Analytica Chimica Acta (v.966, #C)

Passive sampling of anionic pesticides using the Diffusive Gradients in Thin films technique (DGT) by Robin Guibal; Rémy Buzier; Adeline Charriau; Sophie Lissalde; Gilles Guibaud (1-10).
DGT passive samplers using Oasis® HLB or Oasis® MAX sorbent were developed for anionic pesticides sampling. They were tested using four model compounds (i.e. bentazon, chlorsulfuron, ioxynil and mecoprop). Polyacrylamide diffusive gel was found to be more suitable than agarose gel for most anionic pesticides sampling. An elution procedure was optimized and diffusion coefficients were determined for quantitative use of the samplers. Depending on the DGT configuration used (HLB or MAX), accuracies better than 30% were demonstrated in laboratory for pH from 3 to 8 and ionic strengths from 10−2 to 1 M. Combined with the effective binding capacities of samplers (≥9 μg for each pesticide) and limits of quantification of the method (≤13 ng.L−1 using Q-TOF detector) monitoring of numerous aquatic systems can be expected. Except for ioxynil, accurate quantifications were demonstrated in laboratory using a spiked natural water for HLB-DGT whereas MAX-DGT did not give satisfactory results. A further in situ validation was performed in two rivers and showed identical detection frequency between HLB-DGT and POCIS of anionic pesticides (bentazon and mesotrione) whereas calculated concentrations, although within the same order of magnitude, could differ (<70%). HLB-DGT could therefore constitute an interesting alternative to other passive samplers for the monitoring of several anionic pesticides in aquatic systems but more work is required for quantification of molecules from hydroxybenzonitrile chemical group (ioxynil).Display Omitted
Keywords: Anionic pesticides; Herbicides; Passive sampling; Diffusive Gradients in Thin films; Water analysis;

Review: Microbial analysis in dielectrophoretic microfluidic systems by Renny E. Fernandez; Ali Rohani; Vahid Farmehini; Nathan S. Swami (11-33).
Infections caused by various known and emerging pathogenic microorganisms, including antibiotic-resistant strains, are a major threat to global health and well-being. This highlights the urgent need for detection systems for microbial identification, quantification and characterization towards assessing infections, prescribing therapies and understanding the dynamic cellular modifications. Current state-of-the-art microbial detection systems exhibit a trade-off between sensitivity and assay time, which could be alleviated by selective and label-free microbial capture onto the sensor surface from dilute samples. AC electrokinetic methods, such as dielectrophoresis, enable frequency-selective capture of viable microbial cells and spores due to polarization based on their distinguishing size, shape and sub-cellular compositional characteristics, for downstream coupling to various detection modalities. Following elucidation of the polarization mechanisms that distinguish bacterial cells from each other, as well as from mammalian cells, this review compares the microfluidic platforms for dielectrophoretic manipulation of microbials and their coupling to various detection modalities, including immuno-capture, impedance measurement, Raman spectroscopy and nucleic acid amplification methods, as well as for phenotypic assessment of microbial viability and antibiotic susceptibility. Based on the urgent need within point-of-care diagnostics towards reducing assay times and enhancing capture of the target organism, as well as the emerging interest in isolating intact microbials based on their phenotype and subcellular features, we envision widespread adoption of these label-free and selective electrokinetic techniques.Display Omitted
Keywords: Bacteria; Microfluidics; Sensor; Dielectrophoresis; Phenotype; Antibiotics;

Increasing metabolite coverage by combining data from different platforms or methods can improve understanding of related metabolic mechanisms and the identification of biomarkers. However, no one method can obtain metabolomic and lipidomic information in a single analysis. In this work, aiming at collecting comprehensive information on metabolome and lipidome in a single analytical run, we developed an on-line heart-cutting two-dimensional liquid chromatography-mass spectrometry (2D-LC-MS) method. Complex metabolites from biological samples are divided into two fractions by using a precolumn. The first fraction is directly transferred and subjected to metabolomics analysis. Most lipids are retained on the precolumn until the mobile phases for lipidomics flow through; then they are subjected to lipidomics analysis. Up to 447 and 289 metabolites in plasma, including amino acids, carnitines, bile acids, free fatty acids, lyso-phospholipids, phospholipids, sphingomyelins etc. were identified within 30 min in the positive mode and negative mode, respectively. A comparison of the newly developed method with the conventional metabolomic and lipidomic approaches showed that approximately 99% features obtained by the two conventional methods can be covered with this 2D-LC method. Analytical characteristics evaluation showed the method had a wide linearity range, high sensitivity, satisfactory recovery and repeatability. These results demonstrate that this method is reliable, stable and well qualified in metabolomics analysis, particularly for large-scale metabolomics studies with small amount of samples.Display Omitted
Keywords: Metabolomics; Lipidomics; Metabolite coverage; Two-dimensional liquid chromatography; Heart-cutting;

This study demonstrates a simple method for rapid and in situ identification of volatile and endogenous compounds in culinary spice samples through mass spectrometry (MS). This method only requires a holder for solid spice sample (2–3 mm) that is placed close to a mass spectrometer inlet, which is applied with a high voltage. Volatile species responsible for the aroma of the spice samples can be readily detected by the mass spectrometer. Sample pretreatment is not required prior to MS analysis, and no solvent was used during MS analysis. The high voltage applied to the inlet of the mass spectrometer induces the ionization of volatile compounds released from the solid spice samples. Furthermore, moisture in the air also contributes to the ionization of volatile compounds. Dried spices including cinnamon and cloves are used as the model sample to demonstrate this straightforward MS analysis, which can be completed within few seconds. Furthermore, we also demonstrate the suitability of the current method for rapid screening of cinnamon quality through detection of the presence of a hepatotoxic agent, i.e. coumarin.Display Omitted
Keywords: Volatiles; Ionization; Open-air; Mass spectrometry; Cinnamon;

The existing immunoassay format that combines the electrophoretic collection of charged analytes on an antibody microarray with the detection of the bound analytes by magnetic beads coated with secondary antibodies displays extreme sensitivity and speed, but suffers from low precision because of high signal scatter and low signal-to-concentration ratio. Here we report three innovations that substantially improve the precision of this method and enable quantitative measurements of analyte concentrations as low as 10 fg/ml. The improvements were achieved by (i) employing parallel titration of analytes by measuring signal response to a series of sample dilutions with increasing analyte concentration, (ii) internally normalizing the signal (by relating signal intensity to that of positive controls on the same microarray) and (iii) taking measurements in the linear range of the calibration curve at concentrations close to the limit of detection. This improved method was used to quantitatively measure in human serum the titer of immunoglobulins specific to antigens secreted by Mycobacterium tuberculosis.Display Omitted
Keywords: Immunoassay; Antibody microarray; Magnetic beads; Ultra-sensitive;

An ultra-highly sensitive electrochemical immunosensor for SirT1 (a key protein in age-related diseases) evaluation has been designed, employing polymeric nanocomposites as sensing platform and core-shell SiO2@Au to immobilize HRP-Ab2 as nanobioprobes. The approach includes chemical synthesis of PAMAM-Au-MWCNT nanocomposites (PNCs) with abundant PAMAM-Au nanoparticles immobilized on the MWCNT matrix, and biochemically synthesis of nanobioprobes with highly dispersed SiO2@Au tracing tags for successive efficient load functionalized enzyme-antibodies (HRP-Ab2). The PNCs nanocomposites could improve the efficiency of immune response via abundant capture antibodies (Ab1 #1) on the electrode surface, and accelerate electron transfer through MWCNT and Au nanoparticles. Besides, the SiO2@Au was employed as tracing tags to label numerous HRP-Ab2 to further enhance signal readout during HRP−thionine−H2O2 system. Under optimal conditions, the signal intensity was linearly related to the concentration of SirT1 in the range of 20 pg mL-1 to 500 ng ml-1, and the limit of detection was 12.5 pg mL-1. It is noteworthy that the proposed immunoassay protocol has been successfully applied to evaluate SirT1 expression in cells by different treatment with high sensitivity and accuracy.Display Omitted
Keywords: SirT1; Polymeric nanocomposites; Core-shell nanobioprobes; Immunoassay; Electrochemistry;

Determination of cDNA encoding BCR/ABL fusion gene in patients with chronic myelogenous leukemia using a novel FRET-based quantum dots-DNA nanosensor by Mojtaba Shamsipur; Vahid Nasirian; Ali Barati; Kamran Mansouri; Asad Vaisi-Raygani; Soheila Kashanian (62-70).
In the present study, we developed a sensitive method based on fluorescence resonance energy transfer (FRET) for the determination of the BCR/ABL fusion gene, which is used as a biomarker to confirm the clinical diagnosis of both chronic myelogenous leukemia (CML) and acute lymphocytic leukemia (ALL). For this purpose, CdTe quantum dots (QDs) were conjugated to amino-modified 18-mer oligonucleotide ((N)DNA) to form the QDs-(N)DNA nanosensor. In the presence of methylene blue (MB) as an intercalator, the hybridization of QDs-(N)DNA with the target BCR/ABL fusion gene (complementary DNA), brings the MB (acceptor) at close proximity of the QDs (donor), leading to FRET upon photoexcitation of the QDs. The enhancement in the emission intensity of MB was used to follow up the hybridization, which was linearly proportional to concentration of the target complementary DNA in a range from 1.0 × 10−9 to 1.25 × 10−7 M. The detection limit of the proposed method was obtained to be 1.5 × 10−10 M. Finally, the feasibility and selectivity of the proposed nanosensor was evaluated by the analysis of derived nucleotides from both mismatched sequences and clinical samples of patients with leukemia as real samples.Display Omitted
Keywords: BCR/ABL; Chronic myelogenous leukemia (CML); FRET; CdTe QDs; Fluorescence;

This study highlighted the development of a four target nitrocellulose-based nucleic acid lateral flow immunoassay biosensor in a dry-reagent strip format for interpretation of double-labelled double-stranded amplicons from thermostabilised triplex loop-mediated isothermal amplification assay. The DNA biosensor contained two test lines which captured biotin and texas red labelled amplicons; a LAMP internal amplification control line that captured digoxigenin labelled amplicon; and a chromatography control line that validated the functionality of the conjugated gold nanoparticles and membrane. The red lines on detection pad were generated when the gold nanoparticles conjugated antibody bound to the fluorescein labelled amplicons, and the capture agents bound to their specific hapten on the other 5′ end of the double-stranded amplicon. The applicability of this DNA biosensor was demonstrated using amoebiasis-causing Entamoeba histolytica simultaneously with the non-pathogenic but morphologically identical Entamoeba dispar and Entamoeba moshkovskii. The biosensor detection limit was 10 E. histolytica trophozoites, and revealed 100% specificity when it was evaluated against 3 medically important Entamoeba species and 75 other pathogenic microorganisms. Heat stability test showed that the biosensor was stable for at least 181 days at ambient temperature. This ready-to-use and cold-chain-free biosensor facilitated the post-LAMP analysis based on visualisation of lines on strip instead of observation of amplicon patterns in agarose gel.Display Omitted
Keywords: DNA lateral flow biosensor; Multiplex LAMP; Thermostabilization; Entamoeba histolytica; Isothermal amplification;

A 3D printed smartphone optosensing platform for point-of-need food safety inspection by Zhonggang Liu; Yali Zhang; Shujia Xu; Heng Zhang; Yixun Tan; Chenming Ma; Rong Song; Lelun Jiang; Changqing Yi (81-89).
The deficiency in rapid and in-field detection methods and portable devices that are reliable, easy-to-use, and low cost, results in the difficulties to uphold the high safety standards in China. In this study, we introduce a rapid and cost-effective smartphone-based method for point-of-need food safety inspection, which employs aptamer-conjugated AuNPs as the colorimetric indicator, and a battery-powered optosensing accessory attached to the camera of a smartphone for transmission images capture. A user-friendly and easy-to-use Android application is developed for automatic digital image processing and result reporting. Streptomycin (STR) is selected as the proof-of-concept target, and its specific quantitation can be realized with a LOD of 12.3 nM (8.97 μg kg−1) using the reported smartphone-based method. The quantitation of STR in honey, milk and tap water confirm the reliability and applicability of the reported method. The extremely high acceptance of smartphone in remote and metropolitan areas of China and ease-of-use of the reported method facilitate active food contaminant and toxicant screening, thus making the implementation of the whole food supply chain monitoring and surveillance possible and hence significantly improving the current Chinese food safety control system.Display Omitted
Keywords: Smartphone optosensing device; Gold nanoparticles; Two-color ratiometric method; Streptomycin; 3D printing; Point-of-need food safety inspection;