Rapid and ultrasensitive colorimetric detection of mercury(II) by chemically initiated aggregation of gold nanoparticles

The article describes a method for rapid and visual determination of Hg(II) ion using unmodified gold nanoparticles (Au-NPs). It involves the addition of Au-NPs to a solution containing Hg(II) ions which, however, does not induce a color change. Next, a solution of lysine is added which induces the aggregation of the Au-NPs and causes the color of the solution to change from wine-red to purple. The whole on-site detection process can be executed in less than 15 min. Other amines (ethylenediamine, arginine, and melamine) were also investigated with respect to their capability to induce aggregation. Notably, only amines containing more than one amino group were found to be effective, but a 0.4 μM and pH 8 solution of lysine was found to give the best results. The detection limits for Hg (II) are 8.4 pM (for instrumental read-out) and 10 pM (for visual read-out). To the best of our knowledge, this LOD is better than those reported for any other existing rapid screening methods. The assay is not interfered by the presence of other common metal ions even if present in 1000-fold excess over Hg(II) concentration. It was successfully applied to the determination of Hg(II) in spiked tap water samples. We perceive that this method provides an excellent tool for rapid and ultrasensitive on-site determination of Hg(II) ions at low cost, with relative ease and minimal operation.

Rapid and ultrasensitive detection of mercury ions using gold nanoparticle based label-free colorimetric method with excellent sensitivity, easy operation and low cost.

     

Direct colorimetric visualization of mercury (Hg) based on the formation of gold nanoparticles

It is critical to be able to detect and quantify Hg²⁺ ions under aqueous conditions with high sensitivity and selectivity. The technique presented herein provides a direct way for simple colorimetric visualization of Hg²⁺ ions in aqueous solution, based on the formation of gold nanoparticles through the Hg²⁺ catalyzed HAuCl₄/NH₂OH reaction. The outstanding selectivity and sensitivity result from the well-known amalgamation process that occurs between mercury and gold. The entire procedure takes less than 20 min. The limit of detection (2 ppb) shows excellent potential for monitoring ultralow levels of mercury in water samples.     

Simple, sensitive and selective detection of dopamine using dithiobis(succinimidylpropionate)-modified gold nanoparticles as colorimetric probes

In this paper, we report a simple, sensitive and selective colorimetric visualization of dopamine (DA) using dithiobis(succinimidylpropionate) (DSP)-modified gold nanoparticles (AuNPs) as probes and ferric ions as cross-linkers. Via the standard amine coupling reaction between the amino groups of DA and activated carboxyl groups of DSP, DA molecules can be assembled onto the surface of DSP-AuNPs. Accordingly, Fe(3+) ions induce a change of DSP-AuNPs in color and UV-vis absorbance by coordinating to the catechol groups of the anchored DA. The pH dependence and mechanism of this method are discussed. A detection limit of 2 nM was obtained, which is lower than those achievable with currently used chromatographic and electrochemical techniques. The feasibility for the detection of DA in artificial cerebrospinal fluid has been demonstrated.     

Naked-eye sensitive detection of nuclease activity using positively-charged gold nanoparticles as colorimetric probes

Positively-charged gold nanoparticles can effectively differentiate long DNA and fragmented DNA, thus providing a simple and visual approach to colorimetric detection of nuclease activity.     

Enzyme-free colorimetric assay for mercury(II) using DNA conjugated to gold nanoparticles and strand displacement amplification

The authors describe a colorimetric method for the determination of Hg(II) ion. It is based on the color change from red to colorless as displayed by gold nanoparticle (AuNP) modified with thymine - rich DNA. Signal amplification is accomplished by free strand displacement recycling. In this strategy, Hg(II) unfolds the arch-trigger duplex due to the high affinity between Hg(II) and the thymines to form T-Hg(II)-T structures, thereby causing the release of trigger. The liberated trigger unfolds the hairpin structure of H1, and unfolded H1 further unfolds with H2. As a result, the H2 hairpin displaces trigger, and the released trigger unfolds another H1. This results in strong and enzyme-free strand displacement recycling amplification. The aggregation of DNA-AuNPs occurs in the presence of the duplex formed by hairpins H2 and H1. This results in a color change from red to colorless that can be visually observed. Under optimal conditions, the assay has a detection range over 4 orders of magnitude and a 3.4 nM detection limit. The assay is selective, sensitive, rapid and cost-effective. In our perception, it represents a useful platform for determination of Hg(II).

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Graphical abstract Schematic presentation of the  simple, rapid, low cost colorimetric detection of mercury(II) based on enzyme-free strand displacement amplification along with DNA-labeled AuNP.

     

Highly sensitive and selective colorimetric visualization of streptomycin in raw milk using Au nanoparticles supramolecular assembly

Electrostatic interaction between streptomycin and mercaptoacetic acid modified gold nanoparticles can be used for a facile and reliable probe for streptomycin with high sensitivity and selectivity.     

Parameters for selective colorimetric sensing of mercury(II) in aqueous solutions using mercaptopropionic acid-modified gold nanoparticles

We unveil a new homogeneous assay-using mercaptopropionic acid-modified Au nanoparticles in the presence of 2,6-pyridinedicarboxylic acid for the highly selective and sensitive detection of Hg(2+) ions.     

A colorimetric method for the determination of lead(II) ions using gold nanoparticles and a guanine-rich oligonucleotide

We have developed a colorimetric method for the determination of Pb(II) ions. It is based on the use of gold nanoparticles and a guanine-rich synthetic oligonucleotide. On addition of Pb(II), the color of the solution turns from red to blue. The ratio of the UV-vis absorption at 630?nm and 525?nm is proportional to the concentration of Pb(II) ions in the range from 10 to 100?nM, and the detection limit is 20?nM. Other metal ions do not interfere if present in up to a 10-fold molar excess. The method was successfully applied to the detection of Pb(II) in lake water and urine. The recovery in case of spiked samples is 92%. The results show that this method is sensitive, simple and fast.

A novel route to copper(II) detection using 'click' chemistry-induced aggregation of gold nanoparticles

A simple colorimetric method for the detection of copper ions in water is described. This method is based on the 'click' copper(I)-catalyzed azide-alkyne cycloaddition reaction and its use in promoting the aggregation of azide-tagged gold nanoparticles by a dialkyne cross-linker is described. Nanoparticle cross-linking, evidenced as a colour change, is used for the detection of copper ions. The lowest detected concentration by the naked eye was 1.8 μM, with the response linear with log(concentration) between 1.8-200 μM. The selectivity relative to other potentially interfering ions was evaluated.     

Simple and sensitive colorimetric detection of cysteine based on ssDNA-stabilized gold nanoparticles

In this paper, we demonstrate a simple and sensitive colorimetric detection of cysteine based on the cysteine-mediated color change of ssDNA-stabilized gold nanoparticles (AuNPs). Cysteine is capable of absorbing onto AuNPs surfaces via the strong interaction between its thiol group and gold. ssDNA molecules which stabilize AuNPs against salt-induced aggregation are removed away by cysteine encapsulation on the AuNPs surfaces, resulting in a characteristic color change of AuNPs from red to blue as soon as salt is added. The ratio of absorptions at 640 to 525 nm (A ₆₄₀/A ₅₂₅) is linear dependent on the cysteine concentration in the range from 0.1 to 5 μM. Furthermore, amino acids other than cysteine cannot mediate the color change under the identical conditions due to the absence of thiol groups, suggesting the selectivity of the proposed method toward cysteine. The employment of complicated protocols and sophisticated processes such as the preparation of modified AuNPs are successfully avoided in design to realize the simple and low-cost cysteine detection; and the high sensitivity and low cost of the method is favorable for practical applications. Figure In the presence of cysteine, cysteine binds to the AuNPs surface via Au-S bond, spontaneously driving ssDNA molecules away from the nanoparticles, which leads to the AuNPs aggregation under the condition of NaCl introduction, and the corresponding color change from red to blue. However, the presence of other amino acids results in no color change due to the absence of thiol groups. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

纳米金比色法测定多西环素和土霉素

采用柠檬酸钠还原法合成粒径约13nm的纳米金粒子.采用紫外-可见分光光度计、荧光分光光度计研究了纳米金粒子与多西环素/土霉素分子的相互作用;通过改变缓冲溶液、纳米金粒子用量、反应时间确定了比色法测定的最优反应条件.结果表明:在弱酸溶液中,多西环素/土霉素分子中的氨基官能团(-NH_2)得到电子成为带电基团(-NH_3~+)并通过静电引力与纳米金粒子结合,使得纳米金粒子发生聚集,导致纳米金吸收光谱发生红移和展宽,颜色由酒红色变成蓝色;在盐酸-柠檬酸钠的缓冲溶液中加入2mL纳米金,反应时间为10min的条件下测得多西环素和土霉素的线性范围分别为0.06~0.66mg·L~(-1)和0.59~8.85 mg·L~(-1),检出限(3σ)分别为0.008 6、0.083 8mg·L~(-1).该方法前处理简单、灵敏、可靠,有望应用于食品分析和临床分析等领域.     

Self-assembly of core-satellite gold nanoparticles for colorimetric detection of copper ions

Molecule-coated nanoparticles are hybrid materials which can be engineered with novel properties. The molecular coating of metal nanoparticles can provide chemical functionality, enabling assembly of the nanoparticles that are important for applications, such as biosensing devices. Herein, we report a new self-assembly of core-satellite gold nanoparticles linked by a simple amino acid l-Cysteine for biosensing of Cu²⁺. The plasmonic properties of core-satellite nano-assemblies were investigated, a new red shifted absorbance peak from about 600 to 800 nm was found, with specific wavelength depending on ratios with assembly of large and small gold nanoparticles. The spectral features obtained using surface-enhanced Raman spectroscopy (SERS) provided strong evidence for the assembly of the Cu²⁺ ions to the L-Cysteine molecules leading to the successful formation of the core-satellite Cu(l-Cysteine) complex on the gold surfaces. In addition, a linear relationship between the concentration of mediating Cu²⁺ and absorbance of self-assembled gold nanoparticles (GNPs) at 680 nm was obtained. These results strongly address the potential strategy for applying the functionalized GNPs as novel biosensing tools in trace detections of certain metal ions.     

Thermally treated bare gold nanoparticles for colorimetric sensing of copper ions

We demonstrate a sensitive and rapid colorimetric assay for selective detection of copper ions based on the strong coordination between Cu(II) ions and the tetrahydroxyaurate anions [Au(OH)₄]^? on the surface of thermally treated bare gold nanoparticles (GNPs). The method for making the unmodified GNPs is simple and results in a nanomaterial with a highly specific response to Cu(II). The thermal treatment of the bare GNPs and the recognition of Cu(II) ions is accomplished in a single step within 5 min. The presence of Cu(II) causes the color to change from red to purple-blue. The limit of detection (LOD) is 0.04 μM of Cu(II) when using UV–vis spectrometry and ratioing the absorbances at 650 and 515 nm, respectively. The method also is amenable to bare eye (visual) inspection and in this case has an LOD of 2.0 μM of Cu(II).

Rapid and sensitive detection of cholera toxin using gold nanoparticle-based simple colorimetric and dynamic light scattering assay

Herein, a rapid and simple gold nanoparticle based colorimetric and dynamic light scattering (DLS) assay for the sensitive detection of cholera toxin has been developed. The developed assay is based on the distance dependent properties of gold nanoparticles which cause aggregation of antibody-conjugated gold nanoparticles in the presence of cholera toxin resulting discernible color change. This aggregation induced color change caused a red shift in the plasmon band of nanoparticles which was measured by UV–Vis spectroscopy. In addition, we employed DLS assay to monitor the extent of aggregation in the presence of different concentration of cholera toxin. Our assay can visually detect as low as 10 nM of cholera toxin which is lower than the previously reported colorimetric methods. The reported assay is very fast and showed an excellent specificity against other diarrhetic toxins. Moreover, we have demonstrated the feasibility of our method for cholera toxin detection in local lake water.     

A simple and sensitive method for visual detection of heparin using positively-charged gold nanoparticles as colorimetric probes

The electrostatic interaction between the negatively-charged heparin and the positively-charged gold nanoparticles leads to aggregation of gold nanoparticles and a color change from red to blue in solution, thus providing a simple and visual approach to colorimetric detection of heparin.