In this brief review, gold nanoparticles conjugated with functional polymers are described from the viewpoint of application to sensing materials. The optical properties of gold nanoparticles, the ...synthesis of polymer-functionalized gold nanoparticles, and their analytical applications are discussed. Polymer-functionalized gold nanoparticles are categorized into two classes: biopolymer-conjugated gold nanoparticles and artificial-polymer conjugated gold nanoparticles. Fluorometric and colorimetric sensing using gold nanoparticles are focused; fluorometric detection enables us to exploit sensitive assays for practical use. Furthermore, chemical amplification using gold nanoparticles is also discussed for the sensitive probing.
Absorption spectra of pH indicators in aqueous solutions were reproduced from RGB values of microscopic images utilizing principal component analysis (PCA) and linear algebraic treatments. The ...reproduction of absorption spectra comprises the following three steps: (1) determining the loading spectra by PCA, (2) determining the conversion matrix from the RGB values to the score vectors, and (3) reproducing the absorption spectra by linear combination of the loading spectra and the score vectors. The reproducibility of the absorption spectra was demonstrated by employing bromothymol blue and methyl red solutions as pH indicators. The reproduced spectra of both indicators were in good agreement with the spectra measured with a conventional spectrophotometer. The pKa values of both indicators calculated from the reproduced spectra are in good agreement with those obtained from the spectrophotometric spectra and the literature values, confirming validity of the reproduction. This approach was applied to measure pH of freeze concentrated solutions in micro drains formed in ice. A change in pH was successfully observed on freezing and was compared with that reported in previous literature. Since this method does not necessitate the use of grating systems, spectral changes can be traced in milliseconds; this elucidates the phenomena occurring in fluctuating fields.
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•A method to reproduce absorption spectra from RGB values of microscopic images is proposed.•The absorption spectra are reproduced by the linear combination of score values determined from the RGB values and loading spectra determined by principal component analysis.•A change in pH of freeze concentrated solutions on freezing was confirmed by reproducing absorption spectra of the indicator therein.•Non-grating microspectroscopy can be achieved with the present method.
Total iron contents in iron ores have been accurately determined by JIS M 8212, in which iron ions in digested solutions of iron ores are reduced to divalent prior to redox titration. It is necessary ...for the iron reduction process that no reducing chemicals other than iron(II) in the decomposition solutions must not remain after the reduction with titanium(III). However, the redox reactions concerning the chemical species present in the decomposition solution has not been completely elucidated at the present time. In this paper, the redox reactions that occurred in the decomposition solution during the iron reduction in JIS M 8212 were studied by potentiometry and spectrophotometry under nitrogen atmosphere. The redox reaction of tin(II)/(IV) was very slow, causing significant effects on identifying the end point of the indicator for the iron reduction. The copper chloro-complexes were reduced with titanium(III) at a potential higher than that of indigo carmine used as a redox indicator, so that the reduced copper(I) gave a positive error to the potassium dichromate titration. The pentavalent vanadium was reduced with titanium (III) to form a complex with titanium, which also interfered with the potassium dichromate titration positively. To avoid these interferences, titanium(III) chloride was stoichiometrically added to the reaction mixture after addition of tin(II) chloride under nitrogen atmosphere so as to reduce only iron to divalent prior to the following redox titration. Combination of the proposed protocol with the potassium dichromate titration could successfully determine the iron content of certified reference materials of iron ores.
The chemical interaction between antifreeze proteins (AFPs) and ice crystals is evaluated via electrophoresis of AFP-anchored microparticles in fluidic channels formed in frozen aqueous sucrose. ...Straight fluidic channels are created in a flat glass chamber connecting two Ag/AgCl electrodes. This configuration allows us to estimate an electric field strength exerted on probe particles migrating along the channel. When the channel width is comparable to the particle size, the particle is immobile because of the resistance force induced by the interaction with the ice wall. However, when the overall electrophoretic force surpasses the resistance force, the microsphere starts to migrate. From the threshold electric field strengths determined for unmodified and AFP-modified particles, the resistance forces for the chemical interaction between AFPs and ice wall are estimated.
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•The interaction between antifreeze proteins (AFPs) and ice is evaluated via electrophoresis of particles in ice channels.•Ice channel width can be controlled by temperature and the sucrose concentration.•The forces acting on the particles are determined from the threshold electric field strength.•Differences in the interaction force between types of AFPs are discussed.
Magnesium oxide (MgO) contained in steelmaking slags in its liberated form, referred to as free MgO, expands when hydrated. The expansion of free MgO sometimes causes the deterioration of steelmaking ...slags used as construction materials for roads. Therefore, a method that determines the free MgO content in steelmaking slags is required. Solvent extraction is a promising preparation method for determining free MgO in steelmaking slags. Herein, organic solvents were explored for their extraction capabilities, and MgO was successfully extracted with 2,2,2-trichloroethanol (TCE) at 140°C over 3 h. TCE could not be used to extract any other magnesium compounds in blast furnace slags or merwinite, which contain no free MgO, indicating that free MgO was selectively extracted with TCE. The MgO content determined by TCE extraction and atomic absorption spectrometry was found to be reasonably consistent with that determined by other methods, which implies that this method is suitable for measuring the MgO content in steelmaking slags. The mechanism for the extraction of MgO by TCE was also investigated, and it was found that TCE extraction occurred via an acid-base reaction and an oligomerization crosslinking reaction.
Steelmaking slags treated with aqueous H2SO4 were characterized as Se(IV) adsorbents, and notable adsorption ability was shown to develop at H2SO4 concentrations of 0.18–0.20 mol/L. The enhanced ...adsorption performance of slags sulfated in the presence of H2O2 suggested that their Se(IV) adsorption sites contained Fe(III) and resembled those of schwertmannite. Langmuir analysis of Se(IV) adsorption isotherms was used to determine the corresponding adsorption capacities and adsorption constants. Thus, the obtained results allow one to simultaneously solve the problems of slag utilization and Se removal from wastewater or natural water, contributing to the establishment of a greener society.
The optimum composition of mixtures of iodine, ethanol, and ethylene glycol as selective extraction media for free magnesia in steelmaking slags was explored. Hydration of free magnesia in ...steelmaking slags increases its volume to expand the slags, resulting in deteriorate pavement of roads when the steelmaking slags were used as a road-constructing material. Therefore, accurate analytical methods to determine free magnesia in the steelmaking slags have been sought in steel industries. Ethanolic solutions of iodine without ethylene glycol afforded higher selectivity for the extraction of magnesia than ternary mixtures of iodine, ethanol, and ethylene glycol. Although the addition of up to 5 wt% of ethylene glycol to the ethanolic iodine solution increased the amount of magnesia extracted, it also increased the extraction of other magnesium species present in the steelmaking slags, resulting in decreased selectivity toward magnesia. The dissolution of magnesia in ethanolic iodine solution was promoted by the alkalinity of the magnesia. Meanwhile, the dissolution of magnesia promoted the redox reaction between ethanol and iodine in the extraction medium.
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Simple and convenient preparation of metal nanoparticles has been a challenging issue to overcome in nano-technologies. To address this, spontaneous growth of gold nanoclusters to ...form gold nanoparticles in the presence of high molecular weight poly(ethylene glycol) (PEG) was studied under ambient conditions. Gold nanoclusters with a particle size of ∼2 nm spontaneously grew to form larger gold nanoparticles with a plasmonic absorption band at 520 nm only when in the presence of structurally organized PEG with a molecular weight of at least 2 × 106 g/mol, producing a pinkish colored solution. UV–vis absorption spectra indicate the existence of two steps responsible for gold nanocluster growth to form gold nanoparticles. The first step involves an increase in the absorbance of the spectral band at 520 nm during the first 10 min due to aggregation of gold nanoclusters. The second step is the broadening of this band at the same wavelength as a result of fusion followed by growth of the gold nanoclusters. Redox potentials and transmission electron microscopy (TEM) images reveal that structurally organized high molecular weight PEG induces aggregation of the gold nanoclusters and their subsequent growth to form larger nanoparticles, which exhibit plate-like triangular structures with sharp edges. Our study unveils the role that PEG plays in the growth process from gold nanoclusters to gold nanoparticles.
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We describe the development of near-infrared (NIR) fluorescence from non-fluorescent gold nanoclusters as a result of the reaction with sulfhydryl oligopeptides. Non-fluorescent gold ...nanoclusters with a diameter of about 2nm were synthesized by reducing HAuCl4 with NaBH4 in the presence of tetraethyleneglycol. The fluorescence of the gold nanoclusters bearing sulfhydryl compounds arose from the ligand-to-metal charge transfer from the sulfhydryl compounds to the gold atoms at the gold nanocluster surface. The sulfhydryl oligopeptides cysteinylglycine, glutamylcysteine, and glutathione produced a fluorescence band around 830nm in the NIR region, whereas the sulfhydryl monopeptides cysteine and homocysteine produced fluorescence in the visible region. Among the sulfhydryl oligopeptides, only cysteinylglycine exhibited stable fluorescence without heating the solution. Because the fluorescent gold nanoclusters bearing cysteinylglycine were so stable, monothiols, amine compounds except polyethyleneimines, transition metal ions, alkali metal ions, and alkaline earth metal ions did not affect the fluorescence properties of the nanoparticles.
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