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Analytica Chimica Acta (v.688, #2)
Aptamer/quantum dot-based simultaneous electrochemical detection of multiple small molecules by Haixia Zhang; Bingying Jiang; Yun Xiang; Yuyong Zhang; Yaqin Chai; Ruo Yuan (pp. 99-103).
A novel strategy for “signal on” and sensitive one-spot simultaneous detection of multiple small molecular analytes based on electrochemically encoded barcode quantum dot (QD) tags is described. The target analytes, adenosine triphosphate (ATP) and cocaine, respectively, are sandwiched between the corresponding set of surface-immobilized primary binding aptamers and the secondary binding aptamer/QD bioconjugates. The captured QDs yield distinct electrochemical signatures after acid dissolution, whose position and size reflect the identity and level, respectively, of the corresponding target analytes. Due to the inherent amplification feature of the QD labels and the “signal on” detection scheme, as well as the sensitive monitoring of the metal ions released upon acid dissolution of the QD labels, low detection limits of 30nM and 50nM were obtained for ATP and cocaine, respectively, in our assays. Our multi-analyte sensing system also shows high specificity to target analytes and promising applicability to complex sample matrix, which makes the proposed assay protocol an attractive route for screening of small molecules in clinical diagnosis.
Keywords: Aptamers; Multi-analyte detection; Quantum dots; Small molecules; Square wave voltammetry
The role of chemometrics in single and sequential extraction assays: A review by Ornella Abollino; Mery Malandrino; Agnese Giacomino; Edoardo Mentasti (pp. 104-121).
Element mobility and availability in natural solid matrices can be studied with single and sequential extraction procedures; such procedures provide reliable and useful information only if the experiments are correctly planned and executed and the results are properly interpreted. Chemometrics can be a valuable tool for these aims, especially taking into account the large amounts of data generated with extraction essays and the complexity of the processes under investigation. This review deals with the application of chemometrics in research studies involving single and sequential extractions on soils or sediments, for several purposes: the development and optimization of the extraction conditions, the calculation of element fractionation, the visual illustration of the experimental results, the acquisition of different areas of information, including relationships among variables, similarities and differences among samples, causes of the observed behaviour (e.g. source identification), risk assessment, models and predictions of future events. In Part I of the review, following an overview on extraction procedures, the applications of univariate and bivariate chemometric methods are reported; then the principles of multivariate techniques for pattern recognition based on variable reduction, their applications and the main findings obtained are addressed.
Keywords: Single extraction; Sequential extraction; Chemometrics; Multivariate statistics; Soil; Sediment
The role of chemometrics in single and sequential extraction assays: A Review. Part II. Cluster analysis, multiple linear regression, mixture resolution, experimental design and other techniques by Agnese Giacomino; Ornella Abollino; Mery Malandrino; Edoardo Mentasti (pp. 122-139).
Single and sequential extraction procedures are used for studying element mobility and availability in solid matrices, like soils, sediments, sludge, and airborne particulate matter. In the first part of this review we reported an overview on these procedures and described the applications of chemometric uni- and bivariate techniques and of multivariate pattern recognition techniques based on variable reduction to the experimental results obtained. The second part of the review deals with the use of chemometrics not only for the visualization and interpretation of data, but also for the investigation of the effects of experimental conditions on the response, the optimization of their values and the calculation of element fractionation. We will describe the principles of the multivariate chemometric techniques considered, the aims for which they were applied and the key findings obtained. The following topics will be critically addressed: pattern recognition by cluster analysis (CA), linear discriminant analysis (LDA) and other less common techniques; modelling by multiple linear regression (MLR); investigation of spatial distribution of variables by geostatistics; calculation of fractionation patterns by a mixture resolution method (Chemometric Identification of Substrates and Element Distributions, CISED); optimization and characterization of extraction procedures by experimental design; other multivariate techniques less commonly applied.
Keywords: Single extraction; Sequential extraction; Chemometrics; Multivariate statistics; Soil; Sediment
Application of lag- k autocorrelation coefficient and the TGA signals approach to detecting and quantifying adulterations of extra virgin olive oil with inferior edible oils by José S. Torrecilla; Julián García; Silvia García; Francisco Rodríguez (pp. 140-145).
The combination of lag- k autocorrelation coefficients (LCCs) and thermogravimetric analyzer (TGA) equipment is defined here as a tool to detect and quantify adulterations of extra virgin olive oil (EVOO) with refined olive (ROO), refined olive pomace (ROPO), sunflower (SO) or corn (CO) oils, when the adulterating agents concentration are less than 14%. The LCC is calculated from TGA scans of adulterated EVOO samples. Then, the standardized skewness of this coefficient has been applied to classify pure and adulterated samples of EVOO. In addition, this chaotic parameter has also been used to quantify the concentration of adulterant agents, by using successful linear correlation of LCCs and ROO, ROPO, SO or CO in 462 EVOO adulterated samples. In the case of detection, more than 82% of adulterated samples have been correctly classified. In the case of quantification of adulterant concentration, by an external validation process, the LCC/TGA approach estimates the adulterant agents concentration with a mean correlation coefficient (estimated versus real adulterant agent concentration) greater than 0.90 and a mean square error less than 4.9%.
Keywords: Low grade olive oils; Corn oil; Sunflower oil; Thermogravimetric analyzer; Chaotic parameter; Adulteration
Effect of graphene nanosheet addition on the electrochemical performance of anode materials for lithium-ion batteries by Peng Guo; Huaihe Song; Xiaohong Chen; Lulu Ma; Guohua Wang; Feng Wang (pp. 146-155).
The structure and electronic properties of graphene nanosheet (GNS) render it a promising conducting agent in a lithium-ion battery. A graphite electrode loaded with GNS exhibits superior electrochemical properties including higher rate performance, increased specific capacity and better cycle performance compared with that obtained by adding the traditional conducting agent–acetylene black. The high-quality sp2 carbon lattice, quasi-two-dimensional crystal structure and high aspect ratio of GNS provide the basis for a continuous conducting network to counter the decrease in electrode conductivity with increasing number of cycles, and guarantee efficient and fast electronic transport throughout the anode. Effects of GNS loading content on the electrochemical properties of graphite electrode are investigated and results indicate that the amount of conductive additives needed is decreased by using GNS. The kinetics and mechanism of lithium-storage for a GNS-loaded electrode are explored using a series of electrochemical testing techniques.
Keywords: Graphene nanosheets; Conducting agent; Cycle performance; Rate performance; AC impedance
Determination of trace metal speciation parameters by using screen-printed electrodes in stripping chronopotentiometry without deaerating by C. Parat; A. Schneider; A. Castetbon; M. Potin-Gautier (pp. 156-162).
The objective of this study was to exploit the advantages of stripping chronopotentiometry (SCP) and stripping chronopotentiometry at scanned deposition potential (SSCP) for trace metal speciation analyses by using thin-film mercury screen-printed electrodes (TMF-SPE). At first, the SCP parameters were optimised for TMF-SPE, in order to reach the complete depletion regime. It has been shown that a stripping current higher than or equal to 10μA allows this regime to be attained without removing oxygen from the solution.Then, these analytical conditions were used for the construction of SSCP curves for Cd-PDCA and Cd-NTA. When the concentration of free ligand in solution was known, the knowledge of the model describing the SSCP curves in absence and presence of a complex and the use of an effective fitting tool enabled estimating the stability constant and the rate constants for complexation. Further studies with complexes of restricted mobility are however necessary to assess the usefulness of this procedure to also estimate the diffusion coefficient of the complexes. Besides, this study showed that this approach was valid even when ligands were not in excess at the electrode during stripping.
Keywords: Screen printed electrode; Stripping chronopotentiometry at scanned deposition potential; Speciation parameters
Electrochemical biosensors for detection of point mutation based on surface ligation reaction and oligonucleotides modified gold nanoparticles by Qing Wang; Lijuan Yang; Xiaohai Yang; Kemin Wang; Leiliang He; Jinqing Zhu (pp. 163-167).
An electrochemical method for point mutation detection based on surface ligation reaction and oligonucleotides (ODNs) modified gold nanoparticles (AuNPs) was demonstrated. Point mutation identification was achieved using Escherichia coli DNA ligase. This system for point mutation detection relied on a sandwich assay comprising capture ODN immobilized on Au electrodes, target ODN and ligation ODN. Because of the sequence-specific surface reactions of E. coli DNA ligase, the ligation ODN covalently linked to the capture ODN only in the presence of a perfectly complementary target ODN. The presence of ligation products on Au electrode was detected using chronocoulometry through hybridization with reporter ODN modified AuNPs. The use of AuNPs improved the sensitivity of chronocoulometry in this approach, a detection limit of 0.9pM complementary ODN was obtained. For single base mismatched ODN (smODN), a negligible signal was observed. Even if the concentration ratio of complementary ODN to smODN was decreased to 1:1000, a detectable signal was observed. This work may provide a specific, sensitive and cost-efficient approach for point mutant detection.
Keywords: Point mutation; DNA ligase; Gold nanoparticles; Chronocoulometry
Application of micro-thin-layer chromatography as a simple fractionation tool for fast screening of raw extracts derived from complex biological, pharmaceutical and environmental samples by Paweł K. Zarzycki; Magdalena M. Ślączka; Magdalena B. Zarzycka; Elżbieta Włodarczyk; Michał J. Baran (pp. 168-174).
The main goal of present paper is to demonstrate the separation and detection capability of micro-TLC technique involving simple one step liquid extraction protocols of complex materials without multi-steps sample pre-purification. In the present studies target components (cyanobacteria pigments, lipids and fullerenes) were isolated from heavy loading complex matrices including spirulina dried cells, birds’ feathers and fatty oils as well as soot samples derived from biomass fuel and fossils-fired home heating systems. In each case isocratic separation protocol involving less that 1mL of one component or binary mixture mobile phases can be completed within time of 5–8min. Sensitive detection of components of interest was performed via fluorescence or staining techniques using iodine or phosphomolybdic acid. Described methodology can be applied for fast fractionation or screening of whole range of target substances as well as chemo-taxonomic studies and fingerprinting of complex mixtures, which are present in raw biological or environmental samples.
Keywords: Micro-TLC; Spirulina; Birds’ feathers; Soot; Fullerenes; Biomass fuel
A micro gas preconcentrator with improved performance for pollution monitoring and explosives detection by E.H.M. Camara; P. Breuil; D. Briand; N.F. de Rooij; C. Pijolat (pp. 175-182).
This paper presents the optimization of a micro gas preconcentrator based on a micro-channel in porous and non-porous silicon filled with an adequate adsorbent. This micro gas preconcentrator is both applicable in the fields of atmospheric pollution monitoring (Volatil organic compounds—VOCs) and explosives detection (nitroaromatic compounds). Different designs of micro-devices and adsorbent materials have been investigated since these two parameters are of importance in the performances of the micro-device. The optimization of the device and its operation were driven by its future application in outdoor environments. Parameters such as the preconcentration factor, cycle time and the influence of the humidity were considered along the optimization process. As a result of this study, a preconcentrator with a total cycle time of 10min and the use of single wall carbon nanotubes (SWCNTs) as adsorbent exhibits a good preconcentration factor for VOCs with a limited influence of the humidity. The benefits of using porous silicon to modify the gas desorption kinetics are also investigated.
Keywords: Gas preconcentrator; Micro-channel; Porous silicon; Carbon nanotubes; Adsorbent
Shotgun proteomic analysis of microdissected postmortem human pituitary using complementary two-dimensional liquid chromatography coupled with tandem mass spectrometer by Yingchao Liu; Dongxiao Zhuang; Ruiping Hou; Jian Li; Guangming Xu; Tao Song; Luping Chen; Guoquan Yan; Qi Pang; Jianhong Zhu (pp. 183-190).
The pituitary is responsible for multiple homeostatic functions including metabolism, growth and reproduction. Proteome analysis offers an efficient approach for a comprehensive analysis of pituitary protein expression. The pituitary is usually acquired from postmortem specimens, which may potentially affect the proteome profile by proteolysis. The aim of this study was to determine whether the postmortem pituitary could be used in proteomic analysis combining with Laser capture microdissection (LCM). Digested peptides from LCM captured prolactin (PRL) cells were separated by two dimensional-nanoscale liquid chromatography (2D-nanoLC/MS) and characterized by tandem mass spectrometry (MS). All MS/MS spectrums were searched by SEQUEST and a proteome of 1660 proteins was identified. Category analysis of the proteome revealed an extensive unbiased access to cell component proteins with diverse functional characteristics. The results demonstrated the ability of using 2D-nanoLC/MS to perform sensitive proteomic analysis on limited protein quantities through microdissection. Detailed comparisons between the proteome in question and the one derived from the prolactinoma controls at peptide and protein levels indicated that the two proteomes had similar characters. Overall, our results revealed for the first time the possibility of use of postmortem human pituitary for proteomic research which is important for further studies on disease biomarker identification and molecular mechanisms of prolactinoma tumorigenesis.
Keywords: Human pituitary; Laser capture microdissection; Proteome; Mass spectrometry; Two dimensional liquid chromatography
Determination at low ppm levels of dithiocarbamate residues in foodstuff by vapour phase-liquid phase microextraction-infrared spectroscopy by Ana Gonzálvez; Salvador Garrigues; Sergio Armenta; Miguel de la Guardia (pp. 191-196).
A methodology based on the vapour phase (VP) generation of carbon disulphide from non-volatile dithiocarbamate compounds has been developed for determination of pesticide residues in foodstuff at low ppm levels. The method involves a selective reaction combined with liquid phase microextraction (LPME) and transmission infrared measurements. The use of a home made transmission cell improved the detection limits (LOD) compared to the use of attenuated total reflectance measurements by a factor of approximately 80. Using the most appropriate experimental conditions for the CS2 generation and LPME preconcentration, the precision of the methodology, expressed as the relative standard deviation (RSD), was of the order of 3.1% and the absolute LOD was 0.3μg dithiocarbamate, which corresponds to 60–120μgkg−1, for a sample mass ranging from 2.5 to 5g. The usefulness of the methodology has been evidenced by the determination of mancozeb residues in strawberries, lettuce and corn samples at concentrations between 1 and 5mgkg−1, where the VP-LPME IR provided results comparable with those obtained by a head space gas chromatography mass spectrometry reference procedure.
Keywords: Infrared spectroscopy; Preconcentration; Liquid phase microextraction; Vapour phase generation; Dithiocarbamates
Development of an ultrasensitive electrochemiluminescence inhibition method for the determination of tetracyclines by Zhiyong Guo; Panpan Gai (pp. 197-202).
An electrochemiluminescence (ECL) inhibition method is developed for quantitative determination of four tetracyclines (TCs) in honey samples, including tetracycline (TC), oxytetracycline (OTC), chlortetracycline (CTC) and doxycycline (DC). It was found that the four TCs strongly inhibited the ECL signal of the Ru(bpy)32+/DBAE system. Based on the ECL signal changes, a simple and ultrasensitive detection method for TCs was thus established. The optimum experimental conditions including the scan mode and scan rate of the applied potential, the type of the buffer solution and its pH, and the concentration of Ru(bpy)32+ and DBAE for the ECL inhibition method, were investigated in detail. Under the optimized conditions, the quenched ECL intensity versus the logarithm of the concentration of TCs is in good linear relationship over a concentration range from 4.0×10−11 to 4.0×10−9gmL−1. The detection limits were found to be 2.0×10−12gmL−1. The results obtained by the proposed ECL system, in terms of sensitivity, were much better than those of previously reported methods. In addition, the method was applied successfully to determine the total residuals of the four TCs in honey samples. The relative standard deviations were found in a range of 4.9–14.3%, and the recoveries were obtained from 87.5% to 115.0%. A possible mechanism for the quenching effects of Ru(bpy)32+/DBAE system was also proposed.
Keywords: ; Determination; Electrochemiluminescence; Inhibition; Tetracyclines; Ru(bpy); 3; 2+; /DBAE system; Honey
A novel palygorskite-modified carbon paste amperometric sensor for catechol determination by Yong Kong; Xiaohui Chen; Wenchang Wang; Zhidong Chen (pp. 203-207).
A palygorskite-modified carbon paste electrode (CPE) was constructed using graphite powder mixed with palygorskite particles. Compared with the unmodified CPE, the resulting palygorskite-modified CPE remarkably increases the peak currents of catechol, and greatly lowers the peak potential separation. Therefore, the palygorskite exhibits catalytic activity to catechol and significantly improves the determining sensitivity. The electrocatalytic activity of palygorskite is attributed to its high adsorption capability and the –OH groups on its surface, which plays an important role in the electron transfer between the modified CPE and the catechol in the solution. The sensor shows a linear response range between 5 and 100μM catechol with a correlation coefficient of 0.998. The detection limit was calculated as 0.57μM (s/n=3).
Keywords: Catechol; Sensor; Palygorskite; Carbon paste electrode; Electrocatalysis
Highly sensitive and selective pre-column derivatization high-performance liquid chromatography approach for rapid determination of triterpenes oleanolic and ursolic acids and application to Swertia species: Optimization of triterpenic acids extraction and pre-column derivatization using response surface methodology by Guoliang Li; Xiaolong Zhang; Jinmao You; Cuihua Song; Zhiwei Sun; Lian Xia; Yourui Suo (pp. 208-218).
Oleanolic acid (OA) and ursolic acid (UA) are the ubiquitous triterpenic acids in plant kingdom and have multiple biological effects. In the present study, a highly sensitive and selective method using a dual-sensitive probe 2-(5-benzoacridine)ethyl-p-toluenesulfonate (BAETS) as pre-column labeling reagent has been developed for rapid determination of the triterpenes OA and UA by HPLC with fluorescence detection (FLD) and online mass spectrometry identification. Response surface methodology as an efficient tool was employed to optimize the ultrasonic-assisted extraction of triterpenic acids from Swertia plants and the pre-column derivatization reaction, respectively, which ensured the highest triterpenic acids recoveries within the shortest extraction time and the sufficient labeling of the analyzed components. Fast separation of the isomers OA and UA could be achieved on a Hypersil BDS C8 column within 7min. Both of OA and UA gave the good correlation coefficients of 0.9999. This developed method offered the satisfactory detection limits of 1.10 and 1.30ngmL−1 for UA and OA, respectively. When applied to Swertia species, it showed good reproducibility.
Keywords: Oleanolic acids; Ursolic acids; Pre-column derivatization; HPLC-FLD; Swertia; species; Response surface methodology