Citrate-stabilized Gold Research Articles

Aggregated gold nanoparticles as photoactivators for the photopolymerization of proteins.

Photopolymerization of bovine serum albumin was carried out using reactive oxygen species (ROS) generated by the irradiation of citrate-stabilized gold nanoparticles by a pulsed Nd3+:YAG laser. The ROS in this case, singlet oxygen (1O2), targets aromatic amino acids within the protein to induce photopolymerization or crosslinking. Other ROS, like the hydroxyl radical, can also form in solution and under high-energy irradiation. The gold nanoparticles were aggregated using different cations in order to maximize singlet oxygen production. Experimental parameters like exposure time and laser power were optimized to minimize damage and maximize crosslinking efficiency, and damage-free crosslinking was observed at laser exposures up to 60s with samples containing calcium demonstrating most efficient crosslinking. To confirm the role of ROS in crosslinking, the reactive oxygen scavengers sodium azide and mannitol were added at different concentrations to scavenge the singlet oxygen and hydroxyl radical, respectively, and both were observed to stop or slow the formation of crosslinking. The use of gold nanoparticles offers an inert and biocompatible alternative to organic crosslinking agents like rose Bengal and methylene blue.

A Simple and Efficient Colorimetric Detection of Creatinine Based on Citrate-Stabilized Gold Nanoparticles

A Simple and Efficient Colorimetric Detection of Creatinine Based on Citrate-Stabilized Gold Nanoparticles

Gold nanoparticles assisted colorimetric sensing of paroxetine, duloxetine, and olanzapine in aqueous and micellar systems with improved sensitivity

The present study explored a rapid and facile colorimetric identification of two antidepressants (paroxetine and duloxetine) and one antipsychotic drug (olanzapine) in aqueous and micellar systems using citrate-stabilized gold nanoparticles (Cit-AuNPs). The sensing approach involved hydrogen bonding and electrostatic interactions on the surface of Cit-AuNPs. The attributes of Cit-AuNPs and their interactions with the drugs were probed using characterization techniques like UV–Vis spectroscopy, scanning electron microscopy (SEM), dynamic light scattering (DLS), zeta potential measurement, and Fourier-transform infrared spectroscopy (FT-IR). Various factors including the volume of Cit-AuNPs, pH, reaction time, surfactant concentration, and the sequence of addition of reagents were optimized to inspect their impacts on sensing results. Under optimized conditions, the probe showed good linearity for the three drugs at the nanomolar (nM) range. Consequently, the color of the Cit-AuNP solution transformed from red to royal purple and blue, which was visible to the naked eye and monitored by visible absorption spectra. This label-free optical detection approach could recognize paroxetine (Prx), duloxetine (Dlx), and olanzapine (Olz) in aqueous system at concentrations ranging from 1 to 17 nM with a limit of detection (LOD) of 0.312, 0.258, and 0.418 nM (S/N = 3), respectively. Meanwhile, the sensitivity was improved in the Triton X-100 (TX-100) micellar system with LOD of 0.029, 0.030, and 0.029 nM for Prx, Dlx, and Olz, respectively accompanied by a shift in the absorption bands. The micellar system contributes stability to the Cit-AuNP-drug complex. The devised colorimetric approach was convenient and did not require any complex equipment. It was efficaciously used to detect three drugs in pharmaceutical products, spiked human urine, and blood serum samples with satisfactory recoveries of 99.83–103.45% and RSD < 3.5%. Notably, the sensing assay demonstrated good selectivity for three drugs in the existence of commonly encountered foreign species and certain common drugs with a relative error below 3%. The results of the present study were statistically compared with reference methodology. The results were validated with no significant difference between the devised and reported approaches considering precision and accuracy, respectively.

Aptamer-conjugated gold nanoparticles for portable, ultrasensitive naked-eye detection of C-reactive protein based on the Tyndall effect

BackgroundC-reactive protein (CRP) represents an early clinical biomarker that indicates the presence of inflammatory or infectious conditions in the human body. Today's procedures approved by the Food and Drug Administration (FDA) imply expensive equipment and highly trained personnel to perform the test. Therefore, a new diagnostic method with high detection efficiency and less cost is urgently needed for delivering rapid and timely results in point-of-care (POC) service. ResultsHerein, we propose a new, equipment-free, and portable sensing method for the future POC detection of CRP based on the Tyndall effect (TE). In our study, aptamer-conjugated citrate-stabilized gold nanoparticles (apta-AuNPs) are exploited as the sensing platform. The apta-AuNPs’ interaction with CRP in a saline environment leads to their aggregation, thus enhancing the scattering of light when the solution is exposed to a 640 nm pointer laser line. Firstly, the enhancement of the scattering light as a function of increasing concentration of CRP in solution is measured spectroscopically using a typical 90-degree angle spectrofluorometer and then the measurements are compared to the classic colorimetric detection using an UV–Vis spectrophotometer. Finally, to achieve high portability and accessibility, we demonstrate that the measurement of CRP concentration can be performed with similar accuracy but in a more direct and inexpensive way by using a laser pointer pen as the excitation source and a camera of a low-budget smartphone as a quantitative reader instead of most expensive spectrofluorometer. SignificanceThe portable TE-based assay exhibits a wide linear dynamic range (1–60 μg/mL) for the detection of CRP with a limit of detection (LOD) of 92 ng/mL The proposed method is capable to integrate both standard and high-sensitivity CRP analysis in a single procedure with increased sensitivity and prompt delivery of analysis results. Moreover, the sensing procedure is significantly faster than the FDA approved ones with a detection time of only 10 min. Finally, as a proof-of-concept, our findings demonstrate excellent recovery for CRP detection in spiked and diluted urine samples, highlighting the strong potential of this sensing method for POC applications.

Selective cytotoxicity of citrate-stabilized gold nanorods against aggressive cancer cells and their potential in the melanoma treatment

Selective cytotoxicity of citrate-stabilized gold nanorods against aggressive cancer cells and their potential in the melanoma treatment

Near Infrared Responsive Gold Nanorods Attenuate Osteoarthritis Progression by Targeting TRPV1.

Osteoarthritis (OA) is the most common degenerative joint disease worldwide, with the main pathological manifestation of articular cartilage degeneration. It have been investigated that pharmacological activation of transient receptor potential vanilloid 1 (TRPV1) significantly alleviated cartilage degeneration by abolishing chondrocyte ferroptosis. In this work, in view of the thermal activated feature of TRPV1, Citrate-stabilized gold nanorods (Cit-AuNRs) is conjugated to TRPV1 monoclonal antibody (Cit-AuNRs@Anti-TRPV1) as a photothermal switch for TRPV1 activation in chondrocytes under near infrared (NIR) irradiation. The conjugation of TRPV1 monoclonal antibody barely affect the morphology and physicochemical properties of Cit-AuNRs. Under NIR irradiation, Cit-AuNRs@Anti-TRPV1 exhibited good biocompatibility and flexible photothermal responsiveness. Intra-articular injection of Cit-AuNRs@Anti-TRPV1 followed by NIR irradiation significantly activated TRPV1 and attenuated cartilage degradation by suppressing chondrocytes ferroptosis. The osteophyte formation and subchondral bone sclerosis are remarkably alleviated by NIR-inspired Cit-AuNRs@Anti-TRPV1. Furthermore, the activation of TRPV1 by Cit-AuNRs@Anti-TRPV1 evidently improved physical activities and alleviated pain of destabilization of the medial meniscus (DMM)-induced OA mice. The study reveals Cit-AuNRs@Anti-TRPV1 under NIR irradiation protects chondrocytes from ferroptosis and attenuates OA progression, providing a potential therapeutic strategy for the treatment of OA.

Effects of citrate-stabilized gold and silver nanoparticles on some safety parameters of Porphyridium cruentum biomass.

Introduction: Our research raises the question of how realistic and safe it is to use gold and silver nanoparticles in biotechnologies to grow microalgae, which will later be used to obtain valuable products. To this purpose, it was necessary to assess the influence of 10 and 20nm Au and Ag nanoparticles stabilized in citrate on the growth of microalga Porphyridium cruentum in a closed cultivation system, as well as some safety parameters of biomass quality obtained under experimental conditions. Methods: Two types of experiments were conducted with the addition of nanoparticles on the first day and the fifth day of the cultivation cycle. Changes in productivity, lipid content, malondialdehyde (MDA), as well as antioxidant activity of microalgae biomass have been monitored in dynamics during the life cycle in a closed culture system. Results: The impact of nanoparticles on the growth curve of microalgae culture was marked by delaying the onset of the exponential growth phase. A significant increase in the content of lipids and MDA in biomass was noted. Excessive accumulation of lipid oxidation products within the first 24h of cultivation resulted in altered antioxidant activity of red algae extracts. Discussion: Citrate-stabilized gold and silver nanoparticles proved to be a stress factor for red microalga Porphyridium cruentum, causing significant changes in both biotechnological and biomass safety parameters. Addition of Au and Ag nanoparticles during the exponential growth phase of porphyridium culture led to an enhanced lipid accumulation and reduced MDA values in biomass.

Multilayer Coatings Based On Citrate-Stabilized Gold Nanoparticles and Polydiallyldimethylammonium Chloride for the Electrophoretic Separation of Carboxylic Acids

The conditions for the formation of physically adsorbed three-layer coatings of quartz capillary walls in capillary electrophoresis (CE) with successively deposited oppositely charged layers of polydiallyldimethylammonium chloride (PDADMAC) modifiers and citrate-stabilized gold nanoparticles (GNPs) are proposed. It was shown that three-layer PDADMAC–GNP–PDADMAC coatings favorably differ from monolayer coatings with PDADMAC by greater stability in a wide range of pH (2–10). The formed coatings were characterized by scanning electron microscopy, and the presence of a uniform dense layer of nanoparticles on the capillary surface was confirmed. The applicability of the modified capillaries under CE conditions was demonstrated by the separation of a mixture of 16 carboxylic acids. An increase in the separation selectivity achieved with the use of three-layer coatings based on GNPs was explained by the reversible exchange of citrate anions on the GNP surface with negatively charged analytes in the course of electrophoretic analysis.

Multilayer Coatings Based On Citrate-Stabilized Gold Nanoparticles and Polydiallyldimethylammonium Chloride for the Electrophoretic Separation of Carboxylic Acids

Multilayer Coatings Based On Citrate-Stabilized Gold Nanoparticles and Polydiallyldimethylammonium Chloride for the Electrophoretic Separation of Carboxylic Acids

Novel approaches to the formation of coatings based on gold nanoparticles and albumin for chiral separation in capillary electrophoresis

Combination of properties of gold nanoparticles and bovine serum albumin is promising for the formation of chiral stationary phases enabling high enantioselectivity due to developed surface of coatings and increased chiral selector concentration on the capillary walls. In this work we proposed and compared two approaches to the formation of physically adsorbed multilayer coatings based on citrate-stabilized gold nanoparticles (cGNP) and bovine serum albumin (BSA) for the chiral separation in capillary electrophoresis. In the first approach pre-synthesized cGNP modified with BSA were immobilized on the capillary coated by poly(diallyldimethylammonium chloride) (PDADMAC). PDADMAC polymer was used as a binding layer promoting sorption of the nanoparticles on the capillary surface. It was shown that cGNP-BSA was poorly adsorbed on the capillary surface due to low zeta potential and could not be used for the formation of dense coatings. The second approach included sequential layer-by-layer deposition of PDAMAC and cGNP, resulting in the formation of a dense layer of nanoparticles. The main stage included in-capillary functionalization of cGNP with BSA. Scanning electron microscopy confirmed that the layer-by-layer deposition of modifiers ensured the formation of dense layer of nanoparticles on the capillary surface. The coating was stable in the entire range of pH studied (2–10). The application of such coating allowed reduction of BSA concentration (to 5 μM) in the background electrolyte required for the tryptophan enantiomers separation. It confirms the prospectiveness of combining nanoparticles and chiral selectors for the increase of specific surface area of the capillary inner walls.

Charge-driven arrested phase-separation of polyelectrolyte-gold nanoparticle assemblies leading to plasmonic oligomers

Aggregates of charged metal particles obtained by electrostatic coupling with a compound of opposite charge in the vicinity of the net zero charge ratio are of interest in the field of plasmonics because the inter-particle distance is minimal, which favours plasmonic coupling. However, these structures present a low colloidal stability limiting the development of applications. In this article we show that globally neutral aggregates formed by electrostatic complexation of citrate-stabilized gold particles and a quaternized chitosan (i.e., polycation) around the net zero charge ratio could be stabilized at a nanometric size by the subsequent addition of polyelectrolyte chains. Furthermore, the sign of the charge carried by the stabilizing chains determines the sign of the global charge carried by the stabilized complexes. The stabilization is demonstrated in saline environment on a broad pH range as well as in a cell culture media over periods of several days. Contrarily to stabilization by charged particles, our stabilized complexes are found to retain their initial characteristics (i.e. shape, size, internal structure and optical properties) after stabilization. Hence, the plasmonic coupling allows to maximize the optical absorption around the 800nm wavelength at which the lasers used for thermoplasmonic and surface enhanced Raman scattering analysis operate.

Construction of SERS substrates by gold nanoparticles assembly on polymeric matrices

This study reported the fabrication of stable and reproducible large-area SERS substrates based on the assembly of pre-synthesized gold nanoparticles on reconstructed poly(styrene-block-2-vinylpyridine) (PS-b-P2VP) films with different molecular weights and PS/P2VP volume fractions. PS-b-P2VP films on a glass substrate were submitted to different reconstruction procedures: immersion in deionized water or ethanol, exposure to toluene/THF vapor, or thermal annealing. These reconstructed films were immersed in citrate-stabilized gold NPs suspension for different time intervals. P2VP microdomains acted selectively as a binding site for the negatively-charged nanoparticles through electrostatic interactions. The substrates were characterized by UV–vis spectroscopy and atomic force microscopy. The SERS activity was tested using the Nile Blue (NB) dye as a molecular probe. The results demonstrated that the annealing treatment and the molecular weight of the copolymers strongly influence the NPs dispersion and, consequently, the SERS enhancements. Moreover, we established that water and ethanol swelling of the micelles allowed a high uniformity of nanoparticle deposition over the films. In contrast, more efficient SERS enhancement was observed in the nanocomposites treated with toluene/THF vapor annealing and thermal annealing.

Tuning Morphologies and Reactivities of Hybrid Organic-Inorganic Nanoparticles.

Hybrid nanoparticles (hNPs), or nanoparticles composed of both organic and inorganic components, hold promise for diverse energy and environmental applications due to their ability to stabilize reactive nanomaterials against aggregation, enhancing their ability to pervade tortuous spaces and travel long distances to degrade contaminants in situ. Past studies have investigated the use of polymer or surfactant coatings to stabilize nanomaterials against aggregation. However, fabrication of these materials often requires multiple steps and lacks specificity in the control of their morphologies and reactivities. Here, we demonstrated a method of producing stable hNPs with tunable morphologies by incubating polystyrene nanoparticles formed via Flash NanoPrecipitation with citrate-stabilized gold nanocatalysts. Using this simple fabrication technique, we found that gold adsorption to polystyrene nanoparticles was enabled by the presence of a good solvent for polystyrene. Furthermore, changing process parameters, such as gold incubation time, and molecular parameters, such as polymer molecular weight and end-group functionality, provided control over the resultant nanocatalyst loading and dispersal atop hNPs. We classified these morphologies into three distinct regimes─aggregated, dispersed, or internalized─and we showed that the emergence of these regimes has key implications for controlling reaction rates in applications such as heterogeneous catalysis or groundwater remediation. Specifically, we found that hNPs with gold nanocatalysts embedded below the surfaces of polystyrene nanoparticles exhibited slower bulk catalytic reduction capacity than their disperse, surface-decorated counterparts. Taken together, our work demonstrates a simple way by which hNPs can be fabricated and presents a method to control catalytic reactions using reactive nanomaterials.

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.

Role of Common Cell Culture Media Supplements on Citrate-Stabilized Gold Nanoparticle Protein Corona Formation, Aggregation State, and the Consequent Impact on Cellular Uptake

Sodium citrate-stabilized gold nanoparticles (AuNPs) are destabilized when dispersed in cell culture media (CCMs). This may promote their aggregation and subsequent sedimentation, or under the proper conditions, their interaction with dispersed proteins can lead to the formation of a NP-stabilizing protein corona. CCMs are ionic solutions that contain growth substances which are typically supplemented, in addition to serum, with different substances such as dyes, antioxidants, and antibiotics. In this study, the impact of phenol red, penicillin-streptomycin, l-glutamine, and β-mercaptoethanol on the formation of the NP-protein corona in CCMs was investigated. Similar protein coronas were obtained except in the presence of antibiotics. Under these conditions, the protein corona took more time to be formed, and its density and composition were altered, as indicated by UV-vis spectroscopy, Z potential, dynamic light scattering, and liquid chromatography-mass spectrometry analyses. As a consequence of these modifications, a significantly different AuNP cellular uptake was measured, showing that NP uptake increased as did the NP aggregate formation. AuNP uptake studies performed in the presence of clathrin- and caveolin-mediated endocytosis inhibitors showed that neither clathrin receptors nor lipid rafts were significantly involved in the internalization mechanism. These results suggest that in these conditions, NP aggregation is the main mechanism responsible for their cellular uptake.

Some peculiarities of the response of microalga Porphyridium cruentum to the action of citrate-stabilized silver and gold nanoparticles

The article presents the results regarding some peculiarities of the response of microalga Porphyridium cruentum to the action of citrate-stabilized silver and gold nanoparticles with sizes of 10 nm and 20 nm. It has been established that the tested nanoparticles added to the cultivation medium of microalga P. cruentum at the beginning of lag phase did not change significantly its productivity during the cultivation cycle. The effect of this type of nanoparticles on the chlorophyll a and β - carotene synthesis during the cultivation of porphyridium is manifested depending on the size and concentrations applied.

A sensitive nanocomposite design via polydopamine mediated Au and Ag nanoparticles: Voltammetric assay for dopamine in biological samples

In this study, an electrochemical sensor for the sensitive determination of dopamine was developed based on pencil graphite electrodes (PGEs) modified by two different approaches. In the first approach, the polydopamine (PDA)-coated PGEs (PDA@PGE) were decorated with the as-prepared citrate-stabilized gold or silver nanoparticles (cit-AuNPs and cit-AgNPs, respectively). In the second approach, similarly, PDA@PGE was decorated with metallic NPs by reducing silver (r-AgNPs) or gold ions (r-AuNPs). In this process, PDA with its numerous functional groups such as catechol and amine plays an essential role in both the reduction of the metallic ions and the adsorption and stabilization of the NPs. The characterization of the modified electrodes was examined by field-emission scanning electron microscopy, energy-dispersive x-ray spectroscopy, ultraviolet-visible absorption spectra, and cyclic voltammetry. These observations depicted that the density of NPs could be manipulated over time, and 3 h of NPs deposition time was detected as optimal via electrochemical analysis. The PDA@PGEs decorated with AuNPs were also used for the electrochemical analysis of dopamine in calibration and validation studies. In the analysis of dopamine by the square wave voltammetry method, the limit of detection (LOD) and the limit of quantification (LOQ) were 0.53 and 1.77 µM, respectively. For the differential pulse voltammetry, LOD and LOQ were 0.96 and 3.2 µM, respectively. We observed that the PDA-coated PGEs decorated with AuNPs provided high accuracy, precision, reproducibility, and reliability. The experimental results were found to be insignificant at a 95% confidence level. The developed sensor was applied for the determination of dopamine in biological fluids.

Some aspects of the application of gold nanoparticles in the biotechnology of the microalga Porphyridium cruentum

The present study aimed to investigate the effect of gold nanoparticles (AuNPs) on the productivity of red microalga Porphyridium cruentum and the content of some biologically active compounds of technological interest in biomass. We used citrate-stabilized gold nanoparticles (AuNPs) with a diameter of 5 nm at concentrations from 0.5 to 1.5 nM and a diameter of 10 nm at concentrations from 0.005 to 0.1 nM. The results demonstrated the lack of toxicity of the nanoparticles used, which was confirmed by the maintenance of an adequate level of microalgae productivity and protein content in biomass. Concentrations have been established for each of the applied AuNPs, which provide an increased accumulation of phycobiliproteins in porphyiridium biomass.

Substituent Effects Impact Surface Charge and Aggregation of Thiophenol-Labeled Gold Nanoparticles for SERS Biosensors.

SERS immunoassay biosensors hold immense potential for clinical diagnostics due to their high sensitivity and growing interest in multi-marker panels. However, their development has been hindered by difficulties in designing compatible extrinsic Raman labels. Prior studies have largely focused on spectroscopic characteristics in selecting Raman reporter molecules (RRMs) for multiplexing since the presence of well-differentiated spectra is essential for simultaneous detection. However, these candidates often induce aggregation of the gold nanoparticles used as SERS nanotags despite their similarity to other effective RRMs. Thus, an improved understanding of factors affecting the aggregation of RRM-coated gold nanoparticles is needed. Substituent electronic effects on particle stability were investigated using various para-substituted thiophenols. The inductive and resonant effects of functional group modifications were strongly correlated with nanoparticle surface charge and hence their stability. Treatment with thiophenols diminished the negative surface charge of citrate-stabilized gold nanoparticles, but electron-withdrawing substituents limited the magnitude of this diminishment. It is proposed that this phenomenon arises by affecting the interplay of competing sulfur binding modes. This has wide-reaching implications for the design of biosensors using thiol-modified gold surfaces. A proof-of-concept multiplexed SERS biosensor was designed according to these findings using the two thiophenol compounds with the most electron-withdrawing substitutions: NO2 and CN.