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Analytical and Bioanalytical Chemistry (v.397, #4)

A focus on quantum dots for luminescent bioanalysis by Alfredo Sanz-Medel; Rosario Pereiro; José Manuel Costa-Fernández (pp. 1395-1396).

has been Professor in the Department of Physical and Analytical Chemistry of Oviedo University (Spain) since 1982. He is author or co-author of approximately 500 scientific publications in international journals, several patents, and books. His current research interests include new atomic detectors and ion sources for ultra-trace analysis using plasmas, new molecular optical sensors, particularly those based on the use of quantum dots, and hybrid techniques, coupling a separation unit and an atomic detector, for ultra-trace and trace metal speciation to solve biological and environmental problems and speciation for proteomics. This is aimed at by integrating mass spectrometry (MS) “molecular” (matrix-assisted laser desorption/ionization and electrospray MS), and “atomic” (inductively coupled plasma (ICP)MS) techniques, and introducing the extensive use of ICP–MS to carry out “heteroatom-tagged proteomics”, both for qualitative and quantitative purposes. He has been an editor of Analytical and Bioanalytical Chemistry since 2002. At Euroanalysis 2007, in Antwerp, he received the Robert Kellner Award. is an Associate Professor at the University of Oviedo (Spain) and was recently accredited as Full Professor in Analytical Chemistry. Her current research interests include investigation of new strategies to improve selectivity and/or sensitivity in molecular luminescence by using nanostructured sensing phases (e.g. molecular-imprinted polymers, quantum dots), and the development of analytical strategies for in-depth profile quantitative analysis of thin layers in advanced materials using optical emission and mass spectrometry. She has co-authored more than 100 scientific papers and several patents. is an Associate Professor at the Department of Physical and Analytical Chemistry and Vice-Dean of the Chemistry Faculty at the University of Oviedo (Spain). His current research interests include the development of functionalized photoluminescent nanomaterials (e.g. quantum dots and molecularly imprinted polymers) for biolabelling and sensing applications and the use of plasma-based elemental mass spectrometry for direct analysis of solids and for chemical speciation studies. He is co-author of more than 70 papers in international scientific journals, two patents, and chapters in several books, and co-supervises several PhD students.

In vitro and in vivo imaging with quantum dots by Chao Wang; Xue Gao; Xingguang Su (pp. 1397-1415).

Quantum dots (QDs), also named semiconductor nanocrystals, have initiated a new realm of bioscience by combining nanomaterials with biology, which will profoundly influence future biological and biomedical research. In this review, we describe the extraordinary optical properties of QDs and developments in methods for their synthesis. We focus on fluorescent imaging with QDs both in vitro and in vivo, and the cytotoxicity of QDs and potential barriers to their use in practical biomedical applications. Finally, we provide insights into improvements aimed at decreasing the cytotoxicity of QDs and the future outlook of QD applications in biomedical fields. Figure The unique tunable optical and chemical properties of QDs have been exploited in a growing array of biomedical applications including clinical diagnostics and molecular, cellular, and tumor imaging

Keywords: Quantum dots; In vitro; In vivo; Cytotoxicity; Doped quantum dots

Near-infrared quantum dots for deep tissue imaging by Ravindran Girija Aswathy; Yasuhiko Yoshida; T. Maekawa; D. Sakthi Kumar (pp. 1417-1435).

Developments in nanotechnology have paved the way for the early detection, treatment, and prevention of several tumors which affect mankind. In the past few years, near-infrared (NIR) fluorescence imaging techniques have emerged that enable the in vivo imaging of physiological, metabolic, and molecular function. The NIR window, also known as the diagnostic window (700–900 nm), can be explored for sensitive detection techniques. Nanoparticles, particularly semiconductor quantum dots (QDs), can be utilized for the purpose of optical imaging. These semiconductor QDs possess novel electronic, optical, magnetic, and structural properties which are quite different from those of bulk materials. NIR QDs with these unique properties can be utilized as contrast agents for optical imaging, particularly for deep tissue imaging. Deep tissue imaging provides more information about the pathological status of the disease, which makes the treatment more effective and efficient. In this review we highlight the importance of NIR QDs as probes for optical imaging. We describe the different types of NIR QDs, their synthesis, and their application for deep tissue imaging along with recently developed self-illuminating NIR QDs. Figure NIR QDs for deep tissue imaging

Keywords: Quantum dots; Near-infrared imaging; Deep tissue imaging; Nanotechnology; In vivo imaging; Optical imaging

Host-molecule-coated quantum dots as fluorescent sensors by Cuiping Han; Haibing Li (pp. 1437-1444).

“Host” molecules, containing a binding site that is highly specific for an analyte “guest,” are used as sensors to register analyte binding through a variety of mechanisms such as colorimetric, fluorescent, or electrochemical signals. There is increasing interest in the host–guest chemistry on the surface of quantum dots (QDs) and in the changes that it produces in the luminescent properties of QDs. The bulk of this study focuses on those QDs with bound host molecules (crown ether, cyclodextrin, calixarene, and porphyrin) and the selectivity they display toward metal ions and small organic molecules. Figure Applications of host-molecule-coated quantum dots (QDs)

Keywords: Quantum dots; Host molecules; Fluorescence; Sensing

Focus on quantum dots as potential fluorescent probes for monitoring food toxicants and foodborne pathogens by A. C. Vinayaka; M. S. Thakur (pp. 1445-1455).

Water-soluble quantum dots (QDs) are fluorescent semiconductor nanoparticles with narrow, very specific, stable emission spectra. Therefore, the bioconjugation of these QDs for biological fluorescent labeling may be of interest due to their unique physical and optical properties as compared to organic fluorescent dyes. These intrinsic properties of QDs have been used for the sensitive detection of target analytes. From the viewpoint of ensuring food safety, there is a need to develop rapid, sensitive and specific detection techniques to monitor food toxicants in food and environmental samples. Even trace levels of these toxicants can inadvertently enter the food chain, creating severe health hazards. The present review emphasizes the application of water-soluble bioconjugated QDs for the detection of food contaminants such as pesticides, pathogenic bacterial toxins such as botulinum toxin, enterotoxins produced by Staphylococcus aureus, Escherichia coli, and for the development of oligonucleotide-based microarrays. This review also emphasizes the application of a possible resonance energy transfer phenomenon resulting from nanobiomolecular interactions obtained through the bioconjugation of QDs with biomolecules. Furthermore, the utilization of significant changes in the spectral behavior of QDs (attributed to resonance energy transfer in the bioconjugate) in future nanobiosensor development is also emphasized.

Keywords: Nanotechnology; Quantum dots; FRET; Food toxicants; Foodborne pathogens; Biosensors

Optical recognition of salivary proteins by use of molecularly imprinted poly(ethylene-co-vinyl alcohol)/quantum dot composite nanoparticles by Mei-Hwa Lee; Yun-Chao Chen; Min-Hsien Ho; Hung-Yin Lin (pp. 1457-1466).

Molecularly imprinted polymers (MIPs) have long been studied for applications in biomolecule recognition and binding; compared with natural antibodies, they may offer advantages in cost and stability. We report on the development of MIPs that “self-report” concentrations of bound analytes via fluorescence changes in embedded quantum dots (QDots). Composite QDot/MIPs were prepared using phase inversion of poly(ethylene-co-vinyl alcohol) (EVAL) solutions with various ethylene mole ratios in the presence of salivary target molecules (e.g. amylase, lipase, and lysozyme). These major protein components of saliva have been implicated as possible biomarkers for pancreatic cancer. The optimum (highest imprinting effectiveness) ethylene mole ratios of the commercially available EVALs were found to be 32, 38, and 44 mol% for the imprinting of amylase, lipase, and lysozyme, respectively. QD fluorescence quenching was observed on binding of analytes to composite MIPs in a concentration-dependent manner, and was used to construct calibration curves. Finally, the composite MIP particles were used for the quantitative detection of amylase, lipase, and lysozyme in real samples (saliva) and compared with a commercial Architect ci 8200 chemical analysis system.

Keywords: Molecular imprinting; Quantum dots; Salivary proteins; Poly(ethylene-co-ethylene alcohol); Composite particles

Thiol-stabilized luminescent CdTe quantum dot as biological fluorescent probe for sensitive detection of methyl parathion by a fluoroimmunochromatographic technique by Raghuraj Singh Chouhan; Aaydha Chidambara Vinayaka; Munna Singh Thakur (pp. 1467-1475).

Quantum dots (QDs) are preferred as high-resolution biological fluorescent probes because of their inherent optical properties compared with organic dyes. This intrinsic property of QDs has been made use of for sensitive detection of methylparathion (MP) at picogramme levels. The specificity of the assay was attributed to highly specific immunological reactions. Competitive binding between free MP and CdTe QD bioconjugated MP (MP-BSA-CdTe) with immobilized anti-MP IgY antibodies was monitored in a flow-injection system. The fluorescence intensity of MP-BSA-CdTe bioconjugate eluted from the column was found to be directly proportional to the free MP concentration. Hence, it was possible to detect MP in a linear range of 0.1–1 ng mL⁻¹ with a regression coefficient R ² = 0.9905. In this investigation, IgY proved advantageous over IgG class immunoglobulins in terms of yield, stability, cost effectiveness, and enhancement of assay sensitivity. The photo-absorption spectrum of bioconjugated CdTe QD (λ _max = 310 nm) confirmed nano-biomolecular interactions. The results suggest the potential application of bioconjugation and nano-biomolecular interactions of QDs for biological labeling and target analyte detection with high sensitivity.

Keywords: Bioconjugation; CdTe QD; IgY antibodies; Methylparathion; Biosensor

Bibliometric study of journal publications on analytical chemistry 2000–2007: publication productivity and journal preferences by country by Helena Téllez; José M. Vadillo (pp. 1477-1484).

completed her chemistry studies at the University of Granada. After being awarded an FPU fellowship from the Spanish Government, she obtained a Ph.D. in 2010 in the application of secondary ion mass spectrometry to the resolution of nanostructures in microelectronics. During her doctoral period, she was a scientific visitor at the Department of Materials, Imperial College, London, and the Department of Materials, Paul Scherer Institute, Switzerland. completed his biology studies at the University of Navarra, before moving to Malaga to obtain a Ph.D. in analytical chemistry relating to the laser spectroscopy of solids. During his doctoral and postdoctoral studies, placements at Los Alamos National Laboratory (David Cremers, Vahid Majidi), University of Michigan (David Lubman), ETH (Renato Zenobi) and Stanford University (Richard Zare) allowed him to gain experience with mass spectrometers and many ionization sources. He currently holds a tenured position at the University of Malaga, where he focuses his attention on surface mass spectrometry and the laser spectroscopy of solids.

Composition study of CoPt bimetallic nanocrystals of 2 nm by Arnaud Demortière; Rémi Losno; Christophe Petit; Jean-Paul Quisefit (pp. 1485-1491).

The synthesis of bimetallic alloy nanocrystals with a well-controlled relative composition is a real challenge and requires chemical analysis techniques with high accuracy. A new chemical route has been used to synthesize cobalt–platinum nanocrystals of 2-nm diameter in a wide range of relative stoichiometry. A study of the elemental composition of the nanoalloy was carried out by X-ray fluorescence (XRF) spectroscopy and energy-dispersive X-ray analysis. We have developed a set-up for XRF analysis using a silicon wafer as a support to determine the elemental composition with only a small amount of sample. The calibration step and the measurement capabilities are described. In a composition range of 25–75% cobalt, the results of both analytical methods are discussed and compared in detail.

Keywords: CoPt nanoparticles; Nanoparticle composition; X-ray fluorescence spectroscopy; Energy-dispersive; X-ray analysis; Nanoalloy; Bimetallic nanocrystals

3D nanogap interdigitated electrode array biosensors by Kanwar Vikas Singh; Allison M. Whited; Yaswanth Ragineni; Thomas W. Barrett; Jeff King; Raj Solanki (pp. 1493-1502).

Three-dimensional interdigitated electrodes (IDEs) have been investigated as sensing elements for biosensors. Electric field and current density were simulated in the vicinity of these electrodes as a function of the electrode width, gap, and height to determine the optimum geometry. Both the height and the gap between the electrodes were found to have significant effect on the magnitude and distribution of the electric field and current density near the electrode surface, while the width of the electrodes was found to have a smaller effect on field strength and current density. IDEs were fabricated based on these simulations and their performance tested by detecting C-reactive protein (CRP), a stress-related protein and an important biomarker for inflammation, cardiovascular disease risk indicator, and postsurgical recuperation. CRP-specific antibodies were immobilized on the electrode surface and the formation of an immunocomplex (IC) with CRP was monitored. Electrochemical impedance spectroscopy (EIS) was employed as the detection technique. EIS data at various concentrations (1 pg/mL to 10 μg/mL) of CRP spiked in buffer or diluted human serum was collected and fitted into an equivalent electrical circuit model. Change in resistance was found to be the parameter most sensitive to change in CRP concentration. The sensor response was linear from 0.1 ng/mL to 1 μg/mL in both buffer and 5% human serum samples. The CRP samples were validated using a commercially available ELISA for CRP detection. Hence, the viability of IDEs and EIS for the detection of serum biomarkers was established without using labeled or probe molecules.

Keywords: Interdigitated electrodes; CRP; Impedimetric biosensor; EIS; Impedance spectroscopy; Device simulation; Label-free

Combined optoacoustic/ultrasound system for tomographic absorption measurements: possibilities and limitations by Christoph Haisch; Karin Eilert-Zell; Mika M. Vogel; Peter Menzenbach; Reinhard Niessner (pp. 1503-1510).

In this paper, we present the OPUS (optoacoustic plus ultrasound) system, which is a combination of a wavelength-tunable pulsed optical parametrical oscillator (OPO) laser with a commercial ultrasound (US) scanner. Optoacoustic (OA) or, synonymously, photoacoustic (PA) imaging is a spectroscopic technique to measure optical absorption in semitransparent solids and liquids. The measured signal is an acoustical pressure wave, which represents the absorption of pulsed optical radiation. By temporally and spatially resolved detection of the pressure wave on the sample surface, a 2D or even 3D image of the distribution of the optical absorption in the sample can be generated. In recent years, OA tomography has found increasing application in medical imaging. Most of these applications are based on qualitative OA imaging. The reported system is intended primarily for breast cancer detection, in which the optoacoustic imaging modality offers additional information to the ultrasound image. Consequently, the system is developed in a way that the OA imaging mode can be installed without major changes to the US instrument. The capabilities of the OPUS system for the quantitative analysis of absorber concentrations in tissue models are exploited.

Keywords: Photoacoustic; Medical imaging; Quantitative information; Ultrasound

Detection of chemical agents in the atmosphere by open-path FT-IR spectroscopy under conditions of background interference: I. High-frequency flashes by Limin Shao; Christopher W. Roske; Peter R. Griffiths (pp. 1511-1519).

Open-path FT-IR spectra were measured while fireworks were emitting smoke and incandescent particles into the infrared beam. These conditions were designed to simulate the appearance of smoke and explosions in a battlefield. Diethyl ether was used to simulate the vapor-phase spectra of G agents such as sarin. The measured interferograms were corrected by a high-pass filter and were rejected when interfering features were of such high frequency that they could not be removed by application of this filter. The concentration of diethyl ether was calculated correctly by partial least squares regression in the absence of fireworks but significant errors were encountered when the spectra of the oxide particles were not included in the calibration set. Target factor analysis allowed the presence of the analyte to be detected even when the incandescent particles were present in the beam.

Keywords: Open-path FT-IR spectrometry; Battlefield clutter; G agents; Fireworks; PLS regression; Target factor analysis

Detection of chemical agents in the atmosphere by open-path FT-IR spectroscopy under conditions of background interference: II. Fog and rain by Limin Shao; Christopher W. Roske; Peter R. Griffiths (pp. 1521-1528).

Open-path FT-IR spectra of low-concentration releases of diethyl ether were measured both when a glycol fog was passed into the infrared beam and when large water droplets from a lawn sprinkler were sprayed into the beam. It was shown that the glycol fog, for which the droplet size was much less than the wavelength of the infrared radiation, gave rise to a significant interference such that partial least squares (PLS) regression would only yield reasonable values for the ether concentration if background spectra in which the glycol fog was present were included in the calibration set. On the other hand, target factor analysis (TFA) allowed the presence of the ether to be recognized without precalibration. When large water droplets were present in the beam, any infrared radiation entering the droplet was completely absorbed, so that both PLS and TFA would yield accurate results.

Keywords: Open-path FT-IR spectrometry; Fog; Rain; Diethyl ether; Target factor analysis; PLS regression

Hg stable isotope analysis by the double-spike method by Chris Mead; Thomas M. Johnson (pp. 1529-1538).

Recent publications suggest great potential for analysis of Hg stable isotope abundances to elucidate sources and/or chemical processes that control the environmental impact of mercury. We have developed a new MC-ICP-MS method for analysis of mercury isotope ratios using the double-spike approach, in which a solution containing enriched ¹⁹⁶Hg and ²⁰⁴Hg is mixed with samples and provides a means to correct for instrumental mass bias and most isotopic fractionation that may occur during sample preparation and introduction into the instrument. Large amounts of isotopic fractionation induced by sample preparation and introduction into the instrument (e.g., by batch reactors) are corrected for. This may greatly enhance various Hg pre-concentration methods by correcting for minor fractionation that may occur during preparation and removing the need to demonstrate 100% recovery. Current precision, when ratios are normalized to the daily average, is 0.06‰, 0.06‰, 0.05‰, and 0.05‰ (2σ) for ²⁰²Hg/¹⁹⁸Hg, ²⁰¹Hg/¹⁹⁸Hg, ²⁰⁰Hg/¹⁹⁸Hg, and ¹⁹⁹Hg/¹⁹⁸Hg, respectively. This is slightly better than previously published methods. Additionally, this precision was attained despite the presence of large amounts of other Hg isotopes (e.g., 5.0% atom percent ¹⁹⁸Hg) in the spike solution; substantially better precision could be achieved if purer ¹⁹⁶Hg were used.

Keywords: Mercury; Inductively coupled plasma mass spectrometry; Stable isotopes

Validation of ELISA screening and LC–MS/MS confirmation methods for cocaine in hair after simple extraction by P. López; S. Martello; A. M. Bermejo; Eleonora De Vincenzi; M. J. Tabernero; M. Chiarotti (pp. 1539-1548).

This article describes an easy and innovative extraction procedure for cocaine and its primary metabolite, benzoylecgonine (BE), from hair consisting of sonication with H₂O/0.1% formic acid for 4 h. The same extract was used for screening with an enzyme-linked immunoassay (ELISA) and confirmation by liquid chromatography–tandem mass spectrometry (LC–MS/MS). For the ELISA screening test a cutoff of 0.5 ng/mg was used according to the Society of Hair Testing recommendations. LC–MS/MS limits of detection (LODs) were established to be 10 pg/mg and 1 pg/mg for cocaine and BE, respectively. Linearity was obtained over a range of 0.2–5 ng/mg for BE (target analyte) in the ELISA screening test, while in the LC–MS/MS method the range was 0.10–10 ng/mg for cocaine and 0.01–10 ng/mg for BE. Intra- and interbatch coefficients of variation and mean relative errors were less than 20% for all analytes and concentrations studied. The validated ELISA and LC–MS/MS methods were applied to 48 hair samples and the results of both methods were compared; ELISA demonstrated a sensitivity and specificity of 89.2% and 10.8%.

Keywords: Hair; Cocaine; Benzoylecgonine; ELISA; LC/MS/MS

Sampling analytes from cheese products for fast detection using neutral desorption extractive electrospray ionization mass spectrometry by Zhongchen Wu; Konstantin Chingin; Huanwen Chen; Liang Zhu; Bin Jia; Renato Zenobi (pp. 1549-1556).

The development of analytical techniques suitable for sensitive, high-throughput, and nondestructive food analysis has been of increasing interest in recent years. In this study, mass-spectral fingerprints of various cheese products were rapidly recorded in the mass range of m/z 50–300 Da without any sample pretreatment, using neutral desorption extractive electrospray ionization mass spectrometry (ND-EESI-MS) in negative ion mode. The results demonstrate that both volatile and nonvolatile analytes on greasy cheese surfaces can be directly sampled by a neutral desorption gas beam. The influence of the neutral desorption gas flow on the analyte signal was systematically investigated. Under optimized experimental conditions, reproducible results were obtained using ND-EESI-MS. Principal component analysis was applied to differentiate a total of 49 individual cheese samples (four different types), which were purchased from three different supermarkets. All samples were successfully classified according to their types; but distributors and sensory properties were not distinguishable from the spectra data. The principal components 2, 3, and 4 scores showed an excellent capacity of distinguishing types of cheese. Molecular markers of interest can be identified using tandem mass spectrometry and matching the data with those from reference compounds. The experimental data show that ND-EESI-MS is able to sensitively and directly detect analytes on greasy surfaces without chemical contamination, providing a convenient method for high-throughput food analysis with a high degree of safety.

Keywords: Neutral desorption extractive electrospray ionization; Cheese; Food safety; Greasy surfaces; Principal component analysis

Tamoxifen monitoring studies in breast cancer patients by micellar liquid chromatography by Josep Esteve-Romero; Enrique Ochoa-Aranda; Devasish Bose; Maria Rambla-Alegre; Juan Peris-Vicente; Adrià Martinavarro-Domínguez (pp. 1557-1561).

A simple micellar liquid chromatographic procedure is described to determine tamoxifen in plasma. To perform the analysis, tamoxifen solutions were diluted in water and UV-irradiated for 20 min to form the photocycled derivative with a phenanthrene core which shows intense fluorescence. Samples were then directly injected, thus avoiding long extraction and experimental procedures. The resolution from the matrix was performed with a mobile phase containing 0.15 M SDS–7% n-butanol at pH 3 running at 1.5 mL/min through a C18 column at 40 °C. Detection was carried out by fluorescence, and the excitation and emission wavelengths were 260 and 380 nm, respectively. The chromatographic analysis time was less than 15 min. The analytical methodology was validated following the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) guidelines. The response of the drug in plasma was linear and in the 0.5–15 µg/mL range, with r ² > 0.999. Accuracy and precision were <9% in both cases. The limits of detection and quantification (in nanograms per millilitre) were 50 and 150 in plasma, respectively. The method developed herein shows no interferences by endogenous compounds. Finally, the analytical method was used to determine the amount of tamoxifen in the plasma of several breast cancer patients from a local hospital.

Keywords: Micellar liquid chromatography; Pharmaceuticals; Plasma; Tamoxifen; UV

Identification and quantification of daidzein-7-glucuronide-4′-sulfate, genistein-7-glucuronide-4′-sulfate and genistein-4′,7-diglucuronide as major metabolites in human plasma after administration of kinako by Kaori Hosoda; Takashi Furuta; Akitomo Yokokawa; Kazuo Ishii (pp. 1563-1572).

Much attention has been paid to the metabolism and disposition of isoflavones daidzein (Dein) and genistein (Gein) with regard to the prevention of several hormone-dependent diseases. Recent studies have reported that several conjugates as well as aglycones may be biologically active or may be activated within target cells. However, the disposition of Dein and Gein in plasma is still uncertain. This paper describes the identification and quantification of the highly polar metabolites, daidzein-7-glucuronide-4′-sulfate (D-7G-4′S), genistein-7-glucuronide-4′-sulfate (G-7G-4′S), daidzein-4′,7-diglucuronide (D-4′,7-diG), and genistein-4′,7-diglucuronide (G-4′,7-diG) in human plasma after dietary administration of kinako (baked soybean powder) to two healthy volunteers. The structure identification of these conjugated metabolites in plasma was performed in comparison to the LC-ESI-MS and 600 MHz ¹H-NMR spectral data of the chemically synthesized compounds. Furthermore, 16 isoflavone metabolites including D-7G-4′S, G-7G-4′S, D-4′,7-diG, and G-4′,7-diG in plasma were simultaneously measured by a high-performance liquid chromatography–UV-diode-array detector method combined with solid-phase extraction using an Oasis HLB cartridge. D-7G-4′S, G-7G-4′S and G-4′,7-diG were found to be major metabolites of Dein and Gein in plasma, while intact aglycones were detected to be only ca. 2% in both subjects. The findings suggest that the conjugated metabolites could be the key compounds responsible for pharmacological and medicinal properties of isoflavones.

Keywords: Isoflavone; Sulfoglucuronide; Diglucuronide; High-performance liquid chromatography; Identification; Quantification

Probing of ascorbic acid by CdS/dendrimer nanocomposites: a spectroscopic investigation by Srabanti Ghosh; S. C. Bhattacharya; Abhijit Saha (pp. 1573-1582).

The gamma irradiation method has provided a route for synthesis of highly water-soluble, good-quality luminescent CdS/dendrimer nanocomposites with amino- or carboxyl-terminated PAMAM dendrimer. An attempt has been made to probe ascorbic acid with the as-synthesized CdS/dendrimer nanocomposites (DNC). Ascorbic acid (AA) is an important biological antioxidant and marker for different diseases in clinical chemistry as well as in quality control in the food industry. Micromolar concentrations of AA significantly quenched the photoluminescence (PL) of both amino (–NH₂) and carboxylic (–COOH) functionalized semiconductor nanocomposites. The quenching followed a linear Stern–Volmer equation and time-resolved photoluminescence spectroscopy confirmed its static nature. A strong size dependence of the quenching pattern was observed. The binding constants, and the corresponding thermodynamic parameters ΔG ^θ, ΔH ^θ, ΔS ^θ at different temperatures were calculated. CdS DNC showed selectivity towards ascorbic acid even in the presence of possible interfering molecules, such as uric acid, tartaric acid and citric acid. Nanocomposites-based assay techniques could override the complications involved in multitudes of assay procedures, providing a simple and fast new strategy for the quantification of Ascorbic acid in the range of 16.6 to 100 μM (R = 0.998, n = 9). The proposed method was applied to the detection of ascorbic acid in Vitamin C tablets with satisfactory results. Figure

Keywords: CdS; PAMAM dendrimer; Nanocomposites; Ascorbic acid; Photoluminescence

Characterization of a capacitance-coupled contactless conductivity detection system with sidewall electrodes on a low-voltage-driven electrophoresis microchip by Yi Xu; Jing Liang; Haitao Liu; Xiaoguo Hu; Zhiyu Wen; Yongjie Wu; Mingxia Cao (pp. 1583-1593).

A new type of capacitance-coupled contactless conductivity detection (C⁴D) system with sidewall electrodes was proposed for integration on a silicon-on-isolator–poly(dimethylsiloxane) (SOI-PDMS) hybrid low-voltage-driven electrophoresis microchip. By a microelectromechanical system process, the sidewall electrodes were fabricated precisely at either side of the separation channel. The area of the capacitor electrodes was the maximum value to improve the detection sensitivity with an enhanced capacitance effect. According to the simulation results, the structural parameters of the sidewall electrodes were determined as 550-μm length, 15-μm width, 80-μm separation distance, and 1-μm isolator thickness. The integrated microdevice with the SOI-PDMS hybrid electrophoresis microchip was very compact and the size was only 15 cm × 15 cm × 10 cm (width × length × height), which permitted miniaturization and portability. The detector performance was evaluated by K⁺ testing. The detection limit of the conductivity detector was determined to be 10^-9 and 10^-6 M for K⁺ in the static and electric-driven modes, respectively. Finally, the C⁴D was applied to low-voltage-driven electrophoresis on a microchip to carry out real-time measurement of the separation of amino acids. The separations of 10^-4 M lysine and phenylalanine in the low-voltage-driven electrophoresis mode were performed with an electric field of 300 V/cm and were completed in less than 15 min with a resolution of 1.3. The separation efficiency was found to be 1.3 × 10³ and 2.8 × 10³ plates for lysine and phenylalanine, respectively, with a migration time reproducibility of 2.7 and 3.2%. The conductivity detection limit of amino acids achieved was 10^-6 M. The proposed method for the construction of a novel C⁴D integrated on an SOI-PDMS hybrid low-voltage-driven electrophoresis microchip showed the most extensive integration and miniaturization of a microdevice, which is a further crucial step toward the realization of the “lab-on-a-chip” concept.

Keywords: Contactless conductivity detection; Sidewall detecting electrodes; Low-voltage-driven electrophoresis; Lab on a chip

A highly sensitive detection platform based on surface-enhanced Raman scattering for Escherichia coli enumeration by Erhan Temur; İsmail Hakkı Boyacı; Uğur Tamer; Hande Unsal; Nihal Aydogan (pp. 1595-1604).

A very sensitive and highly specific heterogeneous immunoassay system, based on surface-enhanced Raman scattering (SERS) and gold nanoparticles, was developed for the detection of bacteria and other pathogens. Two different types of gold nanoparticles (citrate-stabilized gold nanosphere and hexadecyltrimethylammonium bromide (CTAB)-stabilized gold nanorod particles) were examined and this immunoassay was applied for the detection of Escherichia coli. Raman labels were constructed by using these spherical and rod-shaped gold nanoparticles which were first coated with 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB) and subsequently with a molecular recognizer. The working curve was obtained by plotting the intensity of the SERS signal of the symmetric NO₂ stretching of DTNB at 1,333 cm⁻¹ versus the concentration of the E. coli. The analytical performance of gold particles was evaluated via a sandwich immunoassay, and linear calibration graphs were obtained in the E. coli concentration range of 10¹–10⁵ cfu/mL with a 60-s accumulation time. The sensitivity of the Raman label fabricated with gold nanorods was more than three times higher than spherical gold nanoparticles. The selectivity of the developed sensor was examined with Enterobacter aerogenes and Enterobacter dissolvens, which did not produce any significant response. The usefulness of the developed immunoassay to detect E. coli in real water samples was also demonstrated.

Keywords: Immunoassay; Gold nanoparticle; Surface-enhanced Raman scattering; Escherichia coli

Development and validation of an HPLC-UV method for the simultaneous quantification of carbamazepine, oxcarbazepine, eslicarbazepine acetate and their main metabolites in human plasma by Ana Fortuna; Joana Sousa; Gilberto Alves; Amílcar Falcão; Patrício Soares-da-Silva (pp. 1605-1615).

For the first time, a simple, selective and accurate high-performance liquid chromatography method with ultraviolet detection was developed and validated to quantify simultaneously three structurally related antiepileptic drugs; carbamazepine, oxcarbazepine, and the recently launched eslicarbazepine acetate and their main metabolites, carbamazepine-10,11-epoxide, 10,11-trans-dihydroxy-10,11-dihydro-carbamazepine, and licarbazepine. The method involves a solid-phase extraction and a reverse-phase C18 column with 5 cm length. The mobile phase consisting of water, methanol, and acetonitrile in the ratio 64:30:6 was selected as the best one and pumped at 1 mL/min at 40 °C. The use of this recent column and an aqueous mobile phase instead of buffers gives several advantages over the method herein developed; namely the fact that the chromatographic analysis takes only 9 min. The method was validated according to the guidelines of the Food and Drug Administration, showing to be accurate (bias within ±12%), precise (coefficient variation <9%), selective and linear (r ² > 0.997) over the concentration range of 0.05–30 μg/mL for carbamazepine; 0.05–20 μg/mL for oxcarbazepine; 0.15–4 μg/mL for eslicarbazepine acetate; 0.1–30 μg/mL for carbamazepine-10,11-epoxide; 0.1–10 μg/mL for 10,11-trans-dihydroxy-10,11-dihydro-carbamazepine, and 0.1–60 μg/mL for licarbazepine. It was also shown that this method can adequately be used for the therapeutic drug monitoring of the considered antiepileptic drugs, carbamazepine, oxcarbazepine, eslicarazepine acetate, and their metabolites.

Keywords: Carbamazepine; Oxcarbazepine; Eslicarbazepine acetate; Therapeutic drug monitoring; HPLC; Bioanalytical method validation

Soil-dissipation kinetics of twelve herbicides used on a rain-fed barley crop in Spain by Cristina Díez; Enrique Barrado (pp. 1617-1626).

This study evaluated the dissipation kinetics under actual field conditions of twelve herbicides in a typical xerofluvent soil in Castilla y León (north central Spain) sustaining barley. The type of soil selected was that typically used in the Castilla y León region to cultivate barley under a rain-fed alternating crop–fallow rotation regimen. Treatments were conducted in spring as two replicates and the soil was sampled every day during the first week, once a week for the following few weeks and thereafter once every month. Soil samples were extracted with a suitable mixture of acetone, water and acetic acid (30:7.5:0.3) before their analysis by GC–MS (gas chromatography–mass spectrometry). Dissipation of the herbicides was well described by a biphasic kinetics pattern. The dissipation times DT50 and DT90 were in general lower than those reported in the literature, owing to a high initial dissipation rate because of volatilization and photolysis processes caused by high environmental temperatures. Herbicide degradation was also enhanced by their lack of sorption by this low colloid-content soil. However, the most persistent herbicides, triallate, flamprop, pendimethalin, terbutryn, and isoproturon, remained for 286 to 372 days in the soil, because low water and organic carbon content impaired microbial growth. In contrast, the phenoxy acid herbicides dissipated rapidly, with no detectable residues detected on harvesting the crop.

Keywords: Kinetics; Dissipation; Field conditions; Herbicides; Soil; Barley; GC–MS

Trace determination of triclosan and triclocarban in environmental water samples with ionic liquid dispersive liquid-phase microextraction prior to HPLC–ESI-MS–MS by Ru-Song Zhao; Xia Wang; Jing Sun; Shan-Shan Wang; Jin-Peng Yuan; Xi-Kui Wang (pp. 1627-1633).

A novel and environmentally friendly microextraction method, termed ionic liquid dispersive liquid-phase microextraction (IL-DLPME), has been developed for rapid enrichment of triclosan and triclocarban before analysis by high-performance liquid phase chromatography–electrospray tandem mass spectrometry (HPLC–ESI-MS–MS). Instead of using toxic organic solvents, an ionic liquid was used as a green extraction solvent. This also avoided the instability of the suspending drop in single-drop liquid-phase microextraction, and the heating and cooling step in temperature-controlled ionic liquid dispersive liquid phase microextraction. Factors that may affect the enrichment efficiency, for example volume of ionic liquid, type and volume of dispersive solvent, pH, extraction time, and NaCl content were investigated in detail and optimized. Under optimum conditions, linearity of the method was observed over the range 0.2–12 μg L⁻¹ for triclocarban and 1–60 μg L⁻¹ for triclosan with correlation coefficients ranging from 0.9980 to 0.9990, respectively. The sensitivity of the proposed method was found to be excellent, with limits of detection in the range 0.040–0.58 μg L⁻¹ and precision in the range 7.0–8.8% (RSD, n = 5). This method has been successfully used to analyze real environmental water samples and satisfactory results were achieved. Average recoveries of spiked compounds were in the range 70.0–103.5%. All these results indicated that the developed method would be a green method for rapid determination of triclosan and triclocarban at trace levels in environmental water samples.

Keywords: Triclosan; Triclocarban; Ionic liquid dispersive liquid phase microextraction; High performance liquid phase chromatography–electrospray tandem mass spectrometry

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Analytical and Bioanalytical Chemistry (v.397, #4)

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Analytical and Bioanalytical Chemistry (v.397, #4)