We have developed a rolling circle amplification-procedure as a method to enhance signals of immunoassay (immuno-RCA) to detect one of the major food allergens, ovalbumin (OVA). Immuno-RCA in combination with a fluorescent dye and a circular DNA probe prepared by intramolecular ligation easily allowed the real-time detection of OVA, and could apparently detect signals from OVA with concentrations ranging from 10⁻¹² to 10⁻⁷ g/mL. Therefore, sensitive and easily handled aspects of this method would contribute to an effective signal enhancement in immunoassay for food allergen detections.

View full abstract

1-(2-Tryptanthrinylaminoacetoxy)-14-(1-pyrenecarboxy)-3,6,9,12-tetraoxatetradecane (T2NH-P5P) was synthesized as a fluorescent chemosensor for Al³⁺. Excited at 325 nm, corresponding to absorption of the pyrene unit of T2NH-P5P, emission at 600 nm from the 2-aminotryptanthrin unit has been observed, indicating that intramolecular fluorescence resonance energy transfer (FRET) occurs in T2NH-P5P. However, when Al³⁺ is added to a solution of T2NH-P5P, the fluorescence of 2-aminotryptanthrin is quenched (FRET-off), whereas that of the pyrene group is revived. Such a FRET "on-off" behavior of T2NH-P5P is not observed for other metal cations (Ca²⁺, Ba²⁺, and Zn²⁺).

View full abstract

This review highlights work using the author's method to construct metallic nanoarrays. This method is a DNA-templated assembly, to assemble metal nanoparticles (MNPs) in which DNA molecules are initially stretched and aligned on surfaces. Simple interface (air-liquid) moving and surface coating with polymers containing π-conjugation units, lead to the controlled formation of one-dimensional (1D) nanoarrays of DNA without special equipment. The assembly of MNPs onto DNA can be driven by electrostatic binding of newly prepared gold nanoparticles with positive charges, leading the formation of 1D metallic nanoarrays. Dark-field microscopy observations indicate that MNPs on DNA are uniaxially aligned. Finally, the fabrication and patterning of metallic nanoarrays achieved with DNA nanofibers and transfer printing techniques are discussed.

View full abstract

This paper reports on the development of a micro-potentiometric sensor based on external microelectrodes introduced into a microchip. We miniaturized reference and ion-selective electrodes (ISEs) and embedded them into a plastic (PDMS) microchip; the miniaturization of ISE was attained by using a monolithic capillary-based membrane. This sensor was applied to the detection of alkali ions (Na⁺, K⁺ and NH₄⁺) in a microflow on the μg/L level.

View full abstract

Intestinal absorption rates vary with the nature of the substances involved. In-vitro experiments with cell culture inserts are often conducted to evaluate the intestinal absorption rate. These inserts, however, require large amounts of cells, samples, and culture media, and take a long time to evaluate. To overcome these problems, we developed a microchip-based system that mimics the intestine. The microchip was composed of a glass slide, a permeable membrane, and polydimethylsiloxane (PDMS) sheets, which contained microchannels made by photolithography; Caco-2 cells were cultured on the membrane in the microchip. The system was regulated with a microsyringe pump. We conducted permeation tests; cyclophosphamide, which can permeate the intestinal barrier, displayed a high permeability coefficient and Lucifer yellow, which cannot be absorbed at the intestinal wall, displayed a low permeability coefficient. These results were consistent with those obtained using a conventional method, which supports the validity of our new system. The system realized an 80% reduction of cell consumption.

View full abstract

Quantum dots (QDs) are semiconductor fluorescent nanoparticles, which can be used for food safety or environmental monitoring with high sensitivity. This work demonstrates the feasibility of detecting clenuterol residue in pig urine using CdSe/CdS quantum dots as fluorescent labels based magnetic core/shell Fe₃O₄/Au nanoparticles (MCFN) as solid carriers. The detection of clenbuterol is carried out by a fluoroimmunoassay-based biosensor using competitive binding between conjugated clenbuterol antigen-CdSe/CdS QDs and free clenbuterol with immobilized clenbuterol antibodies on MCFN. This assay method allows for clenbuterol determination in a linear working range of 0.5 − 20000 pg mL⁻¹. It would provide a simple, rapid, and ultra-sensitive detection method for clenbuterol or other biomolecular analysis.

View full abstract

The present study demonstrates a single-molecular bioluminescent probe carrying functional peptides in the N-terminal domain of the androgen receptor (AR NTD) with an improved sensorial property to androgens. The N-terminal peptides in AR were genetically fused to the ligand binding domain of AR (AR LBD) with a flexible linker, and then sandwiched between the N- and C-terminal fragments of split-firefly luciferase (FLuc) dissected at D415. We found that the proline-rich region in AR NTD efficiently interacts with AR LBD and exerts (i) an enhanced signal-to-background ratio and (ii) discrimination between agonists and antagonists with (iii) a 100-times improved sensitivity to androgens, upon comparison with previous references. A deletion mutation to the proline-rich region in AR revealed that this region is critical for the transcriptional activities. The quantum yields of these single-chain probes were estimated to be 37.8 ± 0.6%. This monomeric AR LBD-peptide binding is necessary, and sufficient for discriminating an agonist and an antagonist, where the dimerization of AR LBD is not involved. The present study guides a fundamental methodology on how to discriminate weak protein-peptide binding, and provides a new insight into the contribution of functional peptides in AR NTD to the initial activation of monomeric AR.

View full abstract

A new type of amperometric glucose biosensor based on alginate (Alg)/layered double hydroxides (LDHs) organic-inorganic composite film is described. This hybrid material combines the advantages of an organic biopolymer, Alg and inorganic LDHs. Glucose oxidase (GOD) immobilized in the material maintained its activity. The composite films were characterized by UV-Vis. The results indicated that GOD retained the essential feature of its native structure in the composite film. The Alg/LDHs/GOD-modified platinum electrode exhibited a fast response to glucose (achieve 95% of the maximum in 10 s), which provided a linear response to glucose over a concentration range of 1.6 × 10⁻⁵ − 2 × 10⁻³ M with a detection limit of 4 × 10⁻⁵ M based on S/N = 3. Furthermore, the biosensor exhibited excellent long-term stability, and satisfactory reproducibility. It retained 87% of its original activity after being used for 28 days.

View full abstract

A trioctylamine (TOA) modified carbon paste electrode (TOA/CPE) was firstly utilized to determine Cr(VI) in electronics materials. The effects of preconcentration conditions, that is, TOA amount and accumulation time on Cr(VI) accumulation were examined and the optimum experiment conditions for the determination were identified. A sensitive reduction peak in the stripping voltammogram at −0.45 V, a characteristic of trace Cr(VI), was detected when the accumulation time was 10 min. Under optimized conditions, TOA/CPE demonstrated an enhanced sensitivity for Cr(VI), providing a low detection limit (S/N = 3) at 3.4 × 10⁻⁹ M. Interference studies also displayed high selectivity of the TOA/CPE for Cr(VI); this electrode can accurately determine Cr(VI) in the presence of Cr(III) (600-fold concentration) and other interfering cations.

View full abstract

Carbon paste- and polyvinyl chloride membrane electrodes are simple, precise, rapid and selective sensors for the determination of antidiabetic drugs for type 2 diabetic patients. These electrodes were successfully used for the potentiometric determination of rosiglitazone, pioglitazone, glimepiride and glyburide in their standard forms and also as pharmaceutical preparations. The preparation of these ion-selective electrodes for the potentiometric determination of the drug is based on the construction of a 10% standard drug-ion pair with reineckate or tungstophosphate imbeded as an electro-active material in the carbon paste or in the polyvinyl chloride membrane. The prepared ion-selective electrodes showed a Nernstian response with a limit of detection amounting to 10⁻⁶ M in a pH range of 3 to 5. A good selectivity coefficient and long term stability could be achieved. The developed potentiometric method based on the CPE and PVC sensors is economic and less time consuming compared to the conventionally used high performance liquid chromatography, HPLC, methods.

View full abstract

We describe a method for determining fluoride with ion-selective electrodes (ISEs). Tartrate and Tris-based total ionic strength adjustment buffers (TISABs) were found to lower the interference from aluminum to a greater extent than conventional citrate-based TISABs. We adopted a solid TISAB addition method that is simple to perform, and can be carried out without lowering the level of fluoride. The apparent recovery of fluoride was 95% or higher, even at 500 mg L⁻¹ of Al³⁺ when a tartrate and Tris-based TISAB was used. Interferences from common ions were not observed at 100 mg L⁻¹ levels. We determined the fluoride content in solid silicate samples with ISEs without preliminary steam distillation after alkali fusion processing. Adding a solid TISAB mixture consisting of tartaric acid, sodium tartrate, and Tris, however, eliminated any interference from high levels of aluminum and sodium and potassium carbonates. The proposed analytical method was also applied to the determination of fluoride in geochemical reference samples.

View full abstract

A simple and sensitive solid-phase spectrophotometry procedure was improved for the microdetermination of Cr(VI). A 0.06 cm³ portion of a cation exchanger, Muromac AG 50W-X2, was used to concentrate the target Cr(VI) in a 20 cm³ water sample, and resin beads were introduced in a flow cell of 1.5 mm diameter and having a 10 mm light path length for measurements using a UV-visible spectrophotometer. Three lenses were used for focusing the incident light beam and for recovering light scattered by the solid phase in the cell. The sensitivity achieved was higher by a factor of 277 compared with that of the solution method, and the detection limit was 0.014 μg dm⁻³. The recovery on spiked real water samples by the standard addition method was 96 − 101%. Favorable working and performance characteristics made it possible to directly determine sub-μg dm⁻³ amounts of Cr(VI) in natural water samples.

View full abstract

In the present work, we developed a simple, sensitive and inexpensive method to determine dopamine hydrochloride using potassium ferricyanide-Fe(III) by spectrophotometry. The results show that Fe(III) is deoxidized to Fe(II) by dopamine hydrochloride at pH 4.0, and then Fe(II) reacts with potassium ferricyanide to form a soluble prussian blue (KFe^III[Fe^II(CN)₆]). The absorbance of this product was monitored over time using a spectrophotometer at an absorption maximum of 735 nm, and the amount of dopamine hydrochloride could be calculated based on the absorbance. A good linear relationship of the concentration of dopamine hydrochloride versus absorbance was observed, and a linear regression equation of A = 0.022 + 0.16921C (μg mL⁻¹) was obtained. Moreover, the apparent molar absorption coefficient for the indirect determination of dopamine hydrochloride was 3.2 × 10⁴ L mol⁻¹ cm⁻¹. This described method has been used to determine dopamine hydrochloride in pharmaceutical, banana, urine and serum samples with satisfactory results.

View full abstract

A simple, reliable and sensitive spectrophotometric method for the determination of copper(II) was established with o-bromophenylfluorone (OBPF), a novel chemical probe, in the presence of poly(N-vinylpyrrolidone). Beer's law was obeyed in the range of 8 − 160 ng ml⁻¹, with an apparent molar absorptivity at 570 nm, the relative standard deviation being 3.64 × 10⁵ dm³ mol⁻¹ cm⁻¹ and 0.72% (n = 5). This method was applied to the recovery tests of copper(II) in human urine, bovine serum and tap water; the results were satisfactory.

View full abstract

Based on ultraviolet spectral net analyte signals, this research has studied the determination of the two effective components, sulfamethoxazole (SMZ) and trimethoprim (TMP), contained in compound sulfamethoxazole tablets in acid environment. The linear ranges of SMZ and TMP were 0.48 − 7.84 μg/ml (the regression correlation coefficient r = 0.9981) and 0.12 − 1.5 μg/ml (r = 0.9986), the corresponding average recoveries were 99.5 and 101.0%, respectively, and the relative standard deviations were 1.87 and 3.60%, respectively. The method was simple, fast and accurate. A circulation release system for the determination of the tablet release degree has been built, and the on-line filtering and small-volume sampling could thus be carried out. Thanks to the combination of the circulation release system and the determination method of SMZ and TMP in acid environment, the determination of release degree for compound sulfamethoxazole tablets was fast and accurate, especially for the early time of rapid release.

View full abstract

Based on the reaction of horseradish peroxidase (HRP) with nitric oxide (NO), a novel detection method of NO has been developed. The method uses second-order derivative spectrometry in an anaerobic phosphate buffer solution. The effects of pH and HRP concentration on the determination of NO in HRP system were investigated, and the conditions for the measurements were optimized. Some possible coexisting substances, such as nitrite, nitrate and hydrogen peroxide, were tested. The linear regression equation of standard curve was found to be h = 8.89 × 10⁻²c_NO − 1.56 × 10⁻³ with the relevant coefficient of 0.9966 (n = 5) in the NO concentration range of 0.085 − 1.3 μM. The relative standard deviations were less than 3%. Based on the standard deviation of 5 blank measurements and a signal-to-noise ratio of 3, the detection limit for NO was 0.032 μM. The proposed method was successfully applied to the determination of NO levels in serum samples.

View full abstract

An isotope dilution inductively coupled plasma mass spectrometry (ICP-MS) method has been developed for the determination of Hg and Pb in fuels using flow injection vapor generation (VG) as the sample introduction system. A simple and inexpensive in-situ nebulizer/vapor generator was employed in this study. An emulsion containing 10% v/v fuel, 2% m/v Triton X-100 and 1.0% m/v tartaric acid was injected into VG-ICP-MS system for the determination of Hg and Pb. Sodium borohydride was used for vapor generation. Since the sensitivities of Hg and Pb in emulsion and those in aqueous solution are quite different, isotope dilution and standard addition methods were used for the determination of Hg and Pb in selected fuel samples. The influences of vapor generation conditions and emulsion preparation on the ion signals are reported. This method has been applied for the determination of Hg and Pb in various fuel samples such as diesel, gasoline and engine oil obtained locally. The analytical results obtained by isotope dilution and standard addition methods were in good agreement with each other and also with those of digested samples analyzed by pneumatic nebulization ICP-MS. Under the optimum operating conditions, the detection limits obtained were 0.02 and 0.03 ng mL⁻¹ for Hg and Pb, respectively, in prepared emulsified solutions, corresponding to 0.2 and 0.3 ng mL⁻¹ of Hg and Pb, respectively, in the original fuel samples.

View full abstract

A silica-gel chemically modified with ethyl-2-benzothiazolylacetate (SiB) has been synthesized and characterized. The extractions towards Pb(II), Cu(II), Co(II), Cd(II) and Ni(II) were carried out in batch extraction. The maximum extraction was found at pH > 4 within 10 min. The maximum adsorption capacities, evaluated from Langmuir's model were 221, 141, 13, 7 and 5 μmol g⁻¹ for Pb(II), Cu(II), Co(II), Cd(II) and Ni(II), respectively. Home-made mini-columns were used in the flow system. The parameters that affected the extraction efficiency were explored. Sample volumes of 100.0 mL and 1% HNO₃ of 5.0 mL as the eluent were employed under the optimized conditions. No interfering from Na⁺, K⁺, Mg²⁺, Ca²⁺, Cl⁻ and SO₄²⁻ was observed. This modified silica gel was applied to preconcentrate Pb(II) and Cu(II) from spiked pond water, tap water and drinking water, giving high accuracy and precision. The method detection limits obtained from the desorbed metals determined by FAAS after preconcentration with SiB were 22 and 1 μg L⁻¹ for Pb(II) and Cu(II), respectively.

View full abstract

The absorption spectra of ceftazidime and its generic versions (Modacin, Mosyl, and Mobenzocin) have been measured by terahertz time domain spectroscopy (THz-TDS). Differences in the THz absorption were observed between the original and generic versions. The results show small, but significant differences in the states of ceftazidime hydrate between the original and generic versions. THz-TDS can be used to evaluate the stability of medicines as well as to control their quality.

View full abstract

We have developed a simple, labor-saving, inexpensive and rapid SNP genotyping method that directly uses a human hair root as the template. This single-tube genotyping method was used to successfully and reliably genotype the ADH1B and ALDH2 polymorphisms using a hair root (without DNA isolation) and the polymerase chain reaction (PCR) enzyme kit KOD FX. Since the DNA extraction step was eliminated, the possibility of sample contamination was considerably decreased. The single-tube SNP genotyping was performed by coupling the PCR enzyme kit with allele-specific primer (ASP)-PCR. In the post-genome era, a simple and inexpensive method for diagnostic analysis is in high demand, and this PCR method with a hair root as a template will be very useful for genetic diagnoses in biological and medical laboratories.

View full abstract

Suppressed ion chromatography with a conductivity detector was developed for the determination of trace amounts of underivatized chloroacetic acids (CAAs). When sodium carbonate and methanol were used as a mobile phase, the simultaneous determination of each CAA took approximately 25 min. The linearity, reproducibility and detection limits were determined for the proposed method. For the solid-phase extraction step, the effects of the pH of the sample solution, sample volume and the eluting agent were tested. Under the optimized extracting conditions, the average recoveries for CAAs spiked in tap water were 83 − 107%, with an optimal preconcentration factor of 20. The reproducibility of recovery rate for CAAs was 1.2 − 3.8%, based upon 6 repetitions of the recovery experiments.

View full abstract

A rapid, precise, specific, and accurate ultra performance liquid chromatography (UPLC) method has been developed and subsequently validated for simultaneous determination of amlodipine present as amlodipine basylate (AB) and benazepril hydrochloride (BH) in capsule dosage form. The chromatographic separation was achieved on an Acquity UPLC, BEH C8 (100 mm × 2.1 mm, 1.7 μm) column using a photodiode array detector. The mobile phase used consisted of a mixture of phosphate buffer pH 3.0 (0.01 M aqueous potassium dihydrogen phosphate, pH 3.0 adjusted with orthophosphoric acid) and solvent mixture (equal mixture of acetonitrile and methanol) in the ratio of 45:55 (v/v) at a flow rate of 0.3 mL/min. The described method was linear over ranges of 5.21 − 15.63 μg/mL for AB and 20.24 − 60.72 μg/mL for BH. The mean recoveries were 100.47 and 99.97% for AB and BH, respectively. The lower limit of quantification was determined on the basis of signal-to-noise ratio method; it is 0.01 μg/mL for AB and 0.019 μg/mL for BH.

View full abstract