The magnetic-force quartz crystal microbalance (QCM) method was attempted for the dynamic evaluation of chemical interactions. Thiol-modified magnetic particles bound to a QCM gold electrode of less than three layers were pulled by a magnetic force, and the dissociation dynamics of the magnetic particles was measured based on the change in the weight as a function of time under different temperatures. From an analysis of the dissociated layers and the activation energy for the dissociation, the chemical interactions between particles were evaluated.
An effort is made to critically present the achievements in silver ion chromatography during the last decade. Novelties in columns, mobile-phase compositions and detectors are described. Recent applications of silver ion chromatography in the analysis of fatty acids and triacylglycerols are presented while stressing novel analytical strategies or new objects. The tendencies in the application of the method in complementary ways with reversed-phase chromatography, chiral chromatography and, especially, mass detection are outlined.
One of the ultimate goals of ion chromatography is to determine both anions and cations found in samples with a single chromatographic run. In the present article, recent progress in ion-exclusion/ion-exchange chromatography for the simultaneous determinations of inorganic anions and cations are reviewed. Firstly, the principle and the control for the simultaneous separation and detection of analyte ions using ion-exclusion/cation-exchange chromatography with a weakly acidic cation-exchange column are outlined. Then, advanced chromatographic techniques in terms of analytical time, selectively and sensitivity are summarized. As a related method, ion-exclusion/anion-exchange chromatography with an anion-exchange column could be used for the simultaneous determination of inorganic nitrogen species, such as ammonium, nitrite and nitrate ions. Their usefulness and applications to water-quality monitoring and related techniques are also described.
An electric charge-tunable micro-column (CTMC) was developed as a precolumn for reversed-phase capillary chromatography using conductive carbon fibers as the stationary phase. The carbon fibers, which constitute one electrode, are packed into a heat-shrinkable tube, which is attached to a stainless-steel column body. The mobile phase flows into CTMC through a stainless-steel tube that acts as a counter electrode. The retention times for hydrophobic and ionic compounds are controlled by the applied potential. The characteristics, such as the electrolysis efficiency and shift in retention factor, were evaluated. As a case study, estrogens in spiked beef were analyzed by capillary chromatography. With no applied potential, the resolution between the unknown peak and estriol and the recoveries of estriol were 0.81 and 65.5%, respectively. These values improved to 1.2 and 78.8%, respectively, upon applying +500 mV. These results indicate that a high-resolution capillary chromatography system can be achieved with CTMC.
The development of a rapid and specific assay for 17β-estradiol (E2) will accelerate its in vitro diagnostics and/or environmental pollution control. Here, we employed an open-sandwich (OS) selection scheme to improve the sensitivity for E2 in an OS immunoassay, which is based on antigen-dependent stabilization of the antibody (Ab) variable region, Fv, where the two domains (VH and VL) dissociated in the absence of an antigen. The VH domain of a cloned anti-E2 antibody displayed on M13 phage was randomly mutated, and after three OS biopanning rounds, a mutant that showed higher sensitivity in OS-ELISA for E2 was identified. Interestingly, compared with the wild-type VH, the cross-reactivity of the mutant was significantly decreased for the analogous steroid testosterone, both in OS and competitive ELISAs. This is the first report concerning selection for an anti-hapten Ab without using any hapten-carrier conjugates, and the method will be especially suitable for selecting Ab fragments that show better performance in hapten OS immunoassays.
Wavelet transformation was applied as an elimination method of influence by an interfering substance on an amperometric biosensor. The current responses of a bi-enzyme type lactose biosensor in a solution containing both lactose and ascorbic acid were analyzed by wavelet transformation. The power spectrum density for ascorbic acid was detected selectively at around 0.125 Hz. The current component due to ascorbic acid was eliminated at 98% from the current response of the biosensor by wavelet transformation.
A complementary metal oxide semiconductor (CMOS) image sensor is an intriguing technology for the development of a novel biosensor. Indeed, the CMOS image sensor mechanism concerning the detection of the antigen-antibody (Ag-Ab) interaction at the nanoscale has been ambiguous so far. To understand the mechanism, more extensive research has been necessary to achieve point-of-care diagnostic devices. This research has demonstrated a CMOS image sensor-based analysis of cardiovascular disease markers, such as C-reactive protein (CRP) and troponin I, Ag-Ab interactions on indium nanoparticle (InNP) substrates by simple photon count variation. The developed sensor is feasible to detect proteins even at a fg/mL concentration under ordinary room light. Possible mechanisms, such as dielectric constant and refractive-index changes, have been studied and proposed. A dramatic change in the refractive index after protein adsorption on an InNP substrate was observed to be a predominant factor involved in CMOS image sensor-based immunoassay.
Here, we present a label-free, simple and signal-on architecture for fluorescent alkaline phosphatase (ALP) biosensor utilizing an SYBR Green I (SG) assisted fluorescence amplification method. The strategy relies on the fact that ALP provides a significant barrier to lambda exonuclease (λ exo) activity by a dephosphorylating DNA hairpin probe (HP), and SG shows a considerable fluorescence intensity enhancement upon binding to double-stranded DNA (dsDNA) than single-stranded DNA (ssDNA). Our method is simple, sensitive and selective, which can also successfully detect the activity of ALP in complex biological fluids. The results have revealed that the method allows a specific and quantitative assay of the target ALP with a wide linear response range from 0.4 to 200 U/mL and a detection limit of 0.05 U/mL.
An efficient analytical method for the preconcentration and determination of phosphate in water samples at trace levels was proposed. The method was based on sample enrichment using dispersive solid-phase extraction (dSPE) with tetraethylenepentamine (TEPA)-functionalized nano-size composite materials (TEPA-NCMs) as sorbents, which were fully characterized. Various parameters affecting the extraction efficiency were systematically investigated. After extraction, the post-adsorbed TEPA-NCMs were eluted by a NaOH solution for desorption of the phosphate. The resulting eluate containing phosphate was determined by a spectrophotometric method. The limit of detection (LOD) and the limit of quantification (LOQ) were 0.29 and 0.96 μg L−1, respectively. The relative standard deviations (RSDs) were lower than 8.0% with average recoveries ranging from 91 to 118%. The present method was successfully applied to the determination of phosphate at trace levels in real water samples, and it was confirmed that the TEPA-NCMs are highly effective dSPE materials.
Here, we report on the use of human serum albumin (HSA)-modified Fe3O4 nanoparticles (NPs) (HSA-Fe3O4 NPs) for affinity-SALDI-MS of small drugs in human biological liquids. We demonstrated that HSA-Fe3O4 NPs effectively captured small drugs from human urine and serum via the interactions between HSA and these drugs. The drugs adsorbed on HSA could then be identified by directly introducing the HSA-Fe3O4 NPs into a mass spectrometer for SALDI-MS analysis. The ability of HSA to interact with multiple small drugs facilitated the simultaneous detection of a 4-drug-mixture in serum, viz., phenytoin, ibuprofen, camptothecin, and warfarin sodium, by affinity-SALDI-MS using HSA-Fe3O4 NPs. In contrast, matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) with an organic matrix could detect only warfarin sodium. We also demonstrated the capacity of affinity-SALDI-MS to quantify warfarin sodium in urine samples across a range of 50 – 1000 μM (R2 = 0.998) when using HSA-Fe3O4 NPs. The detection sensitivity was further improved to a range of 5 – 100 μM (R2 = 0.999) by using denatured HSA. The open structure of denatured HSA may enhance the effective extraction of small drugs from biological liquids, and increase the detection-sensitivity of affinity-SALDI-MS. Affinity-SALDI-MS using protein-modified Fe3O4 NPs can open up new approaches to the analytical detection of small drugs in biological liquids by SALDI-MS.
Using alkali-metal cation-substituted zeolites and 2,4,6-trihydroxyacetophenone (THAP), which is a typical organic matrix molecule for matrix-assisted laser desorption ionization (MALDI), mass spectrometry has been performed for maltohexaose and acetylsalicylic acid, and the cation-selective ionization of these analytes was achieved. It is found that a complex of cation-substituted zeolite and THAP can be applicable to a compound that is hard to be ionized by a proton adduction in conventional MALDI.
We describe a high-throughput screening (HTS) assay for transglutaminase (TG) enzyme activity using plasmonic fluorescent nanocomposites. We used TG to covalently crosslink 500 μM solution of 5′-biotinamidopentylamine (BP) to N,N′-dimethylcasein (DMC) which was adsorbed onto 384-well microplates. We then bound 0.2 – 2.0 × 1011/mL of 10 nm gold nanoparticles-streptavidin conjugate (10 nm AuNPs-SA) to BP via biotin-streptavidin interactions. Finally, J-aggregation of cyanine 1 (25 μM) or 2 (10 μM) upon the 10 nm AuNPs elicited absorption and fluorescence signaling of TG catalysis. The cyanines could be added sequentially to elicit green (590 nm) and red (700 nm) spectral responses from the same set of reactions. Catalysis was linear (r2 > 0.98) up to 10 min within a linear dynamic range (LDR) of 0.1 – 5 μg/mL enzyme. The multi-wavelength interrogation offered fast results (< 5 min), sensitivity (limit of detection, LOD of 5 ng or 64 fmol TG) and intermediate precision (relative standard deviation, RSD of < 20% over 42 days). Plasmonic fluorescent nanocomposites offer new ways of interrogating biomolecules in HTS format.
The development of Reference Materials for Nutrients in Seawater (RMNS) has been in progress since 1993. When RMNS were produced for nitrate, silicate, and phosphate, their initial homogeneities were as low as 0.1 to 0.2% in samples of high-nutrient seawater, such as deep water from the Pacific Ocean. The relative standard uncertainties associated with instability during long-term (4.8 years) storage were approximately 0.2, 0.2, and 0.4% for nitrate, silicate, and phosphate, respectively. No instability was observed for 1.9 to 6.4 years based on the ISO Guide 35:2006 criteria; however, the relative standard uncertainties associated with instability during long-term storage were larger than the initial homogeneities of RMNS. RMNS produced by state-of-the-art techniques are currently available for global use to improve the comparability of nutrients data in the open ocean and, as discussed here, are reliable candidates to be used for certified reference materials.
Monomer conversion and the resultant copolymer composition of polymer monolith columns are important factors for controlling column characteristics. We propose a new method to determine monomer conversion to a polymer monolith fixed in a capillary column using pyrolysis–gas chromatography. Small pieces of a poly(butyl methacrylate-co-ethylene dimethacrylate (BMA-co-EDMA)) monolith column were pyrolyzed at 450°C with poly(ethyl methacrylate) as a non-volatile internal standard. The monomer conversions were estimated from the corresponding relative peak intensities in the pyrogram. It was determined that the conversion of EDMA was significantly greater than that of BMA in a low-conversion UV-polymerized poly(BMA-co-EDMA) monolithic capillary column.
Open-tubular capillary chromatography using a ternary solvent mixture consisting of a water–hydrophilic–hydrophobic organic solvent as a carrier solution has been developed. When the ternary carrier solution is fed into the capillary tube, the carrier solvents are radially distributed and generate inner and outer phases in the tube. The outer phase functions as a pseudo-stationary phase in chromatography. In this study, investigations proceeded with reference to the tie lines and solubility curves on the phase diagram of the ternary mixed solvents. Model analytes, 1-naphthol and 2,6-naphthalenedisulfonic acid, were separated in this order with ternary water–acetonitrile–ethyl acetate solvent mixtures (organic solvent-rich solutions) that possessed various solvent compositions on the tie lines. In addition, fluorescence photographs of the dyes dissolved in the ternary solvents in the capillary tubes were observed with a fluorescence microscope-CCD camera system. It was found that the separation performance on the chromatograms and the phase formation observed in the fluorescence photographs were related to data provided through the tie lines and solubility curves on the phase diagram. The solvent compositions on the same tie line that gave different volume ratios of upper and lower phases in a vessel influenced the chromatographic separation, or the resolutions of the analytes, and also the inner and outer phase formation in the chromatography.