The Analyst (Analyst)

Publications in this journal

• Article: Solid phase extraction-capillary electrophoresis determination of sulphonamide residues in milk samples by use of C18-carbon nanotubes as hybrid sorbent materials.

  M L Polo-Luque, B M Simonet, M Valcárcel
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  ABSTRACT: The exceptional sorption capabilities of carbon nanotubes were used to preconcentrate trace sulphonamides from milk samples. To this end, single walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) dispersed in the ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate were retained on a C18 stationary phase to obtain a hybrid material in a simple manner. In this approach ionic liquids are an excellent alternative to improve the dispersion of CNTs, without chemical modification or the use of solid substances or organic solvents. MWNTs provided better results than SWNTs. Carbon nanotubes retained in the C18 sorbent matrix were found to confer aromatic character, increasing its preconcentration capacity as a result. The conventional C18 stationary phase played a two-fold role: as a support to retain carbon nanotubes in the cartridge and as a medium to prevent their aggregation. The modified MWNT/C18 and SWNT/C18 materials were used to preconcentrate residual sulphonamides (SAs) in milk samples for their determination at concentrations as low as 0.03-0.069 mg L(-1) by capillary electrophoresis. Analyte recoveries from spiked samples ranged from 103.2 to 98.8% and precision, as RSD, from 8.2 to 5.4%.
  The Analyst 05/2013;
• Article: Chromatographic separation and detection of target analytes from complex samples using inkjet printed SERS substrates.

  Wei W Yu, Ian M White
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  ABSTRACT: In principle, surface enhanced Raman spectroscopy (SERS) is thought to provide unique identification of a target analyte, even in complex samples or in the presence of multiple analytes. In practice, however, this is not always true for real-world samples due to various forms of interference. In this report, we build upon our previous work on inkjet-printed SERS substrates by using paper and polymer membranes to integrate sample cleanup and analyte separation with SERS detection. Inkjet-printed paper SERS substrates provide a highly sensitive chemical detection platform of unprecedented cost and simplicity. In addition, paper inherently provides unique capabilities, such as capillary-actuated fluid transport and selective molecular retention. Utilizing these properties, we demonstrate two-dimensional chromatographic separation and SERS detection on inkjet-printed paper SERS substrates. Then, we leverage the separation properties of paper and polymer membranes for real applications that feature complex sample matrices, including the detection of down to 5 ppm melamine in infant formula, as well as the quantification of nanograms of heroin in samples contaminated with a highly fluorescent background. The results presented here demonstrate that inkjet-printed paper SERS devices not only provide advantages in terms of sensitivity and cost, but the paper provides inherently integrated sample cleanup capabilities that are not available in traditional SERS substrates and microfluidic SERS devices. These unique capabilities of paper SERS devices enable the identification of targeted analytes even in complex real-world samples.
  The Analyst 05/2013;
• Article: Magnetic particle-based time-resolved fluoroimmunoassay for the simultaneous determination of α-fetoprotein and the free β-subunit of human chorionic gonadotropin.

  Jing-Yuan Hou, Tian-Cai Liu, Zhi-Qi Ren, Mei-Jun Chen, Guan-Feng Lin, Ying-Song Wu
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  ABSTRACT: In this paper, a novel time-resolved fluoroimmunoassay (TRFIA) protocol using magnetic particles for the simultaneous determination of α-fetoprotein (AFP) and the free β-subunit of human chorionic gonadotropin (free β-hCG) in human serum is described. The new approach uses magnetic particles as an immobilization matrix and means of separation, while the luminescent europium and samarium chelates are used as probes. The proposed method was evaluated via a single-step, sandwich-type TRFIA immunoassay of AFP and free β-hCG as model analytes in serum. With the advantages of magnetic particles, the TRFIA immunoassay exhibited a wide dynamic range for AFP of 0.1-750 ng mL(-1), with a lower detection limit of 0.05 ng mL(-1). The dynamic range for free β-hCG was 0.16-450 ng mL(-1), with a lower detection limit of 0.08 ng mL(-1). Satisfactory specificity, reproducibility, and recovery of the immunoassay were demonstrated. Good correlations were obtained in the analysis of 446 human serum samples between the proposed method and a commercial TRFIA kit. These results demonstrate the feasibility and potential of the new method as a rapid and highly sensitive immunoassay that could be developed into a platform for multi-analyte determinations in clinical practice.
  The Analyst 05/2013;
• Article: Profiling intact steroid sulfates and unconjugated steroids in biological fluids by liquid chromatography-tandem mass spectrometry (LC-MS-MS).

  Christina E Galuska, Michaela F Hartmann, Alberto Sánchez-Guijo, Katharina Bakhaus, Joachim Geyer, Gerhard Schuler, Klaus-Peter Zimmer, Stefan A Wudy
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  ABSTRACT: Within the combined DFG research project "Sulfated Steroids in Reproduction" an analytical method was needed for determining sulfated and unconjugated steroids with highest specificity out of different biological matrices such as aqueous solution, cell lysate and serum. With regard to this analytical challenge, LC-MS-MS presents the technique of choice because it permits (1) analysis of the intact steroid conjugate, (2) allows for simultaneous determination of multiple analytes (profiling, targeted metabolomics approach) and (3) is independent of phenomena such as cross-reactivity. Sample work up consisted of incubation of sample with internal standards (deuterium labeled steroids) followed by solid phase extraction. Only serum samples required a protein precipitation step prior to solid phase extraction. The extract was divided in two parts: six steroid sulfates (E1S, E2S, AS, 16-OH-DHEAS, PREGS, DHEAS) were analyzed by C18aQ-ESI-MS-MS in negative ion mode and eleven unconjugated steroids (E3, 16-OH-DHEA, E1, E2, (4)A, DHEA, T, 17-OH-PREG, Prog, An, PREG) were analyzed by C18-APCI-MS-MS in positive ion mode. For steroid sulfates, we found high sensitivities with LoQ values ranging from 0.08 to 1 ng mL(-1). Unconjugated steroids showed LoQ values between 0.5 and 10 ng mL(-1). Calibration plots showed excellent linearity. Mean intra- and inter-assay CVs were 2.4% for steroid sulfates and 6.4% for unconjugated steroids. Accuracy - determined in a two-level spike experiment - showed mean relative errors of 5.9% for steroid sulfates and 6.1% for unconjugated steroids. In summary, we describe a novel LC-MS-MS procedure capable of profiling six steroid sulfates and eleven unconjugated steroids from various biological matrices.
  The Analyst 05/2013;
• Article: Solution-free, in situ preparation of nano/micro CuO/ZnO in dielectric barrier discharge for sensitive cataluminescence sensing of acetic acid.

  Hui Xia, Ronghui Zhou, Chengbin Zheng, Peng Wu, Yunfei Tian, Xiandeng Hou
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  ABSTRACT: The present work describes a new solution-free strategy for preparation of cluster-like nano/micro CuO/ZnO particles in dielectric barrier discharge (DBD) in which the brass acts as the inner electrode. The cataluminescence (CTL) behaviour of such prepared material for acetic acid was studied for analytical application. Under the optimized conditions, the linear range of CTL intensity versus concentration of acetic acid are 6 mg L(-1) to 500 mg L(-1) with the limit of detection (LOD) of 3 mg L(-1), no significant interference was found. The new method shows great advantages because it is a process without any solution and complex equipment. The synthetic material was directly used for the cataluminescence sensing of acetic acid without other preliminary treatment and it shows high selectivity, satisfactory stability, and better sensitivity and linearity.
  The Analyst 05/2013;
• Article: A label-free amplified fluorescence DNA detection based on isothermal circular strand-displacement polymerization reaction and graphene oxide.

  Zhen Li, Wenping Zhu, Jinwen Zhang, Jianhui Jiang, Guoli Shen, Ruqin Yu
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  ABSTRACT: A label-free fluorescent DNA biosensor has been presented based on isothermal circular strand-displacement polymerization reaction (ICSDPR) combined with graphene oxide (GO) binding. The proposed method is simple and cost-effective with a low detection limit of 4 pM, which compares favorably with other GO-based homogenous DNA detection methods.
  The Analyst 05/2013;
• Article: Selective sensing of vapors of similar dielectric constants using peptide-capped gold nanoparticles on individual multivariable transducers.

  Nandini Nagraj, Joseph M Slocik, David M Phillips, Nancy Kelley-Loughnane, Rajesh R Naik, Radislav A Potyrailo
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  ABSTRACT: Peptide-capped AYSSGAPPMPPF gold nanoparticles were demonstrated for highly selective chemical vapor sensing using individual multivariable inductor-capacitor-resistor (LCR) resonators. Their multivariable response was achieved by measuring their resonance impedance spectra followed by multivariate spectral analysis. Detection of model toxic vapors and chemical agent simulants, such as acetonitrile, dichloromethane and methyl salicylate, was performed. Dichloromethane (dielectric constant εr = 9.1) and methyl salicylate (εr = 9.0) were discriminated using a single sensor. These sensing materials coupled to multivariable transducers can provide numerous opportunities for tailoring the vapor response selectivity based on the diversity of the amino acid composition of the peptides, and by the modulation of the nature of peptide-nanoparticle interactions through designed combinations of hydrophobic and hydrophilic amino acids.
  The Analyst 05/2013;
• Article: Development of a label-free aptasensor for monitoring the self-association of lysozyme.

  Alina Vasilescu, Szilveszter Gaspar, Iuliana Mihai, Andreia Tache, Simona Carmen Litescu
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  ABSTRACT: A novel aptamer and surface plasmon resonance (SPR)-based sensor was developed for the label-free detection of lysozyme. The aptasensor is characterised by a detection limit of 1 μg mL(-1) and a linear range of 5-50 μg mL(-1). As an application, we examined the usefulness of the aptasensor for monitoring the early stages of the aggregation of lysozyme. It was surprisingly found that, despite a significant decrease in monomer content during aggregation, the response of the aptasensor for protein solutions aged for 12 hours was similar to that for the fresh protein. To correlate the results obtained with the aptasensor with the composition of lysozyme solutions at various time points, we examined them in detail by atomic force microscopy (AFM), thioflavin T fluorescence, size-exclusion chromatography (SEC) and Matrix Assisted Laser Desorption Ionisation Time of Flight Mass Spectrometry (MALDI-TOF-MS). All methods together indicated that during the initial hours of aggregation, the protein solutions contained small lysozyme oligomers (mainly dimers) and decreasing amounts of monomers. Our results thus suggest that the aptamer also recognizes lysozyme dimers/oligomers. A higher non-specific binding was observed for the aggregated lysozyme at the surface of the aptasensor as compared to the native protein. This was attributed to the hydrophobic patches which are exposed by the unfolded lysozyme and/or oligomer species, allowing for different adsorption and organisation at the surface of the aptasensor. This hypothesis is supported by square wave voltammetry (SWV) studies using solutions of aggregated lysozyme. A higher electrochemical signal due to the direct oxidation of tyrosine/tryptophan residues was observed for aged protein solutions as compared to the fresh solution, indicative of an increased number of such exposed electroactive residues and of overall increased surface hydrophobicity of the protein. Our work presents a label-free lysozyme aptasensor that is useful not only for the detection of the protein monomer but also for observing the onset of aggregation. The approach can be extended to other proteins which are prone to aggregation.
  The Analyst 05/2013;
• Article: A novel platform for sensing an amino acid by integrating hydrogel photonic crystals with ternary complexes.

  Mei Liu, Li-Ping Yu
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  ABSTRACT: A novel sensing platform based on the integration of hydrogel photonic crystals and ternary tetracycline-copper(ii)-amino acid complexes has been proposed. Obvious and gradual diffraction wavelength shifts and color changes can be easily monitored during the stepwise coordination reaction process. This new strategy allows label-free detection and reversible sensing of glycine with high sensitivity.
  The Analyst 05/2013;
• Article: A tyrosinase biosensor based on ordered mesoporous carbon-Au/l-lysine/Au nanoparticles for simultaneous determination of hydroquinone and catechol.

  Lin Tang, Yaoyu Zhou, Guangming Zeng, Zhen Li, Yuanyuan Liu, Yi Zhang, Guiqiu Chen, Guide Yang, Xiaoxia Lei, Mengshi Wu
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  ABSTRACT: A novel biosensor was developed based on tyrosinase immobilization with ordered mesoporous carbon-Au (OMC-Au), l-lysine membrane and Au nanoparticles on a glassy carbon electrode (GCE). It was applied for the simultaneous determination of dihydroxybenzene isomers using differential pulse voltammetry (DPV). The tyrosinase/OMC-Au/l-lysine/Au film was characterized by scanning electron microscopy (SEM) and impedance spectra. Under optimized conditions, the DPV study results for two isomers, hydroquinone (HQ, 1,4-dihydroxybenzene) and catechol (CC, 1,2-dihydroxybenzene) showed low peak potentials, and the peak-to-peak difference was about 135.85 mV, which ensured the anti-interference ability of the biosensor and made simultaneous detection of dihydroxybenzene isomers possible in real samples. DPV peak currents increased linearly with concentration over the range of 4.0 × 10(-7) to 8.0 × 10(-5) M, and the detection limits of hydroquinone and catechol were 5 × 10(-8) M and 2.5 × 10(-8) M (S/N = 3), respectively. The tyrosinase biosensor exhibited good repeatability and stability. In addition, the response mechanism of enzyme catalysed redox on the OMC-Au/l-lysine/Au film modified electrode based on electrochemical study was discussed. The proposed method could be extended for the development of other enzyme-based biosensors.
  The Analyst 05/2013;
• Article: An improved lectin-based method for the detection of mucin-type O-glycans in biological samples.

  Cheng-Siang Lee, Arivalagan Muthusamy, Puteri Shafinaz Abdul-Rahman, Veer P Bhavanandan, Onn Haji Hashim
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  ABSTRACT: Mucins and mucin-type glycoproteins, collectively referred to as mucin-type O-glycans, are implicated in many important biological functions and pathological conditions, including malignancy. Presently, there is no reliable method to measure the total mucin-type O-glycans of a sample, which may contain one or more of these macromolecules of unknown structures. We report the development of an improved microassay that is based on the binding of lectins to the unique and constant GalNAc-Ser/Thr structural feature of mucin-type O-glycans. Since the sugar-amino acid linkage in the mucin-type O-glycans is invariably cryptic, we first chemically removed the heterogeneous peripheral and core saccharides of model glycoconjugates before examining for their interactions using an enzyme-linked lectin assay (ELLA). Desialylation of the model glycoconjugates led to maximal binding of the lectins but additional treatments such as Smith degradation did not result in increased binding. Of the lectins tested for their ability to probe the desialylated O-glycans, jacalin showed the highest sensitivity followed by champedak galactose binding (CGB) lectin and Vicia villosa agglutinin. Further improvement in the sensitivity of ELLA was achieved by using microtiter plates that were pre-coated with the CGB lectin, which increased the specificity of the assay to mucin-type O-glycans. Finally, the applicability of the developed sandwich ELLA to crude samples was demonstrated by estimating trace quantities of the mucin-type O-glycans in the human serum.
  The Analyst 05/2013;
• Article: A novel differential mobility analyzer as a VOC detector and multivariate techniques for identification and quantification.

  V Pomareda, S Lopez-Vidal, D Calvo, A Pardo, S Marco
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  ABSTRACT: A Differential Mobility Analyser (DMA) is a specific configuration of an Ion Mobility Spectrometer (IMS) where ions with different electrical mobilities are separated in space, instead of in time of drift, as in classical drift-time IMS. This work presents results obtained with a parallel plate DMA instrument, with crucial differences in the sheath flow and the detection system when compared to other instruments in the market. These differences improve the resolving powers and sensitivities of the instrument. Additionally, datasets from IMS or DMA instruments are typically processed with univariate techniques when only qualitative detection is of interest. However, good performance in quantitative measurements can be achieved using multivariate data processing. This work presents for the first time, measurements with a stand-alone DMA instrument and the multivariate data processing related to VOCs and environmentally interesting samples.
  The Analyst 05/2013;
• Article: Metal-organic frameworks-based biosensor for sequence-specific recognition of double-stranded DNA.

  Lifen Chen, Hanye Zheng, Xi Zhu, Zhenyu Lin, Longhua Guo, Bin Qiu, Guonan Chen, Zhong-Ning Chen
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  ABSTRACT: A simple, cost-efficient, sensitive and selective fluorescence sensor is developed for sequence-specific recognition of duplex DNA (ds-DNA) in vitro using metal-organic framework (MOF) as the sensing platform. N,N-Bis(2-hydroxy-ethyl)dithiooxamidatocopper(ii) (H2dtoaCu) was chosen as the example MOF, because it strongly chemisorbs the dye-labeled probe TFO (triplex-forming oligonucleotide), and quenches fluorescence from the dye. In the presence of target ds-DNA (the PPT of HIV RNA, a 16-bp ds-DNA sequence), the TFO could interact with the major groove in ds-DNA (via Hoogsteen hydrogen bonding) to form a rigid triplex structure, resulting in fluorescence recovery. The enhanced fluorescence signal has a relationship with the ds-DNA concentration, the detection limit is as low as 1.3 nmol L(-1) (S/N = 3) with good selectivity, which is lower than that based on a graphene oxide platform and electrochemical-DNA sensor.
  The Analyst 05/2013;
• Article: A microfluidic anti-Factor Xa assay device for point of care monitoring of anticoagulation therapy.

  Leanne F Harris, Paul Rainey, Vanessa Castro-López, James S O'Donnell, Anthony J Killard
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  ABSTRACT: The development of new point of care coagulation assay devices is necessary due to the increasing number of patients requiring long-term anticoagulation in addition to the desire for appropriate, targeted anticoagulant therapy and a more rapid response to optimization of treatment. The majority of point of care devices currently available for hemostasis testing rely on clot-based endpoints which are variable, unreliable and limited to measuring only certain portions of the coagulation pathway. Here we present a novel fluorescence-based anti-Factor Xa (FXa) microfluidic assay device for monitoring the effect of anticoagulant therapy at the point of care. The device is a disposable, laminated polymer microfluidic strip fabricated from a combination of hydrophobic and hydrophilic cyclic polyolefins to allow reagent deposition in addition to effective capillary fill. Zeonor was the polymer of choice resulting in low background fluorescence (208.5 AU), suitable contact angles (17.5° ± 0.9°) and capillary fill times (20.3 ± 2.1 s). The device was capable of measuring unfractionated heparin and tinzaparin from 0-0.8 U ml(-1) and enoxaparin from 0-0.6 U ml(-1) with average CVs < 10%. A linear correlation was observed between the device and the fluorescent assay in the plate for plasma samples spiked with UFH, with an R(2) value of 0.99, while correlations with tinzaparin and enoxaparin resulted in sigmoidal responses (R(2) = 0.99). Plasma samples containing UFH resulted in a linear correlation between the device and a standard chromogenic assay with an R(2) value of 0.98, with both LMWHs resulting in sigmoidal relationships (R(2) = 0.99).
  The Analyst 05/2013;
• Article: A miniaturised electron ionisation time-of-flight mass spectrometer that uses a unique helium ion removal pulsing technique specifically for gas analysis.

  Jiang Qing, Zhengxu Huang, Yan Zhang, Hui Zhu, Guobin Tan, Wei Gao, Peng-Yuan Yang
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  ABSTRACT: A miniaturised reflectron time-of-flight mass spectrometer combined with an electron ionisation ion source has been developed for the analysis of gases. An entirely new helium ion removal pulsing technique in this mass spectrometer is used to achieve an improved performance for the first time. The helium carrier gas, which enters into the source along with the gaseous sample, is simultaneously ionised and then orthogonally introduced into the time-of-fight mass analyser. Once the relatively light helium ions in the ion packet become extremely close to the reflectron plate (B-plate for short in this article), a modulated pulse is instantaneously applied on the B-plate and a negative reflectron voltage is set to the B-plate and lasts for a very short period, during which all the helium ions are directly bumped into the B-plate and subsequently removed. The helium ion removal pulsing technique can efficiently avoid saturation of the micro-channel plate caused by too many helium ions. A compact and durable instrument is designed, which has a mass resolving resolution greater than 400 FWHM for online gas analysis. The technology may also be further developed to remove other ions for TOF mass spectrometry.
  The Analyst 05/2013;
• Article: Mepanipyrim haptens and antibodies with nanomolar affinity.

  Francesc A Esteve-Turrillas, Josep V Mercader, Consuelo Agulló, Antonio Abad-Somovilla, Antonio Abad-Fuentes
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  ABSTRACT: Mepanipyrim is an anilinopyrimidine fungicide used worldwide for crop protection. With the aim of developing useful immunoreagents for mepanipyrim immunoanalysis, two new functionalized derivatives were prepared and antibodies were generated. Affinity and specificity were assessed by direct and indirect competitive ELISA using homologous and heterologous conjugates. Although all antibodies were selective for the target analyte, the immunizing hapten structure was revealed as a determinant for high-affinity antibody production (IC50 = 3 nM).
  The Analyst 05/2013;
• Article: Employing aqueous CdTe quantum dots with diversified surface functionalities to discriminate between heme (Fe(ii)) and hemin (Fe(iii)).

  Jishu Han, Ziwei Zhou, Xinyuan Bu, Shoujun Zhu, Hao Zhang, Haizhu Sun, Bai Yang
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  ABSTRACT: The discrimination of ferrous and ferric states in the human body is one of the basic issues for disease control and prevention because Fe(ii) and Fe(iii) are a crucial redox pair during the process of material and energy metabolism. Herein, aqueous CdTe quantum dots (QDs) with diversified surface functionalities are applied to discriminate between heme (Fe(ii)) and hemin (Fe(iii)) by virtue of their difference in quenching QD fluorescence. In aqueous media, the interaction between QDs and heme/hemin mainly involves electrostatic interaction, which is greatly determined by the surface functionalities of the QDs. Thus, by combining the different fluorescence quenching behavior of carboxyl- and/or hydroxyl-functionalized QDs, heme and hemin are discriminated between. In comparison to the discrimination using QDs with single surface functionality, the current method has improved reliability and accuracy.
  The Analyst 05/2013;
• Article: Determination of free acidic and alkaline residues of protein via moving reaction boundary titration in microdevice electrophoresis.

  Hou-Yu Wang, Si Li, Yun-Yun Tang, Jing-Yu Dong, Liu-Yin Fan, Cheng-Xi Cao
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  ABSTRACT: As two important physico-chemical parameters, the acidic and alkaline residues of protein are of evident significance for the evaluation of protein properties and the design of relevant separation and analysis. However, there is still no electrophoretic method used for the direct detection of free acidic and alkaline residues of protein. Herein, we developed the concepts of moving reaction boundary (MRB) and MRB titration, relevant MRB titration theory, and the method of microdevice electrophoresis for the determination of free acidic and alkaline residues of protein. In the MRB titration, the boundary was created with acid or alkali and target protein immobilized via highly cross-linked polyacrylamide gel (PAG). It was theoretically revealed that the number of free acidic or alkaline residues of protein was as a function of MRB displacement in the electrophoretic titration system. As a proof of concept, seven model proteins were chosen for the determination of acidic or alkaline residues of protein via MRB titration. The results showed that the numbers of free acidic and alkaline residues of proteins detected were in good agreement with those obtained from the relevant amino sequences in the NCBI database, demonstrating the feasibility of the developed concept, theory and technique. The general methodology of MRB titration has potential application for inexpensive, facilitative and informative protein structure analysis of free acidic or alkaline residues of protein.
  The Analyst 05/2013;
• Article: An automated method for baseline correction, peak finding and peak grouping in chromatographic data.

  Lea G Johnsen, Thomas Skov, Ulf Houlberg, Rasmus Bro
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  ABSTRACT: An automated method (FastChrom) for baseline correction, peak detection and assignment (grouping) of similar peaks across samples has been developed. The method has been tested both on artificial data and a dataset obtained from gas chromatograph analysis of wine samples. As part of the automated approach, a new method for baseline estimation has been developed and compared with other methods. FastChrom has been shown to perform at least as well as conventional software. However, compared to other approaches, FastChrom finds more peaks in the chromatograms and not only those with retention times defined by the user. FastChrom is fast and easy to use and offers the possibility of applying a retention time index which facilitates the identification of peaks and the comparison between experiments.
  The Analyst 05/2013;
• Article: An in situ electrochemical detection method of cell viability.

  Hongwei Qin, Qingdong Gao, Huiming Niu, Zhefeng Wang, Xiaolin Zhu, Jinlian Li, Xing Yuan, Dongmei Wu
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  ABSTRACT: An in situ electrochemical method of cell viability, which integrated cell culture, pretreatment and detection in a cell culture dish, was developed. The method significantly improved the electrochemical response of cells, simplified the operation process, reduced the experiment time, avoided the use of trypsin, and was applied in the study of the effectiveness of antitumor drugs on tumor suppression.
  The Analyst 05/2013;