AuNPs Solution Research Articles

Fluorometric determination of morphine via its effect on the quenching of fluorescein by gold nanoparticles through a surface energy transfer process.

A method is described for sensitive and selective fluorometric determination of morphine. It is based on the effect of morphine on quenching of the fluorescence of fluorescein by gold nanoparticles (AuNPs) via surface energy transfer. When fluorescein is added to solutions of colloidal AuNPs, its fluorescence becomes quenched due to nanometal surface energy transfer (NSET) because the absorption of AuNPs strongly overlaps the emission spectrum of fluorescein. In the presence of morphine, which contains both a tertiary nitrogen ring atom and a phenolic hydroxy group, it will coordinate to the AuNPs, and this causes recovery of fluorescence. The presence of a tertiary nitrogen ring atom and a phenolic hydroxy group (both required for the effect to occur) in morphine make the probe highly selective and sensitive for morphine. A paper strip assay also was developed by utilizing this detection scheme. The turn-on fluorescent probe was successfully applied to the determination of morphine in spiked serum and urine samples. The method has a 53 pM limit of detection. The paper strip was applied tothe determination of morphine in sweat, urine and other biological fluids. It is perceived to be useful for early detection of drug abuse by adolescent. Graphical abstract Schematic of the mechanism of fluorescence turn on detection of morphine using Au NPs (gold nanoparticles) acting asquencher of the fluorescence of fluorescein.

Colorimetric and visual determination of acrylamide via acrylamide-mediated polymerization of acrylamide-functionalized gold nanoparticles.

A colorimetric assay is described for acrylamide (AA). It is based on color changes induced by an increase in the distance between gold nanoparticles (AuNPs) that is caused by AA copolymerization. First, AuNPs were modified with a thiolated propylene amide poly(ethylene glycol) that also contains the AA functionality. The carbon-carbon double bonds on the modified AuNPs can be polymerized under the catalysis of a photoinitiator and under UV irradiation. This results in the aggregation of the AuNPs and in a color change from red to gray. In the presence of AA, the distance between the AuNPs increases due to copolymerization with AA, and the solution of AuNPs preserves its original red color. Under optimized conditions, the absorption ratio (A525/A740) of the solution increases linearly in the 1nM to 10μM free AA concentration range, with a 0.2nM limit of detection. Hence, the method meets the need for rapid monitoring of trace AA in food. The method has a relative error (RSD) that is lower compared to the accepted HPLC method. Graphical abstract Schematic of a novel colorimetric strategy for acrylamide (AA) detection based on the increase of distance between gold nanoparticles (AuNPs) caused by AA participated polymerization.

Dichroic Behavior of Gold Nanoparticles Synthesized in Aqueous Solution with Insufficient Reducing Agent.

The spherical gold nanoparticles (AuNPs) typically are red in solution. However, in this study, the dichroic and spherical AuNPs were synthesized using a modified seeding growth method under reducing agent insufficiency in an aqueous solution. This particular AuNP solution is orange in reflected light and red in transmitted light. The reflectance curves confirm that the dichroic AuNPs are different from the classic AuNPs. With particle assembling, the AuNP solution is fainter orange in reflected light, but purple in transmitted light when the color of classic spherical AuNP solution is purple in both lights. Furthermore, the aggregated-nanogold solutions were added to HAuCl4 solutions with the addition of an insufficient amount reducing agent. The solution changed from faint orange to bright orange in reflected light and from purple to blue in transmitted light. It indicates that the gold assembling under a reducing agent insufficiency, not the shape of AuNP, causes the dichroic phenomenon. To the best of our knowing, this is the first study to report how the AuNP is synthesized, not the shape, affects the color of the AuNP.

Metallic Nanoparticles Assimilation within Metal-Organic Framework Monolith.

A facile and versatile method is reported for the inclusion of gold nanoparticles (AuNPs) within a monolithic metal-organic framework (HKUST-1 MOF). Simple addition of stabilized colloidal AuNPs solution to the reaction mixture at the early stages of the formation of the MOF monolith resulted in quantitative uptake of the AuNPs within the MOF matrix. Several characterization techniques including solution and solid UV-vis spectroscopy, TEM, and XRD indicated the successful immobilization of the AuNPs. Controllable loading of AuNPs was also demonstrated, where gas sorption measurements indicated the maintained microporosity of the AuNPs-containing monoliths. This methodology has wide potential applications in demanding technologies, including sensing and catalysis, where monolithic materials of controllable physicochemical properties can be readily accessible through pore size and guest selectivity of the host MOF matrix controlling access of guest molecules to immobilized AuNPs.

Effect of Gold Nanoparticles and Unwanted Residues on Raman Spectra of Graphene Sheets

We report the effect of gold nanoparticles (AuNPs) and unwanted sodium citrate residues (UnR) left after deposition of AuNPs by drop-casting method on the Raman spectra of graphene sheets (GS). The AuNPs solution was deposited on three different substrates: 5.0 wt% Yb3+-doped (Q5) phosphate glass, silica glass (S1), and Si/SiO2-300 nm (S2) substrates. For Q5 substrate, a slight increase in intensity of the G peak was observed, mostly for thinner layers, which can be attributed to a weak SERS effect shielded by UnR. The combination of the following aspects: a blue shift of the G band position, a slight increase in the FWHM (Full Width at Half Maximum), and a slight increase of the Raman intensities of both G and 2D bands in other GS without UnR supports the argument of shielded SERS effect. On the other hand, the effects of UnR on the S1 and S2 substrates produce a decrease on the Raman intensities of G and 2D bands, opposite to the effect produced by the AuNPs; this result was found more intense for the S2 substrate in relation to S1. This is possibly caused by the greater amount of UnR accumulated on the Si/SiO2 substrate, due to its higher hydrophilicity in relation to other samples. Additional Raman measurements reveal that the Raman intensity of GS in all substrates is unaffected by the presence of a possible humidity on GS, revealing the effect of UnR. Hence, it is vital to understand how residues influence the salient features of GS/AuNPs.

Aptamer-functionalized AuNPs for the high-sensitivity colorimetric detection of melamine in milk samples

Although aptamer-functionalized AuNPs technology exhibits great potential in analytical and biological chemistry, direct analysis of molecules at a low concentration using colorimetric assay remains challenging. The development of intuitive methods has attracted interest for promising detection of melamine in milk samples due to a demand for stable and understandable process. In this study, we propose a rapid and facile colorimetric measurement method of melamine combined aptamer-functionalized AuNPs in contaminated milk samples. To realize the high stability and the lower limit of detection, the aptamer-functionalized surface of AuNPs via a coordinated bond was used in combination with ultra-sonication. The kinetics of this colorimetric assay based on aptamer-functionalized AuNPs was analyzed to illustrate that the higher the concentration of melamine, the faster the aggregation of AuNPs induced. The sensitivity, selectivity, limit of detection and recovery rate were sufficiently validated to understand the measurement principle of melamine using aptamer-functionalized AuNPs. The calibration curve established by the absorption peak ratio (A640 /A520) was linear in the concentration range of 0~1μM of melamine in aqueous solutions with the correlation coefficient (R2) of 0.986 and the limit of detection (LOD) of 22 nM, whereas, the correlation coefficient (R2) of 0.998 and the LOD of 14.9 nM were achieved at the concentration of melamine below 0.5 μM in milk samples. The optimized performance of this colorimetric assay of melamine using aptamer-functionalized AuNPs in milk samples was obtained with 100 μL of 13 nm AuNPs solution, 40 μL of 1 μM (100 dilutions) aptamers and the pre-reaction time of 30 min. This simple colorimetric measurement of melamine using aptamer-functionalized AuNPs provides a promising target for various applications of the sample source with complex sample matrices.

Study of THP-1 Macrophage Viability after Sonodynamic Therapy Using Methyl Ester of 5-Aminolevulinic Acid Gold Nanoparticles

Sonodynamic therapy (SDT) is emerging as new atherosclerosis treatment. The use of gold nanoparticles (AuNPs) as the vehicle for a sensitizer delivery improves reactive oxygen species formation. In this study, methyl ester of aminolevulinic acid (MALA) gold nanoparticles (MALA:AuNPs) functionalized with polyethylene glycol (PEG) were synthesized by photoreduction and characterized by ultraviolet/visible optical absorption, zeta potential and electron microscopy. The reactive oxygen species generation induced by ultrasound irradiation of MALA:AuNPs solutions was studied by observing the decrease in the 1,3-diphenylisobenzofuran emission band. The potential use of MALA:AuNPs as sensitizer for sonodynamic therapy was investigated on THP-1 macrophages. The cytotoxicity test was also described. The findings suggested that ultrasound combined with MALA:AuNPs provides impressive results in in vitro studies. Sonodynamic therapy with MALA:AuNPs through 2 minutes of ultrasound exposure (1 MHz and 1 W/cm2) culminated with total macrophage reduction. Thus, sonodynamic therapy combined with MALA:AuNPs has potential as a treatment for atherosclerosis.

Peptide-Mediated Controllable Cross-Linking of Gold Nanoparticles for Immunoassays with Tunable Detection Range.

The colorimetric immunoassay based on gold nanoparticles (AuNPs) can hardly enable simultaneous detection of multiple biomarkers in vastly different concentrations (e.g., pg/mL-μg/mL) because of its narrow dynamic range. In this work, we demonstrate an immunoassay with tunable detection range by using peptide-mediated controlled aggregation of surface modification-free AuNPs. Alkaline phosphatase (ALP) removes the phosphate group of the peptide to yield a positively charged product, which triggers the aggregation of negatively charged AuNPs and the color change of the AuNPs solution from red to blue with naked-eye readout. We design and screen 20 kinds of phosphorylated peptides to obtain a broad and controllable detection range for ALP sensing and apply them for detecting multiple inflammatory biomarkers in clinical samples. Our assay realizes straightforward, multiplexed, and simultaneous detection of multiple clinical biomarkers with tunable detection range (from pg/mL to μg/mL) in the same run and holds great potential for chemical/biochemical analysis.

Numerical and experimental investigations of dependence of photoacoustic signals from gold nanoparticles on the optical properties

Gold nanoparticles (AuNPs) are used as a contrast agent of the photoacoustic (PA) imaging. The efficiency of AuNPs has been discussed with the absorption cross section. However, the effects of the scattering of the light by AuNPs and surrounding medium on the PA signal from AuNPs have not been discussed. The PA signals from the aqueous solution of AuNPs were examined in the numerical simulation and the experiment. In the numerical simulation, the absorption and scattering cross sections of spherical and polyhedral AuNPs were calculated by Mie theory and discrete dipole approximation. Monte Carlo simulation calculated the absorbed light energy in the aqueous solution of AuNPs. Based on the PA wave equation, the PA signals were simulated. In the experiment, the PA signal from the aqueous solution of AuNP was measured by use of a piezoelectric film and a Q-switched Nd:YAG laser operated at 532 nm. The results of the numerical simulation and the experiment agreed well. In the numerical simulation and the experiment, a single Au nanocube with 50-nm edge generated the peak value of the PA signal significantly. It was approximately 350 times and twice as large as the peak values of the spherical AuNPs with 10- and 50-nm diameters, respectively. The peak value of the PA signal depended on both the absorption and scattering coefficients of the AuNPs and the surrounding medium. The peak value increased with the scattering coefficient in a quadratic manner. The character of the temporal profile of the PA signal such as full width at half maximum depended on the scattering coefficient of the AuNPs.

Dual approach for the colorimetric determination of unamplified microRNAs by using citrate capped gold nanoparticles.

The authors describe a method for the colorimetric determination of unamplified microRNA. It is based on the use of citrate-capped gold nanoparticles (AuNPs) and, alternatively, a microRNA-probe hybrid or a magnetically extracted microRNA that serve as stabilizers against the salt-induced aggregation of AuNPs. The absorbance ratios A525/A625 of the reacted AuNP solutions were used to quantify the amount of microRNA. The assay works in the range of 5-25pmol microRNA. The lower limit of detection (LOD) is 10pmol. The performance of the method was tested by detection of microRNA-210-3p in totally extracted urinary microRNA from normal, benign, and bladder cancer subjects. The sensitivity and specificity for qualitative detection of urinary microRNA-210-3p using the assay are 74% and 88% respectively, which is consistent with real time PCR based assays. The assay was applied to the determination of specific microRNA by using its specific oligo targeter or following magnetic isolation of the desired microRNA. The method is simple, cost-efficient, has a short turn-around time and requires minimal equipment and personnel. Graphical abstract Schematic of the two detection schemes:In the first approach, matched microRNA hybridizes with its specific probe to stabilize gold nanoparticles (AuNPs) against salt induced aggregation and to leave the red color of theAuNPs unchanged. In the second one, microRNA extracted via magnetic nanoparticles (MNP) stabilizes AuNPs against aggregation.

A colorimetricgold nanoparticle aggregation assay for malathion based on target-induced hairpin structure assembly of complementary strands of aptamer.

The authors describe a method for the colorimetric determination of the pesticide malathion. It is based on the use of a hairpin structure consisting of a complementary strand of aptamer and a double-stranded DNA (dsDNA) structure to protect gold nanoparticles (AuNPs) against salt-induced aggregation. In the absence of malathion, the dsDNA structure is preserved on the surface of AuNPs and the color of the AuNPs in solutions containing NaCl remains red. However, in the presence of malathion, a hairpin structure of complementary strand is formed. The Aptamer/Malathion complex and the complementary strand are released from the surface of the AuNPs. As a result, the AuNPs undergo salt-induced aggregation which is accompanied by a color change to blue. The assay allows malathion to be quantified within 35min (A650/A520 was measured). The detection limit is 1 pM, and response is linear in the 5 pM to 10nM malathion concentration range. The method is specific and was successfully applied to the determination of malathion in spiked human serum samples. Graphical abstract Schematic representation of detection of malathion based on dsDNA-modified gold nanoparticles (AuNPs) and thehairpin structure of thecomplementary strand.

Naked-eye detection of potassium ions in a novel gold nanoparticle aggregation-based aptasensor

In this work, we studied the feasibility of interaction among gold nanoparticles (AuNPs) and a cationic dye in an aptasensor system for the detection of potassium ions. The presence and absence of potassium in the solution was distinguishable by different colors (between orange and green) appeared after reaction. Cationic dye (Y5GL) acts as a new aggregator for AuNP-based sensors which changes the aggregated AuNP solution color from blue-purple to green. In the presence of K+ ions, the aptamer dissociated from the surface of the AuNP so that free AuNPs and cationic dye make the solution green. The aptasensor showed that the analytical linear range was from 10 nM to 50 mM and the detection limit was 4.4 nM. Also, we examined the practicality of this method on a simple paper based platform. The linear range of the colorimetric paper sensor covered of K+ concentration from 10 μM to 40 mM and the detection limit of 6.2 μM was obtained. The selectivity of AuNP aggregation-based sensor improved by the use of cationic dye. Rapidity, simplicity, high sensitivity and excellent selectivity made this assay suitable for practical determination of K+ in real urine samples.

Green Synthesis of Gold Nanoparticles (AuNPS) Using the Extract of Sedum Praealtum

Through the methods of green synthesis we seek to obtain metallic nanoparticles taking advantage of the bioactive principles of plants that serve as reducing and stabilizing agents. In the present work, nanoparticles of gold (AuNPs) were synthesized using the extract of the species Sedum praealtum. When analyzing this extract by Fourier-transform infrared spectroscopy (FTIR), the functional groups present were found attributed to acid groups and OH the reducing capacity of the ions Au+3. The synthesis of AuNPs was carried out under temperatures of 80 to 85°C, with constant agitation and varying the relation of the concentration of extract and precursor agent. Colloidal AuNPs solutions were analyzed using UV-Vis spectroscopy, the obtained spectra presented an absorption band around 550 nm, which proved to obtain AuNPs. Analyzing the extract and colloidal solution of AuNPs by cyclic voltammetry, corroborated the reducing power of the species against the ions Au+3.

Fluorescing aptamer-gold nanosensors for enhanced sensitivity to bisphenol A

An insufficient sensitivity of aptamer-integrated colorimetric gold nanoparticles (AuNPs) is a common challenge in the detection of environmental chemicals. We report the use of a modified aptamer/AuNP-based sensor in conjunction with a fluorescing single-stranded DNA aptamer for the sensitive detection of bisphenol A (BPA), which is a major endocrine disruptor (EDC). While an anti-BPA single-stranded DNA aptamer was bound with BPA, a weak fluorescence signal was observed upon the addition of SYBR Green-I (SG-I), which is specific to a duplex region of the free aptamer. This reaction was accompanied by a subsequent aggregation of unmodified AuNPs (citrate-stabilized AuNPs) at high salt concentrations, leading to a color change from reddish to purple. In contrast, the absence of BPA elicited a high fluorescence signal from SG-I and produced no color change in the AuNP solution even upon the addition of salt ions. Unlike aptamers that are labeled at their ends with fluorophores, our strategy gave rise to neither a loss of target-binding affinity nor a perturbation of the AuNP colorimetry. Thus, a quantitative analysis with a broad dynamic range was achieved by combining the fluorescent and colorimetric measurements at BPA concentrations ranging over four orders of magnitude. Our approach also yielded a greater detection sensitivity (as low as 9 pg·mL−1) than classical AuNP colorimetry or other aptamer-combined methods Moreover, this method enabled the detection of BPA in a small fraction extracted from thermal paper with a high specificity among EDCs. We anticipate that this approach will facilitate further advances in the design of traditional AuNP colorimetric sensors using different aptamers for chemical sensing in the environmental and clinical fields.

Smartphone-based colorimetric chiral recognition of ibuprofen using aptamers-capped gold nanoparticles.

Sensitive and fast detection of ibuprofen enantiomers is very critical for required routine monitoring and risk assessment of trace pollutants in water samples. Here a simple, rapid and highly sensitive android smartphone application for chiral recognition was developed. Aptamer-capped gold nanoparticles (AuNPs) was demonstrated as an efficient detection platform for (S)-(+)-ibuprofen (S-Ibu) and (R)-(-)-ibuprofen (R-Ibu). Detachment of an enantioselective aptamer from the AuNPs surface and binding with an enantiomer of Ibu lead to AuNPs aggregation, which allows a rapid enantiodiscrimination of Ibu by monitoring the absorbance changes of AuNPs solution in the UV-vis spectrum. Under optimal conditions, the limit of detection for S-Ibu and R-Ibu was 1.24 and 3.91pg/mL, respectively. These probes showed good chiral recognition ability in mixed samples (i.e. S-Ibu + R-Ibu) and environmental samples. These advantages can be further developed by quantitative measurement with smartphone, which opens new opportunities for on-site detection of trace chiral pollutants in a simple and practical manner.

Penetration of gold nanoparticles across the stratum corneum layer of thick-Skin

BackgroundTransdermal particulate penetration across thick-skin, such as that of palms and sole, is particularly important for drug delivery for disorders such as small fiber neuropathies. Nanoparticle-based drug delivery across skin is believed to have much translational applications, but their penetration especially through thick-skin, is not clear. ObjectiveThis study specifically investigates the effectiveness of gold nanoparticles (AuNPs) for thick-skin penetration, especially across the stratum corneum (SC) as a function of particle size. MethodsThe thick-skinned hind-paw of rat was used to characterize depth and distribution of AuNPs of varying sizes, namely, 22±3, 105±11, and 186±20nm. Epidermal penetration of AuNPs was characterized both, in harvested skin from the hind-paw using a diffusion chamber, as well as in vivo. ResultsHarvested skin segments exposed to 22nm AuNPs for only 3h demonstrated higher penetration (p<0.05) as compared to the 105 and 186nm particles. In animal studies, hind-paw skin of adult rats exposed to AuNPs solution for the same time, demonstrated nanoparticles in blood on the 4th day, and histological analysis revealed AuNPs in epidermal layers just below the SC, with no apparent tissue response. ConclusionWe conclude that the thick-skin allows nanoparticle penetration and acts as a depot for release of AuNPs into circulation long after the initial exposure has ceased.

Experimental evaluation of the influence of gold nanoparticles and cerium dioxide on normal and malignant cells and tissues.

The results of experimental studies of the effect of gold nanoparticles ( AuNPs ) on the organs of the reproductive system of male rats, cells and tissues of androgen-dependent prostate cancer (PCa) are presented, as well as the effect of cerium dioxide nanoparticles (CeO 2 NPs ) on the testes and fertility of aging male rats. Addition of polydisperse colloidal solution of AuNPs (10-50 nm) to the culture medium in a final concentration of 10 μg/ml inhibited the growth of the LNCaP culture, PCa cells, while monodisperse solution of AuNPs (20 nm) caused no effect. The polydisperse colloidal solution of AuNPs arrested the growth of PCa xenografts in mice, when administered parenterally at a dose range of 0.64-6.4 μg/kg body weight. The selectivity of the drug effect on the malignant epithelium is confirmed by signs of its destruction and decrease in the epithelial stromal ratio on histological preparations of xenografts. There was no significant damaging effect of poly- and monodisperse AuNPs solutions on the organs of the reproductive system of male rats when administered for up to two weeks. The stimulating effect of a low dose of CeO 2 NPs (1 mg/kg b.w.) administered orally on hormonal function of testes and spermatogenesis, proliferative and secretory processes in the prostate of aging male rats was established. However, fertility of animals was reduced in comparison with the control group due to immaturity of the part of spermatozoa. Thus, metal nanoparticles and their salts can have both a stimulating and destructive effect on organs and tissues, which should be taken into consideration when studying their therapeutic potential and in toxicology.

Facile displacement of citrate residues from gold nanoparticle surfaces

The stability of citrate-residues on gold nanoparticles (AuNPs) against ligand displacement has been controversial. Using AuNPs synthesized with deuterated citrate in combination with in-situ surface-enhanced Raman spectroscopic (SERS) analysis, we report that both citrate-residues and solution impurities can be simultaneously adsorbed onto citrate-reduced AuNPs in solution. The citrate-residues can be readily displaced from AuNPs by organosulfur such as organothiols (RS-H), organodisuflide (R-S-S-R), and non-specific ligands including halides and adenine. Control experiments conducted on high-purity gold films sputter-coated onto silicone substrates indicate that air-borne and solvent-borne impurities rapidly contaminate the gold surfaces. Head-to-head comparison of ligand-functionalized AuNPs by in-situ SERS measurements verses those from the ex-situ X-ray photoelectron spectroscopic (XPS) measurements reveal that the impurity deposition can compromise the reliability of ex-situ XPS identification of surface adsorbates on AuNPs in solution. These insights are of general significance to nanoscience research given the broad interest in nanoparticle surface chemistry and popularity of XPS for nanomaterial characterizations.

Green synthesis and stabilization of earthworm-like gold nanostructure and quasi-spherical shape using Caesalpinia sappan Linn. extract

AbstractGreen synthesis of nanoparticles (NPs) has received much attention due to biocompatibility and being facile and eco-friendly.Caesalpinia sappanLinn. (CS) is a plant found in Southeast Asia and is commonly known as sappan wood. In this research, we are the first to successfully use CS extract as reducing and stabilizing agents for the green synthesis of gold NPs (AuNPs). Colloidal solutions of AuNPs after reduction show natural red-wine and dark purple color depending on the size of AuNPs, without the interference of the orange/reddish-orange color from the CS extract. The concentration of CS was investigated for the formation and stabilization of AuNPs in colloidal solution (i.e. morphology, size and zeta potential). It was found that the optimized concentration of the reducing agent for the green synthesis of AuNPs was in the range of 0.004–0.04 wt% of CS. As the concentration of CS was increased, the sizes of AuNPs decreased due to the adsorption and stabilizing effect of CS. Transmission electron microscopy (TEM) analysis showed differences in size and shape of the NPs with earthworm and quasi-spherical characteristics. The zeta potential of AuNPs synthesized in the presence of CS was approximately in the range of −10 mV to −20 mV, indicating the stability of AuNPs synthesized by CS.

Colorimetric detection of methionine based on anti-aggregation of gold nanoparticles in the presence of melamine

Abstract A rapid method for the determination of methionine (Met) based on the anti-aggregation of gold nanoparticles (AuNPs) in serum and urine is presented. Melamine (Mel) can induce the aggregation of AuNPs through the ligand exchange between amine groups on melamine and negatively charged citrate ions and then induce color change of the AuNPs solution from wine red to blue. However, the AuNPs is more prone to combining with Met through both Au S and Au N bonds in the presence of Mel, which hinders the aggregation of AuNPs induced by Mel. A good linear correlation (R 2 = 0.996) between absorbance ratio and the Met concentration is obtained over the range from 0 μM to 1.0 μM. The detection limit was estimated as low as 24.5 nM and the recovery of Met added to serum and urine samples was 95.0-105% and 95.0-104%, respectively. The result represents that the method makes this sensor promising for the applications in the development of detecting Met.