A review of biosensor technology with a specific focus on fiber-optic biosensors is provided. With the advent of optical transducers, better electronics, and improved immobilization methods, fiber-optic biosensors are being increasingly applied to industrial process and environmental monitoring, food processing, and clinical applications. The vitality of the fiber-optics-based biosensing can be seen from the growing number of publications. In summary, fiber-optic biosensors will play a significant role in the development of biosensors because they can be easily miniaturized and integrated for the determination of different target compounds. Industrial collaboration is needed to speed up progress from the research bench, to the field-study stage, and finally commercialization.
A calibration method for the gas-chromatographic (GC) retention time of polychlorinated biphenyl (PCB) congeners is presented. This method calculates retention time of all PCB congeners in the GC system of an analytical laboratory from one reported in the literature with a commercial PCB mixture and some pure congener standards. Two corrections were implemented to compensate for any retention differences arising from the GC condition changes, such as the column dimensions, temperature programs and flow rates. One is an instrument function correction that compensates for common congener behavior. The other is a selectivity correction that compensates for individual congener behavior. For a selectivity correction, new descriptors of a quantitative structure-retention relationship (QSRR) were developed. The method was applied to several stationary phases to evaluate its ability and precision. The standard errors of the calculated retention times were in most cases within a chromatographic peak width.
Fluorescent molecular sensing for endocrine-disrupting chemicals and their analogs has been studied by investigating the fluorescence spectral change of regio-selective dansyl-tosyl-modified β- and γ-cyclodextrins upon the addition of a guest. These host compounds show pure monomer fluorescence at around 526 nm; the intensities of the guest-induced fluorescence either increase or decrease according to the accommodation of such guests as dioxin analogs, p-nonylphenol, 2,4-dichlorophenoxyacetic acid, bisphenol A, and diethylphthalate. The extent of the fluorescence variations with the guest is employed to display the sensing abilities of these hosts. The sensing parameter, ΔI/I0 , was used to describe the sensing ability of the hosts, where I and I0 are the fluorescence intensities in the presence and absence of a guest and ΔI=I-I0. These hosts exhibit highly sensitive and selective molecular-recognition ability, particularly for 2,4,6-trichlorophenol and bisphenol A.
A method for the determination of the herbicides paraquat and diquat in water was developed using liquid-chromatography/electrospray ionization-mass spectrometry (LC/ESI-MS). This method did not include any sample-concentration steps. Only 0.1 M nonafluoropentanoic acid (NFPA) was added to the filtered sample. An aliquot (200 µL) of this sample was analyzed by reversed-phase liquid chromatography with the postcolumn addition of 2-propanol followed by ESI-MS. Paraquat and diquat were detected using the [M2+ -H+] ion at m/z 185 and 183, respectively. Quantification was performed by an external standard method. The detection limits were 0.1 ng/mL (paraquat) and 0.2 ng/mL (diquat). The repeatability and reproducibility were 2.1% and 7.4% for paraquat and 2.7% and 8.1% for diquat.
A simple procedure is presented for selective separation of hafnium from zirconium in both simulated and real samples. The procedure depends on using Alizarin Red sulfonate (ARS) for complexation of both Hf(IV) and Zr(IV), in which a flotation step is applied for floating their complexes using oleic acid (HOL) surfactant. Several factors affecting the flotation process have been studied. It is found that hydrogen ion concentration is of paramount importance. Maximum separation of Zr(IV) (100%) is achieved at pH range 1.5 - 2, whereas at pH range 5.5 - 7 Hf(IV) is completely separated. Interference of various foreign ions is avoided by adding excess ARS. Infra-red data were used for suggesting the flotation mechanism.
Kinetic data previously acquired on the enantiomeric separation of L- and D-phenylalanine anilide (PA) on a polymeric stationary phase imprinted with L-PA were reinterpreted. The parameters characterizing the mass transport processes active in the column, i.e., axial dispersion, fluid-to-particle mass transfer, intraparticle diffusion, and adsorption/desorption were calculated. Intraparticle diffusion was shown to have a dominant contribution to band broadening. The surface diffusion coefficient (Ds) showed a positive concentration dependence which could explain the dependence of the lumped mass transfer rate coefficient on the enantiomer concentration. It is likely that the positive concentration dependence of Ds could be explained by the heterogeneity of the surface of the stationary phase and that the distribution of adsorption energy on the surface of the imprinted polymer has an exponential decay profile.
A new technique for the preconcentration of trace elements and matrix elimination with a chitosan-based chelating resin was proposed as a useful pretreatment prior to a measurement by inductively coupled plasma-mass spectrometry (ICP-MS). A small volume of the sample solution (80 µl) was discretely introduced into a nebulizer of ICP-MS using a segmented flow injection (SFI) system; a maximum of fifteen elements were simultaneously measured by a single injection. A chitosan-based chelating resin containing iminodiacetate (IDA) functional groups was used for matrix elimination and enrichment of analyte metal ions. Several metal ions, such as Al, Fe, Ni, Co, Cu, Zn, Ag, Cd, Pb and U, were quantitatively retained on the IDA chelating resin in a micro-column (resin: 1 ml) at pH 6, whereas Na, K, Mg and Ca were completely eluted from the column by washing with an ammonium acetate solution. The concentrations of 24 and 26 elements in river water certified reference materials, JAC 0031 and JAC 0032, respectively, were determined by the proposed SFI/ICP-MS system after pretreating the samples with the proposed technique, as well as without any pretreatment. The thus-obtained analytical data were evaluated by comparing them with the reference values, as well as with those obtained in other studies.
The effect of various chemical modifiers (KMnO4, AgNO3+KMnO4, Pd, Rh, Ir and Pd+Rh) on ETAAS of Hg with laboratory-made boron nitride tube and platform furnaces was studied. The effectiveness of the chemical modifier was improved by the use of the ceramic furnaces instead of the graphite furnace. The sensitivity, which gives a maximum absorbance of 0.0044 abs for Hg, is found to be 0.11 ng, and the LOD, based on the variability of the blank (3σ), is 27 pg using 10 µg of Pd with the non-pyrolytic boron nitride platform furnace. The good recovery of 102±3% was observed for Hg spiked into a hair sample digested by microwave with nitric acid. The observed Hg content in a certified reference material of human hair was in agreement with its certified value.
A two-color double-pulse excited photothermal lensing measurement was performed to investigate a signal enhancement owing to transient absorption by the excited states of solute molecules in liquid solutions. A colinear, mode-mismatched configuration with a continuous-wave probe laser at 633 nm was adapted with a focused pump pulse (6.9 ns, 355 nm) and a sequentially incident softly focused second-pump pulse (7.2 ns, 532 nm). The signal-intensity dependence on the energies of the pump and the second-pump pulses was measured for 1.0 µM solutions of 2,2′-p-phenylenebis(5-phenyloxazole) in 1-butanol and anthracene in ethanol. A signal enhancement was observed for both solutions. The signal intensity under certain conditions was one order higher than that expected from ground-state absorption. A discussion was made on determination of the absorption coefficient of the transient species and on the absorption saturation of the ground and excited states.
Current-sampled (tast) polarography was used in the determination of the two iron oxidation states Fe2+ and Fe3+ in peat samples. The iron couple was reversible in the 0.1 mol L-1 citrate-supporting electrolyte used. The total iron concentration in the samples was determined by differential pulse polarography. Sample decomposition was done in a nitrogen atmosphere by hydrofluoric acid and sulfuric acid. The accuracy of the determinations was verified by spiking experiments and analyzing in-house standards (Geological Survey of Finland) RS 31 (Rapakivi granite), RS 71 (Diabase) and certified reference material PCC-1 (Peridotite, U.S. Geological Survey). The method, developed for this purpose, proved to be reasonably accurate.
Studies on the electrochemical and immunochemical reaction kinetics of the heterogeneous type of ECL excitations were made comparatively with homogeneous types of ECL excitations by measuring human IgG (hIgG) using an antibody labeled with a ruthenium(II) tris(bipyridyl) (Ru-chelate) as the luminophore (Ru-Ab). Solid-phase sandwich-type immunoassays were carried out on the surface of magnetic micro-beads (MB) with a diameter of 4.5 µm. In the ECL measurement, two types of ECL excitation methods were compared. One was a homogeneous ECL excitation, where the reacted MB together with non-reacted Ru-Ab were excited in a suspending phase without any bind/free (B/F) separation procedure. The other was a heterogeneous one where the reacted MB were excited over the electrode after being collected by a magnet following the B/F separation to remove the non-reacted Ru-Ab. In electrochemical studies, it was revealed that the Ru-Ab reacted with hIgG decreased the ECL emission efficiency. The decreasing ratio was inversely correlated with the cubic root of the luminophore molecular weight. In homogenous ECL excitation for the reacted matrix containing both the reacted MB and the non-reacted Ab, however, a reverse correlating dose response curve appeared only in the area beyond the antigen-antibody equivalent point, the so-called antigen excess zone; as a result the S/N ratio of the ECL signal was as small as only 1.3. In contrast, the heterogeneous ECL excitation for the reacted MB, with the non-reacted Ru-Ab removed by B/F separation, demonstrated 1000 or more times the S/N ratio in the area before the antigen-antibody equivalent point. Thus, this heterogeneous ECL excitation with B/F separation improved the detection sensitivity dramatically up to 1000 or more times higher than that of the homogeneous ECL excitation. Consequently, the sensitivity of heterogeneous ECLIA could be competitive with that of the conventional chemiluminescence immunoassay.
We have developed a method for the simultaneous analysis of two-site gene polymorphisms. The principle developed by us is that two amplicons are produced by duplex PCR using two different primer sets (digoxigenin labeled primer A and biotinylated primer B for BsmI recognition site, biotinylated primer C and FITC labeled primer D for TaqI recognition site) and digested with two restriction enzymes, and the reaction products are analyzed by time-resolved fluorescence immunoassay (TR-FIA) using two different lanthanide ions (Eu and Sm) as labels. In this study, BsmI and TaqI recognition site polymorphisms in intron 8 and exon 9 of the vitamin D receptor (VDR) gene were selected as a target gene. VDR gene polymorphisms of 27 subjects were determined by the proposed method. The results agreed with that obtained by a restriction fragment-length polymorphism (RFLP) analysis using gel electrophoresis. The proposed method is effective, has excellent precision and is well suited to gene analysis for a large number samples.