Anti-aggregation Of Gold Nanoparticles Research Articles

A Simple and Highly Selective Colorimetric Sensing of Hg2+ Ions Based on Anti-Aggregation of Gold Nanoparticles

In this work, a highly sensitive and selective colorimetric sensor assay for the detection of Hg2+ ions is presented utilizing an anti-aggregation sensing approach with AuNPs and an amine-based sensor (S). The addition of sensor (S) to gold nanoparticles (AuNPs) leads to their aggregation and, thus, color variation from red to blue. Whereas, in the presence of Hg2+ ions, i.e., target analyte, sensor (S) preferably binds with Hg2+ ions over AuNPs, thus inhibiting their aggregation and subsequent color change. This approach is optimized in terms of various analytical parameters, such as incubation time, pH effect, and S titration, to obtain high sensitivity and selectivity. The UV–Visible studies validate the performance of developed approach for Hg2+ ions detection, and the limit of detection was calculated to be 17 nM, which is lesser than its permissible limit (30 nM) in drinking water. The interference studies also confirm the develop approach selectivity for Hg2+ ions even in the presence of coexisting ions in aqueous media. The experimental results were further correlated with the computational density functional theory (DFT) studies. The presented method is not only cost-effective but also eliminates tedious synthetic schemes and need of laborious manpower.

A new colorimetric method for determination of formaldehyde in sea food based on anti-aggregation of gold nanoparticles

A new colorimetric method based on anti-aggregation of gold nanoparticles (AuNPs) in the presence of melamine for sensitive and selective determination of formaldehyde was developed. The citrate capped AuNPs was synthesized by Turkevich method. A certain concentration of melamine is responsible for color change of AuNPs from red to purple. The surface plasmon resonance peak was shifted from 520 to 640 nm. In the presence of formaldehyde, the reaction between melamine and formaldehyde to form methylol melamine was occurred, which resulted in the decreasing of aggregation of AuNPs. Based on the anti-aggregation mechanism, formaldehyde can be detected by observing the color change of AuNPs solution containing melamine, which was monitored by UV–visible spectrophotometer. Calibration curve plotted between absorbance ratio (A640/A520) and formaldehyde concentration was made with linearity of 0 – 2000 µg L−1. The limit of detection and the limit of quantitation were found at 26.0 µg L−1 and 88.0 µg L−1, respectively. The method also provided high accuracy (%recovery in range 97.3 – 104%) and high precision (%RSD < 5.6).

Simple and rapid colorimetric visualization of tetramethylthiuram disulfide (thiram) sensing based on anti-aggregation of gold nanoparticles

Thiram is widely used in agriculture and can pose high toxicity to humans through food and soil contamination, suggesting the necessity to develop a method for convenient and rapid detection of thiram residues. Herein, we synthesized gold nanoparticles (Au NPs) encoded with 4-aminothiophenol (4-ABT) (Au NPs@4-ABT), whose aggregation process can be triggered by silver ions (Ag+), but can also be specifically inhibited by the competitive reaction between thiram and Ag+. By monitoring the color change of Au NPs@4-ABT probe, the thiram concentration can be detected within 15 min with detection limit of 0.04 μM over a linear range of 0.05–2.0 µM. This visualization method has the advantages of good sensitivity and specificity, simple operation, rapid detection, and not requiring any large instrument or sophisticated design, and its practicability has also been verified in apple and soil, indicating its great potential for on-site evaluation of thiram in real samples.

Colorimetric Sensor for Thiocyanate Based on Anti-aggregation of Gold Nanoparticles in the Presence of 2-Aminopyridine.

Based on the anti-aggregation mechanism of citrate stabilized gold nanoparticle (AuNPs), a new specific and sensitive colorimetric sensor for thiocyanate (SCN-) was developed. In this scheme, the AuNPs were aggregated in the presence of the aggregating agent 2-aminopyridine (2-AP) due to electrostatic attraction. The solution color changed from red to blue. When SCN- was present, SCN- formed a sulfur-gold bond with the AuNPs to protect the AuNPs from aggregation. Thiocyanate can be detected by the color change of the solution from blue to red. The results showed that the absorbance ratio A675/A520 was linear with the concentration of SCN- in the range of 0.4 - 1.2 μmol L-1 by UV-Vis spectroscopy. The limit of detection (LOD) of this assay was 0.37 μmol L-1. The system also had excellent selectivity and anti-interference ability. In addition, this method was successfully used for the detection of SCN- in actual water samples and achieved good results.

Colorimetric detection of mercury ions based on anti-aggregation of gold nanoparticles using 3, 5-dimethyl-1-thiocarboxamidepyrazole

A colorimetric method based on the anti-aggregation of gold nanoparticles (AuNPs) for the rapid detection of mercury (II) ions in an aqueous medium is proposed. 3, 5-Dimethyl-1-thiocarboxamidepyrazole (Pzl) was synthesized that caused aggregation of AuNPs and induced a color change from red to blue. However, in the presence of Hg2+, the AuNPs remained in the dispersed state without changing color due to the resilient and preferable interactions between Pzl and mercury ions rather than AuNPs. The change in color of the solution containing AuNPs from red to blue was the consequence of the aggregation mechanism and the presence of mercury ions gave rise to the anti-aggregation mechanism among AuNPs. The sulphur and nitrogen-rich different binding sites of ligand Pzl led to the excellent properties of the signature binding of mercury ions. This admirable property imparted the selective and nanomolar sensitivity of the ligand for mercury ions over the other metal ions. The method can be effectively applied to estimate the mercury level in water samples with good accuracy. The experimental results were also corroborated by Density Functional Theory (DFT) calculations.

A label-free hairpin aptamer probe for colorimetric detection of adenosine triphosphate based on the anti-aggregation of gold nanoparticles.

A facile and rapid colorimetric approach was described for selective and sensitive determination of adenosine triphosphate (ATP) based on a hairpin aptamer probe and the anti-aggregation of AuNPs. Poly(diallyldimethylammonium chloride) (PDDA) can induce the aggregation of AuNPs due to the electrostatic interaction causing a red to blue color change. Upon the addition of ATP, aptamer-based hairpin probe is opened and releases flexible ssDNA ends. The released flexible ssDNA ends can interact with PDDA and prevent PDDA-induced AuNPs aggregation. Thus, a visible color change from blue to red and a decrease in the absorption ratio (A610/A520) are observed. Under the optimal conditions, the hairpin aptamer-based colorimetric assay exhibits high sensibility and selectivity for the detection of ATP with a detection limit of 1.7nM. Moreover, this assay is successfully used in the rapid determination of ATP in spiked human serum samples with good recoveries in the range of 102.88 to 104.07%.

Anti-Agglomeration Behavior and Sensing Assay of Chlorsulfuron Based on Acetamiprid-Gold Nanoparticles.

Monitoring of low levels of chlorsulfuron in environmental water samples is important. Although several detection methods have been developed, they all have some drawbacks, such as being time-consuming, requiring expensive instruments and experienced operators, and consuming large volumes of organic solvents. There is an urgent need for a simple, rapid, and inexpensive detection method for chlorsulfuron. Herein, such a method was developed using anti-aggregation of gold nanoparticles (AuNPs) in the presence of acetamiprid in agricultural irrigation water samples. Aggregation of the AuNPs was induced by acetamiprid, and this produced a distinct color change from Bordeaux red to blue. However, the strong hydrogen bonding interaction between chlorsulfuron and acetamiprid could inhibit AuNP aggregation. The effect of chlorsulfuron on the anti-agglomeration behavior of AuNPs was monitored by ultraviolet–visiblespectroscopy (UV-Vis) and the naked eye over a concentration range 0.1–100 mg/L. The detection limit for chlorsulfuron was 0.025 mg/L (signal-to-noise ratio of three). This colorimetric method was successfully applied to the determination of chlorsulfuron in spiked tap water and agricultural irrigation water with satisfactory recoveries (76.3%–94.2%).

Colorimetric sensing of mercury (II) ion based on anti-aggregation of gold nanoparticles in the presence of hexadecyl trimethyl ammonium bromide

A new specific and sensitive colorimetric sensor based on anti-aggregation of unmodified gold nanoparticles (AuNPs) for mercury ion detection was studied by forming Au-Hg alloys deposited onto the surface of AuNPs. In the protocol, hexadecyl trimethyl ammonium bromide (CTAB) could cause the aggregation of AuNPs and induced the color change from red to blue due to the strong electrostatic attraction between CTAB and citrate ion capped gold nanoparticles. In the presence of Hg2+, citrate ion capped AuNPs reduced Hg2+ to Hg and then formed Hg-Au alloys, which could inhibit the aggregation of AuNPs caused by CTAB to some extent. Based on these findings, Hg2+ was detected by a blue-to-red color change of AuNPs solution containing CTAB. Also, the limit of detection (LOD) was 11.9 nM by UV–vis spectroscopy, which was lower than the guideline concentration of Hg2+ (30 nM) in drinking water set by the World Health Organization (WHO). And the results showed the absorbance ratios A650/A520 had a good linear correlation with the Hg2+ concentration from 0 to 680 nM, which could be used for the quantitative detection of Hg2+. This method was successfully used to detect Hg2+ in tap water sample.

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.

Sensitive Colorimetric Detection of Nitrite Ions Based on the Aggregation of Gold Nanoparticles

Determination of nitrite both environmentally and in life processes has been of importance as its presence above a threshold causes detrimental effects. Hence, there is a need to develop new, simple and highly sensitive analytical assays. Nitrite detection has been achieved through various methods, including chemiluminescence, electrochemistry, and surface-enhanced Raman scattering which involve use of expensive equipments, tedious procedures and time consumption. However, colorimetric assays can provide visual, on-site analysis, providing a simple and instantaneous detection method. In this work, a facile colorimetic assay has been proposed based on anti-aggregation of gold nanoparticles. Gold nanoparticles coated with aromatic amines react with nitrite ions that alter the aggregation state of the nanoparticles. The change to the aggregation state causes a shift in the local surface plasmon resonance bands, triggering a colorimetric response. An increase in the concentration of nitrite ions changes the color of the solution, which can be detected by the naked eye. While many approaches have used thiol-based linkers, our use of disulphide cross-linkers, which bind more strongly to gold has increased the sensitivity of detection by an order of magnitude. Furthermore, the effect of this assay on synthetic urine has been explored to understand the effect of the presence of foreign ions on the detection of nitrite. Keywords: Anti- aggregation, gold nanoparticles, surface plasmon, aromatic amines

Specific pH effect for selective colorimetric assay of glutathione using anti-aggregation of label-free gold nanoparticles

An operationally simple colorimetric method for measuring glutathione (GSH) concentration was developed using anti-aggregation of gold nanoparticles (AuNPs) in this work.

Colorimetric sensing of silver ion based on anti aggregation of gold nanoparticles

A colorimetric assay with excellent selectivity is reported for detecting silver ion in aqueous solutions. The system works based on the competitive interaction of gold nanoparticles (AuNPs) and Ag+ with tris(hydroxymethyl) aminomethane (tris). The sensing strategy is quite simple, fast, convenient and the detection is by the naked eye. The aggregation of AuNPs with tris was inhibited in the presence of Ag+ ions resulting in a significant hypsochromic spectral shift of the surface plasmon resonance (SPR) of AuNPs and a color change from blue to red. The interaction between tris and Ag+ ion was investigated with cyclic voltammetry. The effect of Ag+ concentration on the aggregation of AuNPs by tris was monitored by UV–vis spectroscopy with the dynamic range of 1–9μM and detection limit of 0.41μM. The recovery analysis of river water and wastewater samples proved that this colorimetric sensor is successfully operational in environmental monitoring.

Highly selective and sensitive detection of glutathione based on anti-aggregation of gold nanoparticles via pH regulation

Glutathione (GSH) plays a key role in biological systems and serves many cellular functions. Since biothiols all incorporate thiol, carboxylic and amino groups, discriminative detection of GSH over cysteine (Cys) and homocysteine (Hcy) is still challenging. Both Cys and Hcy can induce aggregation of AuNPs via the formation of zwitterionic networks, which is different from GSH. GSH induced aggregation of AuNPs by the hydrogen bonding between the carboxylic groups when pH <4.5, so pH plays a crucial part in our present work. By regulating the pH to 5.8, our proposed sensing system exhibits high selectivity and sensitivity towards GSH even in the presence of other biothiols, realizing the discriminative detection of GSH over Cys/Hcy based on anti-aggregation of AuNPs. In our work, 2-mercapto-1-methylimidazole (MMI) and GSH took the role of aggregation and anti-aggregation agent, respectively. A linear relationship between the intensity ratio A650nm/A520nm and the GSH concentration is obtained (R2=0.998) with a detection limit of 12.0nM.

Visualization and quantification of Hg2+ based on anti-aggregation of label-free gold nanoparticles in the presence of 2-mercaptobenzothiazole

A highly sensitive and simple colorimetric strategy for Hg2+ detection is introduced based on anti-aggregation of gold nanoparticles (AuNPs). 2-Mercaptobenzothiazole (MBT) can cause the aggregation of AuNPs due to strong covalent Au–S bond formation resulting in color change from red to blue. However, the presence of Hg2+ led the AuNPs to remain in the dispersed state because MBT prefers to interact with Hg2+ rather than AuNPs. Based on the anti-aggregation mechanism, Hg2+ can be detected by observing the color change of AuNPs solution containing MBT. The minimum detectable quantity is 0.1μM by the naked eyes, and the limit of the detection (LOD) is 6.0nM by UV–vis spectroscopy with the linear range from 0.05 to 1.0μM. Furthermore, the developed detection system is also environmental-friendly and inexpensive, which has been successfully used in lake water and milk powder samples detection.

A selective, sensitive and label-free visual assay of fructose using anti-aggregation of gold nanoparticles as a colorimetric probe

Abstract A new convenient colorimetric sensor for fructose based on anti-aggregation of citrate-capped gold nanoparticles (AuNPs) is presented. 4-Mercaptophenylboronic acid (MPBA) induces the aggregation of AuNPs, leading to a color change from red to blue. Fructose as a potent competitor has strong affinity for MPBA and a borate ester is formed between MPBA and fructose. There is an obvious color change from blue to red with increasing the concentration of fructose. The anti-aggregation effect of fructose on AuNPs was seen by the naked eye and monitored by UV–vis spectra. Our results showed that the absorbance ratio (A 519 /A 640 ) was linear with fructose concentration in the range of 0.032–0.96 mmol/L ( R 2 = 0.996), with a low detection limit of 0.01 mmol/L (S/N = 3). Notably, a highly selective recognition of fructose was shown against other monosaccharide and disaccharide (glucose, mannose, galactose, lactose and saccharose). With anti-aggregation assays higher selectivity is achievable. The results of this work provide a rapid method for evaluating the quantitative analysis of fructose in human plasma at physiologically meaningful concentrations and at neutral pH. The proposed procedure can be used as an efficient method for the precise and accurate determination of fructose.

Colorimetric detection of thiocyanate based on anti-aggregation of gold nanoparticles in the presence of cetyltrimethyl ammonium bromide

A facile, highly sensitive and selective colorimetric strategy for thiocyanate (SCN−) detection is proposed based on anti-aggregation of gold nanoparticles (AuNPs) which was induced by surfactant cetyltrimethyl ammonium bromide (CTAB). A certain concentration of aggregation agent CTAB is responsible for a visible color change of AuNPs from wine red to blue. The aggregations of AuNPs decrease with increasing concentrations of SCN−, which can be monitored by an ultraviolet–visible spectrophotometer or the naked eyes. The limit of the detection (LOD) is 0.1μM by the naked eyes and 6.5nM by UV–vis spectroscopy with the linear range from 0.1 to 1.5μM. The applicability of our detection system is also verified by analysis of SCN− in milk samples and satisfactory results were obtained.

Facile colorimetric detection of human chorionic gonadotropin based on the peptide-induced aggregation of gold nanoparticles

A facile and rapid optical detection method of human chorionic gonadotropin (hCG) was developed by using the hCG-binding peptide and the anti-aggregation of gold nanoparticles (AuNPs).

Facile colorimetric detection of nitrite based on anti-aggregation of gold nanoparticles

A sensor for the facile colorimetric detection of nitrite using unmodified gold nanoparticles is developed on the basis of a specific diazo reaction between nitrite and 4-aminothiophenol.

Bio-inspired Maillard-Like reactions enable a simple and sensitive assay for colorimetric detection of methylglyoxal.

A simple and selective assay for detecting methylglyoxal (MGO), a metabolite associated with diabetes, was developed by combining a bio-inspired chemical reaction with the anti-aggregation of gold nanoparticles. This assay could detect MGO at as low as 1 μM by the naked eye and 0.05 μM by UV/vis spectrometry, within the clinical range marking oxidative stress in diabetes, and demonstrated high selectivity over other physiologically relevant ketones and aldehydes.

Colorimetric detection of d-amino acids based on anti-aggregation of gold nanoparticles

Abstract A new method has been proposed to realize the visual detection of d -amino acids (DAAs) via the anti-aggregation of 4-mercaptobenzoic acid modified gold nanoparticles (AuNPs) in the presence of d -amino acid oxidase (DAAO). The negatively charged AuNPs were prepared using sodium citrate as a reducer and stabilizer. The presence of 4-mercaptobenzoic acid (4-MBA) and Cu 2+ induces the aggregation of AuNPs, resulting in a color change from ruby red to royal purple. However, DAAO could oxidize DAAs to generate H 2 O 2 . In the presence of H 2 O 2 , the mercapto ( SH) group in 4-mercaptobenzoic acid can be oxidized to form a disulfide ( S S ) bond. Based on these facts, the pre-incubation of DAAs and 4-mercaptobenzoic acid with DAAO would significantly reduce the concentration of free 4-mercaptobenzoic acid molecules, thus the aggregation of AuNPs was interrupted since due to the lack of inducer. As the concentration of DAAs increases, the color of the AuNPs solution would progress from royal purple to ruby red. Consequently, DAAs could be monitored by the colorimetric response of AuNPs using a UV–vis spectrophotometer or even naked eyes. This DAAO mediated visual detection method could determine d -alanine ( d -Ala) as a representative DAA with concentrations ranging from 1.5 × 10 −7 mol L −1 to 3.0 × 10 −5 mol L −1 , and the detection limit was as low as 7.5 × 10 −8 mol L −1 . The proposed method is convenient, low-cost and free of complex equipment, making it feasible to analyze the concentration of d -Ala in real samples of β -amyloid peptide (A β 1–42 ).