Improvement of latex piezoelectric immunoassay: Detection of rheumatoid factor

Latex piezoelectric immunoassay is a method for detection of agglutination of antibody- or antigen-bearing latex by immunoreaction using a piezoelectric quartz crystal; the agglutination decreases the oscillation frequency of the crystal. This is advantageous in that coating the surface of the crystal followed by fixation of antibody or antigen is unnecessary. There is, however, a drawback, and to improve this, we designed a micro-cell in which only one side of the crystal is exposed to the solution. A method for regenerating the crystal was also devised. Measurement was carried out using a calibration curve of the frequency change against rheumatoid factor activity. The improvement made it possible to use one crystal repeatedly and reproducibility was satisfactory. The calibration curve became almost independent of the crystal used.     

Sensitive Superoxide Biosensor Based on Silicon Carbide Nanoparticles

Direct electron transfer of immobilized superoxide dismutase (Cu, Zn‐SOD) onto silicon carbide (SiC) nanoparticles displays a pair of well defined and nearly reversible redox peaks with formal potential (E°′) of −0.03 V in pH 7.4. The heterogeneous electron transfer rate constant (k_s) and surface coverage (Γ) of immobilized SOD are 11.0±0.4 s⁻¹ and 1.42×10⁻¹¹ mol cm⁻². Biosensor shows fast amperometric response (3s) with sensitivity and detection limit of 1.416 nA μM⁻¹, 1.66 μM, and 1.375 nA μM⁻¹, 2.1 μM for cathodically or anodically detection of superoxide, respectively. This biosensor also exhibits good stability, reproducibility and long life‐time.     

Ultra-sensitive immunosensor for detection of hepatitis B surface antigen using multi-functionalized gold nanoparticles

The signal amplification for analytical purposes has considerable potential in detecting trace levels of analytes for clinical, security or environmental applications. In the present report a strategy based on a sandwich type immunoassay system was designed for the detection of hepatitis B surface antigen which exploits the specific affinity interaction between streptavidin and biotin recognition systems. The method involves the specific coupling of multi-functionalized gold nanoparticles (bearing biotin and luminol molecules) to the streptavidin modified by secondary antibody. The chemiluminescent signal is produced by the gold nanoparticles in the presence of HAuCl₄ as catalyst and hydrogen peroxide as oxidant. The immunosensor was able to detect hepatitis B surface antigen in the linear concentration range from 1.7 to 1920 pg mL⁻¹ and the detection limit of 0.358 pg mL⁻¹, at signal/noise = 3.     

Detection and dosimetry of gamma ray emitted from thallium-201 and technetium-99m based on chemiluminescence technique

This report describes the detection and dosimetry of gamma ray emitted from Thallium-201 (²⁰¹Tl) and Technetium-99m (^99mTc) based on chemiluminescence technique. H₂O₂ produced by two gamma emitter radioisotopes of ²⁰¹Tl and ^99mTc were quantitatively measured by chemiluminescence method. Upon producing H₂O₂ in a luminol alkaline solution, in the presence of diperiodatocuprate, as catalyst a chemical reaction was accrued and consequently the emitted light was measured. The determined H₂O₂ concentration was correlated with the gamma ray detection and dosimetry. The sensitivity of chemiluminescence technique for ²⁰¹Tl and ^99mTc dosimetry was determined to be 0.20 and 0.08 MBq/l (Mega Becquerel per liter) respectively (R.S.D. = %5, N = 3). The plotted calibration curves showed detection limits of 3.24 and 1.76 MBq/l for ²⁰¹Tl and ^99mTc, respectively.     

Neural Estimator of Information for Time-Series Data with Dependency

Novel approaches to estimate information measures using neural networks are well-celebrated in recent years both in the information theory and machine learning communities. These neural-based estimators are shown to converge to the true values when estimating mutual information and conditional mutual information using independent samples. However, if the samples in the dataset are not independent, the consistency of these estimators requires further investigation. This is of particular interest for a more complex measure such as the directed information, which is pivotal in characterizing causality and is meaningful over time-dependent variables. The extension of the convergence proof for such cases is not trivial and demands further assumptions on the data. In this paper, we show that our neural estimator for conditional mutual information is consistent when the dataset is generated with samples of a stationary and ergodic source. In other words, we show that our information estimator using neural networks converges asymptotically to the true value with probability one. Besides universal functional approximation of neural networks, a core lemma to show the convergence is Birkhoff’s ergodic theorem. Additionally, we use the technique to estimate directed information and demonstrate the effectiveness of our approach in simulations.     

Accelerating the electron transfer of choline oxidase using ionic-liquid/NH2-MWCNTs nano-composite

A nano-composite consisting of amine functionalized multi-walled carbon nanotubes and a room temperature ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) was prepared and used for modification of glassy carbon electrode. By immobilizing choline oxidase (ChOx) on the modified electrode, the enzyme direct electron transfer has been achieved. The modified electrode exhibited a pair of well-defined cyclic voltammetric peaks at a formal potential of ?0.395?V versus Ag/AgCl in 0.2?M phosphate buffer solution at pH 7.0. This peak was characteristic of ChOx-FAD/FADH₂ redox couple. The electrochemical parameters such as charge transfer coefficient (??) and apparent heterogeneous electron transfer rate constant (k _s) were estimated to be 0.36 and 2.74?s^?1, respectively. When the enzyme electrode was examined for the detection of choline, a relatively high sensitivity (2.59???A?mM^?1) was obtained. Under the optimized experimental conditions, choline was detected in the concentration range from 6.9?×?10^?3 to 6.7?×?10^?1?mM with a detection limit of 2.7???M. The peak currents of ChOx were reasonably stable and retained 90% of its initial current after a period of 2?months.     

Latex piezoelectric immunoassay: Effect of interfacial properties

Latex piezoelectric immunoassay is a technique for detecting agglutination of antibody- or antigen-bearing latex by an immunoreaction using a piezoelectric quartz crystal; the agglutination decreases the oscillation frequency of the crystal. This is advantageous in that immobilization of antibody or antigen on the crystal surface is unnecessary. In this report, different kinds of chemical functional groups were immobilized on the electrode surface, allowing us to consider the effect of interfacial structure on the frequency change. Electrode modifications such as self-assembly of alkanethiol and aminoalkoxysilane monolayers, and polyethylenimine-glutaraldehyde coating as well as plasma treatment were examined. The sensitivity of the system was found to imitate the interfacial properties so that modification of the electrode surface could improve the response. Among the methods examined for this electrode surface modification, the polyethylenimine-glutaraldehyde modification had the advantages of high reproducibility, fast operation and simplicity. It was also suggested that the frequency change originated primarily from the immunoreaction at the interface.     

Ionic liquid/graphene oxide as a nanocomposite for improving the direct electrochemistry and electrocatalytic activity of glucose oxidase

By combination of 1-ethyl-3-methyl immidazolium ethyl sulfate as a typical room temperature ionic liquid (IL) and graphene oxide (GO) nanosheets, a nanocomposite was introduced for improving the direct electrochemistry and electrocatalytic activity of glucose oxidase (GOx). The enzyme on the IL–GO-modified glassy carbon electrode exhibited a quasireversible cyclic voltammogram corresponding to the flavine adenine dinucleotide/FADH₂ redox prosthetic group of GOx. At the scan rate of 100 mV?s^?1, the enzyme showed a peak-to-peak potential separation of 82 mV and the formal potential of ?463 mV (vs Ag/AgCl in 0.1 M phosphate buffer solution, pH?7.0). The kinetic parameters of the charge transfer rate constant, the electron transfer coefficient, and the apparent Michaelis–Menten constant were calculated as 1.36 s^?1 and 0.35 and 2.47 μM, respectively. When the modified electrode was examined as a biosensor for glucose determination, a linear range of 2.5–45 nM with detection limit of 0.175 nM (signal to noise?=?3) was obtained. The biosensor was stable for 2 months.     

Micellar histidinate hematin complex as an artificial peroxidase enzyme model: Voltammetric and spectroscopic investigations

The UV–vis spectrophotometry and cyclic voltammetry were employed to investigate the incorporation of hematin into histidine (His) in a micellar environment of sodium dodecyl sulfate (SDS). Histidine undergoes a reduction process on silver electrode, while, hematin and sodium dodecyl sulfate are not electroreactive species on this electrode. Electrochemistry of twine-by-twine mixture of His, hematin and SDS on silver electrode shows that the peak potential of His in the presence of SDS or hematin shifts negatively which indicates the interaction of SDS and hematin with His. The interaction of SDS and hematin with His was also confirmed using spectrophotometric measurements. However, the peak potential of His on silver electrode shifts positively in the presence of both SDS and hematin which indicates that in a triple-component solution of His–hematin–SDS a unique species is formed and is electroreactive on silver electrode. In this context, this triple-component solution represents unique absorption band in UV–vis spectra, which is related to the formation of a unique structure of a hemoprotein-like biomimetic catalyst. The catalytic activity of this artificial enzyme formed in triple-component solution was examined with respect to hydrogen peroxide and the apparent Michaelis–Menten (K_m) and catalytic rate (k_cat) constants were evaluated to be 3.31 μM and 0.043 s⁻¹, respectively.