Analytical Methods (v.10, #2)

Front cover (161-162).

Contents list (163-167).

Results reported in the companion paper (Zhbanov and Yang, Anal. Methods, 2017, 17, 3302) showed that electrochemical impedance spectroscopy is a highly promising tool for the analysis of blood. In this study, dielectric spectra of human blood at various hematocrits were measured by using a two-electrode system in the frequency range from 40 Hz to 110 MHz. A numerical technique based on a finite difference method has been improved to calculate the effective complex permittivity of blood. Various models of erythrocyte shapes such as spherical, cylindrical, disk-shaped, spheroidal, and biconcave shapes were investigated. The numerical calculations showed that the cylindrical, disk-shaped, and biconcave models give comparable results, which differ significantly from those of the other models. Additionally, the effective complex permittivity of blood was analytically calculated based on the effective medium theory where erythrocytes are modeled as a conducting spheroid surrounded by a thin insulating membrane. The analytical calculation qualitatively reproduces the behavior of the dielectric spectrum, but quantitatively differs from the numerical simulation. The dielectric properties of erythrocyte cytoplasm and membranes were numerically determined based on the experimental data. Numerical analysis of the dielectric spectra of blood samples confirmed β-relaxation at frequencies between 100 kHz and 10 MHz and δ-relaxation in the frequency domain from 10 MHz to 1 GHz. The time-dependent changes in blood conductivity were measured during erythrocyte sedimentation. The measured blood conductivity increased slightly during the first minute and decreased within a few hours. This increase is attributed to the aggregation of erythrocytes. The numerical simulations confirmed that the blood conductivity increases to the maximum and then decreases slightly with growing aggregate size.

The study of erythrocyte aggregation and erythrocyte sedimentation rate (ESR) is very important both for basic research and medical applications. The duration of the Westergren ESR test is one hour which seems excessive. The hematocrit and conductivity of blood demonstrate high correlation. This makes it possible to evaluate the erythrocyte aggregation kinetics and ESR by measuring changes in the blood conductivity. We measured the time-dependent changes in conductivity at the bottom of the blood column during sedimentation. A digital camera is used to obtain the blood sedimentation curve and to determine the hematocrit profile. The effective conductivity of blood is calculated based on effective medium theory. Simple analytical expressions are derived to extrapolate changes in blood conductivity over time. We proposed an improved physical model of sedimentation which reveals additional information about the kinetics of blood sedimentation and erythrocyte aggregation. An explicit expression is obtained to characterize the rate of aggregate formation. A numerical model was developed to investigate these mechanisms, and it was tested by comparing simulation results with experimental data. Based on our model, the ESR, blood sedimentation curve and hematocrit profiles can be numerically restored using only the first 400 seconds of the recorded changes in blood conductivity. The proposed technique allows measuring the erythrocyte aggregation as well as the sedimentation kinetics. The changes in blood conductivity at the bottom of the blood column at the initial stage of sedimentation reliably reflect the erythrocyte aggregation kinetics and ESR over time.

In order to ensure that the results of chromatographic data analysis workflow are well within the chemical and biological premise, the same chromatographic peak must be present at the same position for all the analysed samples. The correlation optimised warping (COW) and interval correlation shifting (icoshift) algorithm are the two most commonly used approaches that are used to correct the drifts in the peak position. Both the approaches work with different algorithms, COW works on expansion and compression approach whereas the icoshift works on an insertion and deletion approach. Both the approaches have their pros and cons. However, both the methods suffer with the problems associated with the selection of the proper reference sample. There are several ways of selecting a reference sample but none of them provides an unambiguous choice. Often, the selection of an inappropriate sample as the reference makes the whole alignment exercise a laborious task with very little success in correcting the drifts in peak position. An unambiguous reference selection procedure is the current prime requirement in the areas of proteomics, metabolomics, and the food industry that use chromatography-based analytical procedures. The present work addresses this issue by taking the advantage of the fact that chromatographic peaks can be approximated using the Gaussian function and proposes an approach that involves synthesis of a reference chromatogram using the Gaussian function for the subsequent COW and icoshift analysis. The proposed approach is successfully validated using the simulated as well as real life chromatograms and the results obtained are evaluated by means of several statistical parameters. The results clearly show that the proposed approach can reduce the ambiguity in the selection of a reference chromatogram and can speed up and automate the whole alignment procedure.

A new wipe-sampling instrument for measuring the collection efficiency of trace explosives residues by Elizabeth L. Robinson; Edward Sisco; Matthew E. Staymates; Jeffrey A. Lawrence (204-213).
Trace explosives detection, a crucial component of many security screening environments, commonly employs wipe-sampling. Since collection of an explosive residue is necessary for detection, it is important to have a thorough understanding of the parameters that affect the efficiency of collection. Current wipe-sampling evaluation techniques for explosive particles have their limits: manual sampling (with fingers or a wand) is limited in its ability to isolate a single parameter and the TL-slip/peel tester is limited to a linear sample path. A new wipe-sampling instrument, utilizing a commercial off-the-shelf (COTS) 3D printer repurposed for its XYZ stage, was developed to address these limitations. This system allowed, for the first time, automated two-dimensional wipe-sampling patterns to be studied while keeping the force and speed of collection constant for the length of the sampling path. This new instrument is not only capable of investigating the same parameters as current technology (wipe materials, test surfaces, forces of collection, and linear sample patterns), it has added capabilities to investigate additional parameters such as directional wipe patterns (i.e.“L” and “U” shapes, square, and serpentine) and allowing for multiple lines to be sampled during a single collection without the need for adjustments by the user. In this work, parametric studies were completed using 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) and the COTS 3D printer for wipe-sampling to establish collection efficiencies for numerous scenarios. Trace explosives detection in field screening environments could be greatly improved with the ability to comprehensively investigate how a wide range of parameters individually affect collection by wipe-sampling. A screener who knows how to properly interrogate any given surface will be much more efficient at detecting trace explosives.

Dengue serotyping with a label-free DNA sensor by S. K. Chan; Y. S. Choong; D. Perera; T. S. Lim (214-222).
Dengue virus (DENV) is one of the most important mosquito-borne viruses in tropical and subtropical regions. Development of severe forms of dengue viral infection such as dengue fever (DF) and dengue hemorrhagic fever (DHF) has claimed many lives. The standard methods for detecting dengue virus are time consuming, laborious, and require skilful personnel. In this study, we propose a method whereby DENV RNA extracted from dengue infected mosquitoes was converted into DNA for probe hybridization to generate silver nanocluster strands that could be visualised under UV light. Label-free silver nanocluster based DNA sensors are able to provide strong fluorescence upon DNA hybridization. Highly specific DNA sequence detection is possible by taking advantage of the specificity of DNA hybridization kinetics. The proposed system is capable of detecting all four dengue DNA serotypes (DENV1–4) without any cross-reactivity. A single tube assay format showed better hybridisation efficiency with higher fluorescence intensity generated and a lower detection limit compared to a cocktail probe assay format. The method was able to detect as low as 100 nM of amplified double stranded dengue DNA targets using both single and cocktail probe assays. This provides an interesting alternative approach for multiplex DNA sensing utilizing DNA silver nanoclusters as a reporter system.

Construction of novel nanocomposite ZnO@CoFe2O4 microspheres grown on nickel foam for high performance electrochemical supercapacitors by Araveeti Eswar Reddy; Tarugu Anitha; Chandu V. V. Muralee Gopi; S. Srinivasa Rao; Bandari Naresh; Hee-Je Kim (223-229).
Novel ZnO@CoFe2O4 and CoFe2O4 nanocomposites have potential applications on account of their high surface area and electrical properties. These two nanocomposite electrodes on nickel foam were developed for high performance electrochemical supercapacitor applications using a low-cost and facile one-step hydrothermal approach. The surface morphologies and electrochemical properties of the ZnO@CoFe2O4 and CoFe2O4 nanocomposites were examined by field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, galvanostatic charge–discharge cycling, and electrochemical impedance spectroscopy. The electrochemical tests indicated that the ZnO@CoFe2O4 nanocomposite electrode achieved a high specific capacitance of 4050.4 F g−1 at 10 mA cm−2 with a high energy density of 77.01 W h kg−1 in a 3 M KOH aqueous solution. This electrode exhibited attractive cycling stability and specific capacitance with approximately 90.9% capacity retention after 1000 cycles. On the other hand, the CoFe2O4 electrode showed lower specific capacitance (3499.9 F g−1) and cycling stability (50.07%) than the ZnO@CoFe2O4 nanocomposite electrode. These results highlight the potential of these ZnO@CoFe2O4 nanocomposite electrodes as electrodes for next generation supercapacitor applications in high energy density storage systems.

Early diagnosis of cancer is critical for the treatment of patients, and can reduce the risk of death. Breast cancer is one of the most common malignant tumors in women, and miR-21, as an important breast cancer biomarker, can be helpful for the early diagnosis of breast cancer. In this work, we have developed an efficient, sensitive and specific fluorescence sensor based on the novel nanomaterial molybdenum disulfide (MoS2) to detect miR-21. The novel nanomaterial MoS2 was introduced to a fluorescent dye-labeled DNA probe to fabricate the fluorescence sensor, and then non-complementary miRNA, one-base mismatched miRNA and complementary miR-21 were separately introduced to the sensor to hybridize with the DNA probe. By monitoring the change of the fluorescence signal before and after DNA-miRNA hybridization, miR-21 could be detected. We found that the sensor could discriminate complementary miR-21 from one-base mismatched miRNA and non-complementary miRNA successfully. Furthermore, the biosensor was able to detect miR-21 down to a concentration of 500 pM, and the detection could be completed in only 40 min. The novel MoS2 fluorescence sensor, with the advantages of fast analysis, high sensitivity and specificity, and low cost, is suitable for miR-21 detection which is of great importance for the early diagnosis of breast cancer. What’s more, the novel sensor, with high sensitivity and selectivity, was also used to detect miR-21 in serum samples, making it a promising method for detection in real samples from patients with cancer. Thus the novel MoS2 fluorescence sensor shows huge potential for early diagnosis of cancer.

On-site monitoring of occupational exposure to volatile organic compounds by a portable comprehensive 2-dimensional gas chromatography device by Jiwon Lee; Stephanie K. Sayler; Menglian Zhou; Hongbo Zhu; Rudy J. Richardson; Richard L. Neitzel; Katsuo Kurabayashi; Xudong Fan (237-244).
A fully automated portable comprehensive 2-dimensional (2-D) gas chromatography (GC) device was utilized for the first time for the field analysis of occupational volatile organic compounds (VOCs) at the Spray and Finishing Shop of the University of Michigan. The instrument contains a full set of micro-preconcentrator/injectors, commercial columns, micro-Deans switches, micro-thermal injectors, micro-photoionization detectors, data acquisition cards, and power supplies, as well as computer control and user interface. The indoor air was sampled and analyzed before, during, and after spraying the five most frequently used paints. The 2-D analysis yields enhanced peak capacity and shortened analysis time as compared to those achieved by portable GC instruments reported to date. In addition, the portable system is able to perform on-site analysis of VOCs, providing the results every 5 to 15 min, which would allow for enhanced acquisition of information regarding workers' safety and health risks from airborne VOCs. The performance of the portable 2-D GC device was validated by comparing the quantitative results of various type of paints using traditional occupational VOCs monitoring techniques in accordance with Occupational Safety and Health Administration Method ORG-07.

Synthesis and modification of mercapto-submicron scavenger for real-time extraction and preconcentration of As(iii) by Nezar H. Khdary; Ahmed E. H. Gassim; Alan G. Howard; Tamil S. Sakthivel; Sudipta Seal (245-255).
The gradual increase of arsenic in aquatic layers over the last decades has necessitated the early detection of low levels of arsenic on real time due to its hazardous impact on health. Here, the mercapto-submicron scavenger was synthesized and utilized for solid-phase dispersion extraction technique for real-time extraction and preconcentration of arsenite As(iii). Because of particle size, they naturally dispersed without the need for any additional power. The formation of particles and the achievement of the modification of the particles were confirmed by SEM, TEM, size distributions, CHN analysis, FT-IR spectroscopy, micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), zeta potential, energy dispersive X-ray analysis and (EDX) and thermogravimetric analysis (TGA), which confirmed the formation of particles in the size of 253 ± 34 nm, the chemical implantation of the mercapto groups on the surface was successfully accomplished with a loading of 0.281 mmol g−1. The particles showed proper dispersion and stability in the aqueous phase before and after being associated with As(iii). The chelating process between As(iii) and mercapto groups was assessed by XPS which confirmed that the mercapto-submicron scavenger can sequestrate As(iii) from water with maximum efficiency. Several factors that could optimize the process were assessed such as the effect of sorbent dose, pH, contact time, sample volumes, eluents, and matrix interference. The As(iii) calibration curve showed a positive linear correlation in the range of 0–100 μg L−1 and coefficient of determination (r2 = 0.9981). Optimum recovery was obtained with an equilibrium time of 30 min at pH = 8.5. It was found that the release of As(iii) from the mercapto-submicron scavenger was eluent dependent and the maximum recovery at the optimum conditions was 98 ± 3%. The average recovery of As(iii) from three different ground water locations was 97.15%.

The need to investigate the fragmentation of fucosylated glycopeptides is driven by recent work showing that at least one, and perhaps many, glycopeptide analysis scoring algorithms are less effective at identifying fucosylated glycopeptides than non-fucosylated glycopeptides. Herein, we study the CID fragmentation characteristics of fucosylated glycopeptides and the scoring rules of the glycopeptide analysis software, GlycoPep Grader, in an effort to improve automated assignments of these important glycopeptides. We identified some prominent product ions from a common fragmentation pathway of fucosylated glycopeptides that were not accounted for in the scoring rules. Based on this finding, we propose new scoring rules for fucosylated glycopeptides that can be incorporated into GlycoPep Grader and other similar analysis software tools to more accurately identify these species. The approach used here, to improve one particular scoring algorithm, could henceforth be used to improve any other algorithm that assigns glycopeptides based on their MS/MS data.

Correction for ‘Tridentate tripodal sulfur ligand as a stable molecular surface anchor for the fabrication of oligonucleotide-gold based label-free biosensors’ by Huancai Yin et al., Anal. Methods, 2017, 9, 600–608.

Back cover (265-266).