Volume 76, Issue 4

In this review, the results of the electrochemical investigations made on the transfer of ionizable drugs at the interface between two immiscible electrolyte solutions (ITIES) in the last decade have been presented. In many of the studies, cyclic voltammetry has been used to investigate the transfer characteristics of the charged species and deduce their partition coefficients, which are very important parameters to infer the lipophilicity of drugs in biological systems. The electrochemical technique allows the precise determination of the distribution of ionic species between two phases in a wider pH range. Such studies point out the complexity of the distribution of ionizable compounds and offer a new approach to relate the structure of such compounds to their passive transport across biological membranes.

The use of liquid membrane-based extractions is increasingly seen as offering an alternative to conventional sample preparation procedures in analysis of chemical species in both environmental and biological media. In this article, emphasis is placed on the attractiveness of liquid membrane-based extraction techniques to a variety of analytical applications such as speciation of metal ions in biological fluids, time-weighted average field sampling, and time-weighted average passive field sampling. Further, the area of designing new and much simpler miniaturized configurations, which is enjoying much attention in liquid membrane-based extraction techniques, is discussed.

Biosensors can be excellent analytical tools for monitoring programs working to implement legislation. In this article, biosensors for environmental analysis and monitoring are extensively reviewed. Examples of biosensors for the most important families of envi-ronmental pollutants, including some commercial devices, are presented. Finally, future trends in biosensor development are discussed. In this context, bioelectronics, nanotechnology, miniaturization, and especially biotechnology seem to be growing areas that will have a marked influence on the development of new biosensing strategies in the next future.

In electrochemical sensing devices, aimed for acute and chronic in vivo application, the active surface of the sensor is often negligible compared to the overall surface area of the device in contact with the biological host. Consequently, to minimize the perturbation of an implanted sensor on the in vivo environment the chemical composition and surface texturing of the complete device (the active sensor, sensor substrate, and “accessories”) have to be considered. In our work, the adsorption of three abundant proteins (albumin, IgG, and fibrinogen) was determined quantitatively on untreated and modified sensor substrates and sensing membrane surfaces. In this study, a flexible polyimide-based material (Kapton ®) was used as sensor substrate with or without an amorphous diamond-like carbon (DLC) or an amorphous oxygen-containing DLC (o-DLC) coating. The ion-sensitive membranes were cast from high-molecular-weight (HMW) or carboxylated poly(vinyl chloride) (PVC) and were doped with increasing concentrations of highly hydrophilic poly(ethylene oxide) (PEO). The potentiometric characteristics of the potassium-selective membranes cast with up to 6 % PEO were the same as those without PEO. However, the PEO-modified PVC membranes elicited a large amount of protein adsorption, especially in terms of albumin.

The search for an enzyme as a reagent for selective bioanalytical detection of the neurotoxic amino acid, β-N-oxalyl L-alpha, β-diaminopropionic acid, β-ODAP (found in grass pea, Lathyrus sativus) led to its redox catalytic reaction by glutamate oxidase (GluOx). Homogeneous kinetic studies and an immobilized GluOx reactor-based flow-injection assay were initially made for beta-ODAP with small immobilized GluOx/catalase glutamate destroying prereactors. The method was applied to examine the toxin content in processed grass pea. The kinetics and the equilibrium of the thermal isomerization of β-ODAP to the nontoxic isomer α-ODAP established that GluOx is specific to the neurotoxin. The first ever GluOx-based amperometric biosensor for liquid chromatography (LC) detection was reported in 1997. This biosensor coupled with a refractive index detector improved LC performance. The most recent work with GluOx resulted in MnO 2 -based screen-printed amperometric biosensor, with offline elimination of glutamate interference by glutamate decarboxylase. A single-shot chemiluminescent sensor developed for hydrogen peroxide is also proposed for β-ODAP with GluOx application. This decade of progress resulted from studies that included four Ph.D. (Ethiopia, Sweden, Austria), four M.Sc. (Ethiopia, Sweden) and Licentiate (Sweden) theses projects, plus one collaborative project in Sweden. The advances in grass pea research may be regarded as a model north–south cooperation for research and education.

Recently,a significant amount of work has focused on metal binding by natural systems for various applications. This review will focus on the utility of amino acids, short peptides, and proteins that have been immobilized onto solid supports for use in metal binding. These systems include single amino acids, poly-amino acids, and peptides immobilized onto supports such as silica, polymer resins, and membranes. Also included are the studies involving the use of immobilized amino acids in ion-exchange chromatography.

Electrosynthetic poly(phenol) nanofilms were deposited in situ on platinum electrodes in the presence and absence of glucose oxidase. The synthesis charges and currents of the nonconducting polymer films were recorded at various applied potentials for films grown from 25 –100 mM phenol concentrations. Film parameters such as the standard rate constant for film deposition, film thickness, and surface concentration of the poly(phenol) films were evaluated from the cyclic and step voltammograms of the polymerization process. A novel electron-transfer mediator consisting of monosubstituted 4-hydroxycyclobut-3-ene-1,2-dione (squarate) was used as a mediator for Pt/poly(phenol) nanofilm/GOx amperometric glucose biosensors. Amperometric responses for 3-diphenylamino-4-hydroxycyclobut-3-ene-1,2-dione (diphenylaminosquarate: E°'=of +328 mV/Ag-AgCl at pH 7.0)-mediated systems were measured by both steady-state amperometric and cyclic voltammetry. The sensor sensitivity was calculated to be 558 nA cm −2 (µM) −1 .

Biosorption is a relatively new process that has proven very promising in the removal of contaminants from aqueous effluents. Microorganisms as well as plant- and animal-derived materials have been used as biosorbents by many researchers. Biomaterial immobilization and chemical modification improves the adsorption capacity and stability of biosorbents. Biosorption experiments over Cu(II), Cd(II), Pb(II), Cr(III), and Ni(II) demonstrated that biomass Cu(II) adsorption ranged from 8.09 to 45.9 mg g −1 , while Cd(II) and Cr(VI) adsorption ranged from 0.4 to 10.8 mg g−1 and from 1.47 to 119 mg g −1 , respectively. Mechanisms involved in the biosorption process include chemisorption, complexation, surface and pore adsorption-complexation, ion exchange, microprecipitation, hydroxide condensation onto the biosurface, and surface adsorption. Chemical modification and spectroscopic studies have shown that cellular components including carboxyl, hydroxyl, sulfate, sulfhydryl, phosphate, amino, amide, imine, and imidazol moieties have metal binding properties and are therefore the functional groups in the biomass. Column studies using support matrices for biomass immobilization such as silica, agar, polyacrilamide, polysulfone, alginates, cellulase, and different cross-linking agents have been performed to improve the biomass adsorption capacity and reusability. In this review, the salient features of plant-derived materials are highlighted as potential phytofiltration sources in the recovery of toxic heavy and precious metals.

Myoglobin (horse heart, Mb) adsorbed on carbon electrodes or in solution at platinum electrodes was used for electrocatalytic reduction of trans -1,2-dibromocyclohexane (DBCH) and trichloroacetic acid (TCA) in a bicontinuous microemulsion, prepared from sodium didodecyl sulfate (SDS) or hexadecyltrimethylammonium bromide (CTAB), tetradecane, pentanol, and water. Carbon electrodes (glassy carbon, GC, and pyrolytic graphite, PG) exhibited adsorption peaks, whereas platinum (Pt) portrayed diffusion-controlled peaks. Electrode reduction of Mb had E 0 ' at −0.179 ± 0.013 V at GC/SDS, −0.189 ± 0.015 at GC/CTAB, and −0.562 ± 0.018 at Pt/SDS and 0.611 ± 0.008 at Pt/CTAB media.Current efficiencies for electrocatalytic reduction of TCA were higher than that for reduction of dibromocyclohexane. For both substrates, dibromocyclohexane and trichhloroacetic acid, a lowering of overpotential of at least 1.3 V was achieved. Overall, the Pt electrode exhibited higher catalytic efficiencies compared to carbon electrodes, suggesting higher surface concentration and unhindered orientation of the substrate on the Pt electrode. For DBCH, catalytic efficiencies decreased with scan rate, at carbon electrodes as expected for homogeneous solutions, whereas an average value of 2.22 ± 0.42 in SDS and 3.29 ± 0.76 in CTAB microemulsion was obtained at Pt electrodes at a scan rate range of 15 to 3000 mVs−1. Pseudo-first-order rate constants ( k ') for the rate-determining step (rds) involving reaction of organohalides with catalyst had an average value of 41 ±1 M −1 s −1 for reduction of DBCH/SDS and 4.8 ± 1.0 ×10 2 M −1 s −1 for reduction of TCA/SDS. Moreover, rate constants were higher in CTAB microemulsion, giving values of 1.5 ±0.016 ×10 2 and 2.75 ±0.67 × 10 3 M −1 s −1 for DBCH and TCA, respectively. Positive interfacial charge of the microemulsion conduits influenced catalytic reaction of catalyst and the substrate. Under the conditions of the experiment, no hydrogen evolution was observed at Pt electrodes.

Proteomics studies rely on high-resolving separation techniques whereby the biological complexity can be unraveled. Both gel-based and liquid-phase separation principles are needed in order to mine deeper into the low abundant area of the proteins expressed in human cell samples. The expression levels that can be reached today with proteomics technology are still only reaching part of all proteins present in complex biological samples. The challenge to be met is not an easy task and will, in many aspects, be determined by the speed and success whereby the analytical field can make milestone progress. Examples will be given from our research group on proteomics studies, as well as principles and challenges within this research area.

Potentiometric detection in high-performance liquid chromatography (HPLC) is shown to be an underexploited technique. The technique can be of great use to less classical potentiometry targets, such as bioorganics, of low as well as of high molecular weight. The understanding of non-faradaic potentiometry is, however, still problematic. Predicting the selectivity and sensitivity of a potentiometric electrode for organic ionizable substances can be done to a certain extent using QSAR methods. Although many new polymer materials and synthetic receptor molecules for organic ionics are being synthesized, few of them are applied in potentiometric membrane coatings. Hydrophilic organics form an interesting target group for these new materials.

Biomining is currently used successfully for the commercial-scale recovery of metals such as copper, cobalt, and gold from their ores. The mechanism of metal extraction is mainly chemistry-driven and is due to the action of a combination of ferric and hydrogen ions, depending on the type of mineral. These ions are produced by the activity of chemolithotrophic microorganisms that use either iron or sulfur as their energy source and grow in highly acidic conditions. Therefore, metal extraction is a combination of chemistry and microbiology. The mixture of organisms present may vary between processes and is highly dependent on the temperature at which mineral oxidation takes place. In general, relatively low-efficiency dump and heap irrigation processes are used for base metal recovery, while the biooxidation of difficult-to-treat gold-bearing arsenopyrite concentrates is carried out in highly aerated stirred-tank reactors. Bioleaching reactions, the debate as to whether the reactions are direct or indirect, the role of microorganisms, and the types of processes by which metals are extracted from their ores are described. In addition, some new processes under development and the challenges that they present are discussed.

Biochemical sensors have emerged as a dynamic technique for qualitative and quantitative analysis of different analytes in clinical diagnosis, environmental monitoring, and food and process control. The need for a low-cost, reliable, ultra-sensitive, and rapid sensor continues to grow as the complexity of application areas increases. New biosensing techniques are emerging due to the need for shorter sample preparation protocols. Such novel biosensor designs make field and bed-site clinical testing simpler with substantial decrease in costs per sample throughputs. In this paper, we will review the recent trends and challenges in clinical and environmental biosensors. The review will focus on immunological, nucleic acid, and cell-based clinical and biological sensors. Special emphasis will be placed on the approaches used for immobilization or biological reagents and low-cost electrochemical biosensors. The promising biosensors for rapid diagnosis of cancer or HIV are also discussed.

A method for the in situ modification of hollow fiber membranes used as sampling units for microdialysis probes is presented. The method consists of adsorption-coating, high molecular-weight poly(ethylene imine), PEI, onto membranes, already fitted on microdialysis probes. Modification of membranes was designed to specifically explore the so-called Andrade effects and thus enhance the interaction of membranes with enzyme. The performances of polysulfone, polyethersulfone, and polyamide membranes modified with PEI-enzyme complex were evaluated based on the membrane extraction fraction for maltose and maltotriose and membrane morphology as examined by scanning electron microscopy. Of the membranes tested, the PEI-enzyme complex least affected the performance of the polysulfone membranes. Conversion of maltoheptaose to maltotriose and maltose was increased reproducibly (within a 5 % relative standard deviation) by 50 % for modified membranes compared to the native hollow fiber membranes. The results demonstrate the potential to effectively modify membranes already fitted on a microdialysis probe. Such a procedure can be modified and employed to either promote or reduce membrane–protein interaction for hollow fibers used as microdialysis sampling units or other similar membrane applications.

The document defines the terms most commonly encountered in the field of polymer reactions and functional polymers. The scope has been limited to terms that are specific to polymer systems. The document is organized into three sections. The first defines the terms relating to reactions of polymers. Names of individual chemical reactions are omitted from the document, even in cases where the reactions are important in the field of polymer reactions. The second section defines the terms relating to polymer reactants and reactive polymeric materials. The third section defines the terms describing functional polymeric materials.