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Analytica Chimica Acta (v.665, #1)

Editorial Board (pp. iii).

Capillary electrophoresis with contactless conductivity detection coupled to a sequential injection analysis manifold for extended automated monitoring applications by Thanh Duc Mai; Stefan Schmid; Beat Müller; Peter C. Hauser (pp. 1-6).

A capillary electrophoresis (CE) instrument with capacitively coupled contactless conductivity detection (C⁴D) based on a sequential injection analysis (SIA) manifold was refined. Hydrodynamic injection was implemented to avoid a sampling bias by using a split-injection device based on a needle valve for precise adjustment. For safety and reliability, the integrity of the high voltage compartment at the detection end was fully maintained by implementing flushing of the high voltage interface through the capillary. With this set-up, extended fully automated monitoring applications are possible. The system was successfully tested in the field for the determination of the concentration levels of major inorganic cations and anions in a creek over a period of 5 days.

Keywords: Sequential injection analysis; Capillary electrophoresis; Capacitively coupled contactless conductivity detection; Inorganic cations and anions

A microfluidic approach for anticancer drug analysis based on hydrogel encapsulated tumor cells by Dan Gao; Jiangjiang Liu; Hui-Bin Wei; Hai-Fang Li; Guang-Sheng Guo; Jin-Ming Lin (pp. 7-14).

A novel method based on fluorescence detection of hydrogel encapsulated cells in microchannels was developed for anticancer drug analysis. In this work, human hepatoma HepG2 cells and human lung epithelial A549 cells were simultaneously immobilized inside two different shapes of three-dimensional hydrogel microstructures using photolithography approach on a same array. Microarrays of living cells offer the potential for parallel detection of many cells and thereby enable high-throughput assays. Using a photolithographic setup, we investigated the prepolymer composition and crosslinking parameters that influenced cell viability inside photocrosslinked hydrogels. The viability of cells encapsulated inside hydrogel microstructures was higher than 90% under optimized photocrosslinking conditions. The cells were further cultured under stable conditions and remained viable for at least three days that were able to carry out cell-based assays. Furthermore, we studied the variation of two intracellular redox parameters (glutathione and reactive oxygen species) in anticancer drug-induced apoptosis in HepG2 and A549 cells. Two anticancer drugs exhibited distinct effects on the levels of intracellular glutathione and reactive oxygen species, indicating the selectivity of these drugs on the disturbance of redox balance within cells. The established platform provides a convenient and fast method for monitoring the effect of anticancer drugs on tumor cells, which is very useful for fundamental biomedical research.

Keywords: Microfluidic device; Hydrogel microstructures; Cell encapsulation; Anticancer drug

Review: Highlights in recent applications of electronic tongues in food analysis by Laura Escuder-Gilabert; Miguel Peris (pp. 15-25).

This paper examines the main features of modern electronic tongues (e-tongues) and their most important applications in food analysis in this new century. The components of an e-tongue (automatic sampler, array of chemical sensors, and data processing system) are described. Applications commented include process monitoring, freshness evaluation and shelf-life investigation, authenticity assessment, foodstuff recognition, quantitative analysis, and other quality control studies. Finally, some interesting remarks concerning the strengths and weaknesses of e-tongues in food analysis are also mentioned.

Keywords: Electronic tongue; Process monitoring; Freshness evaluation and shelf-life investigation; Authenticity assessment; Foodstuff recognition; Quantitative analysis

Disposable biosensors for determination of biogenic amines by M. Asunción Alonso-Lomillo; Olga Domínguez-Renedo; Patricia Matos; M. Julia Arcos-Martínez (pp. 26-31).

This work reports monoamine oxidase (MAO)/horseradish peroxidase (HRP) and diamine oxidase (DAO)/horseradish peroxidase (HRP) based biosensors using screen-printed carbon electrodes for the determination of biogenic amines (BA). The enzymes have been covalently immobilized onto the carbon working electrode, previously modified by an aryl diazonium salt, using hydroxysuccinimide and carbodiimide. The detection has been performed by measuring the cathodic current due to the reduction of the mediator hydroxymethylferrocene at a low potential, 250mV vs screen-printed Ag/AgCl reference electrode. The experimental conditions for the enzymes immobilization, as well as for the main variables that can influence the chronoamperometric current have been optimized by the experimental design methodology. Under these optimum conditions, the disposable biosensors have been characterized. A linear response range from 0.2 up to 1.6μM and from 0.4 to 2.4μM of histamine was obtained for DAO/HRP and MAO/HRP based biosensors, respectively. The biosensor construction was highly reproducible, yielding relative standard deviations of 10% and 11% in terms of sensitivity for DAO/HRP and MAO/HRP based biosensors, respectively. The capability of detection, 0.18±0.01μM in the case of DAO/HRP and 0.40±0.04μM ( α=0.05 and β=0.005) for MAO/HRP based biosensors, and the biosensor sensitivity towards different BA has also been analyzed. Finally, the developed biosensors have been applied to the determination of the total amine content in fish samples.

Keywords: Biogenic amines; Screen-printed electrodes; Diazonium salt; Biosensor

Electrochemiluminescence immunosensor for ultrasensitive detection of biomarker using Ru(bpy)₃²⁺-encapsulated silica nanosphere labels by Jing Qian; Zhenxian Zhou; Xiaodong Cao; Songqin Liu (pp. 32-38).

Here, we describe a new approach for electrochemiluminescence (ECL) assay with Ru(bpy)₃²⁺-encapsulated silica nanoparticle (SiO₂@Ru) as labels. A water-in-oil (W/O) microemulsion method was employed for one-pot synthesis of SiO₂@Ru nanoparticles. The as-synthesized SiO₂@Ru nanoparticles have a narrow size distribution, which allows reproducible loading of Ru(bpy)₃²⁺ inside the silica shell and of α-fetoprotein antibody (anti-AFP), a model antibody, on the silica surface with glutaraldehyde as linkage. The silica shell effectively prevents leakage of Ru(bpy)₃²⁺ into the aqueous solution due to strong electrostatic interaction between the positively charged Ru(bpy)₃²⁺ and the negatively charged surface of silica. The porous structure of silica shell allowed the ion to move easily through the pore to exchange energy/electrons with the entrapped Ru(bpy)₃²⁺. The as-synthesized SiO₂@Ru can be used as a label for ultrasensitive detection of biomarkers through a sandwiched immunoassay process. The calibration range of AFP concentration was 0.05–30ngmL⁻¹ with linear relation from 0.05 to 20ngmL⁻¹ and a detection limit of 0.035ngmL⁻¹ at 3 σ. The resulting immunosensors possess high sensitivity and good analytical performance.

Keywords: Ru(bpy); ₃; ²⁺; -encapsulated silica nanosphere labels; α-fetoprotein; Sandwich immunoassay; Electrochemiluminescence

Fluoride-selective polymeric membrane electrodes based on Zr(IV)- and Al(III)-salen ionophores of various structures by Łukasz Górski; Alexey Matusevich; Paweł Parzuchowski; Iwona Łuciuk; Elżbieta Malinowska (pp. 39-46).

Al(III)- and Zr(IV)-salophens of novel structures were tested as anion-selective ionophores. It was shown that these compounds are highly selective to fluoride and give selectivity greatly deviating from classical Hofmeister pattern, when doped into the polymeric membrane of ion-selective electrode (ISE). The following selectivity sequence has been recorded for both ionophores: F⁻>ClO₄⁻>SCN⁻>NO₃⁻≈Br⁻≈Cl⁻. The results of potentiometric and spectrophotometric measurements allow to conclude that the nature and structure of salophen ligands influence stability of ISE working parameters. An increase in salophen ligands lipophilicity results in prolongation of the ISE lifetime, most likely due to slower ionophore decomposition caused by the hydrolysis of imine bonds in salophen structure. Ion-selective electrodes (ISEs) with the most successful Al(III)-salophen exhibited a stable, fast and near-Nernstian fluoride response and a functional lifetime near 3 weeks and selectivity coefficients withlogKF−,Y−pot. as follows: −2.8 (Y⁻=Br⁻), −2.7 (Cl⁻), −2.8 (NO₃⁻), −1.5 (SCN⁻), −1.3 (ClO₄⁻), which is better than for other ones based on Zr(IV)- and Al(III)-salophens and salens described to date.

Keywords: Salophens; Fluoride ionophore; Ion-selective electrode; Potentiometry

Determination of malachite green residues in fish using molecularly imprinted solid-phase extraction followed by liquid chromatography–linear ion trap mass spectrometry by María Jesús Martínez Bueno; Sonia Herrera; Ana Uclés; Ana Agüera; María Dolores Hernando; Olga Shimelis; Marcus Rudolfsson; Amadeo R. Fernández-Alba (pp. 47-54).

This paper describes the development of an analytical procedure to determine malachite green (MG) residues in salmon samples using molecularly imprinted polymers (MIPs) as the extraction and clean-up material, followed by liquid chromatography–linear ion trap mass spectrometry (LC–QqQLIT-MS/MS). MG and two structurally related compounds, crystal violet (CV) and brilliant green (BG) were employed for the selectivity test. The imprinted polymers exhibited high binding affinity for MG, while CV and BG showed less binding capacity: 47% and 34%, respectively. The recovery values of MG in salmon samples fortified with leucomalachite green (LMG) were determined by measuring the amount of MG in the sample, after carrying out the oxidation reaction with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), which converts the LMG back into chromic-form. The average recovery of MG in spiked salmon muscle over the concentration range 1–100ngg⁻¹ was 98% with a relative standard deviation value (R.S.D.) below 12%. The method detection limits (MDLs) obtained for MG, CV, BG and their leuco-metabolites were in the range of 3–20ngkg⁻¹ (ppt).

Keywords: Molecularly imprinted polymers (MIPs); Malachite green; Crystal violet; Brilliant green; Leuco-metabolites; Fish; Liquid chromatography mass spectrometry (LC–MS)

Validation of method for determination of different classes of pesticides in aqueous samples by dispersive liquid–liquid microextraction with liquid chromatography–tandem mass spectrometric detection by Sergiane Souza Caldas; Fabiane Pinho Costa; Ednei Gilberto Primel (pp. 55-62).

In this study, a simple, rapid and efficient method has been developed for the extraction and preconcentration of different classes of pesticides, carbofuran (insecticide), clomazone (herbicide) and tebuconazole (fungicide) in aqueous samples by dispersive liquid–liquid microextraction (DLLME) coupled with liquid chromatography–tandem mass spectrometric detection. Some experimental parameters that influence the extraction efficiency, such as the type and volume of the disperser solvents and extraction solvents, extraction time, speed of centrifugation, pH and addition of salt were examined and optimized. Under the optimum conditions, the recoveries of pesticides in water at spiking levels between 0.02 and 2.0μgL⁻¹ ranged from 62.7% to 120.0%. The relative standard deviations varied between 1.9% and 9.1% ( n=3). The limits of quantification of the method considering a 50-fold preconcentration step were 0.02μgL⁻¹. The linearity of the method ranged from 1.0 to 1000μgL⁻¹ for all compounds, with correlation coefficients varying from 0.9982 to 0.9992. Results show that the method we propose can meet the requirements for the determination of pesticides in water samples. The comparison of this method with solid-phase extraction indicates that DLLME is a simple, fast, and low-cost method for the determination of pesticides in natural waters.

Keywords: Dispersive liquid–liquid microextraction; Pesticides; Liquid chromatography–tandem mass spectrometry; Sample preparation; Aqueous samples

Multiplex immunodetection of tumor markers with a suspension array built upon core–shell structured functional fluorescence-encoded microspheres by Yao Long; Zhiling Zhang; Xiaomei Yan; Jinchun Xing; Kaiyan Zhang; Jingxiong Huang; Jiaxin Zheng; Wei Li (pp. 63-68).

A new suspension array built upon laboratory-prepared functional fluorescence-encoded polystyrene beads (FFPBs) was developed for multiplex immunodetection of tumor markers. The FFPBs were synthesized by copolymerizing rhodamine 6G (R6G) and carboxyl function groups on the surface of the seed beads forming a core–shell structure. The fabrication process was facile and the encoding fluorescence intensity of the beads can be precisely controlled by adjusting the quantity of R6G. In present work, we demonstrated that the quantity variation of impregnated R6G had negligible effect on the coupling efficiency of biomolecules onto the surface of the FFPBs. The R6G encoding fluorescence remained good monodispersity upon capture probe coupling and immunocomplex formation. No fluorescence resonance energy transfer was observed between the R6G doped in the bead shell and fluorophore used for antibody labeling. Under the optimal conditions, the proposed suspension array allowed simultaneous detection of α-fetoprotein, carcinoembryonic antigen, and prostate specific antigen in the ranges of 0.07–500ngmL⁻¹, 1–2000ngmL⁻¹, and 0.5–500ngmL⁻¹, respectively, with detection limits of 0.0626ngmL⁻¹, 0.554ngmL⁻¹, and 0.250ngmL⁻¹. Test on clinical serum samples demonstrated that the results obtained with suspension array were in good agreement with those of the reference electrochemiluminescence immunoassay method. We conclude that the laboratory-made FFPBs are sufficient as the microcarrier for the construction of suspension array in clinical diagnosis.

Keywords: Polystyrene beads; Flow cytometry; Suspension array; Multiplex assay; Tumor marker detection

Flow injection method for the determination of silver concentration in drinking water for spacecrafts by Maria Concetta Bruzzoniti; Dorota Korte Kobylinska; Mladen Franko; Corrado Sarzanini (pp. 69-73).

A flow injection method has been developed for determination of silver. The method is based on a reduction reaction with sodium borohydride which leads to the formation of a colloidal species which is monitored at a wavelength of 390nm.The reaction variables flow rate, sodium borohydride concentration and pH, which affect sensitivity, were investigated and their effects were established using a two-levels, three-factor experimental design. Further optimization of manifold variables (reaction coil and injection volume) allowed us to determine silver in the range 0.050–5.0mgL⁻¹ with a minimum detectable concentration of 0.050mgL⁻¹. Silver is added, as biocide, to drinking water for spacecrafts. The chemical species of silver, present in this kind of sample, were characterized by a procedure based on the selective retention of Ag⁺ onto a 2.2.2. cryptand based substrate followed by determination of the non-bound and bound (after elution) Ag⁺ by the FIA method. The method optimized was applied to a drinking water sample provided for the launch with the Automated Transfer Vehicle (ATV) module Jule Verne to the International Space Station (March 9, 2008).

Keywords: Silver species; Flow analysis; Disinfection; Drinking water

Evaluation of chemiluminescence reagents for selective detection of reactive oxygen species by Shinya Yamaguchi; Naoya Kishikawa; Kaname Ohyama; Yoshihito Ohba; Maiko Kohno; Toshinobu Masuda; Akira Takadate; Kenichiro Nakashima; Naotaka Kuroda (pp. 74-78).

In order to evaluate the chemiluminescence (CL) reagents for selective detection of reactive oxygen species (ROS), we comprehensively measured the CL responses of 20 CL reagents (three luminol derivatives, two imidazopyrazinone derivatives, eight lophine derivatives, six acridinium ester derivatives and lucigenin) against six types of ROS (superoxide anion: O₂⁻, hydroxyl radical:OH, hydrogen peroxide: H₂O₂, hypochlorite anion: ClO⁻, singlet oxygen:¹O₂, and nitric oxide: NO). As a result of the screening, it was found that nine CL reagents selectively detected O₂⁻ while one CL reagent selectively detectedOH. However, no CL reagent had selectivity on the detection of H₂O₂, ClO⁻,¹O₂ and NO. Our screening results could help to select the most suitable CL reagent for selective determination of different ROS.As an application study, 4-methoxyphenyl-10-methylacridinium-9-carboxylate (MMAC), one of the acridinium ester derivatives, showed high selectivity on the detection of O₂⁻, and thus was applied to the assay of superoxide dismutase (SOD) activity. The dynamic range and detection limit of the developed CL assay were 0.1–10 and 0.06UmL⁻¹, respectively. Significant correlation ( r=0.997) was observed between the results by the CL assay using MMAC and the spectrophotometric assay using 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2 H-tetrazolium monosodium salt.

Keywords: Reactive oxygen species; Chemiluminescent probe; Screening; Acridinium ester; Superoxide dismutase

Detection of mutant p53 using field-effect transistor biosensor by Sang Hee Han; Sang Kyu Kim; Kyoungsook Park; So Yeon Yi; Hye-Jung Park; Hong-Kun Lyu; Moonil Kim; Bong Hyun Chung (pp. 79-83).

We assessed the abilities of wild p53 and mutant p53 proteins to interact with the consensus DNA-binding sequence using a MOSFET biosensor. This is the first report in which mutant p53 has been detected on the basis of DNA–protein interaction using a FET-type biosensor. In an effort to evaluate the performance of this protocol, we constructed the core domain of wild p53 and mutant p53 (R248W), which is DNA-binding-defective. After the immobilization of the cognate DNA to the sensing layer, wild p53 and mutant p53 were applied to the DNA-coated gate surface, and subsequently analyzed using a semiconductor analyzer. As a consequence, a significant up-shift in drain current was noted in response to wild p53, but not mutant p53, thereby indicating that sequence-specific DNA–protein interactions could be successfully monitored using a field-effect-based biosensor. These data also corresponded to the results obtained using surface plasmon resonance (SPR) measurements. Taken together, our results show that a FET-type biosensor might be promising for the monitoring of mutant p53 on the basis of its DNA-binding activity, providing us with very valuable insights into the monitoring for diseases, particularly those associated with DNA–protein binding events.

Keywords: Metal oxide semiconductor field-effect transistor; Biosensor; p53; Mutant p53; DNA-binding domain

Hapten synthesis and antibody production for the development of a melamine immunoassay by Hongtao Lei; Yudong Shen; Lijun Song; Jinyi Yang; Olivier P. Chevallier; Simon A. Haughey; Hong Wang; Yuanming Sun; Christopher T. Elliott (pp. 84-90).

The incorporation of melamine into food products is banned but its misuse has been widely reported in both animal feeds and food. The development of a rapid screening immunoassay for monitoring of the substance is an urgent requirement. Two haptens of melamine were synthesized by introducing spacer arms of different lengths and structures on the triazine ring of the analyte molecular structure. 6-Aminocaproic acid and 3-mercaptopropionic acid were reacted with 2-chloro-4,6-diamino-1,3,5-triazine (CAAT) to produce hapten 1 [3-(4,6-diamino-1,6-dihydro-1,3,5-triazin-2-ylamino) hexanoic acid] and hapten 2 [3-(4,6-diamino-1,6-dihydro-1,3,5-triazin-2-ylthio) propanoic acid], respectively. The molecular structures of the two haptens were identified by¹H nuclear magnetic resonance spectrometry, mass spectrometry and infrared spectrometry. An immunogen was prepared by coupling hapten 1 to bovine serum albumin (BSA). Two plate coating antigens were prepared by coupling both haptens to egg ovalbumin (OVA). A competitive indirect enzyme-linked immunosorbent assay (ciELISA) was developed to evaluate homogeneous and heterogeneous assay formats. The results showed that polyclonal antibodies with high titers were obtained, and the heterogeneous immunoassay format demonstrated a better performance with an IC₅₀ of 70.6ngmL⁻¹, a LOD of 2.6ngmL⁻¹ and a LOQ of 7.6ngmL⁻¹. Except for cyromazine, no obvious cross-reactivity to common compounds was found. The data showed that the hapten synthesis was successful and the resultant antisera could be used in an immunoassay for the rapid and sensitive detection of this banned chemical.

Keywords: Abbreviations; CAAT; 2-chloro-4,6-diamino-1,3,5-triazine; BSA; bovine serum albumin; DCC; dicyclohexylcarbodiimide; NHS; N-hydroxysuccinimide; TMB; 3,3′,5,5′-tetramethylbenzidine; DMF; dimethylformamide; TLC; thin-layer chromatography; PBS; phosphate-buffered saline; PBST; phosphate-buffered saline with TW-20; HRMS; high-resolution mass spectrometry; hapten 1; 3-(4,6-diamino-1,6-dihydro-1,3,5-triazin-2-ylamino) propanoic acid; hapten 2; 3-(4,6-diamino-1,6-dihydro-1,3,5-triazin-2-ylthio) propanoic acid; ELISA; enzyme-linked immunosorbent assay; iELISA; indirect ELISA; ciELISA; competitive indirect ELISA; CR; cross-reactivity; UV; ultraviolet spectrometry; IR; infrared spectrometry; NMR; nuclear magnetic resonanceMelamine; Hapten; Antibody; Enzyme-linked immunosorbent assay

Selective immobilization of double stranded DNA on a gold surface through threading intercalation of a naphthalene diimide having dithiolane moieties by Shinobu Sato; Akinori Hirano; Shigeori Takenaka (pp. 91-97).

Newly synthesized naphthalene diimide1 having two dithiolane moieties at its substituted termini bound to double stranded DNA by threading intercalation and the resulting complex was immobilized on the gold surface through a dithiolane–gold linkage as revealed by quartz crystal microbalance (QCM) experiments. DNA with 20-meric double stranded and 24-meric single stranded regions was indirectly immobilized on the gold electrode using this characteristic of1. Hybridization efficiency was 92%, a value higher than 50% for a thiolated oligonucleotide under identical conditions. When this electrode was subjected to hybridization with a 124-meric target DNA in the presence of ferrocenylnaphthalene diimide (FND) as an electrochemical hybridization indicator, a large current increase was observed deriving from FND bound in the double stranded region newly formed between the probe and target DNA.

Keywords: Naphthalene diimide; Dithiolane; Immobilization; Double stranded DNA; Quartz crystal microbalance; Electrochemical detection

An electrochemical immunosensor for carcinoembryonic antigen enhanced by self-assembled nanogold coatings on magnetic particles by Jianping Li; Huiling Gao; Zhiqiang Chen; Xiaoping Wei; Catherine F. Yang (pp. 98-104).

A quick and reproducible electrochemical-based immunosensor technique, using magnetic core/shell particles that are coated with self-assembled multilayer of nanogold, has been developed. Magnetic particles that are structured from Au/Fe₃O₄ core–shells were prepared and aminated after a reaction between gold and thiourea, and additional multilayered coatings of gold nanoparticles were assembled on the surface of the core/shell particles. The carcinoembryonic antibody (anti-CEA) was immobilized on the modified magnetic particles, which were then attached on the surface of solid paraffin carbon paste electrode (SPCE) by an external magnetic field. This is an assembly of a novel immuno biosensor for carcinoembryonic antigen (CEA). The sensitivity and response features of this immunoassay are significantly affected by the surface area and the biological compatibility of the multilayered nanogold. The linear range for the detection of CEA was from 0.005 to 50ngmL⁻¹ and the limit of detection (LOD) was 0.001ngmL⁻¹. The LOD is approximately 500 times more sensitive than that of the traditional enzyme-linked immunosorbent assay for CEA detection.

Keywords: Magnetic particles; Carcinoembryonic antigen; Gold nanoparticle; Immunoassay; Layered assembly

Corrigendum to “Simple and sensitive fluorimetric method for determination of environmental hormone bisphenol A based on its inhibitory effect on the redox reaction between peroxyl radical and rhodamine 6G” [Anal. Chim. Acta 585 (2007) 134–138] by Jing Fan; Huiqin Guo; Guoguang Liu; Pingan Peng (pp. 105-105).

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Analytica Chimica Acta (v.665, #1)