4-Aminothiophenol functionalized gold nanoparticles as colorimetric sensors for the detection of cobalt using UV–Visible spectrometry

The 4-aminothiophenol functionalized gold nanoparticles (4-ATP-Au NPs) were used as colorimetric sensors for the detection of Co²⁺ in aqueous solution by using UV–Visible spectrometry. The 4-ATP-Au NPs were characterized by UV–Visible, FT-IR, TEM and dynamic light scattering (DLS) which confirmed their higher binding affinity towards Co²⁺ through coordinate covalent interactions that can be observed with the naked eye. The absorbance ratio (A₅₇₀/A₅₂₃) was linear with Co²⁺ concentration in the range of 15 × 10^?3 to 1 × 10^?3 M with a correlation coefficient of (R ²) 0.994, and the limit of detection was 5.79 × 10^?5 M.     

A colorimetric assay for measuring iodide using Au@Ag core–shell nanoparticles coupled with Cu

Au@Ag core–shell nanoparticles (NPs) were synthesized and coupled with copper ion (Cu²⁺) for the colorimetric sensing of iodide ion (I⁻). This assay relies on the fact that the absorption spectra and the color of metallic core–shell NPs are sensitive to their chemical ingredient and dimensional core-to-shell ratio. When I⁻ was added to the Au@Ag core–shell NPs-Cu²⁺ system/solution, Cu²⁺ can oxidize I⁻ into iodine (I₂), which can further oxidize silver shells to form silver iodide (AgI). The generated Au@AgI core–shell NPs led to color changes from yellow to purple, which was utilized for the colorimetric sensing of I⁻. The assay only took 10 min with a lowest detectable concentration of 0.5 μM, and it exhibited excellent selectivity for I⁻ over other common anions tested. Furthermore, Au@Ag core–shell NPs-Cu²⁺ was embedded into agarose gels as inexpensive and portable “test strips”, which were successfully used for the semi-quantitation of I⁻ in dried kelps.     

Effect of pH on phenolphthalein immobilized gold nanoparticles/nanostructures for pH sensing evaluations: sol–gel method

Journal of Sol-Gel Science and Technology - Sol–gel-based phenolphthalein immobilized AuNPs (phph-AuNPs) of different shapes such as spherical, dendrites, and flower are observed by varying...     

Sensitive colorimetric assays for α-glucosidase activity and inhibitor screening based on unmodified gold nanoparticles

A colorimetric sensor has been developed in this work to sensitively detect α-glucosidase activity and screen α-glucosidase inhibitors (AGIs) utilizing unmodified gold nanoparticles (AuNPs). The sensing strategy is based on triple-catalytic reaction triggered by α-glucosidase. In the presence of α-glucosidase, aggregation of AuNPs is prohibited due to the oxidation of cysteine to cystine in the system. However, with addition of AGIs, cysteine induced aggregation of AuNPs occurs. Thus, a new method for α-glucosidase activity detection and AGIs screening is developed by measuring the UV–vis absorption or visually distinguishing. A well linear relation is presented in a range of 0.0025–0.05 U mL⁻¹. The detection limit is found to be 0.001 U mL⁻¹ for α-glucosidase assay, which is one order of magnitude lower than other reports. The IC₅₀ values of four kinds of inhibitors observed with this method are in accordance with other reports. The using of unmodified AuNPs in this work avoids the complicated and time-consuming modification procedure. This simple and efficient colorimetric method can also be extended to other enzymes assays.     

Aptasensor for ampicillin using gold nanoparticle based dual fluorescence–colorimetric methods

A gold nanoparticle based dual fluorescence–colorimetric method was developed as an aptasensor to detect ampicillin using its single-stranded DNA (ssDNA) aptamer, which was discovered by a magnetic bead-based SELEX technique. The selected aptamers, AMP4 (5′-CACGGCATGGTGGGCGTCGTG-3′), AMP17 (5′-GCGGGCGGTTGTATAGCGG-3′), and AMP18 (5′-TTAGTTGGGGTTCAGTTGG-3′), were confirmed to have high sensitivity and specificity to ampicillin (K _d, AMP7 = 9.4 nM, AMP17 = 13.4 nM, and AMP18 = 9.8 nM, respectively). The 5′-fluorescein amidite (FAM)-modified aptamer was used as a dual probe for observing fluorescence differences and color changes simultaneously. The lower limits of detection for this dual method were a 2 ng/mL by fluorescence and a 10 ng/mL by colorimetry for ampicillin in the milk as well as in distilled water. Because these detection limits were below the maximum residue limit of ampicillin, this aptasensor was sensitive enough to detect antibiotics in food products, such as milk and animal tissues. In addition, this dual aptasensor will be a more accurate method for antibiotics in food products as it concurrently uses two detection methods: fluorescence and colorimetry.     

Electrodeposition of polypyrrole–Au nanoparticles composite from one solution containing gold salt and monomer

An easy method of preparation of polymer/metal–nanoparticle composites is reported. KAu(CN)₂ and pyrrole do not react (redox reaction) in solutions of moderate pH. The gold complex, due to its inertness, is stable in the presence of 10 μM CN^? for weeks. Therefore the electrodeposition of controlled amounts of polypyrrole and Au nanoparticles on the graphite surface can be done in one solution by applying a sequence of 0.75 and ? 1.6 V potentials. Pulse deposition of both components leads to substantial improvement of the layer smoothness and homogenous distribution of Au nanocrystallites.     

Preparation and characterization of acrylic polymer–nanogold nanocomposites from 3-mercaptopropyltrimethoxysilane encapsulated gold nanoparticles

In this study, acrylic polymer–nanogold nanocomposites and their cast films were prepared from an acrylic copolymer and 3-mercaptopropyltrimethoxysilane (MPS) stabilized gold nanoparticles by a sol–gel reaction. The acrylic copolymer was synthesized from methyl methacrylate (MMA) and 3-(trimethoxysilyl)propyl methacrylate (MSMA). The Si–OMe groups of MPS on the surface of gold nanoparticles (MPS–Au) provided the further reaction with the same groups of MSMA, hence the covalent bonds between polymers and MPS–Au nanoparticles were formed. FE-SEM images show MPS–Au nanoparticles are dispersed well in the prepared nanocomposites, and no large aggregation is occurred. TGA results indicate that the decomposed temperatures (T_d) of low Au-content (0.1 wt.%) nanocomposites are higher than these of the acrylic copolymer and high Au-content (1.0 wt.%) nanocomposites. The temperature of maximum decomposed rate (T_p) of each prepared nanocomposite is higher than that of the acrylic copolymer. The hardness of the cast film increases with increasing the Au content. The results show the improved thermal stability and application potentials of the prepared acrylic polymer–nanogold nanocomposites.     

Bimetallic palladium–gold nanoparticles synthesized in ionic liquid microemulsion

The palladium and gold precursors were dissolved in dispersive and continuous phase of ionic liquid microemulsion (H₂O/Triton X-100 (TX-100)/1-butyl-3-methylimidazolium hexafluorophosphate), respectively. [PdCl₆]^2? ions were reduced in situ by TX-100 in dispersive phase (H₂O) to prepare Pd nanoparticles (NPs) and then [AuCl₄]^? crossed through the interface film and reacted with the as-prepared Pd NPs to form Pd₄Au NPs. The as-prepared Pd₄Au NPs were characterized by transmission electronic microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and ultraviolet–visible spectroscopy. The as-prepared Pd₄Au NPs suspension and carbon nanotubes (CNTs) suspension were vigorously stirred to prepare the electrocatalyst supported on the CNTs with a total metal loading of 20?wt.% (denoted by Pd₄Au/CNTs). Cyclic voltammetry and chronoamperometry tests show that the Pd₄Au/CNTs are very promising for the oxidation of ethanol in alkaline medium. The result can be attributed to the synergistic effect between Pd and Au during the catalytic process.     

Palladium nanoparticles generated from allylpalladium chloride in situ: A simple and highly efficient catalytic system for Mizoroki–Heck reactions

The Mizoroki–Heck reactions of aryl halides catalyzed by palladium nanoparticles generated in situ from a simple allyl palladium precursor were investigated in argon. The high turnover numbers of 9,300,000 have been obtained with 4-bromobenzonitrile as substrate and 3500 with 4-nitrochlorobenzene. When the reaction was performed in air, a low yield was given, but it could be improved obviously by addition of PEG-400. The main reason was that inactive Pd(II) species could be rapidly reduced to the active Pd(0) by PEG. In other word, the existence of air and PEG led to a synergistic effect which the oxidation by air prevents the aggregation of Pd NPs and the reduction by PEG maintains the high activity of Pd(0) species.     

Polyaniline–DNA microsphere formation by simple electropolymerization

Polyaniline (PANI) microspheres were prepared by electrochemical polymerization. To obtain PANI having novel micro- and nanostructures, by the potential scan technique, aniline was electropolymerized in the presence of DNA using four polymerizing solutions containing different acids: H₂SO₄, C₆H₅SO₃H, HClO₄, and CF₃COOH. The growth rate of the PANI film on the electrode surface decreased by the presence of DNA, suggesting that DNA interacted with the growing PANI molecules during the electropolymerization. The growth rate also depended on the type of acid, i.e., the anion, in the polymerizing solution and was in the order of SO₄ ²⁻ > C₆H₅SO₃ ⁻ > ClO₄ ⁻ > CF₃COO⁻, which significantly coincided with the reverse order of the Hofmeister series representing the lyophilicity of the anion. When aniline was electropolymerized in the CF₃COOH polymerizing solution containing DNA, PANI microspheres were obtained without any templates. This PANI showed a sufficient redox activity in the less acidic solution in which the ordinary PANI has a slight redox activity. On the other hand, the electronic state of the PANI differed from the ordinary ones; a new absorption band was evident at 620 nm. The difference in the redox activity and electronic state suggested that the DNA molecules were incorporated in the PANI and electronically interacted with the PANI molecules.     

A simple template-free sol–gel synthesis of spherical nanosilica from agricultural biomass

Mesoporous silica nanoparticles with a spherical morphology have been synthesized from rice husk (agricultural biomass) by a simple, template-free synthetic approach, which was carried out via sol–gel technique at ambient condition. Transmission electron micrographs revealed the formation of spherical silica nanoparticles with an average diameter of 50.9 nm. From the nitrogen adsorption–desorption analysis, the rice husk silica shows a high specific BET surface area of 245 m² g⁻¹. The silica nanoparticles have a narrow pore size distribution of 5.6–9.6 nm.     

A new preparation method of gold nanoparticles by intra-reduction of sodium gold（I） sulfite

In this study, well-dispersed gold nanoparticles were prepared by using intra-molecular reduction of sodium gold sulfite, without using additional reductants and chloride free. The technical parameters including transformation temperature, pH, and concentration were optimized by the single-factor method as 90 C, pH 1, and 0.01 mmol/L [Na3Au（SO3）2], respectively. The resultant colloidal transmission electron microscopy images （TEM） and UV-vis absorption spectrophotometer spectra were acquired to check their properties, and the results show this kind of colloidal gold is controlled to 6 nm in sizes and has good stability in solution.     

A novel colorimetric aptasensor for detection of chloramphenicol based on lanthanum ion–assisted gold nanoparticle aggregation and smartphone imaging

A label-free, rapid response colorimetric aptasensor for sensitive detection of chloramphenicol (CAP) was proposed, which was based on the strategy of ssDNA-modified gold nanoparticle (AuNP) aggregation assisted by lanthanum (La³⁺) ions. The AuNPs generated a color change that could be monitored in the red, green, and blue and analyzed by the smartphone imaging app. La³⁺, as a trigger agent, strongly combined with the phosphate groups of the surface of ssDNA-AuNPs probe, which helps create AuNP aggregation and the color change of AuNPs from red to blue. On the contrary, when mixing with CAP, the aptamer (Apt) bound to CAP to form a rigid structure of the Apt-CAP complex, and La³⁺ attached to the phosphate groups of the complex, which prevented the aptamer from binding to the surface of the AuNPs. As a result, the color of the AuNPs changed to violet-red. Finally, UV-vis absorption spectroscopy and the smartphone imaging app were employed to determine CAP with a lower detection limit of 7.65 nM and 5.88 nM, respectively. The proposed strategy featuring high selectivity and strong anti-interference ability for detection of CAP in practical samples was achieved. It is worth mentioning that the simple and portable colorimetric aptasensor will be used for facilitating on-site detection of food samples.

     

A plasmonic mercury sensor based on silver–gold alloy nanoparticles electrodeposited on indium tin oxide glass

We construct silver–gold alloy nanoparticles (Ag–AuNPs) as the basis of a reagentless, sensitive and simple mercury sensor. Ag–AuNPs were electrodeposited directly on transparent indium tin oxide film coated glass. Hg(II) ions in aqueous solution could be reduced by Ag atoms existing in Ag–AuNPs; the deposition/amalgamation of Hg on the nanoparticles resulted in a blue shift of the localized surface plasmon resonance peak. Therefore, Hg^2 + can be detected quantitatively by using a spectrophotometer. The sensor response is linear in the range from 0.05 to 500 ppb of Hg(II) concentration. No sample separation or preconcentration is required for detection of ultralow levels of mercury in water samples. The results shown herein have potential applications in the development of a new optical sensor for the detection of low concentrations of mercury.     

A series of new hybrid compounds constructed from Dawson-type phosphomolybdates and metal–organic coordination complexes

In this study, a series of compounds based on Dawson-type phosphomolybdates, H₃(C₆NO₂H₆)₂[K(H₂O)₃(C₆NO₂H₅)₃][P₂Mo₁₈O₆₂] ? 5.5H₂O (1), (C₆NO₂H₆)₆[Ln(H₂O)₇(C₆NO₂H₅)₂]₂[P₂Mo₁₈O₆₂]₂·13.5H₂O (Ln = Ce (2), La (3)) have been synthesized and characterized by elemental analysis, IR and UV-Vis spectroscopy methods, TG analysis, and single-crystal X-ray diffraction. Compound 1 consists of [P₂Mo₁₈O₆₂]^6? building units joined by potassium-pyridine-3-carboxylic acid complexes, resulting in a wavelike polyoxometalate (POM) chain, which further interacts with each other via intermolecular interactions to form a 3-D supramolecular channel framework containing guest water molecules. Compounds 2 and 3 possess a 3-D supramolecular framework with 1-D tunnel constructed from [P₂Mo₁₈O₆₂]^6? and mononuclear lanthanide coordination complex fragments. To the best of our knowledge, 1 not only represents the first example of 1-D hybrid assembly based on Dawson-type phosphomolybdate, but also the first hybrid compound constructed from Dawson-type POMs and alkali–metal coordination complex fragments.     

Voltammetric determination of the Alzheimer’s disease-related ApoE 4 gene from unamplified genomic DNA extracts by ferrocene-capped gold nanoparticles

Microchimica Acta - A nanozyme composed of mesoporous silica and platinum nanoparticles (MS-PtNPs) was synthesized and is shown to display peroxidase-like activity. Its activity can be controlled...