A monodispersed molecularly imprinted polymer (MIP) for creatinine was prepared by modified precipitation polymerization. The retention and molecular-recognition properties of the prepared MIP were evaluated by the hydrophilic interaction chromatography mode using a mixture of ammonium acetate buffer and acetonitrile as a mobile phase in liquid chromatography. The MIP had a specific recognition ability for creatinine, while other structurally related compounds, such as hydantoin, 1-methylhydantoin, 2-pyrrolidone, N-hydroxysuccinimide and creatine, could not be recognized on the MIP. In addition to shape recognition, hydrophilic interactions could work for the recognition of creatinine on the MIP.
We have successfully developed a novel technique for inserting viable bacilliform bacteria into polypyrrole films. All of the five different bacterial cells (Pseudomonas aeruginosa, Acinetobacter calcoaceticus, Serratia marcescens, Bacillus subtilis and Escherichia coli) studied in this work were inserted normal to the film surface, and the viability of P. aeruginosa was unaffected by this immobilization procedure. It was also found that the polypyrrole layer was important to keep the cells alive.
Until recently, there had been two conflicting views about the order of copper oxides (Cu2O and CuO) in their cathodic reduction with a neutral or weak alkaline electrolyte (typically 0.1 M KCl). In 2001, we successfully employed a strongly alkaline electrolyte (SAE; i.e., 6 M KOH + 1 M LiOH) to achieve a perfect separation of the reduction peaks of the two oxides. It was then found that the oxides were reduced in SAE according to a thermodynamic order, i.e., “CuO → Cu2O”, and also that the reduction of CuO occurred in one step. At an extremely slow scan rate of <0.2 mV s−1, however, CuO appears to be reduced in two steps via Cu2O. It has also been shown that the developed method with SAE can be applied to analysis of various corrosion products, including Cu2S, Cu(OH)2, and patinas. Use of the developed method has allowed researchers to clarify the mechanism of the atmospheric corrosion of copper.
A test strip for detection of Hg2+ in aqueous solution based on the DNA-functionalized gold nanoparticles (DNA-AuNPs) was developed and evaluated. When Hg2+ ions were introduced, the biotinylated DNA2 hybridized with thiolated DNA1 functionalized on the AuNPs (DNA1-AuNPs) to form mismatch complexes through thymine-Hg2+-thymine (T-Hg2+-T) coordination. The formed mismatch complexes and excess DNA1-AuNPs could be captured on the test line formed by streptavidin and the control line formed by DNA3-BSA, respectively. Two red lines appeared due to the accumulation of AuNPs, enabling visual detection of Hg2+ with a detection limit of about 6 nM. The assay results can be obtained within 5 min. The results show that the test strip has excellent sensitivity and selectivity for detection of Hg2+; thus it holds a great potential for rapid, on-site and real time detection of Hg2+.
The dynamics of liposome solubilization was monitored by dynamic light scattering and optical microscopy. A newly designed Y-shape microchannel connected to a room was incorporated into a microchip and the reaction processes of the liposome suspension and surfactant solution were observed in the room after mixing the two fluids and stopping the flow. By using this microchip, we succeeded in real-time monitoring of liposome solubilization and the following dynamic processes of solubilization were proposed: 1) Deformed liposomes become spherical. 2) The liposome size increases until the surfactant/liposome ratio in the liposome membrane reaches a threshold value. 3) Mixed micelles of surfactants and phospholipids are released and the liposomes collapse.
The solubilization dynamics of dimyristoylphosphatidylcholine (DMPC) liposomes, as induced by sodium dodecyl sulfate (SDS), were investigated; this investigation was motivated by several types of atypical behavior that were observed in the solubilization in this system. The liposomes and surfactants were mixed in a microchip, and the solubilization reaction of each liposome was observed using a microscope. We found that solubilization occurred not only via a uniform dissolution of the liposome membrane, but also via a dissolution involving the rapid motion of the liposome, or via active emission of protrusions from the liposome surface. We statistically analyzed the distribution of these patterns and considered hypotheses accounting for the solubilization mechanism based on the results. When the SDS concentration was lower than the critical micelle concentration (CMC), the SDS monomers entered the liposome membrane, and mixed micelles were emitted. When the SDS concentration was higher than the CMC, the SDS micelles directly attacked the liposome membrane, and many SDS molecules were taken up; this caused instability, and atypical solubilization patterns were triggered. The size dependence of the solubilization patterns was also investigated. When the particle size was smaller, the SDS molecules were found to be homogeneously dispersed throughout the whole membrane, which dissolved uniformly. In contrast, when the particle size was larger, the density of SDS molecules increased locally, instability was induced, and atypical dissolution patterns were often observed.
We examined the elution behavior of isoluminol isothiocyanate (ILITC)-labeled biomolecules (α-amino acids, peptides, and proteins) in an open-tubular capillary chromatography system using an untreated fused-silica capillary tube and a water–acetonitrile–ethyl acetate mixture carrier solution. Such an open-tubular capillary chromatography is called “tube radial distribution chromatography (TRDC)” for convenience. A mixture of ILITC and ILITC-labeled biomolecules was analyzed using TRDC with chemiluminescence detection that provided simple instrument without a light source and complex optical devises. The ILITC and the labeled twenty α-amino acids were separated, in this order or the reverse order, or not separated with an organic solvent-rich and water-rich carrier solution. Their elution behavior was considered to be of hydrophilic or hydrophobic nature of ILITC and the labeled α-amino acids. The ILITC and the labeled protein, alcohol dehydrogenase and bovine serum albumin, were separated in this order with an organic solvent-rich carrier solution, while they were eluted in the reverse order with a water-rich carrier solution, based on the TRDC separation performance. The TRDC system worked with the untreated open-tubular capillary tube not using any specific capillary tubes, such as coated, packed, or monolithic.
Wide-bore capillary hydrodynamic chromatography (W-HDC) resolves analytes on the basis of a difference in the extent of radial diffusion simply by their passage through an empty capillary. The combination of this method with ICP-MS proves efficient for the evaluation of the interaction of metal ions with molecular aggregates. Lecithin vesicles are suitable molecular aggregates for the uptake of the lanthanide ions in the presence of the first row transition metal ions, suggesting that the present method is applicable to the screening of the molecular aggregate system suitable for selective extraction of a particular targeted small molecule. The visual inspection of the elution profiles gives us qualitative but useful information on the interaction between the vesicle and metal ions. In addition, studying the slope of the front edge of an elution curve provides more quantitative implications.
A non-suppressed capillary ion chromatographic method with a laboratory-made packed cation-exchange column (100 mm × 0.32 mm i.d.) was developed for the separation and simultaneous determination of five common inorganic cations (sodium, ammonium, potassium, magnesium and calcium). Cation exchangers were prepared by the reaction of the hydroxyl group on the surface of diol-group bonded silica gel with 1,3-propanesultone in methanol. Simultaneous separation of these five common inorganic cations were achieved within 17 min using 1 mM methanesulfonic acid and 0.1 mM 15-crown-5 ether in methanol–water (8:2, v/v) as the eluent. The effects of organic solvents and crown ethers in the eluent on the retention of analytes were investigated. The limits of detection (S/N = 3) of the cations were in the range of 18 – 124 μg/l, the linear correlation coefficients were 0.9991 – 0.9998, and the RSD values of retention time and peak height were all smaller than 2.1%. The present analytical method was successfully applied to the rapid and direct determination of inorganic cations in samples of river water and commercial drinks, with satisfactory results.
A novel method for preparing enzyme membranes was developed. The enzyme was attached onto the electrode surface by dropping the enzyme solution and allowing it to dry. Glucose oxidase was used for entrapment. Then, the electrode surface was coated with an ionic liquid containing cellulose, and the ionic liquid was removed by immersing the electrode into water. Enzyme activity was retained in the membrane; the enzyme electrode can be used for detecting glucose in the range of 10 μM to 1 mM, and the response time was ∼10 s. The stability duration of the electrode was examined: the enzyme electrode could be used for glucose detection for 6 months. The membrane was observed by atomic force microscopy in the force modulation mode; crystalline and amorphous parts were intermingled. In conclusion, the cellulose membrane can be a suitable immobilization matrix for enzymes.
A practical, sensitive and environment-benign protocol for the detection of DNA on polyacrylamide gels was described. In this method, the most commonly used formaldehyde-based developer in DNA silver stain, which poses potential hazards to the health of operators, is firstly replaced by vitamin C (Vc) in sodium thiosulfate solution. This allows user-friendly and efficient visualization of DNA that takes about 20 min to complete all the procedures, and provides comparable sensitivity (8 pg of single band) to the most sensitive formaldehyde-based silver staining method developed before.
For the real-time measurements of volatile organic compounds (VOCs) in vehicle exhaust, we employed a vacuum ultraviolet single-photon ionization time-of-flight mass spectrometer (VUV-SPI-TOFMS). Exhaust measurements from gasoline and diesel engine vehicles were performed using a chassis dynamometer. Hydrocarbons such as alkylbenzenes, alkenes, alkanes, and dienes were the major organic compounds present in both gasoline and diesel engine exhaust. The concentrations of organic compounds in gasoline exhaust were higher under running conditions than during idling. The VOC concentrations in diesel exhaust were higher during idling than during running conditions. The VUV-SPI-TOFMS measured composition and emission profiles of many hydrocarbons, including aliphatics and aromatics, in vehicle exhaust simultaneously with real time response.
Nowadays, nitrite and nitrate ions are analyzed in biological samples using laborious and expensive methods; such as HPLC, CE, MS-MS. In this work, the simultaneous analysis of nitrite and nitrate ions was conducted by electrospray ionization–ion mobility spectrometry (ESI-IMS), without using any complicated or laborious derivitization step. Ion mobility spectrometry with low cost, inexpensive maintenance and very fast analysis makes an attractive technique for the simultaneous determination of these ions in foodstuff and drinking water samples. The analyte interference was systematically investigated for binary mixture analysis. The obtained results provided detection limits of 3.8 and 4.7 μg/L for nitrite and nitrate, respectively. A linear dynamic range of about 2 orders of magnitude, and relative standard deviations below 5% were obtained by the proposed method for the analysis of both ions. Also, the proposed method was used to analyze various real samples of potato and drinking water samples, and the obtained results confirmed the capability of negative ESI-IMS for the simultaneous detection of nitrite and nitrate.
A very sensitive, simple, and fast solid-phase spectrophotometric procedure for the determination of phenol using the p-nitrobenzenediazonium reagent (DAR reagent) was developed. This procedure is based on the simultaneous concentration of the orange product on a Dowex 1-X2 anion exchanger within 15 min, and a direct absorbance measurement of the sorbed species at both 530 nm (the absorption maximum of the phenol-DAR in the resin phase) and 700 nm (the range where only the resin absorbs light). Quality control and evaluation of the analytical parameters was carried out using a comprehensive prevalidation strategy. The linearity of the method was confirmed within an analyte working range from 0.01 to 0.10 μmol (0.2 to 2.0 nmol mL−1). The precision ranged from ±1.17 to ±9.61%; the accuracy ranged from −17.50 to +17.81%. The evaluated limiting values were LD = 0.0013 μmol and LQ = 0.0082 μmol. The DAR-SPS method was successfully applied to the determination of phenol in a pharmaceutical sample of salicylic acid (98.0 – 100.0%) and vaccines (98.0 – 103.4%).
Gold dendrites (AuD) were synthesized with egg white as the soft template and a novel nitrite (NO2−) biosensor was fabricated by assembly of a myoglobin (Mb)-L-cysteamine (Cys)-AuD biological hybrid. The results of Fourier transform infrared spectra and UV-visible spectra indicated that Mb retained its original structure in the resulting Mb-Cys-AuD. Electrochemical investigation of the biosensor showed a pair of well-defined, quasi-reversible redox peaks with Epa = −0.314 V and Epc = −0.344 V (vs. SCE) in 0.1 M, pH 7.0 sodium phosphate buffered saline at the scan rate of 200 mV/s. The transfer rate constant (ks) was 1.49 s−1. The Mb-Cys-AuD showed a good electrochemical catalytic response for the reduction of NO2−, with the linear range from 0.5 to 400 μM and the detection limit of 0.3 μM (S/N = 3). The apparent Michaelis–Menten constant (KMapp) was estimated to be 0.2 mM. Therefore, the assembled bio-hybrid as a novel matrix opened up a further possibility for study on the design of enzymatic biosensors with potential applications.
The electrochemical behavior and application of a new sensor, a silver solid amalgam paste electrode (AgSA-PE), based on the mixture of a fine silver solid amalgam powder (60:40 (wHg/wAg)) and a suitable organic pasting liquid (Paraffin oil) in a ratio of 20:1 (w/w), was investigated in an aqueous–methanolic media (1:1). This alternative working electrode provides simple preparation and handling, adequate mechanical stability, easily renewable electrode surface, sufficiently wide cathodic potential window (up to −1200 mV within a pH range of 2.7 – 12.3), and sufficient sensitivity without any necessary pretreatment. The practical usability of the AgSA-PE was verified by the development of voltammetric methods for the determination of selected environmentally important pollutants (1,3-, 1,5-, and 1,8-dinitronaphthalenes) in an aqueous–methanolic media (1:1). The differential pulse voltammetric methods at AgSA-PE give linear concentration dependences in the range of 1 – 100 μmol l−1 with limits of detection of about 1 μmol l−1 in a mixture of Britton–Robinson buffer of appropriate pH and methanol (1:1).
A separation and preconcentration method based on solid-phase extraction using sulfoxide adsorbent was developed for the determination of Hg(II) in natural water samples by inductively coupled plasma mass spectrometry (ICP-MS). The sulfoxide adsorbent was packed into a commercially available syringe-driven column (with a bed volume of 1.0 mL), which permitted off-line sample loading and on-line elution/measurement. The optimized operating conditions were as follows: sample condition for Hg(II) adsorption, 0.5% HCl; sample-loading flow rate, 10 mL min−1; eluent for recovering Hg(II), 1% cysteine water solution. A test using multi-element mixed solution showed that most trace elements in natural water, except for Bi, could be completely separated from Hg(II). The recoveries of Hg(II) were 99.0 ± 3.2 and 100.7 ± 4.3%, respectively, when 0.64 and 0.16 ng mL−1 of Hg(II) were added into the test sample. The detection limit of Hg(II) using a quadrupole ICP-MS after 10-fold preconcentration was 1.5 pg mL−1. The blank value was 2.8 ± 0.5 pg mL−1.
The mixing process of ternary solvents (water–hydrophilic/hydrophobic organic mixture) prepared in microchannels in a microchip was examined by fluorescence observation of the dyes dissolved in the solvents under laminar flow conditions. A microchip incorporating microchannels was used. In it, three narrow channels were combined to form one wide channel. Water–acetonitrile (hydrophilic) mixture containing relatively hydrophilic Eosin Y (green) was fed into the narrow center channel and an acetonitrile–ethyl acetate (hydrophobic) mixture containing hydrophobic perylene (blue) was fed into the two narrow side channels in the microchip. The mixtures in the narrow channels combined in the wide channel to prepare the ternary solvents of water–acetonitrile–ethyl acetate, causing the tube radial distribution of the solvents. We observed the mixing process of the ternary solvents in the wide channel through fluorescence of the green and blue dyes, including an aqueous-organic interface. For example, the green dye that was fed into the center channel was distributed near the inner side walls and the blue dye that was fed into the two side channels was distributed around the center area in the wide channel. Such specific mixing behavior was not observed for two-component solvents in the wide channel, such as water–acetonitrile mixture and water–ethyl acetate mixture.