Real-Time Dark-Field Scattering Microscopic Monitoring of the <i>in Situ</i> Growth of Single Ag@Hg Nanoalloys

A comprehensive understanding of the growth mechanism of nanoalloys is beneficial in designing and synthesizing nanoalloys with precisely tailored properties to extend their applications. Herein, we present the investigation in this aspect by real-time monitoring of the <i>in situ</i> growth of single Ag@Hg nanoalloys, through direct amalgamation of Ag nanoparticles with elemental mercury, by dark-field scattering microscopy. Four typically shaped Ag nanoparticles, such as rods, triangular bipyramids, cubes, and spheres, were used as seeds for studying the growth of Ag@Hg nanoalloys. The scattered light of Ag nanoparticles of different shapes, on exposure to the growth solution, exhibited a noticeable blue-shift followed by a red-shift, suggesting the growth of Ag@Hg nanoalloys. The formation of Ag@Hg nanoalloys was confirmed by scanning electron microscopy, high-resolution transmit electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and elemental mapping and line scanning. Further analysis of the time-dependent spectral data and morphological change of single nanoparticles during the growth led to the visual identification of the growth mechanism of single Ag@Hg nanoalloys. Three important steps were involved: first, rapid adsorption of Hg atoms onto Ag nanoparticles; second, initial diffusion of Hg atoms into Ag nanoparticles, rounding or shortening the particles; third, further diffusion of Hg atoms leading to the formation of spherical Ag@Hg nanoalloys. On the basis of these results, Ag@Hg nanoalloys with given optical properties can be synthesized. Moreover, dark-field scattering microscopy is expected to be a powerful tool used for real-time monitoring of the <i>in situ</i> growth of other metal nanoparticles

Real-Time Dark-Field Scattering Microscopic Monitoring of the <i>in Situ</i> Growth of Single Ag@Hg Nanoalloys

A comprehensive understanding of the growth mechanism of nanoalloys is beneficial in designing and synthesizing nanoalloys with precisely tailored properties to extend their applications. Herein, we present the investigation in this aspect by real-time monitoring of the <i>in situ</i> growth of single Ag@Hg nanoalloys, through direct amalgamation of Ag nanoparticles with elemental mercury, by dark-field scattering microscopy. Four typically shaped Ag nanoparticles, such as rods, triangular bipyramids, cubes, and spheres, were used as seeds for studying the growth of Ag@Hg nanoalloys. The scattered light of Ag nanoparticles of different shapes, on exposure to the growth solution, exhibited a noticeable blue-shift followed by a red-shift, suggesting the growth of Ag@Hg nanoalloys. The formation of Ag@Hg nanoalloys was confirmed by scanning electron microscopy, high-resolution transmit electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and elemental mapping and line scanning. Further analysis of the time-dependent spectral data and morphological change of single nanoparticles during the growth led to the visual identification of the growth mechanism of single Ag@Hg nanoalloys. Three important steps were involved: first, rapid adsorption of Hg atoms onto Ag nanoparticles; second, initial diffusion of Hg atoms into Ag nanoparticles, rounding or shortening the particles; third, further diffusion of Hg atoms leading to the formation of spherical Ag@Hg nanoalloys. On the basis of these results, Ag@Hg nanoalloys with given optical properties can be synthesized. Moreover, dark-field scattering microscopy is expected to be a powerful tool used for real-time monitoring of the <i>in situ</i> growth of other metal nanoparticles

Quantitation and Differentiation of Bioparticles Based on the Measurements of Light-Scattering Signals with a Common Spectrofluorometer

By simultaneously scanning both the excitation and emission monochromators of a common spectrofluorometer with same starting excitation and emission wavelength (namely, Δλ = 0), we obtained synchronous light scattering (SLS) signals that related to Rayleigh and Mie scatterings. It was found that the SLS signals could be applied for quantitation and differentiation of model bioparticles such as Saccharomyces cerevisiae, Schizosaccharomyces pombe, Staphylococcus aureus, Escherichia coli, Bacillus subtilis, Bacillus thuringiensis and Bacillus megaterium. In PBS buffer, these model bioparticles could form colloidal suspensions or dispersions of sizes ranging from hundreds of nanometers to tens of micrometers, giving SLS signals with the intensity being proportional to the amount of bioparticles in the range from 1.7 × 105 to 1.7 × 109 CFU/mL. A further finding is that polarized synchronous light scattering (PSLS) signals of I0°−30° against I0°−0°, which could be obtained by introducing polarizing sheets accessory of the spectrofluorometer, and the derivative synchronous light scattering (DrSLS) signals, which could be obtained directly with the extension function of the spectrofluorometer, offer differentiation information of bioparticles connected with their size, shape, refractive indexes, and inner structure. Refractive indexes of spherical bacteria were then calculated based on light scattering signals

Identification of Iodine-Induced Morphological Transformation of Gold Nanorods

The morphological transformation process resulting from the reaction between Au nanorods (NRs) and iodine in situ produced from the redox between potassium iodide and copper chloride was monitored by virtue of the transmission electron microscope (TEM) images and the plasmon resonance absorption (PRA) spectra. It was found that the presence of copper chloride or potassium iodide could make the longitudinal PRA band of Au-NRs shift without any change of morphological transformation owing to the change of the refractive index of the medium. Different from that, iodine, which was in situ produced from the redox of potassium iodide and copper chloride, could fuse Au-NRs in the side-by-side mode, resulting in morphological transformation of Au-NRs to sphericity with the characteristics of the decrease of aspect ratio, blue-shift of the longitudinal PAR band, red-shift of transverse PRA band, and broadening of both longitudinal and transverse PRA bands of Au-NRs. The blue-shifted wavelength of the longitudinal PRA band was found to be in proportion to the concentration of copper chloride or potassium iodide when potassium iodide or copper chloride is sufficient, supplying the possibility to detect copper and iodine element in samples with spectrophotometry

Ultrasensitive Electrochemiluminescence Detection of MicroRNA via One-Step Introduction of a Target-Triggered Branched Hybridization Chain Reaction Circuit

High sensitivity and accuracy are two key issues that are critical for electrochemiluminescence (ECL) detection, especially for low-abundance nucleic acid detection. However, research on the construction of biosensors has mainly been through a step-by-step approach, which will increase the systematic error and affect the accuracy of the detection. Here we propose a novel strategy of introduction of a branched hybridization chain reaction (bHCR) circuit to a terbium­(II) organic gel (TOG) modified electrode in one step to achieve both sensitive detection and simplified modification steps. The sensitivity of the biosensor was elevated by the cascade bHCR circuit that was activated by miRNA-141 and operated like a molecular machine to form hyperbranched DNA nanostructures. Benefiting from molecular programming, the obtained nanostructures carried a large number of dopamine molecules, which can effectively quench the ECL signal of emitters and achieve a low limit of detection (0.18 fM). Impressively, the proposed one-step approach was almost the easiest way to modify nucleic acids to electrodes. In this way, the introduction of a high-molecular-weight DNA structure in one step avoided the errors that may result from the stepwise modification of low-molecular-weight nucleic sequences into the electrode. Considering the accessible operation, favorable performance, and high universality of this strategy, this work may be used to analyze other microRNAs and further clinical diagnosis

Synergetic Catalytic Effect of Cu_2–<i>x</i>Se Nanoparticles and Reduced Graphene Oxide Coembedded in Electrospun Nanofibers for the Reduction of a Typical Refractory Organic Compound

A new heterogeneous catalytic composite composed of nonstoichiometric Cu_2–<i>x</i>Se nanoparticles (NPs) with high copper deficiency and graphene oxide (GO) is prepared by coembedding in electrospun nanofibers of a poly­(vinylpyrrolidone) (PVP) support, wherein GO in the nanofibers is converted into reduced GO (rGO) via heat treatment. The as-prepared composite Cu_2–<i>x</i>Se/rGO/PVP nanofibers have demonstrated superior catalytic activity toward the reduction of a refractory organic compound by taking 4-nitrophenol (4-NP) as an example. In the presence of NaBH₄, the Cu_2–<i>x</i>Se/rGO/PVP nanofibers display a synergetic effect between Cu_2–<i>x</i>Se and rGO in PVP nanofibers compared to their independent components or corresponding nanofibers. Furthermore, the Cu_2–<i>x</i>Se/rGO/PVP nanofibers exhibit a favorable water-stable property via heat treatment to solidify the hydrophilic PVP matrix, which makes the composite display good reusability, stability in aqueous solution, and separability from a water medium. This work not only presents a direct, convenient, and effective approach to doping semiconductor nanomaterials into polymer nanofibers but also provides fundamental routes for further investigations about the synergetic effect between different materials based on the platform of electrospun nanofibers

Fluorescence spectra of the TAPP, TAPP/RGO complex and that in presence of iron (III) ions.

<p>Concentrations: TAPP, 2.4 µM; RGO, 13.5 µg ml⁻¹; iron (III) ions, 60.0 µM. <i>λ</i>_ex, 413.0 nm, pH, 4.1.</p

Fluorescence Assay Based on Preconcentration by a Self-Ordered Ring Using Berberine as a Model Analyte

A novel assay for trace amounts of fluorescent analytes is proposed based on the assembly of a self-ordered ring (SOR) through capillary flow in a sessile droplet on a glass slide support. After solvent evaporation of the sessile droplet containing a fluorescent analyte on a hydrophobic-treated glass slide, an outward capillary flow of the solvent from the interior of the droplet occurs. The resultant outward capillary flow then carries the analyte to the perimeter of the droplet spot where the analyte deposits and forms a fluorescent SOR. For the model analyte of berberine, SORs with outer diameter less than 1.2 mm and ring belt width less than 19 μm can be obtained depending on the droplet volume of the berberine solution. Data analysis for the digitally imaged SOR by using a CCD camera showed that the berberine molecules across the SOR belt section follow a Gaussian distribution, and the maximum fluorescent intensity (Imax) was found to be proportional to berberine content at the femtomole level. With the proposed technique, the content in tablets and the average excretion rates of berberine through human urine after oral administration could be satisfactorily monitored

A One-Pot Green Method for One-Dimensional Assembly of Gold Nanoparticles with a Novel Chitosan−Ninhydrin Bioconjugate at Physiological Temperature

With our newly prepared novel chitosan−ninhydrin (CHIT-NH) bioconjugate in this contribution, we made one-dimensional (1-D) assemblies of gold nanoparticles (NPs) at physiological temperature. This 1-D assembly method is simple, one-pot, and totally green wherein multiplex functional groups of the CHIT-NH conjugate make the nonuniform spatial distribution of stabilizers to form organized 1-D assemblies. UV−vis and infrared spectroscopy have been employed for identifying the molecular structure of CHIT-NH conjugate, while scanning electron microscopy (SEM), transmission electron microscopy (TEM) for confirming the 1-D morphology of gold NP assemblies. Mechanism investigations on the basis of the measurements of dynamic light scattering (DLS), time-dependent optical spectra, visible observation on the change of solution color and SEM imaging showed that the CHIT-NH conjugate, a novel environmentally benign and excellently biocompatible material, serves not only as a reducing agent but also as a stabilizer for the growth and 1-D assembly of gold NPs

Fluorescence response of TAPP/GO complex to various metal ions.

<p>Concentration: TAPP, 2.4 µM; GO, 16.0 µg ml⁻¹; iron (III) ions, 15.0 µM; Other metal ions were all 30.0 µM. All data were collected at 645.0 nm.</p