Cu Nanoparticle-Based Solution and Paper Strips for Colorimetric and Visual Detection of Heavy Metal Ions

The intrinsic toxicity of heavy metal ions to human health or other species calls for the need to develop an analytical tool for the easy and rapid detection of these ions based on inexpensive and stable nanomaterials. This article describes the potential utility of stable Cu nanoparticles (CuNPs) in the detection of toxic metal ions by solution and paper strip-based methods. For this, first, a dodecyl sulfate ion-stabilized CuNP (DS-CuNP) colloid was synthesized by a chemical reduction method. This was followed by treating the dispersion with heavy metal ions and monitoring the spectral change by spectrophotometric and colorimetric techniques. Among a host of metal ions, Hg²⁺, Cd²⁺, and Pb²⁺ have been found to significantly affect the surface plasmon resonance band of CuNPs by concomitantly altering the color of its solution. Notably, the brownish color of CuNP solution changed readily to milky white in the presence of Hg²⁺. Furthermore, the fabricated brownish-yellow test paper strips containing DS-CuNPs transformed to a prominent white color in the presence of a few drops of Hg²⁺ solution. This change in color of the paper strips could be visually detected by the naked eye. The experiments involving the detection of the various ions were carried out by optimizing the experimental conditions qualitatively as well as quantitatively. The limit of detection of the analytes (metal ions) has been found to be 10 μM. Routine analytical techniques like UV-vis spectroscopy, dynamic light scattering, transmission electron microscopy, and Fourier transform infrared spectroscopy formed part of the experiments.

Rapid and ultrasensitive surface-enhanced Raman spectroscopy detection of mercury ions with gold film supported organometallic nanobelts

Rapid, ultrasensitive and reliable detection of mercury ions (Hg²⁺) by surface enhanced Raman spectroscopy (SERS) is of importance, but is restricted by the extremely low Raman cross section of the Hg²⁺. Here, we report a facile methodology that can realize such detection based on the organometallic Cu(CH₄N₂S)Cl · 0.5H₂O nanobelts and SERS. In the assay, Hg²⁺ react with the nanobelts coated on a SERS active gold nanoparticle (NP) film to form ultrafine HgS NPs in situ. Subsequently, solid HgS is SERS determined to mirror the presence of Hg²⁺. Importantly, such detection is rapid and ultrasensitive. Within 10 min, limit of detection (LoD) of ppt level can be realized. The high detection efficiency is attributed to the superhydrophilicity, rich micropores and ultrathin nature of the organometallic nanobelts besides the strong SERS effect of Au NP film. In addition, this detection is highly resistant to various metal ions (Cu²⁺, Fe³⁺, Bi³⁺, Cr³⁺, Na⁺, Ni²⁺, Cd²⁺, etc) and is highly reliable in actual water (lake and tap water). Finally, influences of some substrate parameters and detection conditions on the test results are revealed. The optimal thickness of the gold NP film is about 80 nm, and the optimal wavelength of excitation light is about 633 nm. A small amount of Cu(CH₄N₂S)Cl · 0.5H₂O nanobelts or a large volume of Hg²⁺ contaminated solution contributes to low LoDs. We believe that this work provides a rapid and sensitive detection for Hg²⁺.

Valence States Modulation Strategy for Picomole Level Assay of Hg2+ in Drinking and Environmental Water by Directional Self-Assembly of Gold Nanorods

In this study, we present a valence states modulation strategy for picomole level assay of Hg²⁺ using directional self-assembly of gold nanorods (AuNRs) as signal readout. Hg²⁺ ions are first controllably reduced to Hg⁺ ions by appropriate ascorbic acid, and the reduced Hg⁺ ions react with the tips of the preadded AuNRs and form gold amalgam. Such Hg⁺ decorated AuNRs then end-to-end self-assemble into one-dimensional architectures by the bridging effects of lysine based on the high affinity of NH₂-Hg⁺ interactions. Correspondingly, the AuNRs' longitudinal surface plasmon resonance is gradually reduced and a new broad band appears at 900-1100 nm region simultaneously. The resulting distinctly ratiometric signal output is not only favorable for Hg²⁺ ions detection but competent for their quantification. Under optimal conditions, the linear range is 22.8 pM to 11.4 nM, and the detection limit is as low as 8.7 pM. Various transition/heavy metal ions, such as Pb²⁺, Ti²⁺, Co²⁺, Fe³⁺, Mn²⁺, Ba²⁺, Fe²⁺, Ni²⁺, Al³⁺, Cu²⁺, Ag⁺, and Au³⁺, do not interfere with the assay. Because of ultrahigh sensitivity and excellent selectivity, the proposed system can be employed for assaying ultratrace of Hg²⁺ containing in drinking and commonly environmental water samples, which is difficult to be achieved by conventional colorimetric systems. These results indicate that the present platform possesses specific advantages and potential applications in the assay of ultratrace amounts of Hg²⁺ ions.

A Rapid Colorimetric Sensor of Clenbuterol Based on Cysteamine-Modified Gold Nanoparticles

Demonstrated was a simple visual and rapid colorimetric sensor for detection of clenbuterol (CLB) based on gold nanoparticles (AuNPs) modified with cysteamine (CA) and characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), UV-vis. The solution color from red to blue gray with increasing clenbuterol concentration resulted from the aggregation of AuNPs. The detection limit of clenbuterol is 50 nM by naked eyes. The selectivity of CA-AuNPs detection system for clenbuterol is excellent compared with other interferents in food. This sensor has been successfully applied to detect clenbuterol in real blood sample.

Gold nanoparticle-based nanosystems for the colorimetric detection of Hg2+ ion contamination in the environment

This review highlights the impact of Hg²⁺ contamination on the human population and the need for its detection.

Colorimetric detection of lead(ii) ions based on accelerating surface etching of gold nanorods to nanospheres: the effect of sodium thiosulfate

The lead ion-participated etching of gold nanorods leads to qualitative spectral change from double bands to single band LSPR, which results in a distinct irreversible color change of the gold colloid from blue to red.

Selective colorimetric detection of Cr(iii) and Cr(vi) using gallic acid capped gold nanoparticles

A colorimetric assay is proposed for the selective detection of Cr(iii) and Cr(vi) via the aggregation-induced color change of gallic acid capped gold nanoparticles (GA-AuNPs). The AuNPs are characterized using UV-vis spectroscopy, transmission electron microscopy (TEM), dynamic light scattering (DLS) and Fourier-transform infrared spectrometry (FT-IR). To detect Cr(iii) and Cr(vi) coexisting in a sample, citrate and thiosulfate were applied to mask Cr(vi) for the detection of Cr(iii), and ethylenediaminetetraacetic acid disodium salt (EDTA) was applied to mask Cr(iii) for the detection of Cr(vi). At optimized experimental conditions, the selectivity of these AuNPs-based detection systems is excellent for Cr(iii) and/or Cr(vi) compared with other types of metal ions. The limit of detections (LODs) of a mixture of Cr(iii) and Cr(vi), Cr(iii) and Cr(vi) by eye vision are 1.5, 1.5 and 2 μM, respectively, and those by UV-vis spectroscopy are 0.05, 0.1 and 0.1 μM, respectively. The minimum detectable concentrations for Cr(iii) or Cr(vi) are all below the guideline value set by the US Environmental Protection Agency (EPA). The applicability of the AuNPs-based colorimetric sensor is also validated by the detection of Cr(iii) and Cr(vi) in electroplating wastewater and real water samples with high recoveries.

Fluorescent and colorimetric sensors for environmental mercury detection

The development of fluorescent and colorimetric sensing strategies for environmental mercury is described.

Synthesis of a carbon-dot-based photoluminescent probe for selective and ultrasensitive detection of Hg2+ in water and living cells

Nitrogen and sulphur co-doped carbon dots with high PL quantum yield and photostability have been synthesized by a simple hydrothermal synthesis and successfully used for bioimaging of Hg²⁺ in living cells.

Optical reading of contaminants in aqueous media based on gold nanoparticles

With increasing trends of global population growth, urbanization, pollution over-exploitation, and climate change, the safe water supply has become a global issue and is threatening our society in terms of sustainable development. Therefore, there is a growing need for a water-monitoring platform with the capability of rapidness, specificity, low-cost, and robustness. This review summarizes the recent developments in the design and application of gold nanoparticles (AuNPs) based optical assays to detect contaminants in aqueous media with a high performance. First, a brief discussion on the correlation between the optical reading strategy and the optical properties of AuNPs is presented. Then, we summarize the principle behind AuNP-based optical assays to detect different contaminants, such as toxic metal ion, anion, and pesticides, according to different optical reading strategies: colorimetry, scattering, and fluorescence. Finally, the comparison of these assays and the outlook of AuNP-based optical detection are discussed.

A new rapid colorimetric detection method of Al³⁺ with high sensitivity and excellent selectivity based on a new mechanism of aggregation of smaller etched silver nanoparticles

As a pathogenic factor of the Alzheimer׳s disease, aluminum has been associated with the damage of the central nervous system in humans. In this study, we propose a new facile and rapid colorimetric detection method of Al(3+) with excellent selectivity and high sensitivity based on silver nanoparticles (AgNPs) stabilized by reduced glutathione (GSH) in the presence of l-cysteine (Cys). The new mechanism of our Al(3+) detection system based on GSH-AgNPs, i.e., aggregation of smaller etched GSH-AgNPs, are confirmed by TEM, EDS and DLS. The aggregation of smaller etched GSH-AgNPs results in obvious color change of the nanoparticle dispersion from yellow to reddish brown, and red shift and intensity decrease of the surface plasmon resonance (SPR) absorption. The GSH concentration, Cys concentration and pH value of the GSH-AgNPRs-based detection system are respectively optimized to be 10.0 mM, 50.0 mM and 6.0 according to the sensing effect of Al(3+). At the optimized conditions, the selectivity of the GSH-AgNPs detection system for Al(3+) is excellent compared with other ions including K(+), Mg(2+), Fe(3+), Co(2+), Mn(2+), Zn(2+), Cd(2+), Pb(2+), Ca(2+), Ba(2+), Cu(2+), Cr(3+), Hg(2+), Ni(2+), [Formula: see text] , [Formula: see text] , [Formula: see text] , [Formula: see text] and [Formula: see text] . Furthermore, this detection system is very sensitive for Al(3+). The limit of detection (LOD) is 1.2 µM by the naked eyes and 0.16 µM by UV-vis spectra, which are both much lower than the national drinking water standards (7.4 µM). Furthermore, the UV-vis detection offers a good linear detection range from 0.4 to 4.0 µM (R(2)=0.9924), which indicates that our developed detection system can also be used for the quantitative analysis of Al(3+). The detection results of real water samples indicate that this method can be used for real water detection.

Sensitive naked-eye detection of Hg2+based on the aggregation and filtration of thymine functionalized vesicles caused by selective interaction between thymine and Hg2+

A sensitive and low-cost method based on rapid interaction between functionalized PDA vesicles and Hg²⁺for the naked-eye detection of Hg²⁺.

An ultrasensitive quantum dots fluorescent polarization immunoassay based on the antibody modified Au nanoparticles amplifying for the detection of adenosine triphosphate

In this work, an ultrasensitive fluorescent polarization immunoassay (FPIA) method based on the quantum dot/aptamer/antibody/gold nanoparticles ensemble has been developed for the detection of adenosine triphosphate (ATP). DNA hybridization is formed when ATP is present in the PBS solution containing the DNA-conjugated quantum dots (QDs) and antibody-AuNPs. The substantial sensitivity improvement of the antibody-AuNPs-enhanced method is mainly attributed to the slower rotation of fluorescent unit when QDs-labeled oligonucleotides hybridize with antibody modified the gold nanoparticle. As a result, the fluorescent polarization (FP) values of the system increase significantly. Under the optimal conditions, a linear response with ATP concentration is ranged from 8×10(-12) M to 2.40×10(-4) M. The detection limit reached as low as 1.8 pM. The developed work provides a sensitive and selective immunoassay protocol for ATP detection, which could be applied in more bioanalytical systems.

Colorimetric detection of mercury ions based on plasmonic nanoparticles

The development of rapid, specific, cost-effective, and robust tools in monitoring Hg(2+) levels in both environmental and biological samples is of utmost importance due to the severe mercury toxicity to humans. A number of techniques exist, but the colorimetric assay, which is reviewed herein, is shown to be a possible tool in monitoring the level of mercury. These assays allow transforming target sensing events into color changes, which have applicable potential for in-the-field application through naked-eye detection. Specifically, plasmonic nanoparticle-based colorimetric assay exhibits a much better propensity for identifying various targets in terms of sensitivity, solubility, and stability compared to commonly used organic chromophores. In this review, recent progress in the development of gold nanoparticle-based colorimetric assays for Hg(2+) is summarized, with a particular emphasis on examples of functionalized gold nanoparticle systems with oligonucleotides, oligopeptides, and functional molecules. Besides highlighting the current design principle for plasmonic nanoparticle-based colorimetric probes, the discussions on challenges and the prospect of next-generation probes for in-the-field applications are also presented.

The colorimetric detection of Pb2+ by using sodium thiosulfate and hexadecyl trimethyl ammonium bromide modified gold nanoparticles

A simple, rapid colorimetric detection method for Pb(2+) in aqueous solution has been developed by using sodium thiosulfate (Na2S2O3) and hexadecyl trimethyl ammonium bromide (CTAB) modified gold nanoparticles (Au NPs). Na2S2O3 was added into the Au NP solution and thiosulfate ions (S2O3(2-)) were adsorbed on the surface of the Au NPs due to electrostatic interactions. Au atoms on the surface of the Au NPs were then oxidized to Au(i) by the O2 that existed in the solution in presence of thiosulfate. The addition of Pb(2+) (the final concentration was lower than 10 μM), accelerated the leaching of the Au NPs, and Pb-Au alloys also formed on the surface of the Au NPs. There was an obvious decrease in the surface plasmon resonance (SPR) absorption of the Au NPs. The lowest concentration for Pb(2+) that could be detected by the naked eye was 0.1 μM and using UV-vis spectroscopy was 40 nM. This is lower than the lead toxic level defined by the US Environmental Protection Agency (US EPA), which is 75 nM. In this method, CTAB, as a stabilizing agent for Au NPs, can accelerate the adsorption of S2O3(2-) on the surface of the Au NPs, which shortened the detection time to within 30 min. Moreover, this detection method is simple, cheap and environmentally friendly.

Highly sensitive and selective colorimetric sensing of Hg2+ based on the morphology transition of silver nanoprisms

A simple colorimetric approach for mercury ion (Hg(2+)) sensing was developed that was based on the Hg(2+)-induced deprotection and morphology transition of 1-dodecanethiol (C(12)H(25)SH)-capped silver nanoprisms (Ag NPRs) upon the presence of iodides at room temperature. The abstraction of C(12)H(25)SH from the surface of Ag NPRs by Hg(2+) led to their deprotection of Ag NPRs and the formation of complexation between silver ions and excess iodide ions. Also, the silver atoms were consumed and moved from the surface of Ag NPRs, accompanying the changes in the particle morphology that resulted in a change of color and UV-vis absorption spectra of the colloidal solution. With increasing concentrations of Hg(2+) from 10 to 500 nM, the surface plasma resonance spectral band of Ag NPRs emerged as a blue shift and exhibited a good linear relationship, and the limit of detection was 3.3 nM. Furthermore, the developed method was applied for detecting Hg(2+) in different real water samples with satisfying recoveries over 92%.

A rapid and sensitive colorimetric assay method for Co2+ based on the modified Au nanoparticles (NPs): understanding the involved interactions from experiments and simulations

We previously reported a colorimetric assay method for Co(2+) based on the thioglycolic acid (TGA) functionalized hexadecyl trimethyl ammonium bromide (CTAB) modified Au NPs. However, the detection limit of 3×10(-7) M was still higher than that of the sanitary standard for drinking water (6.8×10(-8) M). In addition, the interactions between the modifier and Au NPs, and between the modifier-Au NPs and Co(2+) remain to be clarified and confirmed. Thus, in the present study, the modified Au NPs solution was dialyzed and its detection limit was optimized to be 5×10(-10) M. The interactions between the modifier and Au NPs, and between the modifier-Au NPs and Co(2+) were investigated in both experimental characterizations and theoretical calculations, consistently confirming that the Au NPs were modified by the negatively charged anions of [SCH(2)CO(2)](2-) through Au-S bonds and Co(2+) was recognized by the modifier-Au NPs through Co-O chelate bonds. The results of X-ray photoelectron spectroscopy (XPS) suggest that there were no chemical bonds formed between CTAB and Co(2+). Moreover, the colorimetric assay of Co(2+) using the modified Au NPs has been proved to be a rapid, very sensitive and highly selective method. The validation of the method was carried out by analysis of a certified reference material, GSBZ 50030-94.

A gold nanoparticle-based immunochromatographic assay: the influence of nanoparticulate size

Four different sized gold nanoparticles (14 nm, 16 nm, 35 nm and 38 nm) were prepared to conjugate an antibody for a gold nanoparticle-based immunochromatographic assay which has many applications in both basic research and clinical diagnosis. This study focuses on the conjugation efficiency of the antibody with different sized gold nanoparticles. The effect of factors such as pH value and concentration of antibody has been quantificationally discussed using spectra methods after adding 1 wt% NaCl which induced gold nanoparticle aggregation. It was found that different sized gold nanoparticles had different conjugation efficiencies under different pH values and concentrations of antibody. Among the four sized gold nanoparticles, the 16 nm gold nanoparticles have the minimum requirement for antibody concentrations to avoid aggregation comparing to other sized gold nanoparticles but are less sensitive for detecting the real sample compared to the 38 nm gold nanoparticles. Consequently, different sized gold nanoparticles should be labeled with antibody under optimal pH value and optimal concentrations of antibody. It will be helpful for the application of antibody-labeled gold nanoparticles in the fields of clinic diagnosis, environmental analysis and so on in future.