Analytical and Bioanalytical Chemistry (v.385, #3)

Young German chemist wins ABC Best Paper Award by Christina E. Dyllick (401-402).

European Analytical Column No. 34 (January 2006) by Bo Karlberg; Ernst-Heiner Korte (406-407).

Cell trapping in microfluidic chips by Robert M. Johann (408-412).

Hair analysis: an excellent tool for confirmation of drug abuse by Mitsuhiro Wada; Kenichiro Nakashima (413-415).

Charge-transfer reactions at liquid/liquid interfaces and their applications in bioassays by Ping Jing; Shali He; Zhongwei Liang; Yuanhua Shao (428-432).

Transport across artificial membranes–an analytical perspective by Andreas Janshoff; Claudia Steinem (433-451).
Biosensors that make use of transport processes across lipid membranes are very rare even though a stimulus, the binding of a single analyte molecule, can enhance the sensor response manifold if the analyte leads to the transport of more than one ion or molecule across the membrane. Prerequisite for a proper function of such membrane based biosensors is the formation of lipid bilayers attached to a support that allow for the insertion of membrane peptides and proteins in a functional manner. In this review, the current state of the art technologies to obtain lipid membranes on various supports are described. Solid supported membranes on transparent and electrically conducting surfaces, lipid bilayers on micromachined apertures and on porous materials are discussed. The focus lies on the applicability of such membranes for the investigation of transport phenomena across lipid bilayers facilitated by membrane embedded peptides, channel proteins and transporters. Carriers and channel forming peptides, which are easy to handle and rather robust, are used frequently to build up membrane based biosensors. However, channel forming proteins and transporters are more difficult to insert functionally and thus, there are yet only few examples that demonstrate the applicability of such systems as biosensor devices.
Keywords: Solid-supported membranes; BLMs; Impedance spectroscopy; Channel-forming peptides; Channel proteins; Transporters

Biosensors based on carbon nanotubes by Kannan Balasubramanian; Marko Burghard (452-468).
Carbon nanotubes (CNTs) exhibit a unique combination of excellent mechanical, electrical and electrochemical properties, which has stimulated increasing interest in the application of CNTs as components in (bio)sensors. This review highlights various design methodologies for CNT-based biosensors and their employment for the detection of a number of biomolecules. In addition, recent developments in the fields of CNT-based chemiresistors and chemically sensitive field-effect transistors are presented. After a critical discussion of the factors that currently limit the practical use of CNT-based biosensors, the review concludes with an outline of potential future applications for CNTs in biology and medicine.
Keywords: Carbon nanotubes; Enzymatic biosensors; Electrochemical biosensors; Amperometric detection; DNA sensing; Chemiresistors

All presently used batteries contain reactive, corrosive or toxic components and require strong cases, usually made of steel. As a battery is miniaturized, the required case dominates its size. Hence, the smallest manufactured batteries are about 50 mm3 in size, much larger then the integrated circuits or sensors of functional analytical packages, as exemplified by implantable glucose sensors for diabetes management. The status of the miniaturization of the power sources of such implantable packages is reviewed. Three microcells, consisting only of potentially harmless subcutaneously implantable anodes and cathodes, are considered. Because their electrolyte would be the subcutaneous interstitial fluid, the cells do not have a case. One potentially implantable cell has a miniature Nafion-coated Zn anode and a biocompatible hydrogel-shielded Ag/AgCl cathode. The core innovation on which the cell is based is the growth of a hopeite-phase Zn2+ conducting solid electrolyte film on the discharging anode. The film blocks the transport of O2 to the Zn, preventing its corrosion, while allowing the necessary transport of Zn2+. The second cell, with the same anode, would have a bioinert hydrogel-shielded wired bilirubin oxidase-coated carbon cathode, on which O2 dissolved in the subcutaneous fluid would be electroreduced to water. In the third cell, the glucose of the subcutaneous interstitial would be electrooxidized to gluconolactone at an implanted wired glucose anode, similar to that tested now for continuous glucose monitoring in diabetic people, and O2 in the subcutaneous fluid would be electroreduced to water on its wired bilirubin oxidase cathode.
Keywords: Battery; Fuel cell; Miniaturization; Implantable; Subcutaneous; Zn-anode

Electroporation of cells in microfluidic devices: a review by M. B. Fox; D. C. Esveld; A. Valero; R. Luttge; H. C. Mastwijk; P. V. Bartels; A. van den Berg; R. M. Boom (474-485).
In recent years, several publications on microfluidic devices have focused on the process of electroporation, which results in the poration of the biological cell membrane. The devices involved are designed for cell analysis, transfection or pasteurization. The high electric field strengths needed are induced by placing the electrodes in close proximity or by creating a constriction between the electrodes, which focuses the electric field. Detection is usually achieved through fluorescent labeling or by measuring impedance. So far, most of these devices have only concerned themselves solely with the electroporation process, but integration with separation and detection processes is expected in the near future. In particular, single-cell content analysis is expected to add further value to the concept of the microfluidic chip. Furthermore, if advanced pulse schemes are employed, such microdevices can also enhance research into intracellular electroporation.
Keywords: Electroporation; Microtechnology; Microfluidics; PEF

Over the last few decades, mass spectrometry has become a powerful tool for exploring various aspects of molecular processes occurring in biological systems. Such exploration is leading to a greater understanding of various complex life processes; unraveling these processes poses the greatest challenge to contemporary bioscience. With due respect to sample preparation, data analysis is rapidly becoming a major obstacle to the conversion of experimental knowledge into valid conclusions. It is interesting to note that many problems related to mass spectrometry can be solved using techniques from computer science, graph theory and discrete mathematics. The aim of this manuscript is to recollect several essays that demonstrate the power and the need to apply such skills to mass spectrometry data interpretation. Special attention is paid to situations where traditional chemical analysis reaches its limits but mathematical reasoning can still allow us to reach valid conclusions.
Keywords: Mass spectrometry; Elemental speciation; Proteomics; Data analysis and visualization; Mathematical methods

Microarray formats have become an important tool for parallel (or multiplexed) monitoring of biomolecular interactions. Surface-immobilized probes like oligonucleotides, cDNA, proteins, or antibodies can be used for the screening of their complementary targets, covering different applications like gene or protein expression profiling, analysis of point mutations, or immunodiagnostics. Numerous reviews have appeared on this topic in recent years, documenting the intriguing progress of these miniaturized assay formats. Most of them highlight all aspects of microarray preparation, surface chemistry, and patterning, and try to give a systematic survey of the different kinds of applications of this new technique. This review places the emphasis on optical technologies for microarray analysis. As the fluorescent read out of microarrays is dominating the field, this topic will be the focus of the review. Basic principles of labeling and signal amplification techniques will be introduced. Recent developments in total internal reflection fluorescence, resonance energy transfer assays, and time-resolved imaging are addressed, as well as non-fluorescent imaging methods. Finally, some label-free detection modes are discussed, such as surface plasmon microscopy or ellipsometry, since these are particularly interesting for microarray development and quality control purposes.
Keywords: DNA microarrays; Protein microarrays; Imaging; Fluorescent labels; Signal amplification

FloDots: luminescent nanoparticles by Gang Yao; Lin Wang; Yanrong Wu; Josh Smith; Jinsheng Xu; Wenjun Zhao; Eunjung Lee; Weihong Tan (518-524).
Luminescent dye-doped silica nanoparticles (FloDots) have been developed for ultrasensitive bioanalysis and diagnosis in the past several years. Those novel nanoparticles are highly luminescent and extremely photostable. In this paper, we review the preparation, characterization, bioconjugation and bioapplication of FloDots. All the results clearly demonstrated that FloDots have many advantages over currently used luminescent probes, such as traditional fluorophores and quantum dots.
Keywords: Dye-doped silica nanoparticles; Nanotechnology; Bioanalysis

Environmental analysis based on luminescence in organized supramolecular systems by J. J. Santana Rodríguez; R. Halko; J. R. Betancort Rodríguez; J. J. Aaron (525-545).
The use of organized supramolecular systems—including micellar media and cyclodextrin inclusion complexes—combined with luminescence techniques in the study and determination of compounds and elements of environmental interest from 1990 to 2005 is reviewed. Analyses of environmental samples performed using fluorescence, photochemically induced fluorescence and phosphorescence spectroscopy as well as liquid chromatography, capillary electrophoresis and flow injection with luminescence detection in the presence of these organized media are described in detail.
Keywords: Micellar media; Cyclodextrins; Fluorescence; Phosphorescence; Separation methods; Environmental analysis

Applications of the luminol chemiluminescent reaction in analytical chemistry by Christophe A. Marquette; Loïc J. Blum (546-554).
This critical review discusses the results published between 2000 and 2005 on the development of analytical systems based on the luminol chemiluminescent and electrochemiluminescent reactions. An increasing number of non-specific detection systems based on the enhancing, inhibiting or catalysing effect of a large range of compounds have been published. Possible detected compounds and their concomitant presence in samples are discussed. Chemiluminescent and electrochemiluminescent reactions were also found to merge in biochip and microarray development as a possible substitute to the well-established but hardly quantitative fluorescent detections.
Keywords: Biochip; Chemiluminescence; FIA; Luminol; Microarray

The analytical methodology for speciation of metals and metalloids associated with alkyl groups and biomacromolecules is critically reviewed. Alkylated metals and metalloids are not only known to be produced by microbial methylation within most anaerobic compartments in the environment, but also in the course of enzymatic transformations during human metabolism. Because of the toxicological relevance of these compounds present in trace to ultratrace concentrations, firm species identification and exact quantification are essential. While many instrumental techniques coupling chromatography (GC, HPLC, CE, GE) with plasma mass spectrometry (ICP-MS) are available for quantification, methods used for structural identification often suffer from inadequate sensitivity (EI-MS, ESI-MS, MALDI-MS, FT-ICRMS). Other problems encountered are sample derivatisation artefacts, lack of suitable standards for quantification, lack of equilibrium between spikes and sample, and the integrity of metal–protein association during separation, in particular during SDS-PAGE. Selected application examples with respect to mercury and arsenic speciation will be discussed critically.
Keywords: Elemental speciation; Hyphenated instrumental techniques; Organometallic compounds; Alkylated metal(loid)s; Metalloproteins; Biomethylation

The concept of constant emission yield in GDOES by Arne Bengtson; Thomas Nelis (568-585).
This review paper describes the evolution of the quantification procedure for compositional depth profiling (CDP) in glow discharge optical emission spectrometry (GD-OES), based on the constant emission yield concept. The concept of emission yield (EY) is defined and ways of measuring it experimentally are discussed. The history of the development of quantitative CDP is reviewed, which shows that all of the different approaches depend on the assumption that the EY is essentially a matrix-independent quantity. Particular emphasis is placed on the dependence of the EY on the plasma parameters of current, voltage, power and pressure. In short, impedance changes (current voltage) can significantly affect the emission yield and should either be corrected mathematically or the impedance should be kept constant by pressure regulation in order to obtain reliable results from GDOES CDP. On the other hand, the effect of varying the pressure on the emission yield can be considered to be minor within the limits of practical operating conditions for most CDP applications. It is worth, however, bearing in mind that varying the discharge pressure has a significant effect on the plasma processes, and does affect the emission yield when these variations are large. The experimental results obtained for the emission yield are related to the results from theoretical model calculations published on the subject.
Keywords: Glow discharge optical emission spectroscopy; Emission yield; Compositional depth profiling

Two new HPTLC methods for quantification of isopropyl-9H-thioxanthen-9-one (ITX) in milk, yoghurt and fat samples have been developed. Extraction of ITX from milk and yoghurt was performed with a mixture of cyclohexane and ethyl acetate by employment of accelerated solvent extraction (ASE). For soy bean oil and margarine, a simple partitioning of ITX into acetonitrile was used. ITX and 2,4-diethyl-9H-thioxanthen-9-one (DTX) used as internal standard have been separated on silica gel 60 HPTLC plates with a mixture of toluene and n-hexane (4:1, v/v) and on RP18 HPTLC plates with a mixture of acetonitrile and water (9:1, v/v). Development was performed anti-parallel from both plate sides leading to a throughput of 36 separations in 7 min. Fluorescence measurement at 254/>400 nm was used for quantification. Limits of detection (S/N of 3) have been established to be 64 pg for ITX and DTX on both types of HPTLC plates. In fatty matrix (spiked butter) LOD of ITX was determined to be 1 μg kg−1. In the working range monitored (20–200 μg kg−1) polynomial regression of ITX showed a relative standard deviation (sdv) of ±1.51 % (r=0.99981). Starting with the limit of quantification the response was linear (sdv=±2.18 %, r=0.99893). Regarding repeatability (n=9) a coefficient of variation (CV) of 1.1 % was obtained for ITX at 32 ng on silica gel plates and of 2.9 % on reversed-phase plates. Repeatabilities (n=4) of ITX determination at 20, 50 and 100 μg kg−1 in milk, yoghurt, soybean oil and margarine showed CVs between ±1.0 and 6.4 %. The results prove that modern planar chromatography is a rapid and cost-efficient alternative method to quantify ITX in milk-based or fatty matrices. Only positive results are confirmed by online ESI/MS in the SIM mode (LOQ 128 pg) and by DART/MS involving a minimal employment of the MS device, which is a further advantage of HPTLC. Overall mean recovery rates of ITX at 20 or 50 and 100 μg kg−1 (n=8) were 41 % for milk, 70 % for yoghurt, 6 % for margarine and 12 % for soy bean oil. However, with the internal standard correction recoveries were about 130 % for milk and yoghurt and 70 and 97 % for margarine and soy bean oil, respectively.
Keywords: Planar chromatography; Isopropyl-9H-thioxanthen-9-one (ITX); 2,4-Diethyl-9H-thioxanthen-9-one (DTX); HPTLC-ESI/MS; HPTLC-DART/MS

Integration of microcolumns and microfluidic fractionators on multitasking centrifugal microfluidic platforms for the analysis of biomolecules by Elizabeth A. Moschou; Adrianne D. Nicholson; Guangyao Jia; Jim V. Zoval; Marc J. Madou; Leonidas G. Bachas; Sylvia Daunert (596-605).
This work demonstrates the development of microfluidic compact discs (CDs) for protein purification and fractionation integrating a series of microfluidic features, such as microreservoirs, microchannels, and microfluidic fractionators. The CDs were fabricated with polydimethylsiloxane (PDMS), and each device contained multiple identical microfluidic patterns. Each pattern employed a microfluidic fractionation feature with operation that was based on the redirection of fluid into an isolation chamber as a result of an overflow. This feature offers the advantage of automated operation without the need for any external manipulation, which is independent of the size and the charge of the fractionated molecules. The performance of the microfluidic fractionator was evaluated by its integration into a protein purification microfluidic architecture. The microfluidic architecture employed a microchamber that accommodated a monolithic microcolumn, the fractionator, and an isolation chamber, which was also utilized for the optical detection of the purified protein. The monolithic microcolumn was polymerized “in situ” on the CD from a monolith precursor solution by microwave-initiated polymerization. This technique enabled the fast, efficient, and simultaneous polymerization of monoliths on disposable CD microfluidic platforms. The design of the CD employed allows the integration of various processes on a single microfluidic device, including protein purification, fractionation, isolation, and detection.
Keywords: Microfluidic; Compact disk; Microwave-polymerized monolithic microcolumns; Biomolecules; Lab-on-a-chip

Pyochelin is a siderophore and virulence factor common to Burkholderia cepacia and several Pseudomonas strains. It is isolated from bacterial media as a mixture of two epimers, which readily equilibrate in most solvents. Experiments based on high-performance liquid chromatography/electrospray ionization mass spectrometry are reported here, allowing the investigation of the different Fe(III)-chelating properties of pyochelin diastereomers in solution without the need for labourious isolation. It is demonstrated in this study that only one of the two pyochelin diastereomers is able to chelate Fe(III); no Fe(III) complexes of the other diastereomer could be detected. The Fe(III)–pyochelin complex exhibited a 1:1 metal-to-siderophore ratio and no evidence for other stoichiometries was found.
Keywords: Pyochelin; Pseudomonas siderophore; Iron complex; Electrospray ionization; Liquid chromatography/mass spectrometry

Development of a new standard reference material: SRM 1955 (homocysteine and folate in human serum) by Mary B. Satterfield; Lorna T. Sniegoski; Katherine E. Sharpless; Michael J. Welch; Adriana Hornikova; Nien-Fan Zhang; Christine M. Pfeiffer; Zia Fazili; Mindy Zhang; Bryant C. Nelson (612-622).
Total homocysteine (tHCY) and folate are interrelated biomarkers for arteriosclerosis and coronary heart disease. Although many different methods for both tHCY and folate are clinically available, the intermethod and interlaboratory results are often poor, resulting in the need for a matrix reference material and reference methods. The National Institute of Standards and Technology (NIST) has developed isotope dilution liquid chromatography/mass spectrometry (LC/MS) and liquid chromatography/ tandem mass spectrometry (LC/MS/MS) methods for determination of tHCY and several folate forms including 5-methyltetrahydrofolic acid (5MT) and folic acid (FA). Additionally, a method for simultaneous measurement of tHCY, 5MT, and FA has been developed and validated. In collaboration with the Centers for Disease Control and Prevention (CDC), mass spectrometric methods and methods used in clinical laboratories have been applied to characterize a new Standard Reference Material (SRM), SRM 1955, “Homocysteine and Folate in Human Serum,” containing low, medium, and high levels of tHCY and 5MT. Additionally, FA, 5-formyltetrahydrofolic acid (5FT), vitamin B12, and total folate values are provided. Use of the new SRM should improve clinical measurements and will permit traceability to internationally recognized certified reference materials, as described by European Directive 98/79/EC on in vitro diagnostic medical devices.
Keywords: Isotope dilution mass spectrometry; Standard reference material; Homocysteine; Folate; 5-Methyltetrahydrofolic acid; 5-Formyltetrahydrofolic acid; Folic acid

Two wastewater treatment plants (WWTPs) of northern Colorado were monitored for anhydroerythromycin and tylosin. An analytical method has been developed and validated for the trace determination and confirmation of these compounds in the raw influent and final effluent water matrices. This method was used to evaluate the occurrence and fate of these compounds in WWTPs. The method uses solid-phase extraction and liquid chromatography–tandem mass spectrometry with positive electrospray ionization. Detection and quantification was performed using selected reaction monitoring, and a method detection limit of between 0.01 and 0.06 μg/L was obtained. Unequivocal confirmation analysis of analyte identity according to the criteria (based on the use of identification points) of the 2002/657/EC European Commission Decision was possible with satisfactory results. Average recoveries for the two compounds ranged from 89.2±9.7% for raw influent to 93.7±6.9% for effluent wastewaters. The within-run precision of the assay was found to be always less than 14.1% for the two analytes. The overall precision was always less than 13.7%. The relative uncertainty of the present assay was also evaluated and the combined relative uncertainty ranged from 6.4 to 15.5% over three days of the validation study. These compounds were partially removed in the WWTPs with a removal efficiency of >50%. The measured concentrations in raw influents and effluents ranged from 0.09–0.35 and 0.04–0.12 μg/L for anhydroerythromycin to 0.06–0.18 and ND–0.06 μg/L for tylosin, respectively. The results indicate that WWTP effluents are relevant point sources for residues of these compounds in the aquatic environment. These occurrence results were compared with those in WWTP wastewaters of other countries.
Keywords: Antibiotics; Macrolides; Wastewater; WWTPs; Environmental fate

A headspace solid-phase microextraction gas chromatography coupled with tandem mass spectrometry (HSSPME-GC-MS-MS) methodology for determination of brominated flame retardants in sediment and soil samples is presented. To the best of our knowledge, this is the first time that SPME has been applied to analyze polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers (PBDEs) in environmental solid samples. Analyses were performed using 0.5-g solid samples moisturized with 2 mL water, employing a polydimethylsiloxane (PDMS) fiber coating, exposed to the headspace at 100 °C for 60 min. Several types of environmental solid samples were included in this study and the extraction efficiency was related to the organic matter content of the sample. Calibration was performed using real samples, and the method showed good linearity over a wide concentration range, precision, and afforded quantitative recoveries. The obtained detection limits were in the sub-ng g−1 for all the target analytes in both samples. The proposed procedure was applied to several marine and river sediments and soils, some of which were found to contain PBDEs at concentrations in the ng g−1 level; BDE-47, BDE-100, and BDE-99 were the major congeners detected. The proposed method constitutes a rapid and low-cost alternative for the analysis of the target brominated flame retardants in environmental solid samples, since the clean-up steps, fractionation, and preconcentration of extracts inherent to the classical multi-step solvent extraction procedures are avoided.
Keywords: SPME; Headspace analysis; Brominated flame retardants; PBDEs; PBBs; Sediment; Soil; Environmental analysis; GC-MS-MS

The performance of twelve laboratories with previously established proficiency in the determination of the mineral oil content in a fresh water sediment is described. The summation parameter total petrol hydrocarbon (TPH) is defined according to ISO 16703:2004 with regard to the sample preparation to be applied, the flame ionisation detection (FID) and the boiling range of C10–C40 to be integrated. Comprehensive tests of homogeneity and stability have been carried out on the candidate material using appropriate models. The outcome of the study served as the basis for the certification of the candidate reference material as ERM-CC015a. The certified mass fraction is 1,820±130mgkg−1and traceability was established by using an appropriate calibration standard certified for the mass fraction of C10–C40. The interlaboratory scatter of measurement results in this exercise can largely be explained by the variability of the individual calibrations based on this common calibration standard.
Keywords: Total petroleum hydrocarbons; Extraction; Gas chromatography; Calibration; Interlaboratory study

The in vivo and in vitro effects of Cd2+ and the CYP1A inductor β-naphthoflavone(β-NF) on the hepatic cytochrome P450 (Cyt 450) monooxygenases were studied in silver carp (Hypophthalmichtys molitrix V.), wels (Silurus glanis L.), and carp (Cyprinus carpio). In vivo treatment of carp with a high dose of Cd2+ (10 mg kg−1, for 3 days) caused a strong inhibition of 7-ethoxyresorufin-O-deethylase (EROD) and a lower inhibition of 7-ethoxycoumarin-O-deethylase (ECOD) activity. The low-dose cadmium treatment (2 mg kg−1 Cd2+, for 6+3 days) resulted in 4-fold increase in EROD and a 3-fold increase in ECOD activity. The combined treatment with Cd2+ and β-NF in both cases led to a loss of EROD inducibility. The silver carp and wels were treated with 10 mg L−1 Cd2+ for 72 h in water. The Cyt P450 content in the wels liver microsomes was increased significantly after treatment for 48 h, whereas there was only a slight, not significant increase in Cyt P450 content in the silver carp microsomes. While the Cd2+ treatment resulted in inhibition of the CYP1A isoenzymes (EROD and ECOD), the APND (aminopyrene-N-demethylase, CYP2B or CYP3A isoenzyme) activity was increased 3- to 4-fold in both fish species. In vitro experiments of the effect of Cd2+ led to a concentration-dependent inhibition in all three investigated fish species. The ECOD isoenzyme of silver carp was the most sensitive to Cd2+. The lowest concentration of Cd2+ resulted in 50% inhibition. The APND isoenzyme was similarly sensitive to Cd2+ in all three investigated fish species. The most sensitive species was the wels, and the least sensitive were the carp isoenzyme. FTIR spectroscopy confirmed that cadmium caused damage to the protein structure. These results support the enzyme activity measurements measured in vivo and in vitro.
Keywords: Cytochrome P450; Monooxygenases; Cd2+ acetate; Freshwater fish; IR spectroscopy