Electrochemical biosensing of DNA hybridization by ferrocenyl groups functionalized polypyrrole

We have developed a new material based on polypyrrole functionalized with both ferrocenyl group and DNA probe. We have developed a precursor polymer based on a pyrrole 3-acetic acid and a pyrrole bearing ferrocenyl groups substituted by easy leaving group in which amino-labeled oligonocleotides probe were directly linked. The electrochemical response of the modified electrode was examined both in aqueous and organic media and shows high electroactivity in both media. A large modification of redox activity of ferrocenyl groups was obtained upon addition of ODN target to the electrolytic media, which is determined by amperometric methods. The detection limit of this electrochemical biosensor is about 10⁻¹⁴ mol without any signal processing.     

Breath biosensing: using electrochemical enzymatic sensors for detection of biomarkers in human breath

Detection of biomarkers for disease by noninvasive methods is critical for the early diagnosis and screening of disease, enabling prompt treatment. Breath biosensors are a viable option as the exhaled breath contains several biomarkers linked to lung cancer, oxidative stress, diabetes, and other diseases. Breath analysis has been achieved by advanced analytical techniques such as gas chromatography and infrared spectroscopy. However, electrochemical enzymatic breath biosensors offer a cost-effective, sensitive platform for biomarker detection without complex analysis and interpretation by trained laboratory personnel. This review aims to summarize recent advances in the field of electrochemical enzymatic breath biosensors and offer future opportunities from other applications of nonelectrochemical enzymatic breath biosensors.     

单原子材料在电化学生物传感中的研究进展

电化学传感器具有响应速度快、 专一性强及准确性高等特点, 已成为生物传感快速检测的重要发展方向之一, 但目前难以达到对单个生物分子的检测水平, 这主要受限于作为核心部件的探针材料. 单原子材料由于其简单明确的原子局域结构, 且具有媲美于生物酶的统一活性位点, 是一种极具潜力的探针材料, 因此受到了广泛关注. 本文综合评述了具有均一局域配位环境的单原子材料的合成, 以及其在电化学生物传感中的应用, 并对单原子材料在未来电化学生物传感中面临的挑战和机遇进行了展望.     

Approaches to optimisation of precision in capillary electrophoresis

Summary A study has been performed to obtain insight into the relative importance of critical factors affecting the repeatability of hydrodynamic injections in CE. Precision was measured for repeated analysis of a test mixture containing two acidic compounds.The use of an internal standard was clearly shown to improve precision especially when peak area precision was poor. It is suggested that precision is maximised by employing a combination of a constant temperature, an appropriate electrolyte system, an internal standard, long injection times, and high sample concentrations. Other factors are discussed, but are classified as having only a minor impact.     

Patterns in the precision of quantitative data from multicomponent gas chromatographic or gas chromatographic-mass spectrometric analysis

The dispersion of the quantitative results in the analysis of volatile compounds from multicomponent mixtures by different fractionation techniques (solid-phase microextraction and direct thermal desorption) followed by GC or GC-MS presents nonrandom patterns related to the existence of different factors in the fractionation process or in the chromatographic separation which affect, to a different extent, the recovery of the sample components. Statistical techniques have been used to show the relative importance of these factors. The improvement in data precision achieved by using volatile compound concentration ratios is discussed.     

Electrochemical quartz crystal microbalance analysis of the cathodic process in a lithium-ion battery

The surface processes at carbon and platinum electrodes have been studied using the electrochemical quartz crystal microbalance technique in organic electrolyte solutions for lithium ion batteries. The changes in resonance frequency were analyzed as a function of the electrode potential, indicating that the process depended not only on the electrode material but also on the cathode potential. In the solution containing LiBF₄ as the electrolyte, the main product at the platinum surface was Li₂CO₃ and LiF, whereas formation of lithium alkylcarbonates was the primary process at the platinum and carbon electrodes in LiPF₆ solution.     

快速检测中药材中黄曲霉毒素B1的电化学生物传感器

结合新型纳米传感膜材料,以黄曲霉毒素Bl(AFBl)单克隆抗体为生物识别元件,通过考察AFB1与抗体之间的相互作用对测试底液中[Fe(CN)6]3-/[Fe(CN)6]4-([Fe(CN)6]3-/4-)氧化还原体系的影响,构建了一种可用于中药材中AFB1快速检测的电化学生物传感器.在最佳条件下,对AFB1浓度的线性响...     

Electrochemical impedance spectroscopy analysis for oxygen reduction reaction in 3.5% NaCl solution

The electrochemical impedance spectroscopy (EIS) at different potentials has been used to study the oxygen reduction reaction (ORR) in 3.5% NaCl solution on glassy carbon (GC) electrode in this work. Results show that ORR consists of three two-electron reaction steps and both superoxide ion (O₂ ^–) and hydrogen peroxide (H₂O₂), which are produced by ORR, obstruct the diffusion of oxygen to the surface of the electrode and make the EIS results change into a transmissive finite diffusion process with the real part contraction and a reflective finite diffusion process from a semi-infinite diffusion process. The values of electron transfer resistance (R _t) and diffusion resistance (R _d) were calculated from EIS. O₂ ^– influenced strongly on the R _t values and induced a maximum at −0.45 V.     

Robust estimates of the theoretical standard deviation to be used in interlaboratory precision experiments

Interlaboratory experiments often contain results that strongly deviate from other results obtained in the same laboratory under repeatability conditions, or laboratory means that strongly deviate from other laboratory means. In ISO 5725-2 [1] and IUPAC [2], the basic standards for the organisation and analysis of interlaboratory experiments for the determination of precision of a measurement method, outlier tests are performed in order to detect such situations and to finally decide whether these values are retained in the analysis or discarded as outliers. This outlier treatment, which always has a subjective aspect, becomes unnecessary by using robust estimates of the repeatability and reproducibility standard deviation. This paper proposes to use Rousseeuw’s Q _n as an extremely robust and efficient estimate of the standard deviation. Two examples show the performance of the new method.     

Assessment of accuracy and precision in speciation analysis by competitive ligand equilibration-cathodic stripping voltammetry (CLE-CSV) and application to Antarctic samples

The analytical performances of Competitive Ligand Equilibration with Cathodic Stripping Voltammetric detection of the labile fraction (CLE-CSV) were assessed. This speciation method enables the concentration of natural ligand(s) and their conditional stability constants for the complexation of the investigated metal to be determined through thermodynamic considerations.Literature data were discussed and general trends in the precision of the determined parameters identified: ligand concentrations were affected, on average, by a 10% relative percentage standard deviation (RSD%), whereas conditional stability constants showed much lower precision, with an average RSD% of 50%.New experimental data were collected to obtain a complete assessment of accuracy and precision attainable for the determination of strong ligands at the ultra trace level, enabling the whole protocol to be evaluated. Firstly, the side reaction coefficient alpha for the formation of the complex between the added ligand and the investigated metal (α_CuL) was determined. The method was subsequently applied to the analysis of solution containing ligand at trace levels (5-50 nM) with known complexing characteristics. Copper was used as the model metal ion and ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) as the model ligands. Results evidenced that the CLE-CSV protocol is not affected by systematic errors in the determination of both ligand concentration and the conditional stability constants. Good precision is obtained for ligand concentrations, with an average relative standard deviation (RSD%) of 5%; an average RSD% of 23% was calculated for the conditional stability constants. Including the contribution of the uncertainty in the value of α_CuL in the evaluation of the uncertainty in the latter parameter increased the RSD% up to 40%. The CLE-CSV protocol was subsequently applied to the detection of strong ligands in water samples collected in Antarctica: precision was shown to be comparable with literature data.     

Electrochemical droplet-based microfluidics using chip-based carbon paste electrodes for high-throughput analysis in pharmaceutical applications

This paper presents the first example of a pharmaceutical application of droplet-based microfluidics coupled with chronoamperometric detection using chip-based carbon paste electrodes (CPEs) for determination of dopamine (DA) and ascorbic acid (AA). Droplets were generated using an oil flow rate of 1.80 μL min⁻¹, whereas a flow rate of 0.80 μL min⁻¹ was applied to the aqueous phase, which resulted in a water fraction of 0.31. The optimum applied potential for chronoamperometric measurements in droplets was found to be 150 mV. Highly reproducible analysis of DA and AA was achieved with relative standard deviations of less than 5% for both intra-day and inter-day measurements. The limit of detection (LOD) and limit of quantitation (LOQ) were found to be 20 and 70 μM for DA and 41 and 137 μM for AA, respectively. Linearity of this method was in the ranges of 0.02–3.0 mM for DA and 0.04–3.0 mM for AA. This system was successfully applied to determine the amounts of DA and AA in intravenous drugs. Calibration curves of DA and AA for quantitative analysis were obtained with good linearity with R² values of 0.9984 and 0.9988, respectively. Compared with the labeled amounts, the measured concentrations of DA and AA obtained from this system were insignificantly different, with error percentages of less than ±3.0%, indicating a high accuracy of the developed method.     

Electrochemical study and flow injection analysis of paracetamol in pharmaceutical formulations based on screen-printed electrodes and carbon nanotubes

Acetaminophenol or paracetamol is one of the most commonly used analgesics in pharmaceutical formulations. Acetaminophen is electroactive and voltammetric mechanistic studies for the electrode processes of the acetaminophenol/N-acetyl-p-quinoneimine redox system are presented. Carbon nanotubes modified screen-printed electrodes with enhanced electron transfer properties are used for the study of the electrochemical-chemical oxidation mechanism of paracetamol at pH 2.0.Quantitative analysis of paracetamol by using its oxidation process (in a Britton-Robinson buffer solution pH 10.0) at +0.20 V (vs. an Ag pseudoreference electrode) on an untreated screen-printed carbon electrode (SPCE) was carried out. Thus, a cyclic voltammetric based reproducible determination of acetaminophen (R.S.D., 2.2%) in the range 2.5 × 10⁻⁶ M to 1 × 10⁻³ M, was obtained. However, when SPCEs are used as amperometric detectors coupled to a flow injection analysis (FIA) system, the detection limit achieved for paracetamol was 1 × 10⁻⁷ M, one order of magnitude lower than that obtained by voltammetric analysis. The repeatability of the amperometric detection with the same SPCE is 2% for 15 successive injections of 10⁻⁵ M acetaminophen and do not present any memory effect.Finally, the applicability of using screen-printed carbon electrodes for the electrochemical detection of paracetamol (i.e. for quality control analysis) was demonstrated by using two commercial pharmaceutical products.     

Processing of shot-to-shot raw data to improve precision in laser-induced breakdown spectrometry microprobe

In order to set up the precision limit that can be reached with laser-induced breakdown spectrometry microprobe, a steel sample was scanned by using a 6-µm diameter spot. Besides being close to the limit of the technique, such a spot diameter resulted in a small plasma size that minimized self-absorption effects. To minimize shot noise, Cr and Fe were used as test elements because of their high contents. Scan consisted of 25 successive matrices formed by 5 × 6 shots, i.e. a total of 750 shots. Results were studied as a whole, as well as between matrices and within matrices, to search for inhomogeneity, outliers and drift. Except a few outliers, the main contribution in the experimental RSD was the drift either within a matrix or between matrices. Drift attributed to laser warm up could be compensated for either by using a polynomial fitting or by using the other element. %RSD significantly below 2 were then obtained demonstrating that there is no penalty in terms of precision to perform laser microprobe using a series of single shots.     

Using Ferrocenes to Assist in Voltammetric Characterization of Carbon Fiber Microelectrodes after Electrochemical and Laser Activation

In this report the voltammetry of water‐soluble ferrocene derivatives is used to characterize the surface of carbon fiber microelectrodes before and after both electrochemical and laser activation procedures. Activation of carbon electrodes is necessary to produce a reproducible surface that will allow fast electron transfer. However, the activation method that is best suited for a given analysis can differ with analyte. In order to directly compare activation methods and characterize the resulting electrode performance, the voltammetry of a set of ferrocenes which have fast and well‐known electrochemistry has been used. As expected, electrochemical activation (0.000 to 2.000 V (vs. SSCE) at 500 V/s for 15 seconds) resulted in a hydrophilic surface with increased surface area. Laser pretreatment (20 Hz pulsed nitrogen laser irradiation for 15 seconds) appeared to remove surface oxides thereby producing a more hydrophobic surface that facilitates the adsorption of neutral analytes. In general, anionic ferrocene derivatives exhibited more quasi‐reversible voltammetry and were not as strongly adsorbed as the neutral analyte, particularly with electrochemically activated probes. In addition, neutral analytes show considerable adsorption, particularly at laser‐activated electrodes, while the cationic analyte shows significant adsorption at only the electrochemically‐pretreated electrodes, indicating surface‐specific interactions.     

Electrochemical Sensing of Dissolved Hydrogen in Aqueous Solutions as a Tool to Monitor Magnesium Alloy Corrosion

Magnesium and its alloys have been the focus of the development of biodegradable metallic implant materials for years. Since water is reduced to form hydrogen gas during their corrosion, the amount and rate of hydrogen evolution, and therefore the dissolved hydrogen, could be used as an indicator to monitor and compare the corrosion. Here we report on a commercially available Clark‐Type amperometric microsensor and a simple potentiometric sensor for hydrogen to monitor the corrosion of a magnesium alloy in aqueous solutions. The sensors were compared using rare‐earth containing Mg alloy discs (Mg with 4 % Y, 2 % Nd, 0.5 % Ga, 0.5 % Dy) immersed in phosphate buffered saline (pH 7.4) and 3.5 % NaCl.     

Electrochemical Kinetics of Anodic Ni Dissolution in Aqueous Media as a Function of Chloride Ion Concentration at pH Values Close to Physiological Conditions

We have studied the electrochemical kinetics of anodic Ni dissolution as a function of chloride ion concentration, at pH 5, 6 and 7, in order to mimic the conditions of sweat samples. Our results show that the rate‐determining step for Ni dissolution in the mentioned pH range is the transfer of one first electron, as suggested by the Tafel slopes close to 0.120 V/decade. However, the reaction order in chloride ion varies from ca. 2 at pH 7 to values close to unity for pH values between 5 and 6. This finding is very important for sensor applications in sweat fluids since the sensitivity of the Ni electrode to chloride ions is higher in neutral solutions (pH ca. 7) compared to that in slightly acid solutions (pH between 5 and 6). Small variations in pH in real samples are expected so this change in sensitivity should be considered when sensing chloride ions in sweat fluids.     

Direct analysis in real time mass spectrometry and multivariate data analysis: A novel approach to rapid identification of analytical markers for quality control of traditional Chinese medicine preparation

The paper presents a novel strategy to identify analytical markers of traditional Chinese medicine preparation (TCMP) rapidly via direct analysis in real time mass spectrometry (DART-MS). A commonly used TCMP, Danshen injection, was employed as a model. The optimal analysis conditions were achieved by measuring the contribution of various experimental parameters to the mass spectra. Salvianolic acids and saccharides were simultaneously determined within a single 1-min DART-MS run. Furthermore, spectra of Danshen injections supplied by five manufacturers were processed with principal component analysis (PCA). Obvious clustering was observed in the PCA score plot, and candidate markers were recognized from the contribution plots of PCA. The suitability of potential markers was then confirmed by contrasting with the results of traditional analysis methods. Using this strategy, fructose, glucose, sucrose, protocatechuic aldehyde and salvianolic acid A were rapidly identified as the markers of Danshen injections. The combination of DART-MS with PCA provides a reliable approach to the identification of analytical markers for quality control of TCMP.