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Analytica Chimica Acta (v.699, #2)

Editorial Board (pp. i).

Investigation into the voltammetric behaviour and detection of selenium(IV) at metal electrodes in diverse electrolyte media by Valerio Beni; Gillian Collins; Damien W.M. Arrigan (pp. 127-133).

Display Omitted► Electroanalytical behaviour of selenium at gold and platinum electrodes. ► Sensitive detection of selenium(IV) based on a stripping voltammetry approach using underpotential deposition (UPD). ► Combination of UPD and stripping analysis is implemented at a microband electrode array. ► Enhanced sensitivity and lower detection limits achieved by use of the microband array.The voltammetric behaviour of selenium(IV) was studied at platinum and gold electrodes in sulphuric acid, perchloric acid and potassium chloride media as a basis for its voltammetric detection. The best voltammetric behaviour was recorded at gold electrodes with perchloric acid as the supporting electrolyte. The concomitant presence of metals, such as copper or lead, and of model biomolecules, such as bovine serum albumin, in the solution resulted in a deterioration of the electrochemical response for selenium(IV). Quantitative detection of selenium(IV) by square wave anodic stripping voltammetry at both a millimetre-sized gold disc electrode and a microband electrode array revealed linear responses to selenium concentration in the ranges 5–15μM and 0.1–10μM, respectively, with 60s preconcentration. The sensitivities were 6.4μAμM⁻¹cm⁻² and 100μAμM⁻¹cm⁻² at the disc and the microband array, respectively. The detection limit at the microband electrode array was 25nM, illustrating the potentiality of such microelectrodes for the development of mercury-free analytical methods for the trace detection of selenium(IV).

Keywords: Selenium; Gold electrode; Microelectrode array; Anodic stripping voltammetry

Analytical aspects of microRNA in diagnostics: A review by Mariàngels de Planell-Saguer; María Celina Rodicio (pp. 134-152).

Display Omitted► Altered expression of miRNAs in diseases. ► miRNA as feasible biomarkers. ► Determination of miRNA profiles in the provision of personalized treatments. ► Detection methods and applications of microRNAs as biomarkers. ► Advantages and limitations of the current methods for miRNA detection.MicroRNAs (miRNA) are short (∼22 nucleotides) non-coding RNA molecules that regulate gene expression at the post-transcriptional level. Their expression is specific to cells and tissues and is temporally regulated. miRNAs are known to be involved in developmental and physiological processes, and their dysregulation leads to development of diseases. Since their profiles reflect pathological processes, miRNAs have recently been proposed as being useful in diagnostics as biomarkers of the onset, prognosis and risk of diseases, as well as in the classification of different types of cancer. The establishment of miRNA profiles that are representative of diseases and the detection of different types and levels of miRNA in samples are therefore critical milestones in diagnostics. miRNAs can be detected in blood and body fluids as well as in tissues, thus making non-invasive collection of samples possible. For a method to be useful in diagnostics, it should be simple, inexpensive and highly sensitive. Here, we will review current methods of detecting miRNAs and indicate the advantages and disadvantages of each techniques. We will then summarize some of the clinical evidence for the potential application of miRNAs as biomarkers in diagnostics. We conclude providing some general perspectives on the use of miRNAs in clinical situations, including therapeutic applications.

Keywords: Abbreviations; AMI; acute myocardial infarction; FFPE; formalin fixed paraffin embedded; fM; femtomolar; ISH; in situ; hybridization; LNA; locked nucleic acid; mRNA; messenger RNA; miRNA; microRNA; PNA; peptide nucleic acid; qRT-PCR; quantitative real-time polymerase chain reaction; Rluc; Renilla luciferase; SERS; surface-enhanced Raman spectroscopy; SPR; surface plasmon resonance; SPRI; SPR imagingmiRNA; Detection methods; Biomarker; Disease diagnosis

An integrated experimental and analytical approach to the chemical state imaging of iron in brain gliomas using X-ray absorption near edge structure spectroscopy by Magdalena Szczerbowska-Boruchowska; Marek Lankosz; Mateusz Czyzycki; Dariusz Adamek (pp. 153-160).

The Fe XANES profiles for brain glioma tissue samples (g1–g3) in comparison with reference materials of Fe²⁺ and Fe³⁺ (a, b, c, d – the factors used in quantitative evaluation).Display Omitted► Fe X-ray absorption near-edge structure spectroscopy was used for human brain tumors. ► The determination of iron oxidation states was performed in thin cryo-sectioned tissues. ► We propose the external standard method as a useful way to quantitative evaluation in XANES imaging. ► Presence of microstructures where Fe²⁺ is dominant as well as those with a high abundance of the oxidized form of Fe was found. ► The content of the oxidized form of Fe is significantly higher in comparison with Fe²⁺.X-ray absorption near-edge structure spectroscopy is used for human neoplastic tissues in order to investigate distributions and chemical states of iron. The specimens used in this study were obtained intraoperatively from brain gliomas of different types and various grades of malignancy and from a control subject. An integrated experimental and analytical approach toward topographic and quantitative analysis in thin freeze-dried cryo-sections is presented. The full XANES spectra at the Fe absorption K edge show the presence of both chemical forms of Fe in the analyzed points of the tissues. The main goal of the work is the chemical state imaging of Fe in tissue areas. Topographic analysis of Fe speciation in the tissues investigated with the use of the XANES technique indicates the presence of microstructures where Fe²⁺ is dominant as well as those with a high abundance of the oxidized form of Fe. The quantitative analysis shows that for all cases the content of the oxidized form of Fe is significantly higher in comparison with Fe²⁺. The highest level of Fe³⁺ is found in the control sample, and the lowest one for the glioma of the highest grade of malignancy. The content of either Fe²⁺ or Fe³⁺ is increased in low grade gliomas in comparison to high-grade malignant tumors.

Keywords: Fe oxidation states; X-ray absorption near edge structure spectroscopy; Microimaging; Brain gliomas

Optimization of the determination of chemical oxygen demand in wastewaters by Alexandra M.E. Viana da Silva; Ricardo J.N. Bettencourt da Silva; M. Filomena G.F.C. Camões (pp. 161-169).

Variation of the percentage contribution, P_j, of the major uncertainty components, of the measurement expanded uncertainty ( U) and of the target measurement expanded uncertainty [ U_Tg(HS)] with the COD value.Display Omitted► Optimization of the determination of COD based on models of uncertainty components. ► Uncertainty propagation law and numerical Kragten method produced equivalent results. ► Uncertainty propagation law allowed optimizing sensitivity coefficient of variables. ► Strategies for uncertainty magnitude and cost reduction were developed. ► ISO6060:1989 standard is adequate for assessment of compliance with Directive 91/271/EEC.Chemical oxygen demand (COD) is one of the most relevant chemical parameters for the management of wastewater treatment facilities including the control of the quality of an effluent. The adequacy of decisions based on COD values relies on the quality of the measurements. Cost effective management of the minor sources of uncertainty can be applied to the analytical procedure without affecting measurement quality. This work presents a detailed assessment of the determination of COD values in wastewaters, according to ISO6060:1989 standard, which can support reduction of both measurement uncertainty and cost of analysis. This assessment includes the definition of the measurement traceability chain and the validation of the measurement procedure supported on sound and objective criteria. Detailed models of the measurement performance, including uncertainty, developed from the Differential Approach, were successfully validated by proficiency tests. The assumption of the measurement function linearity of the uncertainty propagation law was tested through the comparison with the numerical Kragten method. The gathered information supported the definition of strategies for measurement uncertainty or cost reduction. The developed models are available as , in an MS-Excel file, to be updated with the user's data.

Keywords: Abbreviations; BOD; biological oxygen demand; COD; chemical oxygen demand; CV; coefficient of variance; DL; determination limit; FAS; ferrous ammonium sulphate; MLOD; maximum admissible LOD; LOD; limit of detection; NKM; numerical Kragten method; PHP; potassium hydrogenophtalate; PDC; potassium dichromate; PV; parametric value for the monitoring of drinking water according to Directive 98/83/EC [19]; RELACRE; Portuguese Association of Accredited Laboratories; SD; standard deviation; Solution A; K; ₂; Cr; ₂; O; ₇; ≅; 0.04; mol; L; ⁻¹; , HgSO; ₄; ≅; 80.0; g; L; ⁻¹; , H; ₂; SO; ₄; ≅; 1.80; mol; L; ⁻¹; Solution B; AgSO; ₄; ≅; 10.0; g; L; ⁻¹; , H; ₂; SO; ₄; ≅; 17.4; mol; L; ⁻¹; Solution C; (NH; ₄; ); ₂; Fe(SO; ₄; ); ²; ·6H; ₂; O; ≅; 0.12; mol; L; ⁻¹; , H; ₂; SO; ₄; ≅; 0.360; mol; L; ⁻¹; Solution D; solution of PHP with a COD value of ≅500; mg; L; ⁻¹; Solution E; solution of PHP with a COD value of ≅30; mg; L; ⁻¹; TC; total carbon; TOC; total organic carbon; UPL; uncertainty propagation lawChemical oxygen demand; Wastewaters; Optimization; Validation; Uncertainty

Application of graphene for preconcentration and highly sensitive stripping voltammetric analysis of organophosphate pesticide by Shuo Wu; Xiaoqin Lan; Lijun Cui; Lihui Zhang; Shengyang Tao; Hainan Wang; Mei Han; Zhiguang Liu; Changgong Meng (pp. 170-176).

Display Omitted► An electrochemical sensor is fabricated based on β-CD dispersed graphene. ► The sensor could selectively detect organophosphate pesticide with high sensitivity. ► The β-CD dispersed graphene owns large adsorption capacity for MP and superconductivity. ► The β-CD dispersed graphene is superior to most of the porous sorbents ever known.Electrochemical reduced β-cyclodextrin dispersed graphene (β-CD-graphene) was developed as a sorbent for the preconcentration and electrochemical sensing of methyl parathion (MP), a representative nitroaromatic organophosphate pesticide with good redox activity. Benefited from the ultra-large surface area, large delocalized π-electron system and the superconductivity of β-CD-graphene, large amount of MP could be extracted on β-CD-graphene modified electrode via strong π–π interaction and exhibited fast accumulation and electron transfer rate. Combined with differential pulse voltammetric analysis, the sensor shows ultra-high sensitivity, good selectivity and fast response. The limit of detection of 0.05ppb is more than 10 times lower than those obtained from other sorbent based sensors. The method may open up a new possibility for the widespread use of electrochemical sensors for monitoring of ultra-trace OPs.

Keywords: Graphene; β-Cyclodextrin; Solid phase extraction; Differential pulse voltammetry; Methyl parathion

Investigation of DGT as a metal speciation tool in artificial human gastrointestinal fluids by Aurélie Pelfrêne; Christophe Waterlot; Francis Douay (pp. 177-186).

Display Omitted► DGT technique is a simple, effective and reliable tool for the investigation of TE speciation in digestive fluids. ► UBM, DGT and JESS program allowed to investigate the TE species available for transport across the intestinal epithelium. ► Evaluation of DGT as a metal speciation tool in human digestive fluids is novel and opens a wide field of practical research.This paper reports the results of an investigation on the performance of the diffusive gradient in thin film technique (DGT) as a speciation tool for trace elements (TEs) in artificial human gastrointestinal fluids. The validity of Cd, Pb, and Zn sampling by DGT in digestive fluids was checked. The TE bioaccessibility in highly contaminated soils was determined using the in vitro Unified Barge Method (UBM) test. DGT devices were deployed in the gastrointestinal solutions obtained after carrying out the UBM test. The computer speciation code JESS (Joint Expert Speciation System) was used to predict the metal speciation of Cd, Pb, and Zn. Combining the in vitro test with the DGT technique and JESS provided an approach to the TE species available for transport across the intestinal epithelium. The gastrointestinal absorption of ingested TE ranged from 8 to 30% for Cd, 0.6 to 11% for Pb, and 0.8 to 7% for Zn and was influenced by TE speciation. In this original approach, the DGT technique was found to be simple and reliable in the investigation of TE chemical speciation in digestive fluids. Extrapolation to the in vivo situation should be undertaken very cautiously and requires further investigation.

Keywords: Trace elements; Digestive fluids; Bioaccessibility; Diffusive gradient in thin film; Computer modeling; Absorption

Extraction tool and matrix effects on arsenic speciation analysis in cell lines by Lucy Yehiayan; Nellymar Membreno; Shannon Matulis; Lawrence H. Boise; Yong Cai (pp. 187-192).

Display Omitted► Sonication probe can be used efficiently to extract As species from cell lines with high recoveries (>92%). ► Water or PBS is the optimum solvents that prevent the decomposition of arsenicals upon storage. ► The stability of As–GSH complexes in cell extracts is highly dependent upon glutathione (GSH) concentration. ► Upon extraction, GSH concentration in cell lines decreases (diluted by PBS). Therefore, biological conditions (GSH concentration) should be mimicked to maintain the stability of DMA(GS) in the extracts.Arsenic glutathione (As–GSH) complexes have been suggested as possible metabolites in arsenic (As) metabolism. Extensive research has been performed on the toxicological and apoptotic effects of As, while few reports exist on its metabolism at the cellular level due to the analytical challenges. In this study, an efficient extraction method for arsenicals from cell lines was developed. Evaluation of extraction tools; vortex, ultrasonic bath and ultrasonic probe and solvents; water, chemicals (methanol and trifluoroacetic acid), and enzymes (pepsin, trypsin and protease) was performed. GSH effect on the stability of As–GSH complexes was studied. Arsenic metabolites in dimethylarsino glutathione (DMA(GS)) incubated multiple myeloma cell lines were identified following extraction. Intracellular GSH concentrations of myeloma cell lines were imitated in the extraction media and its corresponding effect on the stability and distribution of As metabolites was studied. An enhancement in both extraction recoveries and time efficiency with the use of the ultrasonic probe was observed. Higher stabilities for the As species in water, pepsin and trypsin were obtained. The presence of 0.5mM GSH in the extraction media (PBS, pH 7.4) could not stabilize the As–GSH complexes compared to the 5mM GSH, where high stabilization of the complexes was observed over a 5 day storage study. Finally, the speciation analysis of the DMA(GS) culture incubated cell lines in the presence or absence of GSH revealed the important role GSH plays in the preservation of DMA(GS) identity. Hence, caution is required during the extraction of arsenicals especially the As–GSH complexes, since their identification is highly dependent on GSH concentration.

Keywords: Arsenic speciation; Extraction; Glutathione; Liquid chromatography Inductively coupled mass spectrometry

Quantum dots assisted photocatalysis for the chemiluminometric determination of chemical oxygen demand using a single interface flow system by Cristina I.C. Silvestre; Christian Frigerio; João L.M. Santos; José L.F.C. Lima (pp. 193-197).

Display Omitted► A novel flow method for the determination of chemical oxygen demand is proposed. ► CdTe nanocrystals are irradiated with UV light to generate strong oxidizing species. ► Reactive species promote a fast catalytic degradation of organic matter. ► Luminol is used as a chemiluminescence probe for indirect COD assessment. ► A single interface flow system was implemented to automate the assays.A novel flow method for the determination of chemical oxygen demand (COD) is proposed in this work. It relies on the combination of a fully automated single interface flow system, an on-line UV photocatalytic unit and quantum dot (QD) nanotechnology. The developed approach takes advantage of CdTe nanocrystals capacity to generate strong oxidizing species upon irradiation with UV light, which fostered a fast catalytic degradation of the organic compounds. Luminol was used as a chemiluminescence (CL) probe for indirect COD assessment, since it is easily oxidized by the QD generated species yielding a strong CL emission that is quenched in the presence of the organic matter. The proposed methodology allowed the determination of COD concentrations between 1 and 35mgL⁻¹, with good precision (R.S.D.<1.1%, n=3) and a sampling frequency of about 33h⁻¹. The procedure was applied to the determination of COD in wastewater certified reference materials and the obtained results showed an excellent agreement with the certified values.

Keywords: Single interface flow analysis; Chemical oxygen demand; Quantum dots; UV photocatalysis; Chemiluminescence

Dicyanostilbene-derived two-photon fluorescence probe for lead ions in live cells and living tissues by Chibao Huang; Cairong Ding (pp. 198-205).

. Dicyanostilbene-derived two-photon fluorescence probe for lead ions in live cells is developed. The probe exhibits large two-photon absorption cross-section (1020GM), non cytotoxic effect, excellent photostability and good cell-permeability.Display Omitted► We developed a novel two-photon fluorescence probe for Pb²⁺, and an original Pb²⁺ ligand of bis[2-(2-aminophenylsulfanyls)ethyl]amine. ► The probe has small molecule size, large TP absorption cross-section (1020GM), noncytotoxic effect, long-wavelength emission at 609nm (adjacent to the ideal imaging visual window 650−900nm), large Stokes shift (209nm), excellent photostability, moderate water-solubility and good cell-permeability. ► The probe can selectively detect Pb²⁺ ions in live cells and living tissues at a depth of 120μm without interference from other metal ions and the membrane-bound probes. It is the first such bioimaging probe for Pb²⁺ in two-photon fluorescence probes.A novel two-photon fluorescence probe for Pb²⁺ derived from 4-methyl-2,5-dicyano-4′-amino stilbene as a two-photon fluorophore and bis[2-(2-aminophenylsulfanyls)ethyl]amine as a novel Pb²⁺ ligand was developed. The probe possesses small molecule size, large two-photon absorption cross-section (1020GM), noncytotoxic effect, long-wavelength emission at 609nm, large Stokes shift (209nm), excellent photostability, moderate water-solubility, good cell-permeability, and pH-insensitivity in the biologically relevant pH range. The probe can selectively detect Pb²⁺ ions in live cells and living tissues without interference from other metal ions and the membrane-bound probes, and its quenching constant (KSVTP) is 7.58×10⁵M⁻¹.

Keywords: Dicyanostilbene; Lead; Cell-imaging; Two-photon fluorescence probe

Multi-step surface functionalization of polyimide based evanescent wave photonic biosensors and application for DNA hybridization by Mach-Zehnder interferometer by Eva Melnik; Roman Bruck; Rainer Hainberger; Michael Lämmerhofer (pp. 206-215).

Display Omitted► We realize a biosensing platform for polyimide evanescent photonic wave sensors. ► We show that the surface functionalization via silanisation and biotinylation followed by streptavidin immobilization do not destroy or damage the thin polyimide film. ► A highly dense streptavidin layer enables the immobilisation of biotinylated ligands such as biotinylated ssDNA for the selective measurement of DNA hybridization.The process of surface functionalization involving silanization, biotinylation and streptavidin bonding as platform for biospecific ligand immobilization was optimized for thin film polyimide spin-coated silicon wafers, of which the polyimide film serves as a wave guiding layer in evanescent wave photonic biosensors. This type of optical sensors make great demands on the materials involved as well as on the layer properties, such as the optical quality, the layer thickness and the surface roughness. In this work we realized the binding of a 3-mercaptopropyl trimethoxysilane on an oxygen plasma activated polyimide surface followed by subsequent derivatization of the reactive thiol groups with maleimide-PEG₂-biotin and immobilization of streptavidin. The progress of the functionalization was monitored by using different fluorescence labels for optimization of the chemical derivatization steps. Further, X-ray photoelectron spectroscopy and atomic force microscopy were utilized for the characterization of the modified surface. These established analytical methods allowed to derive information like chemical composition of the surface, surface coverage with immobilized streptavidin, as well as parameters of the surface roughness. The proposed functionalization protocol furnished a surface density of 144fmolmm⁻² streptavidin with good reproducibility (13.9% RSD, n=10) and without inflicted damage to the surface. This surface modification was applied to polyimide based Mach-Zehnder interferometer sensors to realize a real-time measurement of streptavidin binding validating the functionality of the MZI biosensor. Subsequently, this streptavidin surface was employed to immobilize biotinylated single-stranded DNA and utilized for monitoring of selective DNA hybridization. These proved the usability of polyimide based evanescent photonic devices for biosensing application.

Keywords: Polyimide spin-coated silicon wafer; Surface modification; Biosensor; Biotin–streptavidin DNA hybridization; Mach-Zehnder interferometer

A new light emitting diode–light emitting diode portable carbon dioxide gas sensor based on an interchangeable membrane system for industrial applications by I.M. Pérez de Vargas-Sansalvador; C. Fay; T. Phelan; M.D. Fernández-Ramos; L.F. Capitán-Vallvey; D. Diamond; F. Benito-Lopez (pp. 216-222).

Display Omitted► We present a new, portable, low-power optical system for CO₂ detection (0–100%). ► It is based on a PEDD arrangement as a colorimetric detection system. ► The device is a versatile handheld instrument for industrial applications. ► It measures very low CO₂ concentrations, to below atmospheric value, and up to 1%. ► Faster response & recovery times than other similar CO₂ detection devices.A new system for CO₂ measurement (0–100%) based on a paired emitter–detector diode arrangement as a colorimetric detection system is described. Two different configurations were tested: configuration 1 (an opposite side configuration) where a secondary inner-filter effect accounts for CO₂ sensitivity. This configuration involves the absorption of the phosphorescence emitted from a CO₂-insensitive luminophore by an acid–base indicator and configuration 2 wherein the membrane containing the luminophore is removed, simplifying the sensing membrane that now only contains the acid–base indicator. In addition, two different instrumental configurations have been studied, using a paired emitter–detector diode system, consisting of two LEDs wherein one is used as the light source (emitter) and the other is used in reverse bias mode as the light detector. The first configuration uses a green LED as emitter and a red LED as detector, whereas in the second case two identical red LEDs are used as emitter and detector. The system was characterised in terms of sensitivity, dynamic response, reproducibility, stability and temperature influence. We found that configuration 2 presented a better CO₂ response in terms of sensitivity.

Keywords: Carbon dioxide sensor; Gas sensor; Optical sensor; Paired emitter detector–diode sensor; Portable instrumentation

A membrane-based immunosensor for the analysis of the herbicide isoproturon by Damian E.H. Baskeyfield; Frank Davis; Naresh Magan; Ibtisam E. Tothill (pp. 223-231).

Display Omitted► A membrane based immunosensor for the detection of the herbicide isoproturon was developed using screen-printed electrode. ► Two different amperometric systems, hydroquinone and o-phenylenediamine (OPD) mediation reduction were utilised and compared. ► A flow injection apparatus was also developed utilising the immunosensor and achieving a limit of detection for isoproturon (LLD₉₀) of 0.84ngmL⁻¹. ► The senor was validated using spiked extracted soil samples and isoproturon contaminated samples.A membrane based heterogeneous competitive enzyme-linked immunosorbent assay (ELISA) was used in this work to develop an immunosensor for the detection of a common herbicide, isoproturon. A screen-printed carbon working electrode with carbon counter and silver–silver chloride pseudo-reference electrode was utilized incorporating a membrane fixed into intimate contact with the working electrode to facilitate signal transduction. The membrane containing an immobilized isoproturon–ovalbumin conjugate was laminated onto the carbon working electrode and horseradish peroxidase (HRP) labeled polyclonal antibody was then applied for the competitive assay. Two different amperometric systems, hydroquinone and o-phenylenediamine (OPD) mediation reduction were utilised and the properties of the resultant sensors were compared. A flow injection apparatus was also developed utilising the immunosensor. Limits of detection for isoproturon (LLD₉₀) were found to be as low as 0.84ngmL⁻¹. The senor was also validated using spiked extracted soil samples and also isoproturon contaminated samples.

Keywords: Immunosensor; Isoproturon; Herbicides; Soil analysis

Label-free capacitive immunosensors for ultra-trace detection based on the increase of immobilized antibodies on silver nanoparticles by Supaporn Dawan; Proespichaya Kanatharana; Booncharoen Wongkittisuksa; Warakorn Limbut; Apon Numnuam; Chusak Limsakul; Panote Thavarungkul (pp. 232-241).

Display Omitted► Label-free capacitive detection at ultra-trace level was achieved using electrode modified with nanoparticles. ► There is an optimal amount of AgNPs that provided the highest immobilization yield. ► AgNPs can enhance the sensitivity and LOD of the immunosensors. ► LOD can be reduced by 2 and 1 orders of magnitude for large and small molecules. ► Under the same conditions AuNPs and AgNPs provided the same performance.Detection of ultra-trace amounts of antigens by label-free capacitive immunosensors was investigated using electrodes modified with silver nanoparticles (AgNPs) that allows for an increase in the amount of immobilized antibodies. The optimal amount of AgNPs that provided the highest immobilization yield was 48pmol (in 2.0mL). The performances of immunosensor electrodes for human serum albumin prepared with AgNPs, were compared to electrodes prepared with gold nanoparticles. The two systems provided the same linear range (1.0×10⁻¹⁸ to 1.0×10⁻¹⁰M) and detection limit (1.0×10⁻¹⁸M). The system with AgNPs was used to analyze albumin in urine samples and the results agreed well with the immunoturbidimetric assay ( P>0.05). Electrodes modified with AgNPs and appropriate antibodies were tested for their performances to detect analytes of different sizes. For a macromolecule (human serum albumin) the incorporation of AgNPs improved the detection limit from 100 to 1aM. For small molecules, microcystin-LR and penicillin G, the detection limits were lowered from 100 and 10fM to 10 and 0.7fM, respectively. The high sensitivity and very low detection limits are potentially useful for the analysis of toxins or residues present in samples at ultra-trace levels and this method could easily be applied to other affinity pairs.

Keywords: Capacitance; Label-free biosensor; Small molecule; Macromolecule; Nano material; High sensitivity

Analysis of urinary neurotransmitters by capillary electrophoresis: Sensitivity enhancement using field-amplified sample injection and molecular imprinted polymer solid phase extraction by Bérengère Claude; Reine Nehmé; Philippe Morin (pp. 242-248).

Display Omitted► Field-amplified sample injection (FASI) improves the sensitivity of capillary electrophoresis through the online pre-concentration samples. ► The cationic analytes are stacked at the capillary inlet between a zone of low conductivity - sample and pre-injection plug - and a zone of high conductivity - running buffer. ► The limits of quantification are 500 times lower than those obtained with hydrodynamic injection. ► The presence of salts in the matrix greatly reduces the sensitivity of the FASI/CE–UV method.Capillary electrophoresis (CE) has been investigated for the analysis of some neurotransmitters, dopamine (DA), 3-methoxytyramine (3-MT) and serotonin (5-hydroxytryptamine, 5-HT) at nanomolar concentrations in urine. Field-amplified sample injection (FASI) has been used to improve the sensitivity through the online pre-concentration samples. The cationic analytes were stacked at the capillary inlet between a zone of low conductivity - sample and pre-injection plug - and a zone of high conductivity - running buffer. Several FASI parameters have been optimized (ionic strength of the running buffer, concentration of the sample protonation agent, composition of the sample solvent and nature of the pre-injection plug). Best results were obtained using H₃PO₄–LiOH (pH 4, ionic strength of 80mmolL⁻¹) as running buffer, 100μmolL⁻¹ of H₃PO₄ in methanol–water 90/10 (v/v) as sample solvent and 100μmolL⁻¹ of H₃PO₄ in water for the pre-injection plug.In these conditions, the linearity was verified in the 50–300nmolL⁻¹ concentration range for DA, 3-MT and 5-HT with a determination coefficient ( r²) higher than 0.99. The limits of quantification (10nmolL⁻¹ for DA and 3-MT, 5.9nmolL⁻¹ for 5-HT) were 500 times lower than those obtained with hydrodynamic injection. However, if this method is applied to the analysis of neurotransmitters in urine, the presence of salts in the matrix greatly reduces the sensitivity of the FASI/CE–UV method.Therefore, a solid phase extraction (SPE) on a dedicated imprinted polymer (MIP) was developed to extract specific neurotransmitters, catecholamines, metanephrines and indolamines, from urine. Matrix salts were thus discarded after sample extraction on AFFINIMIP™ Catecholamine & Metanephrine (100mg) cartridge.Therefore, lower limits of quantification were determined in artificial urine (46nmolL⁻¹ for DA, 11nmolL⁻¹ for 3-MT and 6nmolL⁻¹ for 5-HT).The application of this protocol MIP-SPE/FASI–CE–UV analysis of neurotransmitters in human urine gave rise to electropherograms with a very good base line and signal to noise ratios above 15.

Keywords: Neurotransmitters; Capillary electrophoresis; Field-amplified sample injection; Molecular imprinted polymer; Solid phase extraction; Urine

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Analytica Chimica Acta (v.699, #2)