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Analytica Chimica Acta (v.748, #)

Editorial Board (pp. iii).

Preparation of molecularly imprinted polymers for organophosphates and their application to the recognition of organophosphorus compounds and phosphopeptides by Jun Haginaka; Hiromi Tabo; Hisami Matsunaga (pp. 1-8).

Display Omitted► Monodisperse MIPs for organophosphates by multi-step swelling and polymerization. ► Application of MIPs to the separation of adenosine phosphates. ► Application of MIPs to the trapping of phosphopeptides in tryptic protein-digests.Monodisperse molecularly imprinted polymers (MIPs) for diphenyl phosphate (DPP) and 1-naphthyl phosphate (1-NapP) have been prepared by a multi-step swelling and polymerization method using 4-vinylpyridine as a functional monomer, glycerol dimethacrylate as a crosslinker and cyclohexanol or 1-hexanol as a porogen. The retention and molecular-recognition properties of these MIPs for organophosphorus compounds were evaluated by HPLC using a mixture of phosphate buffer and acetonitrile as an eluent. In addition to shape recognition, hydrogen bonding and hydrophobic interactions could play an important role in the retention and molecular recognition of DPP and 1-NapP. Furthermore, the MIPs were applied to the separation of adenosine and adenosine phosphates (AMP, ADP and ATP). These phosphates were retained on the MIPs according to the number of phosphate groups in the molecule and were well separated from one another. Hydrogen bonding and hydrophobic interactions seemed to affect the retention and recognition of adenosine phosphates in low acetonitrile content, while hydrophilic interactions affected these properties in high acetonitrile content. Finally, the MIPs were applied to the trapping of phosphopeptides. The MIPs non-selectively trapped phosphopeptides, which have phosphorylated tyrosine, serine or threonine in the sequences, and successfully trapped four phosphopeptides in tryptic digests of bovine α-casein.

Keywords: Molecularly imprinted polymer; Multi-step swelling and polymerization; Diphenyl phosphate; Organophosphorus compound; Phosphopeptide

Application of semi-permeable membrane dialysis/ion trap mass spectrometry technique to determine polybrominated diphenyl ethers and polychlorinated biphenyls in milk fat by Marek Roszko; Małgorzata Rzepkowska; Arkadiusz Szterk; Krystyna Szymczyk; Renata Jędrzejczak; Marcin Bryła (pp. 9-19).

Display Omitted► We have investigated the usefulness of SPM dialysis for determination of PCB/PBDE. ► The factors affecting the dialysis process were evaluated. ► The ion trap MS was optimized for determination of PCB/PBDE in milk fat. ► Described extraction/clean up method proves usefulness for the milk fat analysis.Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are hazardous food contaminants, their maximum legally allowable levels in food and environment are in the low pgg⁻¹ range. Therefore some highly selective and sensitive analytical methods must be used to determine them. The 96/23/EC Directive implemented by EC Decision of 12 August 2002 requires recovery rate of an analyte at a concentration below 1ngg⁻¹ within the 50–120% range at relative standard deviation (RSD) as low as possible.A method to determine low level PCBs and PBDEs in milk fat based on the semi-permeable membrane dialysis/ion trap GC MS technique was developed. Validation experiments proved that the method performance was within bounds set by the currently standing UE regulations. Recovery rates calculated on the basis of labeled internal standards for majority of the studied indicator PCB congeners and PBDE congeners were close to 100% at RSD below 20%. Also, dioxin-like PCBs recovery rates were compatible with the 1883/2006 EC Regulation (80–120%, RSD below 15%).The developed method turned out to be linear within a far broader concentration range than the studied 0.0025–10pgμL⁻¹ range entirely sufficient for analyses of PCB and PBDE in milk fat. Within that range coefficient of linear correlation ( R²) of calibration curves exceeded 0.98.

Keywords: Polychlorinated biphenyl; Polybrominated diphenyl ether; Ion trap mass spectrometry; Semi-permeable membrane dialysis

Determination of eight fluoroquinolones in groundwater samples with ultrasound-assisted ionic liquid dispersive liquid–liquid microextraction prior to high-performance liquid chromatography and fluorescence detection by M.M. Parrilla Vázquez; P. Parrilla Vázquez; M. Martínez Galera; M.D. Gil García (pp. 20-27).

Display Omitted► A novel method by US-IL-DLLME-LC-FD for fluoroquinolones determination. ► Simple, rapid and efficient method for water samples. ► Advantages over conventional methods. ► Low detection limits.An ultrasound-assisted ionic liquid dispersive liquid–liquid microextraction (US-IL-DLLME) procedure was developed for the extraction of eight fluoroquinolones (marbofloxacin, norfloxacin, ciprofloxacin, lomefloxacin, danofloxacin, enrofloxacin, oxolinic acid and nalidixic acid) in groundwater, using high-performance liquid chromatography with fluorescence detection (HPLC-FD). The ultrasound-assisted process was applied to accelerate the formation of the fine cloudy solution using a small volume of disperser solvent (0.4mL of methanol), which increased the extraction efficiency and reduced the equilibrium time.For the DLLME procedure, the IL 1-octyl-3-methylimidazolium hexafluorophosphate ([C₈MIM] [PF₆]) and methanol (MeOH) were used as extraction and disperser solvent, respectively. By comparing [C₈MIM] [PF₆] with 1-hexyl-3-methylimidazolium hexafluorophosphate ([C₆MIM] [PF₆]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄MIM] [PF₆]) as extraction solvents, it was observed that when using [C₈MIM] [PF₆] the cloudy solution was formed more readily than when using [C₆MIM] [PF₆] or [C₄MIM] [PF₆]. The factors affecting the extraction efficiency, such as the type and volume of ionic liquid, type and volume of disperser solvent, cooling in ice-water, sonication time, centrifuging time, sample pH and ionic strength, were optimised.A slight increase in the recoveries of fluoroquinolones was observed when an ice-water bath extraction step was included in the analytical procedure (85–107%) compared to those obtained without this step (83–96%).Under the optimum conditions, linearity of the method was observed over the range 10–300ngL⁻¹ with correlation coefficient >0.9981. The proposed method has been found to have excellent sensitivity with limit of detection between 0.8 and 13ngL⁻¹ and precision with relative standard deviation values between 4.8 and 9.4% (RSD, n=5). Good enrichment factors (122–205) and recoveries (85–107%) were obtained for the extraction of the target analytes in groundwater samples.This simple and economic method has been successfully applied to analyse real groundwater samples with satisfactory results.

Keywords: Fluoroquinolones; Ionic liquid; DLLME; Water; LC-FD

A new HPLC-DAD-MS/MS method for the simultaneous determination of major compounds in the crude extract of Lychnophora salicifolia Mart. (Brazilian arnicão) leaves: Application to chemical variability evaluation by Dayana Rubio Gouvea; Fernando Meloni; Arthur de Barros Bello Ribeiro; João Luis Callegari Lopes; Norberto Peporine Lopes (pp. 28-36).

Statistical analysis revealed that there is a correlation between geographical localization of Lychnophora salicifolia samples and polar metabolites profile for specimens collected from different locations.Display Omitted► A new HPLC-DAD-MS method for analysis of the crude extract of L. salicifolia leaves. ► Twenty substances were identified. ► Ninety-three wild specimens were analyzed. ► A correlation between geographic isolation and decrease of the chemical similarity. ► The pattern of metabolites depends on the geographical distribution of the specimens. Lychnophora salicifolia Mart., which occurs in the Brazilian Cerrado in the states of Bahia and Minas Gerais as well as in the southeast of the state of Goiás, is the most widely distributed and also the most polymorphic species of the genus. This plant is popularly known to have anti-inflammatory and analgesic activities. In this work, we have studied the variation in terms of polar metabolites of ninety-three Lychnophora salicifolia Mart. specimens collected from different regions of the Brazilian Cerrado. Identification of the constituents of this mixture was carried out by analysis of the UV spectra and MS data after chromatographic separation. Twenty substances were identified, including chlorogenic acid derivatives, a flavonoid C-glucoside, and other sesquiterpenes. The analytical method was validated, and the reliability and credibility of the results was ensured for the purposes of this study. The concentration range required for analysis of content variability within the analyzed group of specimens was covered with appropriate values of limits of detection and quantitation, as well as satisfactory precision and recovery. A quantitative variability was observed among specimens collected from the same location, but on average they were similar from a chemical viewpoint. In relation to the study involving specimens from different locations, there were both qualitative and quantitative differences among plants collected from different regions of Brazil. Statistical analysis revealed that there is a correlation between geographical localization and polar metabolites profile for specimens collected from different locations. This is evidence that the pattern of metabolites concentration depends on the geographical distribution of the specimens.

Keywords: Lychnophora salicifolia; Asteraceae; Chemical variability; HPLC-DAD-MS/MS

Characterizing uranium oxide reference particles for isotopic abundances and uranium mass by single particle isotope dilution mass spectrometry by M. Kraiem; S. Richter; N. Erdmann; H. Kühn; M. Hedberg; Y. Aregbe (pp. 37-44).

Display Omitted► A method to quantify the U mass in single micron particles by ID-TIMS was developed. ► Well-characterized monodisperse U-oxide particles produced by an aerosol generator were used. ► A linear correlation between the mass of U and the volume of particle(s) was found. ► The method developed is suitable for determining the amount of U in a particulate reference material.Uranium and plutonium particulate test materials are becoming increasingly important as the reliability of measurement results has to be demonstrated to regulatory bodies responsible for maintaining effective nuclear safeguards. In order to address this issue, the Institute for Reference Materials and Measurements (IRMM) in collaboration with the Institute for Transuranium Elements (ITU) has initiated a study to investigate the feasibility of preparing and characterizing a uranium particle reference material for nuclear safeguards, which is finally certified for isotopic abundances and for the uranium mass per particle. Such control particles are specifically required to evaluate responses of instruments based on mass spectrometric detection (e.g. SIMS, TIMS, LA-ICPMS) and to help ensuring the reliability and comparability of measurement results worldwide. In this paper, a methodology is described which allows quantifying the uranium mass in single micron particles by isotope dilution thermal ionization mass spectrometry (ID-TIMS). This methodology is characterized by substantial improvements recently achieved at IRMM in terms of sensitivity and measurement accuracy in the field of uranium particle analysis by TIMS. The use of monodisperse uranium oxide particles prepared using an aerosol generation technique developed at ITU, which is capable of producing particles of well-characterized size and isotopic composition was exploited. The evidence of a straightforward correlation between the particle volume and the mass of uranium was demonstrated in this study. Experimental results have shown that the uranium mass per particle can be measured via the ID-TIMS method to a relative expanded uncertainty of about 10% (coverage factor k=2). The availability of reliable and validated methods for the characterization of uranium particles is considered to be essential for the establishment of SI-traceable measurement results. It is therefore expected that the method developed in this study is valuable for the certification of particulate materials in which the isotopic composition and the content of uranium must be accurately known.

Keywords: Reference material; Single particle; Uranium mass; Isotope dilution; TIMS

A mass spectrometric method to determine activities of enzymes involved in polyamine catabolism by Shunsuke Moriya; Kaori Iwasaki; Keijiro Samejima; Koichi Takao; Kohfuku Kohda; Kyoko Hiramatsu; Masao Kawakita (pp. 45-52).

Display Omitted► Compounds in polyamine catabolic pathway were determined by a column-free ESI-TOF MS. ► N¹- and N⁸-acetylspermidine were determined by a column-free ESI-MS/MS. ► The method was applied to determine activities of APAO, SMO, and SSAT in the pathway. ► The assay method contained stable isotope-labeled natural substrates. ► It is applicable to biological samples containing natural substrate and product.An analytical method for the determination of three polyamines (putrescine, spermidine, and spermine) and five acetylpolyamines [N¹-acetylspermidine (N¹AcSpd), N⁸-acetylspermidine (N⁸AcSpd), N¹-acetylspermine, N¹,N⁸-diacetylspermidine, and N¹,N¹²-diacetylspermine] involved in the polyamine catabolic pathway has been developed using a hybrid tandem mass spectrometer. Heptafluorobutyryl (HFB) derivatives of these compounds and respective internal standards labeled with stable isotopes were analyzed simultaneously by TOF MS, based on peak areas appearing at appropriate m/z values. The isomers, N¹AcSpd and N⁸AcSpd were determined from their fragment ions, the acetylamidopropyl and acetylamidobutyl groups, respectively, using MS/MS with¹³C₂-N¹AcSpd and¹³C₂-N⁸AcSpd which have the¹³C₂-acetyl group as an internal standard. The TOF MS method was successfully applied to measure the activity of enzymes involved in polyamine catabolic pathways, namely N¹-acetylpolyamine oxidase (APAO), spermine oxidase (SMO), and spermidine/spermine N¹-acetyltransferase (SSAT). The following natural substrates and products labeled with stable isotopes considering the application to biological samples were identified; for APAO, [4,9,12-¹⁵N₃]-N¹-acetylspermine and [1,4,8-¹⁵N₃]spermidine (¹⁵N₃-Spd), respectively; for SMO, [1,4,8,12-¹⁵N₄]spermine and¹⁵N₃-Spd, respectively; and for SSAT,¹⁵N₃-Spd and [1,4,8-¹⁵N₃]-N¹-acetylspermidine, respectively.

Keywords: Abbreviations; SSAT; spermidine/spermine N; ¹; -acetyltransferase; APAO; N; ¹; -acetylpolyamine oxidase; SMO; spermine oxidase; N; ¹; AcSpd; N; ¹; -acetylspermidine; N; ⁸; AcSpd; N; ⁸; -acetylspermidine; N; ¹; AcSpm; N; ¹; -acetylspermine; DiAcSpd; N; ¹; ,N; ⁸; -diacetylspermidine; DiAcSpm; N; ¹; ,N; ¹²; -diacetylspermine; AcSpd; a mixture of N; ¹; AcSpd and N; ⁸; AcSpd; ¹⁵; N; ₂; -Put; [1,4-; ¹⁵; N; ₂; ]putrescine; ¹³; C; ₂; ,; ¹⁵; N; ₂; -Put; [1,4-; ¹³; C; ₂; ,1,4-; ¹⁵; N; ₂; ]putrescine; ¹⁵; N; ₃; -Spd; [1,4,8-; ¹⁵; N; ₃; ]spermidine; ¹⁵; N; ₂; ,D; ₄; -Spd; N-(3-aminopropyl)-1,4-; ¹⁵; N; ₂; -butanediamine-1,1,4,4-d; ₄; ¹⁵; N; ₄; -Spm; [1,4,9,12-; ¹⁵; N; ₄; ]spermine; ¹⁵; N; ₄; ,D; ₄; -Spm; N,N′-(3-aminopropyl-; ¹⁵; N)-1,4-; ¹⁵; N; ₂; -butanediamine-1,1,4,4-d; ₄; ¹⁵; N; ₃; -N; ¹; AcSpd; [1,4,8-; ¹⁵; N; ₃; ]-N; ¹; -acetylspermidine; ¹⁵; N; ₃; -DiAcSpd; [1,4,8-; ¹⁵; N; ₃; ]-N; ¹; ,N; ⁸; -diacetylspermidine; ¹⁵; N; ₄; -DiAcSpm; [1,4,9,12-; ¹⁵; N; ₄; ]-N; ¹; ,N; ¹²; -diacetylspermine; ¹³; C; ₂; -N; ⁸; AcSpd; [acetyl-1,2-; ¹³; C; ₂; ]-N; ⁸; -acetylspermidine; ¹³; C; ₂; -N; ¹; AcSpd; [acetyl-1,2-; ¹³; C; ₂; ]-N; ¹; -acetylspermidine; ¹³; C; ₃; ,; ¹⁵; N; ₃; -N; ¹; AcSpd; [acetyl-2-; ¹³; C,5,8-; ¹³; C; ₂; ,1,4,8-; ¹⁵; N; ₃; ]-N; ¹; -acetylspermidine; ¹⁵; N; ₃; -N; ¹; AcSpm; [4,9,12-; ¹⁵; N; ₃; ]-N; ¹; -acetylspermine; HFB; heptafluorobutylic; RSD; relative standard deviation; MDL72527; an inhibitor of APAOESI-TOF MS; MS/MS; Stable isotope; N; ¹; -acetylpolyamine oxidase; Spermidine/spermine N; ¹; -acetyltransferase; Spermine oxidase

Direct quantification of creatinine in human urine by using isotope dilution extractive electrospray ionization tandem mass spectrometry by Xue Li; Xiaowei Fang; Zhiqiang Yu; Guoying Sheng; Minghong Wu; Jiamo Fu; Huanwen Chen (pp. 53-57).

Display Omitted► High throughput analysis of urinary creatinine is achieved by using ID-EESI–MS/MS. ► Urine sample is directly analyzed and no sample pre-treatment is required. ► Accurate quantification is accomplished with isotope dilution technique.Urinary creatinine (CRE) is an important biomarker of renal function. Fast and accurate quantification of CRE in human urine is required by clinical research. By using isotope dilution extractive electrospray ionization tandem mass spectrometry (EESI–MS/MS) a high throughput method for direct and accurate quantification of urinary CRE was developed in this study. Under optimized conditions, the method detection limit was lower than 50μgL⁻¹. Over the concentration range investigated (0.05–10mgL⁻¹), the calibration curve was obtained with satisfactory linearity ( R²=0.9861), and the relative standard deviation (RSD) values for CRE and isotope-labeled CRE (CRE-d3) were 7.1–11.8% ( n=6) and 4.1–11.3% ( n=6), respectively. The isotope dilution EESI–MS/MS method was validated by analyzing six human urine samples, and the results were comparable with the conventional spectrophotometric method (based on the Jaffe reaction). Recoveries for individual urine samples were 85–111% and less than 0.3min was taken for each measurement, indicating that the present isotope dilution EESI–MS/MS method is a promising strategy for the fast and accurate quantification of urinary CRE in clinical laboratories.

Keywords: Creatinine; Urine; Extractive electrospray ionization; Tandem mass spectrometry; Isotope dilution

Use of temperature dependent Raman spectra to improve accuracy for analysis of complex oil-based samples: Lube base oils and adulterated olive oils by Mooeung Kim; Sanguk Lee; Kyeol Chang; Hoeil Chung; Young Mee Jung (pp. 58-66).

Display Omitted► Temperature dependent Raman spectral variation was effectively used to improve accuracy for analysis of complex oil-based samples. ► Enhanced spectral features of lube base oils occurred at 50°C described the variation of viscosity more accurately. ► The temperature-induced spectral variation around 80–90°C improved the authentication of adulterated olive oils.A simple and effective strategy to improve accuracy for Raman spectroscopic analysis of complex mixture samples by probing a measurement temperature yielding enhanced spectral selectivity has been demonstrated. For the evaluation, the determination of Kinematic Viscosity at 40°C (KV@40) of lube base oil (LBO) samples was initially attempted. Partial least squares (PLS) was used to determine the KV@40 using Raman spectra of the samples collected at 8 different temperatures from 20 to 90°C with 10°C increments. Interestingly, the distinct temperature-induced spectral variation among the samples occurred at 50°C, thereby resulting in the improved accuracy for determination of KV@40. Two-dimensional (2D) correlation analysis was also performed to find an additional supportive rationale for the improved accuracy. The strategy was further evaluated for the identification of soybean oil-adulterated olive oils using linear discriminant analysis (LDA). Similarly, the discrimination accuracy was improved around 80–90°C due to the enhanced spectral selectivity between olive and soybean oils. In overall, these two results successfully demonstrate analytical effectiveness of the strategy.

Keywords: Raman spectral selectivity; Temperature-sensitive molecular vibration; Generalized two-dimensional correlation analysis; Lube base oil; Viscosity; Adulterated olive oil

In vitro selection and characterization of deoxyribonucleic acid aptamers for digoxin by Zahra Kiani; Massoumeh Shafiei; Parvaneh Rahimi-Moghaddam; Ali Asghar Karkhane; Soltan Ahmed Ebrahimi (pp. 67-72).

Display Omitted► Immobilized digoxin was used to select single stranded DNA aptamers. ► Digoxin binding properties of the selected aptamers were investigated. ► One of the aptamers was shown to bind digoxin but not ouabain. ► This aptamer could be used for measuring digoxin in human serum. ► The aptamer maybe useful for treatment of digoxin toxicity.The low therapeutic index of digoxin necessitates careful monitoring of its serum levels. Most of digoxin immunoassays suffer from interferences with digoxin-like immunoreactive substances. Since aptamers have been shown to be highly specific for their targets, the aim of this study was to develop DNA aptamers for this widely used cardiac glycoside. Digoxin was coated onto the surface of streptavidin magnetic beads. DNA aptamers against digoxin were designed using Systematic Evolution of Ligands by Exponential enrichment method (SELEX) by 11 iterative rounds of incubation of digoxin-coated streptavidin magnetic beads with synthetic DNA library, DNA elution, electrophoresis and PCR amplification. The PCR product was cloned and sequenced. Binding affinity was determined using digoxin–BSA conjugate, coated onto ELISA plate. Inhibitory effect of anti-digoxin aptamer was conducted using isolated guinea-pig atrium. Three aptamers (D1, D2 and D3) were identified. Binding studies of fluorescein-labeled truncated (without primer binding region) D1 and D2 and full length D1 anti-digoxin aptamers were performed and their corresponding dissociation constants values were 8.2×10⁻⁹, 44.0×10⁻⁹ and 17.8×10⁻⁹M, respectively. This is comparable to what other workers have obtained for interaction of monoclonal antibodies raised against digoxin. There was little difference in binding affinity between full length and truncated anti-digoxin D1 aptamer. D1 anti-digoxin aptamer also inhibited the effects of digoxin on the isolated guinea-pig atrium. D1 anti-digoxin aptamer distinguished between digoxin and ouabain in both tissue study and binding experiments. Our finding indicated that D1 anti-digoxin aptamer can selectively bind to digoxin. Further studies might show its suitability for use in digoxin assays and as a therapeutic agent in life-threatening digoxin toxicity.

Keywords: Digoxin; DNA aptamer

Highly sensitive and ultrafast response surface acoustic wave humidity sensor based on electrospun polyaniline/poly(vinyl butyral) nanofibers by Qianqian Lin; Yang Li; Mujie Yang (pp. 73-80).

Display Omitted► Polyanline/poly(vinyl butyral) nanofibers are prepared by electrospinning. ► Nanofiber-based SAW humidity sensor show high sensitivity and ultrafast response. ► The SAW sensor can detect very low humidity.Polyaniline (PANi) composite nanofibers were deposited on surface acoustic wave (SAW) resonator with a central frequency of 433MHz to construct humidity sensors. Electrospun nanofibers of poly(methyl methacrylate), poly(vinyl pyrrolidone), poly(ethylene oxide), poly(vinylidene fluoride), poly(vinyl butyral) (PVB) were characterized by scanning electron microscopy, and humidity response of corresponding SAW humidity sensors were investigated. The results indicated that PVB was suitable as a matrix to form nanofibers with PANi by electrospinning (ES). Electrospun PANi/PVB nanofibers exhibited a core–sheath structure as revealed by transmittance electron microscopy. Effects of ES collection time on humidity response of SAW sensor based on PANi/PVB nanofibers were examined at room temperature. The composite nanofiber sensor exhibited very high sensitivity of ∼75kHz/%RH from 20 to 90%RH, ultrafast response (1s and 2s for humidification and desiccation, respectively) and good sensing linearity. Furthermore, the sensor could detect humidity as low as 0.5%RH, suggesting its potentials for low humidity detection. Attempts were done to explain the attractive humidity sensing performance of the sensor by considering conductivity, hydrophilicity, viscoelasticity and morphology of the polymer composite nanofibers.

Keywords: Surface acoustic wave; Polyaniline; Electrospinning; Humidity sensor; Composite nanofibers

A rational design of the multiwalled carbon nanotube–7,7,8,8-tetracyanoquinodimethan sensor for sensitive detection of acetylcholinesterase inhibitors by Lucian Rotariu; Lucian-Gabriel Zamfir; Camelia Bala (pp. 81-88).

Display Omitted► A new concept based on the interaction between MWCNTs and TCNQ was developed. ► Synergistic effect of MWCNT and TCNQ allow thiocholine detection with high sensitivity. ► Low detection limit of 7ppt for paraoxon-methyl and 0.1ppb for chlorpyrifos, respectively.A new, simple and effective amperometric acetylcholinesterase biosensor was developed using screen-printed carbon electrodes modified with carbon nanotubes (MWCNTs)–7,7,8,8-tetracyanoquinodimethane (TCNQ). The design of the biosensor was based on the supramolecular arrangement resulted from the interaction of MWCNTs and TCNQ. This arrangement was confirmed by spectroscopic and electrochemical techniques. Two different supramolecular arrangements were proposed based on different MWCNTs:TCNQ ratios. The synergistic effect of MWCNTs and TCNQ was, for the first time, exploited for detection of thiocholine at low potential with high sensitivity. The biosensor developed by immobilization of acetylcholinesterase (AChE) in sol–gel allowed the detection of two reference AChE inhibitors, paraoxon-methyl and chlorpyrifos with detection limits of 30pM (7ppt) and 0.4nM (0.1ppb), respectively. Efficient enzyme reactivation was obtained by using obidoxime.

Keywords: Carbon nanotube; TCNQ; Acetylcholinesterase; Supramolecular arrangement; Screen printed electrode; Biosensor

Ultrasensitive and facile electrochemical deoxyribonucleic acid biosensor based on the conformational change of the recognition interface by Wei Chen; Yin-Huan Liu; Hong-Na Li; Ai-Lin Liu; Xin-Hua Lin; Yuan-Zhong Chen (pp. 89-94).

Display Omitted► A quite simple electrochemical impedance spectroscopic DNA biosensor was introduced. ► The sensing protocol was based on the conformational change of DNA. ► This approach is sensitive with a detection limit of 40fM.An ultrasensitive electrochemical impedance spectroscopic deoxyribonucleic acid biosensor has been developed based on the conformational change of the deoxyribonucleic acid recognition interface with lodging probes. Pairing process leads to desorption of deoxyribonucleic acid bases from the gold surface, leading to a significant change of the interfacial conformation and the charge transfer resistance. Remarkably low detection limits down to 40fM are thus obtained without any additional amplification step.

Keywords: Biosensor; Electrochemical impedance spectroscopy; Deoxyribonucleic acid; Conformational change; Recognition interface

Optimization of an immunoassay of 2,6-dichlorobenzamide (BAM) and development of regenerative surfaces by immunosorbent modification with newly synthesised BAM hapten library by Basil Uthuppu; Jens Aamand; Claus Jørgensen; Spire M. Kiersgaard; Natalie Kostesha; Mogens Havsteen Jakobsen (pp. 95-103).

Display Omitted► An existing immunoassay is optimised to use it as the sensing event of an immunosensor. ► Regenerative surfaces were achieved by surface modification. ► New haptens were synthesised and immobilised on surfaces. ► Interaction of antibody with new haptens was studied in detail.Dichlobenil is an extensively used herbicide worldwide which is transformed to the mobile 2,6-dichlorobenzamide (BAM) in soil. BAM has been found in many European groundwater resources that are exploited for drinking water. Currently, immunoassay based monitoring technique (plate based ELISA) is being employed to quantitatively detect BAM in water samples. In this work, as a starting step of developing immunoassay based on-site monitoring systems for pesticide analysis, the heterogeneous BAM immunoassay is optimised in terms of surface (polymer) regeneration. We have synthesised a small library of BAM haptens which are slightly different in chemical structures, immobilised them on surfaces and compared the affinity constants of the monoclonal antibody HYB 273 towards them. By using ELISA technology, we also have checked the regeneration potentials of the haptens, correlated these results to the affinity constants and found that BAM hapten with an intermediate affinity has better regeneration potential.

Keywords: Abbreviations; BAM; 2,6-dichlorobenzamide; ELISA; enzyme linked immuno sorbent assay; HYB 273; anti-BAM monoclonal antibody; RB flask; round bottomed flask; TLC; thin layer chromatography; UV; ultraviolet radiation; hapt; hapten; OA; ovalbumin; EQ 0028; photoactive anthraquinone entity; UV–vis; ultraviolet–visible spectroscopy; HRP; horseradish peroxidase enzyme; TMB; 3,3′,5,5′-tetramethylbenzidine dihydrochloride (substrate for HRP); [Ag]; concentration of hapten conjugate; OD; optical density (absorption values from UV–vis analysis); RT; room temperature; CV; coefficient of variation; SE; standard error; EC50; half maximal effective concentration; IC50; inhibition concentration at 50%; DL; ₁₀; detection limit at 10% inhibition2,6-Dichlorobenzamide; BAM; Dichlobenil; BAM-haptens; Anti-BAM monoclonal antibody; ELISA; Electrochemistry; Real-time sensor; In-line sensor; Surface modification; Surface regeneration

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Analytica Chimica Acta (v.748, #)