Analytical Methods (v.10, #36)

Front cover (4353-4353).

Inside front cover (4354-4354).

Contents list (4355-4360).

Extracellular hydrogen peroxide (H2O2) plays a significant role in regulating a variety of neural functions, such as atherosclerosis, ischemia and so on. It is necessary to develop a sensing platform for monitoring H2O2 in the central nervous system, especially during pathological processes. However, the design and synthesis of fluorescent probes, which can detect H2O2 in living cells or tissue, still have problems with toxicity. Herein, an effective and biocompatible H2O2 stimuli-responsive chemical sensing platform has been developed based on mesoporous silica nanoparticles (MSNPs). Firstly, MSNPs were functionalized with phenylboronic acid groups. Then the functionalized MSNPs reacted with glucose modified Au nanoparticles (Au NPs@glucose) through the carbohydrate–boronic acid interaction, encapsulating the molecular cargo inside the MSNPs. Transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), and zeta potential were employed to characterize the morphology and surface properties of these materials. The cargo was held in the blocked mesopores of the MSNPs with high efficiency and almost no leakage was detected. The target, H2O2, oxidized the arylboronic esters, causing the release of Au NPs from MSNPs and thereby resulting in the release of cargo. This sensing platform can be used to monitor the extracellular H2O2 concentration, which will help in physiological and pathological studies associated with H2O2 in the rat brain.

Ion mobility mass spectrometry workflows for characterizing bioactive isomer conformation, isomerization and drug–protein–liposome interaction by Hui Ouyang; Tao Bo; Zhengxiang Zhang; Xinqiu Guo; Mingzhen He; Junmao Li; Shilin Yang; Xin Ma; Yulin Feng (4367-4377).
In drug discovery, understanding the drug structure is essential because it is closely associated with the absorption, distribution, metabolism, and excretion properties of the drug. As a complex drug system, traditional Chinese medicine (TCM) has been effective in the prevention and treatment of chronic diseases in a synergic manner with milder healing effects and lower side effects compared to western medicines. The active components from TCM exhibit high structural diversity, while involving multiple isomers with the same molecular weights but different biological activities. In practice, these active compounds also undergo conformational changes and transformations. Thus it is important to estimate these structural changes and the related changes in biological interactions. In this study, we developed a novel strategy using ion mobility mass spectrometry (IM-MS) and molecular modeling for accurate characterization of conformational changes of TCM active isomers, their isomerization in degradation and the isomer–protein interactions. The relationship between the anti-inflammatory bioactivity and binding affinity to protein has been studied. Our work showed that IM-MS and molecular modeling can effectively differentiate structural isomers, associated conformation variants and their biological interactions with proteins and lipids. These workflows are essential for deeper pharmacological and toxicological understanding.

In this paper, we present a novel colorimetric sensor for the detection of arsenate in aqueous solution. Magnetic nanoparticles (Fe3O4 NPs) prepared by a hydrothermal process were characterized by SEM, XRD, FT-IR, and VSM analysis. The Fenton-like catalytic reaction of Fe3O4 NPs promoted the oxidation of methylene blue indicator (MB) in the presence of H2O2 which resulted in the diminishing of the dark blue colour of the solution, due to generation of ·OH radicals in the solution. This can be viewed by the naked eye and monitored by UV-Vis spectroscopy at 664 nm. Upon addition of arsenate to this system the blue colour regenerated in solution due to the agglomeration of As(v) on Fe3O4 which may block the active sites of the Fe3O4 NPs and decrease their intrinsic catalytic activity. Under optimal conditions, the proposed colorimetric sensor exhibited rapid and selective detection of As(v) in aqueous solution with a detection limit of 0.358 nM with a linear relationship with R2 = 0.997. To the best of our knowledge, this is the first report where arsenates can be detected colorimetrically by this sensing system (Fe3O4/MB/H2O2). The designed colorimetric strategy may provide a promising alternative method for detection of arsenates in real water samples.

A Cu(ii) coordination polymer-based catalytic sensing system for detecting cysteine and sulfur anions by Xiang-Ying Sun; Zhen-Fa Qin; Jiang-Shan Shen; Xue-Gong Cao; Bin Liu; Huai-Qian Wang (4387-4393).
Developing metal coordination polymer (CP)-based artificial enzyme mimics for establishing novel bio-chemosensing systems is important due to their high catalytic activity. Herein, a Cu(ii)-based CP (Cu-aspartic acid CP, that is Cu-Asp CP) was successfully prepared by a simple interface growth method. It was found that the as-prepared Cu-Asp CP has excellent peroxidase-like activity for 3,3′,5,5′-tetramethylbenzidine (TMB) as the substrate in the presence of H2O2. On the basis of these findings, taken together with high complexing stability constants between Cu2+ ions and cysteine (Cys)/S2− anions, simple, highly sensitive and selective colorimetric assays for detecting Cys and S2− anions were successfully developed, with low limits of detection estimated to be 0.625 μM and 0.206 μM, respectively.

TransFEr: a new device to measure the transfer of volatile and hydrophobic organic chemicals across an in vitro intestinal fish cell barrier by Hannah Schug; Frédéric Begnaud; Christian Debonneville; Fabienne Berthaud; Sylvia Gimeno; Kristin Schirmer (4394-4403).
Transfer of compounds across cellular barriers is a critical step of compound uptake into organisms. Using in vitro barrier systems to evaluate such transfer is attractive because of the higher throughput and reduced resource needs compared to animal studies. Thus far, however, studying the transfer of hydrophobic and volatile compounds was hampered by the unavailability of in vitro exposure systems that allow for stable and predictable chemical exposure concentrations. To overcome this limitation, we constructed a novel exposure chamber, TransFEr, and tested it with an in vitro epithelial barrier model using the rainbow trout (Oncorhynchus mykiss) intestinal cell line, RTgutGC. Key features of the chamber are its closed design and rotatable silicon segments, which can serve for chemical dosing and sampling. Using the fragrance damascone beta (log KOW: 3.7, log HLC: −3.9) as a pilot chemical, we were able to demonstrate that our exposure chamber provides for stable chemical exposure concentrations and full mass balance. The RTgutGC epithelium served as barrier for damascone beta transfer, which we attribute to chemical retention and biotransformation in the intestinal cells. Nevertheless, substantial transfer of the chemical across the epithelium occurred. When a chemical sink, i.e. a silicon segment, was included in the basolateral chamber to mimic blood constituents binding in vivo, transfer was about three-fold enhanced. We suggest that the presented methodology can help to obtain insights into chemical uptake mechanisms via the intestinal or other epithelia of fish and other animals for hydrophobic and volatile chemicals.

A sensitive and reliable analytical method for the simultaneous enantiomeric analysis of chiral non-steroidal anti-inflammatory drugs (ibuprofen, ketoprofen, and flurbiprofen) in water, river sediment, and sludge was established. Enantioseparation of the analytes was performed on a Chiralpak IG column using a mobile phase of 0.1% aqueous formic acid and acetonitrile. Magnetic solid-phase extraction, based on dummy-template molecularly imprinted polymer-coated magnetic multi-walled carbon nanotubes combined with dispersive liquid–liquid microextraction, was employed to pretreat complex environmental samples. Parameters affecting the extraction efficiency of the pretreatment processes were systematically optimized. Under the optimized conditions, recoveries of all enantiomers from environmental matrices were in the range 75.8–92.1% with relative standard deviations no higher than 12.4%. The quantification limits for enantiomers ranged from 6.17 to 11.94 ng L−1 in water samples and from 1.16 to 2.54 ng g−1 in river sediment and sludge samples. This method was successfully used to analyze the enantiomeric composition of three chiral non-steroidal anti-inflammatory drugs in real environmental samples, which will improve understanding of their degradation processes and aid evaluation of their ecological toxicity.

A flow-through column electrolytic cell for supercritical fluid chromatography has recently been developed. To examine the applicability of the cell to real samples, the determination of tocopherols in edible vegetable oils was carried out. Tocopherols (α, β, γ and δ) and 2,2,5,7,8-pentamethyl-6-hydroxychroman (internal standard) were eluted and fully separated within 10 min using a mixture of supercritical carbon dioxide and methanol containing 1.0 mol L−1 ammonium acetate (98 : 2, v/v) as a mobile phase and a conventional silica gel column as a stationary phase. The current peak area detected in the electrochemical cell was found to be linear with the amount of samples injected in the range from 5 μmol L−1 to 200 μmol L−1 (r≧ 0.997). The repeatability was not more than 1.82% RSD (n = 6) and the intermediate precision was also not more than 3.55% RSD (n = 3). The limit of detection (S/N = 3) on the column was less than 3.43 pmol. By the present internal standard method, tocopherols in various vegetable oils were determined with a simple sample preparation procedure.

Many glycoproteins can be used as disease biomarkers for early clinical diagnostics and treatment of diseases. Selective enrichment is critical for the analysis of glycoproteins. Molecularly imprinted polymers (MIPs) have found important applications in the separation and enrichment of glycoproteins. However, template immobilization-based boronate affinity surface imprinting has not been used to prepare glycoprotein-imprinted silica nanoparticles using a new hydrophilic imprinting coating, poly(4-aminobenzyl alcohol). In this study, we use this imprinting strategy to prepare boronate affinity-based molecularly imprinted silica nanoparticles using poly(4-aminobenzyl alcohol) as an imprinting coating. After a glycoprotein template was covalently immobilized onto the surface of boronic acid functionalized silica nanoparticles, a thin imprinting coating of poly(4-aminobenzyl alcohol) was formed to cover the silica nanoparticle surface via in-water self-polymerization. After removing the template with an acidic solution, 3D cavities were formed in the imprinting layer. The imprinting coating was highly hydrophilic and presented limited residual boronic acid and therefore non-specific binding was avoided. The MIPs prepared under the optimal conditions exhibited several highly favorable features, including excellent specificity, a high binding strength of (0.71 ± 0.06) × 10−7 M and a low binding pH of 5.0. The MIPs prepared using this method were successfully applied in the determination of a TRF concentration of 2.75 ± 0.25 mg mL−1 in human serum.

In this study, we developed a novel and facile electrochemical aptasensor for β-amyloid (Aβ) oligomer detection based on metal–organic frameworks (MOFs) as signal probes. By using an aptamer-tethered gold nanoflower (AuNF) modified electrode for target capture and aptamer-tagged gold nanoparticles/Cu-MOF (AuNPs/Cu-MOF) conjugates for sensitive signal generation, an effective sandwich sensor was obtained for the detection of Aβ oligomers. The unique physico-chemical properties of AuNPs/Cu-MOF conjugates, such as high electrochemical activity and large surface area, endow the sensor with excellent analytical performances. The designed aptasensor exhibits a wide linear range from 1 nM to 2 μM with a linear correlation coefficient of 0.996 and a relatively low detection limit of 0.45 nM for the detection of Aβ oligomers. For the evaluation of Aβ oligomers in artificial cerebrospinal fluid, the high recoveries and accuracy indicate the feasibility, which will provide valuable information for the early diagnosis of Alzheimer's disease. Moreover, the proposed electrochemical aptasensor based on multifunctional MOFs will provide a general strategy for sensing other analytes.

Aptamer-based colorimetric determination of Pb2+ using a paper-based microfluidic platform by Neda Fakhri; Morteza Hosseini; Omid Tavakoli (4438-4444).
In this research, a novel paper-based microfluidic aptasensor was designed in order to detect different concentrations of lead in water. The principle based on which this aptasensor works is the interaction of gold nanoparticles with NaCl which leads to a color change from red to purple in the presence of lead ions due to AuNP aggregation. Furthermore, two types of filter paper, namely Whatman No.1 and nylon filter papers, were used as the platform of this paper-based microfluidic assay, and the properties of each one was investigated. It was seen that Pb2+ can be detected with linear trends for the calibration of each paper type at concentrations within the 10 nM to 1 mM range in both Whatman No.1 and nylon filter papers. A detection limit of 1.2 nM and 0.7 nM was obtained for Whatman No.1 and nylon filter papers, respectively. Moreover, the Whatman No.1 filter paper was used for the detection in real water samples, and it showed good potential for the detection of Pb2+ in environmental samples.

Metal oxide-based pH sensors have received considerable attention owing to their advantages and potential applications in biomedicine, materials science, environmental science, and analytical science. The occurrence of multidrug resistance (MDR) hinders the efficiency of chemotherapy. In addition, a low extracellular pH (pHe), which is a common feature of the tumor microenvironment, contributes to resistance to chemotherapy. Therefore, in this work we demonstrate the facile fabrication of a solid-state Sb/Sb2O3 (SSO) electrode for high-performance pH sensing to monitor the pHe of two cell lines (MCF-7/ADR Adriamycin-resistant breast cancer cells and their MCF-7 parent cells). To achieve this aim, the electrode was prepared by melting antimony (Sb) in a U-type glass tube and subsequent oxidation via the molten sodium nitrate method. The fabricated SSO electrode was characterized by scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. It was found that the SSO electrode-based pH sensor exhibited high performance with a sensitivity of −57.30 ± 0.60 mV pH−1 and a correlation coefficient (R2) of greater than 0.9966 in aqueous buffer solutions (pH = 2–12). In addition, the fabricated pH sensor displayed not only a short response time (about 2 s) but also long-term stability (pH deviation of <0.15 after three months). Furthermore, the differences in pHe between MCF-7/ADR and MCF-7 cells were determined by the fabricated SSO electrode, and MCF-7/ADR cells and MCF-7 cells maintained pHe values of about 6.83 and 7.02, respectively, after 12 h. The results showed that the fabricated SSO electrode could be used to measure differences in pHe and also used to monitor the metabolic activity of cells.

A simple one-step assay for the trace determination of Co2+ was developed on filter paper modified with solubilized polymethyl methacrylate (PMMA) and arrays of 3-[(2-mercapto-vinyl)-hydrazono]-1,3-dihydro-indol-2-one (MHDI) reagent. The paper modified with a thin film of PMMA transformed its surface wettability from hydrophilic (θ∼ 0°) to hydrophobic (θ∼ 92°). Goniometry and scanning electron microscopy confirmed modification of cellulose fibers. On a low-wetting surface, analyte droplet could be confined onto the MHDI spot, allowing visual detection of 1 μM concentration of Co2+ within 10 min. The limit of detection (LOD) was three orders of magnitude superior to that of a similar assay executed on unmodified paper. The established method is the first of its kind for Co2+ determination with a wide linear dynamic range (101 to 104μM) coupled with good reproducibility, ruggedness and point-of-use testing. Due to high selectivity towards Co2+ and minimum interference from diverse ions, the developed probe was successfully applied for the trace analysis of Co2+ in tap and industrial wastewater samples. The established method was successfully validated using ICP-OES analysis. The proposed assay could be compared favorably to most of the reported methods for Co2+ determination in terms of ease, cost-effectiveness and analysis time. The recoveries from the recognized method were >90%, confirming its potential use for sensing Co2+.

Iodine determination in table salts by digital images analysis by Geovanna de O. Costa; Fernanda N. Feiteira; Hanna de M. Schuenck; Wagner F. Pacheco (4463-4470).
For human health reasons the World Health Organization (WHO) stated in 2014 that the amount of iodine present on table salts should lie within the range of 15 to 65 mg per kilogram of salt, depending on the salt intake levels presented in each population. This means that booth industrial laboratories (for quality control) and governmental agencies (for external quality control) should perform iodide quantification in table salts. The main method for this determination is based on volumetric analyses or WYD iodine checker. This work proposes an alternative approach for the quantification of iodine in table salt samples, that combine the good accuracy and precision obtained by titrimetric methods with the convenience of using a spectrophotometer, using just a polyurethane foam and a scanner, trough digital image analysis. The results here obtained indicate that the proposed method offers satisfactory precision and accuracy as well as sufficient sensitivity to address the resolutions provided by the WHO and the Brazilian legislation relating to iodine content in table salts. The limit of detection (LOD) was calculated as 3.94 mg kg−1 and the limit of quantification (LOQ) as 13.2 mg kg−1. When compared to the standard iodometric method, the developed method presented no statistical difference at 95% confidence level.

Correction: Analysis of dialkyl urine metabolites of organophosphate pesticides by a liquid chromatography mass spectrometry technique by Sukesh Narayan Sinha; B. Venkat Reddy; Kasturi Vasudev; M. Vishnu Vardhana Rao; M. Noor Ahmed; Shaik Ashu; Alka Kumari; Vijay Bhatnagar (4471-4471).
Correction for ‘Analysis of dialkyl urine metabolites of organophosphate pesticides by a liquid chromatography mass spectrometry technique’ by Sukesh Narayan Sinha et al., Anal. Methods, 2014, 6, 1825–1834.

Correction: ATR-FTIR spectroscopy with chemometric algorithms of multivariate classification in the discrimination between healthy vs. dengue vs. chikungunya vs. zika clinical samples by Marfran C. D. Santos; Yasmin M. Nascimento; Joelma D. Monteiro; Brenda E. B. Alves; Marília F. Melo; Anne A. P. Paiva; Hannaly W. B. Pereira; Leandro G. Medeiros; Ingryd C. Morais; João Ciro Fagundes Neto; José V. Fernandes; Josélio M. G. Araújo; Kássio M. G. Lima (4472-4473).
Correction for ‘ATR-FTIR spectroscopy with chemometric algorithms of multivariate classification in the discrimination between healthy vs. dengue vs. chikungunya vs. zika clinical samples’ by Marfran C. D. Santos et al., Anal. Methods, 2018, 10, 1280–1285.

Back cover (4475-4476).