Analytica Chimica Acta (v.649, #1)

The specific interactions between sugar-binding proteins (lectins) and their complementary carbohydrates mediate several complex biological functions. There is a great deal of interest in uncovering the molecular basis of these interactions. In this study, we demonstrate the use of an efficient one-step amination reaction strategy to fabricate carbohydrate arrays based on mixed self-assembled monolayers. These allow specific lectin carbohydrate interactions to be interrogated at the single molecule level via AFM. The force required to directly rupture the multivalent bonds between Concanavalin A (Con A) and mannose were subsequently determined by chemical force microscopy. The mixed self-assembled monolayer provides a versatile platform with active groups to attach a 1-amino-1-deoxy sugar or a protein (Con A) while minimizing non-specific adhesion enabling quick and reliable detection of rupture forces. By altering the pH of the environment, the aggregation state of Con A was regulated, resulting in different dominant rupture forces, corresponding to di-, tri- and multiple unbinding events. We estimate the value of the rupture force for a single Con A–mannose bond to be 95 ± 10 pN. The rupture force is consistent even when the positions of the binding molecules are switched. We show that this synthesis strategy in conjunction with a mixed SAM allows determination of single molecules bond with high specificity, and may be used to investigate lectin carbohydrate interactions in the form of carbohydrate arrays as well as lectin arrays.
Keywords: Carbohydrate array; Lectin interaction; Atomic force microscopy; Self-assembled monolayers;

Optical probes for detection and quantification of neutrophils’ oxidative burst. A review by Marisa Freitas; José L.F.C. Lima; Eduarda Fernandes (8-23).
Neutrophils, also known as polymorphonuclear leukocytes (PMN), are the most common type of white blood cells, comprising about 50–70% of all white blood cells. In the event of inflammatory processes, neutrophils display increased mobility, tissue influx ability, prolonged life span, and an increased phagocytic capacity, constituting the initial participants in the cellular defense of the organism. One of the most important defense systems of neutrophils corresponds to their ability to mediate a strong oxidative burst through the formation of reactive oxygen species (ROS) and reactive nitrogen species (RNS). While oxidative burst is important for the elimination of invading microorganisms, the overproduction of ROS and RNS or the impairment of endogenous antioxidant defenses may result to detrimental effects to the host. The nature and the extent of ROS and RNS production by neutrophils in response to different stimuli is, consequently, a matter of extensive research, with scientific reports showing an enormous variability on the detection methodologies employed. This review attempts to provide a critical assessment of the most common approaches to identify and quantify reactive species formed during the neutrophils’ oxidative burst. The detection mechanisms and performance, as well as advantages and limitations of the different methodologies, are scrutinized, focusing on the use of fluorimetric, chemiluminometric and colorimetric probes.
Keywords: Optical probes; Neutrophils; Oxidative burst; Reactive oxygen species; Reactive nitrogen species;

Potential antioxidant compounds in Mallotus species fingerprints. Part I: Indication, using linear multivariate calibration techniques by C. Tistaert; B. Dejaegher; N. Nguyen Hoai; G. Chataigné; C. Rivière; V. Nguyen Thi Hong; M. Chau Van; J. Quetin-Leclercq; Y. Vander Heyden (24-32).
Some Mallotus species are used in traditional medicine in Vietnam and China. Some also show interesting activities, such as antioxidant and cytotoxic ones. Combining fingerprint technology with data-handling techniques allows indicating the peaks potentially responsible for given activities. In this study it is aspired to indicate from chromatographic fingerprints the peaks potentially responsible for the antioxidant activity of several Mallotus species. Relevant information was extracted using linear multivariate calibration techniques, both before and after alignment of the fingerprints with correlation optimized warping (COW). From the studied techniques, Stepwise Multiple Linear Regression is least recommended as it made an inadequate variable selection. Principal Component Regression theoretically can take largely varying variables uncorrelated to the antioxidant activity into account. However, in practice in the actual case study this problem was limited. These problems in principle do not occur using Partial Least Squares (PLS) models. Of the tested PLS methods, Orthogonal Projections to Latent Structures was preferred because of its simplicity, reproducibility, reduced model complexity and improved interpretability of the regression coefficients, yielding a clearer view on the individual contribution of the compounds. Furthermore, reducing analysis times from 60 min to 35 and 22.5 min resulted in the same main compounds, indicated responsible for the antioxidant activity. Models built after alignment by COW did not result in additional information.
Keywords: Fingerprints; Antioxidant activity; Multivariate calibration; Indication of peaks;

Inductively Coupled Plasma Atomic Emission Spectroscopy measurements of six trace elements were performed on the scalp hair of 155 donors, 73 of which have been diagnosed with Hepatitis C and 82 Controls. Principal Components Analysis (PCA) was employed to visualise the separation between groups and show the relationship between the elements and the diseased state. Pattern recognition methods for classification involving Quadratic Discriminant Analysis and Partial Least Squares Discriminant Analysis (PLS-DA) were applied to the data. The number of significant components for both PCA and PLS were determined using the bootstrap. The stability of training set models were determined by repeatedly splitting the data into training and test sets and employing visualisation for two components models: the percent classification ability (CC), predictive ability (PA) and model stability (MS) were computed for test and training sets.
Keywords: Inductively Coupled Plasma Atomic Emission Spectroscopy; Hair; Hepatitis; Pattern recognition; Partial Least Squares; Quadratic Discriminant Analysis;

Tangerine peels are herbal materials of two coupled traditional Chinese medicines, Pericarpium Citri Reticulatae (PCR) and Pericarpium Citri Reticulatae Viride (PCRV). In this paper, high-performance liquid chromatographic fingerprints of tangerine peels during growth were firstly measured for deliberately collected 34 samples from three species (Citrus reticulataChachi’, Citrus reticulataDahongpao’ and Citrus erythrosa Tanaka). After sixteen characteristic components which have similar change trends in the grown process were screened out with the help of heuristic evolving latent projection (HELP) method, score plots of principal component analysis (PCA) successfully presented the grown footprints of tangerine peels. It implied that July might be the best harvest time for PCRV, November and December were better for PCR. Furthermore, hesperidin, nobiletin and tangeretin were screened as chemical markers by loadings of PCA. The HPLC–HELP–PCA strategy has shown its potential in optimization of harvest time and chemical markers’ screening, which will have wide perspective in the analysis of “coupled TCMs”.
Keywords: Pericarpium Citri Reticulatae; Pericarpium Citri Reticulatae Viride; Principal components analysis (PCA); Heuristic evolving latent projection (HELP); Metabolic fingerprinting;

QSPR models for the prediction of UV maximum absorption wavelength (λ max) of 69 flavones were developed based on their structures alone. A six-descriptor linear correlation by heuristic method (HM) and a nonlinear model using radial basis function neural network (RBFNN) approach were reported. The statistical parameters provided by the HM model (R 2  = 0.961, F  = 207.820, RMS = 6.555 for the training set and R 2  = 0.967, F  = 293.218, RMS = 7.176 for the test set) and the RBFNN model (R 2  = 0.971, F  = 1826.086, RMS = 5.350 for the training set, and R 2  = 0.978, F  = 452.512, RMS = 5.722 for the test set) indicated satisfactory stability and predictive ability. The descriptors appearing in these models are discussed. This QSPR approach is suitable for the prediction of maximum absorption wavelength of flavones, and can contribute to a better understanding of structural factors of the organic compounds responsible for it.
Keywords: Maximum absorption wavelength; Heuristic method; Radial basis function neural network; Flavones;

In this work, the applicability of mean centering (MC) of ratio kinetic profiles method to the kinetic voltammetry data is verified. For this purpose, a procedure is described for the determination of Sb(III) and Sb(V) by adsorptive linear sweep voltammetry using pyrogallol (py) as a complexing agent. The method is based on the differences between the rate of complexation of pyrogallol with Sb(V) and Sb(III) at pH 1.2. The results show that the mean centering of ratio kinetic profiles method is suitable for the speciation of antimony. Sb(III) and Sb(V) can be determined in the ranges of 3.0–120.0 and 10.0–240.0 ng mL−1, respectively. Moreover, the solution is analyzed for any possible effects of foreign ions. The obtained results show that the method of MC in combination to electroanalytical techniques is a powerful method with high sensitivity and selectivity. The procedure is successfully applied to the speciation of antimony in pharmaceutical preparations.
Keywords: Mean centering; Ratio kinetic profiles; Antimony; Speciation; Adsorptive linear sweep voltammetry;

A novel methodology is proposed for food specifications associated with the origin of food. The methodology was tested on honey samples collected within the TRACE EU project. The data were sampled in various regions in Europe and analysed for the trace elements content. The sampling sites were characterized by different geological origins, such as limestone, shale, or magmatic. We have chosen 14 elements, B, Na, Mg, A, K, Ca, Mn, Co, Ni, Cu, Zn, Rb, Sr, and Ba, due to their influence on the separation of samples regarding the geology of the sampling sites. A special architecture of an error back-propagation neural network, so called bottle-neck type of neural network was used to project the data into a 2D plane. The data were fed into the 14-nodes input layer and then transferred through the 2-nodes hidden layer (compared to a bottle-neck) to the 14-nodes output layer. The two hidden nodes representing the two coordinates of the projection plane enable us to map the samples used for training of the bottle-neck network. With the knowledge about the classes of individual samples we determine the clusters in the projection plane and consequently obtain the coordinates of the centroid (gravity point) of a particular cluster. The clusters are characterized with an ellipse shape borders spanning the length of up to 3σ in each dimension. Since the data were classified as regard to the geology, three main clusters were sought: (i) limestone, (ii) shale/mudstone/clay/loess, and (iii) acid-magmatic origin of honey samples. The novel methodology proposed for food specifications was demonstrated on a reduced set of samples, which shows good clustering of all three classes in the projection plane, and on the third class of the original data set.
Keywords: Bottle-neck neural network; Clusters; Mapping; Food specifications; Food quality; Traceability; Honey;

An electrochemical assay for the determination of Se (IV) in a sequential injection lab-on-valve system by Yang Wang; Zaiqing Liu; Guojun Yao; Peihua Zhu; Xiaoya Hu; Chun Yang; Qin Xu (75-79).
A sequential injection lab-on-valve (LOV) unit, integrating a miniaturized electrochemical flow cell (EFC), has been constructed for the determination of trace amounts of Se (IV) by employing cathodic stripping voltammetry (CSV) technique. The procedure is carried out on a mercury film coated glassy carbon electrode. The analyte solution and electrolyte solution were continuously aspirated and merged in the holding coil (HC) by using a single syringe pump, which were afterwards pushed into the EFC, where the peak current was generated during the subsequent deposition/stripping procedure and measured as the basis of quantification. Assay parameters were optimized in order to achieve the best analytical performance, including mercury film preparation, supporting electrolyte composition, deposition potential and deposition time, and flow variables in the LOV. By loading a sample volume of 500 μL, a linear calibration graph was derived within 1–600 μg L−1, and a detection limit (3б) of 0.11 μg L−1 was achieved along with a sampling frequency of 20 h−1. By integrating the EFC into the LOV unit, the assembling system not only minimized the sample/reagent consumption and waste generation, but also enhanced the sampling frequency. The work itself extended the applications of electrochemical detection techniques and provided a good platform for Se (IV) electrochemical analysis.
Keywords: Sequential injection; Lab-on-valve; Cathodic stripping voltammetry; Mercury film; Se (IV);

Development of a broad toxicological screening technique for urine using ultra-performance liquid chromatography and time-of-flight mass spectrometry by Hon Kit Lee; Chung Shun Ho; Yan Ping Heidi Iu; Po Shan Judy Lai; Chi Chung Shek; Yun-Chuen Lo; Helene Bendstrup Klinke; Michelle Wood (80-90).
Withdrawal of the support for the REMEDi HS drug profiling system has necessitated its replacement within our laboratories with an alternative broad toxicological screening technique. To this end, a novel method, based on ultra-performance liquid chromatography (UPLC) and time-of-flight (TOF) mass spectrometry, was developed for the routine analysis of urine samples. Identification was achieved by comparison of acquired data to libraries containing more than 300 common drugs and metabolites, and was based on a combination of retention time, exact mass and fragmentation patterns. Validation data for the method is presented and comprised an evaluation of the following parameters: precision; transferability of the methodology between the six collaborating laboratories; specificity; extraction recovery and stability of processed samples; matrix effects and sensitivity.This paper presents the benefits of supplementary fragmentation data with particular regard to increasing specificity and confidence of identification and its usefulness with overdosed samples. The utility of the method was assessed by the parallel analysis of 30 authentic urine samples using the REMEDi HS and UPLC–TOF. The latter provided enhanced detection, leading to the identification of twice as many drugs. Furthermore it did not miss any compounds that were identified by REMEDi HS. The UPLC–TOF findings were further verified by a combination of data from three other conventional screening techniques, i.e., GC–MS, HPLC-DAD and UPLC–MS/MS.
Keywords: Systematic toxicological analysis; REMEDi HS; Ultra-performance liquid chromatography; Time-of-flight mass spectrometry;

This paper describes a fast method for the sensitive and selective determination of melamine in a wide range of food matrices, including several milk-based products. The method involves an extraction with aqueous 1% trichloroacetic acid before the injection of the 10-fold diluted extract into the liquid chromatography–electrospray tandem mass spectrometry (LC–ESI-MS/MS) system, using labelled melamine as the internal standard. As melamine is present in aqueous media in the cationic form, the chromatographic separation in reversed-phase LC requires the use of anionic ion-pair reagents, such as tridecafluoroheptanoic acid (THFA). This allows a satisfactory chromatographic retention and peak shape in all the types of food samples investigated. The method has been validated in six food matrices (biscuit, dry pasta and four milk-based products) by means of recovery experiments in samples spiked at 1 and 5 mg kg−1. Average recoveries (n  = 5) ranged from 77% to 100%, with excellent precision (RSDs lower than 5%) and limits of detection between 0.01 and 0.1 mg kg−1. In addition, accuracy and robustness of the method was proven in different soya-based matrices by means of quality control (QC) sample analysis. QC recoveries, at 1 and 2.5 mg kg−1, were satisfactory, ranging from 79% to 110%. The method developed in this work has been applied to the determination of melamine in different types of food samples. All detections were confirmed by acquiring two MS/MS transitions (127 > 85 for quantification; 127 > 68 for confirmation) and comparing their ion intensity ratio with that of reference standards. Accuracy of the method was also assessed by applying it to a milk-based product and a baking mix material as part of an EU proficiency test, in which highly satisfactory results were obtained.
Keywords: Melamine; Food and beverage; Milk-based products; Ion-pair liquid chromatography; Tandem mass spectrometry; Triple quadrupole;

An international collaborative study of isotopic methods applied to control the authenticity of vinegar was organized in order to support the recognition of these procedures as official methods. The determination of the 2H/1H ratio of the methyl site of acetic acid by SNIF–NMR (site-specific natural isotopic fractionation–nuclear magnetic resonance) and the determination of the 13C/12C ratio, by IRMS (isotope ratio mass spectrometry) provide complementary information to characterize the botanical origin of acetic acid and to detect adulterations of vinegar using synthetic acetic acid. Both methods use the same initial steps to recover pure acetic acid from vinegar. In the case of wine vinegar, the determination of the 18O/16O ratio of water by IRMS allows to differentiate wine vinegar from vinegars made from dried grapes. The same set of vinegar samples was used to validate these three determinations.The precision parameters of the method for measuring δ13C (carbon isotopic deviation) were found to be similar to the values previously obtained for similar methods applied to wine ethanol or sugars extracted from fruit juices: the average repeatability (r) was 0.45 ‰, and the average reproducibility (R) was 0.91‰. As expected from previous in-house study of the uncertainties, the precision parameters of the method for measuring the 2H/1H ratio of the methyl site were found to be slightly higher than the values previously obtained for similar methods applied to wine ethanol or fermentation ethanol in fruit juices: the average repeatability was 1.34 ppm, and the average reproducibility was 1.62 ppm. This precision is still significantly smaller than the differences between various acetic acid sources (δ13C and δ18O) and allows a satisfactory discrimination of vinegar types. The precision parameters of the method for measuring δ18O were found to be similar to the values previously obtained for other methods applied to wine and fruit juices: the average repeatability was 0.15‰, and the average reproducibility was 0.59‰. The above values are proposed as repeatability and reproducibility limits in the current state of the art.On the basis of this satisfactory inter-laboratory precision and on the accuracy demonstrated by a spiking experiment, the authors recommend the adoption of the three isotopic determinations included in this study as official methods for controlling the authenticity of vinegar.
Keywords: Vinegar; Authenticity; SNIF–NMR; IRMS; Deuterium; Carbon 13; Oxygen 18;

It has been proved to be a very useful method to distinguish similar samples by two-dimensional correlation spectroscopy when they are hardly distinguished by the conventional one-dimensional spectroscopy. To acquire the quantitative description of the differences between samples, the similarity of the series dynamic spectra, which reflects the similarity of the samples themselves if obtained under the same perturbation condition, is evaluated by the symmetry of hetero 2DCOS map. Two parameters, the Euclidian distance and correlation coefficient between the upper left and lower right triangular parts of a hetero 2DCOS map, are introduced for the quantitative measure of the symmetry, which in turn characterizes the similarity of the responses of samples to a given perturbation. The above method is used to discriminate one genus of Astragalus from the others to ensure the medicinal efficacy and safety of the herb. Hypothesis tests show that the inter-distances between samples from different genera are significantly larger than the intra-ones within the same genera, while the inter-correlation coefficients are smaller than the intra-ones. The excellent result of the identification for all samples carried out by a t-test based on the distances indicates that this method provides an efficient technique for the quantitative evaluation of similarity between samples.
Keywords: Two-dimensional hetero correlation spectroscopy; Euclidian distance; Correlation coefficients; Astragalus;

Effect of layer structures of gold nanoparticle films on surface enhanced Raman scattering by Min Kyung Oh; Sukang Yun; Seong Kyu Kim; Sungho Park (111-116).
Using a method of collecting nanoparticles at a water/hexane interface in a close-packed monolayer film and transferring such films onto a solid substrate, three-dimensional multilayer films of nanoparticles were formed. The packed nanoparticles were gold nanospheres (NS) with a 26 nm diameter or gold nanorods (NR) with a 31 nm diameter and 74 nm length. We investigated variations in the surface enhanced Raman scattering (SERS) intensities from such nanoparticle films as the layer compositions were changed. The films stacked with NR layers generated much higher SERS intensity than those of NS layers. The SERS intensities from both kinds of films increased as the number of layers were increased. However, when the NR layer and NS layer were stacked alternately, SERS intensity varied in a zigzag fashion. It was found that the structure of top layer plays a distinguishable role in generating strong SERS enhancement while the lower layers contribute to SERS with less dependency on structures. Interlayer coupling as well as intralayer coupling was considered in order to explain the observations.
Keywords: Nanoparticle; Gold film; Surface enhanced Raman scattering; Plasmon; Extinction spectroscopy;

The adsorption of dopamine (DA) molecules on gold and their interactions with Fe3+ were studied by a microcantilever in a flow cell. The microcantilever bent toward the Au side with the adsorption of DA due to the change of surface stress induced by the intermolecular hydrogen bonds of DA or the charge transfer effect between adsorbates and the substrate. The interaction process between DA adsorbates and Fe3+ was revealed by the deflection curves of microcantilever. As indicated by the appearance of a variation during the decline of curves, two steps were observed in the curve at relative high concentrations of Fe3+. In this case, Fe3+ reacted with DA molecules only in the outer layers and the complexes removed with solution. Then Fe3+ reacted further with DA molecules forming the surface complex in the first layer next to the gold. At this stage, the stability of surface complexes was time dependent, i.e., unstable initially and stable finally. This may be due to the surface complexes change from mono-dentate to bi-dentate complexes. In another case, i.e., at relative low concentration of Fe3+, only the first step was observed as indicated by the absence of a variation. X-ray photoelectron spectroscopy (XPS) and cycling voltammetry (CV) results provided complementary evidence for the result of microcantilever and proposal. As low as 5 × 10−10  M Fe3+ was detected by DA modified microcantilever with a good selectivity over other common metal ions.
Keywords: Microcantilever; Interaction; Adsorption; Dopamine; Iron(III);

Sensitive and rapid chemiluminescence enzyme immunoassay for microcystin-LR in water samples by F. Long; H.C. Shi; M. He; J.W. Sheng; J.F. Wang (123-127).
A highly sensitive, specific, simple, and rapid chemiluminescence enzyme immunoassay (CLEIA) was developed for the determination of microcystin-LR (MC-LR). Several physicochemical parameters such as the chemiluminescent assay mediums, the dilution ratio of MC-LR–OVA conjugate, monoclonal antibody concentration, and peroxidase labeled antibody concentration were studied and optimized. Under optimum conditions, calibration curve obtained for MC-LR had detection limits of 0.032 ± 0.003 μg L−1, the 50% inhibition concentration (IC50) was 0.20 ± 0.02 μg L−1 and the quantitative detection range was 0.062–0.65 μg L−1. The proposed methods was successfully applied to the monitoring of MC-LR in spiked water samples without significant effect of the matrix, and the recovery of MC-LR added to water samples at different concentrations ranged from 80% to 115% with the coefficients of variation (CVs) less than 9%. The LOD attained from the calibration curves and the results obtained for the real samples demonstrate the potential use of CLEIA as a screening tool for the analysis of MC-LR in environmental samples.
Keywords: Chemiluminescence; Enzyme immunoassay; Microcystin-LR; Environmental analysis;

Multimodal electrophoresis of gold nanoparticles: A real time approach by Hirak K. Patra; Dwijit GuhaSarkar; Anjan Kr. Dasgupta (128-134).
A real time multimodal data acquisition imaging setup is developed for the electrophoretic movement of plasmonic nanoparticles. Movement of the nanoparticles is recorded by time-lapse digital imaging at 8-megapixel resolutions. The analysis of the moving nanoparticle band is performed using threshold image and color extraction at respective time frames. The migration dynamics is sensitive to size, nature and the extent of the surface conjugation to the nanoparticle. The dynamics of color intensity of the nanoparticles is shown to be dependent on the extent of stabilization of nanoparticle (by a given agent). The stability of nanoparticle is determined by stationary nature and also the relative proportions of pixel intensities in respective color planes (R, G and B). Detergents stabilize nanoparticles in a concentration dependent fashion. In case of neutral polymers the extent of stabilization depends on the relative proportion of the polymer and also on the nature of the same, e.g., PEG (polyethylene glycol) at low concentration imparts higher stability as compared to PVP (polyvinylpyrilidone). The ascending or declining temporal dynamics of color profiles observed in case of citrate stabilized or amino acid conjugated nanoparticles, represent enrichment of plasmonic particles, or their diffusion resulting from loss of charge during migration. The higher dimensional imaging technique thus can be exploited for discriminating the nanoparticles on the basis of their migration behavior and their stability as reflected from color dynamics. The technique is applicable to other nano-sized colored objects, e.g. proteins like hemoglobin where the protein color has important clinical value.
Keywords: Gold nanoparticles; Real time imaging; Electrophoresis; Migration dynamics; Color dynamics; Stability;