Magnetic orientational linear dichroism (MOLD) spectra of magnetic nanoparticles (MNPs) in the UV-Vis wavelength region were found to be useful as a probe to detect changes of the dispersion state due to a restriction of the rotational Brownian motion of MNPs; a change of the medium from liquid to resin and the formation of agglomerates in solution. The magnetic-field dependence of MOLD was analyzed by using the Langevin equation, which gave information about the magnetic moment of MNPs.
A new liquid–liquid extraction method, called the “emulsion flow” method, is expected to realize an ideal liquid–liquid extraction by controlling the emulsion generation and separation using liquid spraying, only by solution sending. In order to understand the mechanism of emulsion control in the emulsion flow method, the size distribution of droplets in two liquid-phase mixtures was compared by using originally designed apparatuses 1) for the case of liquid spraying and 2) for the case of mechanical stirring. We demonstrated that the size distribution of droplets generated near a mixing device (a nozzle for liquid spraying or an impeller head for mechanical stirring) determines the phase-separation property.
A rapid and simple method has been developed for simultaneous determinations of the concentrations of nine aminoglycosides (AGs) in livestock and fishery products using phenylboronic acid (PBA) solid-phase extraction (SPE) clean-up. Unlike the widely employed SPE approaches, based on cation-exchange, PBA SPE relies on the reversible formation of covalent bonds with the analytes. The advantage of using PBA lies in the fact that this compound strongly and stably retains analytes, and the pH of the loading solution can be easily adjusted using a high-concentration buffer. The clean-up conditions, such as the pH of the loading solution and the acetonitrile concentration in the elution and wash solvents, were optimized. The degree of recovery measured for nine AGs in six samples (bovine muscle, bovine liver, milk, chicken egg, fish and shrimp) were in the 73 – 98% range, and the values for the relative standard deviation were 9.3% or less.
Nucleic acid aptamers have been widely used as synthetic probes for bioanalytical applications. Herein, we carried out a detailed study on the immobilization of a series of aptamers ranging from 37 to 88 bases, which are specific to either Escherichia coli (E. coli) or Staphylococcus aureus (S. aureus), on a planar gold substrate via a polyadenine-mediated immobilization method. The resultant surfaces were characterized by both surface plasmon resonance spectroscopy (SPR) and X-ray photoelectron spectroscopy. The results clearly show that the aptamer solution at a lower ionic strength gives rise to a higher lateral density of the aptamer when compared to that at a higher ionic strength. The SPR aptasensors are then employed for detecting their corresponding bacteria (i.e., E. coli and S. aureus, respectively). The data indicate that the SPR aptasensor with a higher density of aptamer exhibits a better capture of target bacteria.
In this study, a direct and label-free immunosensor was designed and constructed by modifying the screen-printed electrode with graphene nanoplatelets (GNPs) for the detection of the cardiac troponin T (cTnT). Firstly, GNPs were drop-casted onto carbon working electrode. Monoclonal cTnT antibodies were then immobilized on the GNPs via physical adsorption; finally, BSA was introduced to block non-specific binding sites. The detection of cTnT was performed using an electrochemiluminescence (ECL) technique with tris(bipyridine)ruthenium(II) chloride ([Ru(bpy)3]Cl2) used as a luminophore and TPrA (tripropylamine) as a co-reactant. The ECL intensity was demonstrated to be directly proportional to the cTnT concentration where a linear range from 100 pg mL−1 to 5 fg mL−1 of the cTnT detection was established. An extremely low limit of detection was achieved to be 0.05 fg mL−1 with an outstanding specificity. Additionally, this immunosensor showed excellent percentage recovery for real samples analyses in artificially spiked human serum.
This paper presents a sensitive voltametric procedure for the determination of norfloxacin (NF) by a tetraoxocalixarenetriazine (TOCT) covalently functionalized multi-walled carbon nanotubes (MWCNTs) modified electrode. The electrochemical sensing of NF was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Through a combination of the excellent selective recognition of TOCT and the outstanding electronic properties of MWCNTs, this electrochemical sensor shows excellent sensitivity and high selectivity for an electrochemical detection of NF. The stripping response is highly linear (R = 0.996) over the NF concentration range of 0.5 – 8.0 μM with the LOD of 0.1 μM. The fabricated sensors were successfully applied for quantitative detection of NF in pharmaceutical formulations and human urine samples. A high anti-interference ability to common interferences and satisfactory results were obtained. This is expected to play a huge potential in the real-time monitoring of NF in clinical applications.
A colorimetric and turn-on fluorescent chemodosimeter 1 based on diaminomaleonitrile was synthesized for Cu2+ detection. It showed high selectivity and sensitivity towards Cu2+ over the other tested metal ions. Probe 1 in acetonitrile exhibited a strong absorption band at 530 nm and weak fluorescence emission when excited at 480 nm, while the addition of Cu2+ could lead to a 30-nm blue shift of the absorption band and a remarkable fluorescence enhancement. Moreover, the detection limit of probe 1 for Cu2+ was calculated to be 28 nM. Quite different from the reported mechanism based on a metal-complexation induced fluorescence enhancement, the sensing mechanism was proved to be based on the Cu2+-promoted hydrolysis reaction, which was confirmed by 1H NMR, 13C NMR and mass spectrum analysis. Studies on probe 2 were carried out to verify the universality of this sensing mechanism.
An asymmetric flow field–flow fractionation (AF4) combined with inductively coupled plasma mass spectrometry (ICP-MS) was applied to measure the concentration and size distribution of nanometer-sized carbides in steel sheets, such as titanium carbides (TiC) and vanadium carbides (VC). Prior to AF4-ICP-MS measurement, TiC and VC nanoparticles in steel were extracted into a solution via selective potentio-static etching by electrolytic dissolution (SPEED) method. The SPEED method enabled the selective dissolution of iron and the carbide nanoparticles were dispersed as primary particles in solution with surfactant. However, sulfur-free surfactant was required in AF4-ICP-MS carrier solutions because sulfur in SDS, generally used to disperse various nanoparticles, causes a spectral interference with titanium and vanadium in ICP-MS analysis. In this study, sulfur-free sodium cholate (SC) was applied as the dispersant of carbide nanoparticles for the SPEED method and AF4 measurements. SC provides a high absolute value of zeta potential on a particle surface and membrane of an AF4 separation channel to prevent particle adsorption on the membrane. Additionally, SC does not generate the spectral interference due to sulfur, in contrast to SDS. Thus, it enabled the sensitive detection of titanium and vanadium in carbide nanoparticles extracted from a steel sheet in AF4-ICP-MS. These results indicate that sulfur-free surfactants are useful for analyzing some precipitates in steels using AF4-ICP-MS.
Ionic liquid (IL) chelate extraction behavior of trivalent Group 13 metals including aluminum(III), gallium(III) and indium(III) with 8-quinolinol (HQ) was investigated using three 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (CnmimTf2N, n = 2, 4 and 8) ILs. Although the three extraction systems showed similar extraction selectivity among the metals, the extractability order for the metals among the extraction systems was C8mimTf2N > C4mimTf2N > C2mimTf2N, which was the same as the order of hydrophobicity in the IL cation. Only the neutral 1:3 complex species was extracted in use of more-hydrophobic C8mimTf2N, whereas use of less-hydrophobic C4mimTf2N and C2mimTf2N resulted in competitive extraction of neutral 1:3 and cationic 1:2 complexes. For each of the metals, in addition, similar extraction constants were obtained in these three extraction systems.
Surface-enhanced Raman scattering (SERS) is a powerful technique that enhances Raman signals by adsorbing probe molecules on rough metal surfaces. However, SERS is limited because target molecules must strongly interact with metal to enhance a stable Raman signal. In this study, to improve long-term SERS stability, we use cucurbiturils (CB) as bridge molecules and sample containers to probe Rhodamine 6G (R6G) molecules. We observed interactions between gold nanorods (AuNRs) and CB via aggregate formation, which enhanced the Raman signal and improved long-term R6G probe stability by up to 20 days when encapsulated within CB during SERS analysis.
Zirconium, niobium, hafnium, and tantalum are dissolved in seawater as hydroxide complexes at a concentration as low as 0.01 – 370 pmol kg−1 and are expected to be potential tracers for water masses in the ocean. Herein, we report a new analytical method for the multielemental determination of the four elements on the basis of column extraction, using a NOBIAS Chelate-PA 1 resin that contains ethylenediaminetriacetic acid groups. The elements were collected on the resin from seawater that had been added with 3.8 mM HF at pH 6.0, and were eluted with 5 M HF. After the evaporation of 5 M HF, the elements were dissolved in 0.5 M HNO3–6 mM H2SO4–1 mM HF and were determined by a high resolution ICP-MS, using a calibration curve method. We optimized the procedure to achieve quantitative recoveries and low backgrounds for the elements, although the complex formation between the metal ions and NOBIAS Chelate-PA 1 was decelerated by the seawater matrix. The method was tested by investigating the seawater samples of reference material and those collected from the depths at a station in the western North Pacific Ocean.
Polyhexamethylene biguanide (PHMB) is a cationic disinfectant widely used for personal-care products and for sanitizers in swimming pools. This paper describes a promotion effect of PHMB on a glucose oxidase (GOx) enzymatic reaction with ferricyanide ion and its analytical application. The promotion effect arose from a polyion complex formation between polycationic PHMB and polyanionic GOx. The promoted GOx reaction was analyzed by Michaelis–Menten equation, and the Michalis constant and catalytic constant were estimated to be 240 μM and 31 s−1, respectively. Utilizing the promotion effect, PHMB was successfully determined in the range of 0.05 to 0.40 ppm, and the detection limit was calculated to be 0.027 ppm. The visual detection and semi-determination of PHMB with the same concentration level were also possible. As an application, the method was applied to the determination of PHMB in a contact lens detergent and its model solution.
Seborrheic keratosis (SK) is a common, noncancerous growth on the skin. However, the paramagnetic species (radicals) in pigmented SK have not been investigated yet. X-band (9 GHz) electron paramagnetic resonance (EPR) and EPR imaging (EPRI) were used to nondestructively investigate paraffin-embedded SK. Paramagnetic species in SK specimens were analyzed using linewidth, spectral pattern, and X-band EPRI. The EPR spectra of the SK showed a single line pattern. The EPR results revealed that the peak-to-peak linewidths (ΔHpp) of paraffin-embedded SK samples were 0.58 ± 0.02 mT. The g-value was 2.004 for those samples using EPR standards. EPR signal intensities of the SK samples reasonably corresponded to those for permeability values that are directly related to pigment color tone. Moreover, the two-dimensional (2D) EPRI of the SK showed the distribution of paramagnetic species in the samples with different magnitudes for the first time. The distribution corresponds to the pigmented region. We established that the paramagnetic species was melanin radicals, based on the EPR results obtained in addition to in vivo oxidation of melanin pigments. The present results suggest that EPR and 2D EPRI techniques can be useful for the radical characterization and evaluation of various types of SK.
The transfer of hydrophilic, lipophilic, and fluorophilic ions at the interface between water (W) and a mixed solvent (MIX) of 2H,3H-decafluoropentane (DFP) and 1,2-dichloroethane (DCE) was studied voltammetrically and potentiometrically, and the formal Gibbs transfer energies of the ions from MIX to W, ΔG0′tr,MIX→W, were determined. The ΔG0′tr,MIX→W values of all the ions tested were higher than those from DFP to W. Namely, the ions would exist more stably in MIX than DFP, even for fluorophilic ions. This is due to the addition of DCE, which has a higher dielectric constant. A comparison of ΔG0′tr,MIX→W with that from DCE to W showed a superior affinity of fluorophilic ions to the fluorous solvent in spite of equivolume addition of DCE. Therefore, the mixed solvent would be a practically superior extraction medium for fluorophilic ions. In practice, the MIX | methylene blue+ (W) system showed higher extractability of a fluorophilic ion C8F17SO3− than the DFP | W and DCE | W systems.
The characteristics of an electrochemical biosensor based on a Prussian-blue screen-printed electrode containing glucose oxidase incorporated into polyelectrolyte microcapsules (PMC) are considered. PMC with the embedded enzyme were formed using sodium polystyrene sulfonate and poly(allylamine hydrochloride). The characteristics were compared with those of the enzyme immobilized in chitosan gel. We assessed the dependences of biosensor signals on the composition of the buffer solution, on the glucose concentration; the operational and long-term stabilities. The enzyme immobilized in PMC proved to be more sensitive to buffer molarity at a maximum within 35 – 40 mM. The apparent Michaelis constants were 1.5 and 4.1 mM at the immobilization in, respectively, chitosan and PMC. The developed biosensors were used to assay commercial juices. The biosensors’ data on the glucose contents were shown to have a high correlation with the standard spectrophotometric assay (0.92 – 0.95%), which implies a possible application of the fabricated biosensors in foodstuff analysis.
The most important parameter for light-scattering measurements in the Rayleigh scattering region is the Rayleigh ratio, which is necessary to obtain the absolute scattered light intensity from the relative scattered light intensity. The absolute scattered light intensity is directly related to the molar masses of polymers, colloids, biomolecules, and the like. A new Rayleigh ratio was determined by measuring static light scattering from certified reference materials with highly accurate certified values of the molecular weight determined by several other techniques, such as MALDI-TOF mass spectrometry or size-exclusion chromatography. The new Rayleigh ratio can be used for evaluating the uncertainty of the molecular weight of polymers and macromolecules, as measured by light scattering.
A sensitive analytical method was developed for individual analyses of D- and L-glyceric acids by chiral derivatization — liquid chromatography–tandem mass spectrometry. To elucidate rapid and efficient optimization for derivatization we newly introduced a concept of design of experiments (DOE). The optimization of major 5 factors in the derivatization could be predicted with only 28 measurements. By applying DOE to optimization, the yields of desired derivatives increased five-fold against before optimization.