malathion determination in environmental samples.

Convenient and ultra-sensitive fluorescence detection of bovine serum albumin by using Rhodamine-6G modified gold nanoparticles in biological samples.

This study comprises a convenient, rapid and very sensitive method for the determination of bovine serum albumin (BSA). The technique is based on fluorescence resonance energy transfer (FRET) between Rhodamine-6G (R6G) acting as donor and gold nanoparticles (AuNPs) acting as acceptors. This method takes advantage of AuNPs that have high quenching efficiency, therefore the absorption spectra range shifts from 521to 635nm when aggregation of the AuNPs takes place. Furthermore, when R6G was electrostatically self-adsorbed to the citrate-stabilized AuNPs surface the fluorescence intensity was quenched. After addition of BSA, the fluorescence intensity of the R6G recovered as BSA induced aggregation of the AuNPs and the adsorbed R6G was released to the solution. The recovery of intensity displays a linear relationship with BSA concentration over the range from 0.8×10-11 M to 5.6×10-11 M. The detection limit for BSA was found to be 4.58×10-11 M. The proposed method exhibited rapid analysis with high selectivity for BSA determination in human urine, blood and serum samples.