Nuclear magnetic resonance of mass-limited samples using small RF coils

Figure Schematic diagram of a typical arrangement used for hyphenating chemical microseparations (e.g. capillary HPLC, CE, or CEC) with microcoil NMR detection     

Estimating relative carbonyl levels in muscle microstructures by fluorescence imaging

The increase in the levels of protein carbonyls, biomarkers of oxidative stress, appears to play an important role in aging skeletal muscle. However, the exact distributions of carbonyls among various skeletal muscle microstructures still remain largely unknown, partly owing to the lack of adequate techniques to carry out these measurements. This report describes an immunohistochemical approach to determine the relative abundance of carbonyls in the intermyofibrillar mitochondria (IFM), the subsarcolemmal mitochondria (SSM), the cytoplasm, and the extracellular space of skeletal muscle. These morphological features were defined by labeling the nucleus, the Z-lines, and mitochondria. Carbonyls were detected by derivatization with dinitrophenylhydrazine followed by labeling with an Alexa 488-labeled anti-dinitrophenyl primary antibody. Alexa 488 fluorescence (green) in different fiber microstructures was used to estimate the relative abundance of carbonyls. On the basis of the samples examined, preliminary results suggest that the most dramatic age-related changes in carbonyl levels occur in the extracellular space, followed in a decreasing order by SSM, IFM, and the cytoplasm. These observations were confirmed in the soleus and semimembranosus muscles composed predominantly of type I and type II fibers, respectively. This approach could easily be extended to the investigation of carbonyl levels in other muscles (composed of mixed skeletal muscle fiber types) or other tissues in which protein carbonyls are present. Figure Imaging of Labeled Carbonyls in Rat Skeletal Muscle     

Two-dimensional electrophoresis on a microfluidic chip for quantitative amino acid analysis

Analysis of complex biological samples requires the use of high-throughput analytical tools. In this work, a microfluidic two-dimensional electrophoresis system was developed with mercury-lamp-induced fluorescence detection. Mixtures of 20 standard amino acids were used to evaluate the separation performance of the system. After fluorescent labeling with fluorescein isothiocyanate, mixtures of amino acids were separated by micellar electrokinetic chromatography in the first dimension and by capillary zone electrophoresis in the second. A double electrokinetic valve system was employed for the sample injection and the switching between separation channels. Under the optimized conditions, 20 standard amino acids were effectively separated within 20 min with high resolution and repeatability. Quantitative analysis revealed linear dynamic ranges of over three orders of magnitudes with detection limits at micromolar range. To further evaluate the reliability of the system, quantitative analysis of a commercial nutrition supplement liquid was successfully demonstrated. Figure       

Dual-cardiac marker capillary waveguide fluoroimmunosensor based on tyramide signal amplification

The early diagnosis of acute myocardial infarction requires the determination of several markers in serum shortly after its incidence. The markers most widely employed are the isoenzyme MB of creatine kinase (CK-MB) and the cardiac troponin I (cTnI). In the present work, a capillary waveguide fluoroimmunosensor for fast and highly sensitive simultaneous determination of these markers in serum samples is demonstrated. The dual-analyte immunosensor was realized using glass capillaries internally modified with an ultrathin poly(dimethylsiloxane) film by creating discrete bands of analyte-specific antibodies. The capillary was then filled with a mixture of sample and biotinylated detection antibodies followed by reaction with streptavidin–horseradish peroxidase and incubation with a fluorescently labeled tyramide derivative to accumulate fluorescent labels onto immunoreaction bands. Upon scanning the capillary with a laser beam, part of the emitted fluorescence is trapped and waveguided through the capillary wall to a photomultiplier placed on one of its ends. The employment of tyramide signal amplification provided detection limits of 0.2 and 0.5 ng/mL for cTnI and CK-MB, respectively, in a total assay time of 30 min compared to 0.8 and 0.6 ng/mL obtained for the corresponding assays when the conventional fluorescent label R-phycoerythrin was used in a 65-min assay. In addition, the proposed immunosensor provided accurate and repeatable measurements (intra-assay and interassay coefficients of variation lower than 10%), and the values determined in serum samples were in good agreement with those obtained with commercially available enzyme immunoassays. Thus, the proposed capillary waveguide fluoroimmunosensor has all the required characteristics for fast and reliable diagnosis of acute myocardial infarction.      

Analysis of biosensors by chemically specific optical techniques. Chemiluminescence-imaging and infrared spectroscopic mapping ellipsometry

The standard methods currently used to read out microarrays are fluorescent and chemiluminesent imaging techniques. These methods require labeling of a component with a marker and, usually, only the concentration of the marker molecule is detected. A label-free imaging method that also enables quantitative spectroscopic analysis of the composition and component interaction would be of great advantage. In this article it is shown for the first time that IR mapping ellipsometry enables label-free imaging of a biochip before and after incubation with peptide solution. The measurements prove that IR ellipsometry is a sensitive tool for laterally resolved identification of the different materials and determination of the composition of a biochip. The lateral resolution required was achieved by using radiation from an infrared synchrotron beamline.      

Simultaneous use of multiple fluorescent reporter dyes for glucose sensing in aqueous solution

The simultaneous use of several fluorescent reporter dyes in a multicomponent boronic acid-based glucose sensing system is reported. In one application, two dyes with widely different emission wavelengths are used to report changes in glucose concentration. A third glucose-insensitive dye was then added to act as a reference dye and provide for a ratiometric correction to the two reporter dye signals. The inclusion of such a reference dye reduces errors arising from sources such as fluctuations in lamp intensity and sample dilution. The simultaneous use of multiple fluorescent reporter dyes     

Prediction of retention times of polycyclic aromatic hydrocarbons and <Emphasis Type="Italic">n</Emphasis>-alkanes in temperature-programmed gas chromatography

We have developed an iterative procedure for predicting the retention times of polycyclic aromatic hydrocarbons (PAHs) and n-alkanes during separations by temperature-programmed gas chromatography. The procedure is based on estimates of two thermodynamic properties for each analyte (the differences in enthalpy and entropy associated with movements between the stationary and mobile phases) derived from data acquired experimentally in separations under isothermal conditions at temperatures spanning the range covered by the temperature programs in ten-degree increments. The columns used for this purpose were capillary columns containing polydimethylsiloxane-based stationary phases with three degrees of phenyl substitution (0%, 5%, and 50%). Predicted values were mostly within 1% of experimentally determined values, implying that the method is stable and precise. Figure Predicted values were mostly within 1 % of experimentally determined values, thus implying that the method is stable and precise     

Playing tag with quantitative proteomics

There is steady need for new proteomic strategies on quantitative measurements that provide essential components for detailing dynamic changes in many cellular functions and processes. Stable isotope labeling is a rapidly evolving field, which can be used either after protein extraction with chemical labeling, or in cell culture with metabolic incorporation. In this review, we explore the most frequently utilized quantitation techniques with particular attention paid to chemical labeling using different isotopic tags, including a recent labeling strategy—soluble polymer-based isotopic labeling (SoPIL)—that achieves efficient labeling in homogeneous conditions. Special care should be devoted to the selection of appropriate quantitation approaches according to the needs of the sample and overall experimental design. We evaluate recent advances in quantitative proteomics using stable isotope labeling and their applications to current insightful biological inquiries. Figure Chemical modules of isotopic tags for quantitative proteomics.     

Biosensors based on carbon nanotubes

Carbon nanotubes (CNTs) exhibit a unique combination of excellent mechanical, electrical and electrochemical properties, which has stimulated increasing interest in the application of CNTs as components in (bio)sensors. This review highlights various design methodologies for CNT-based biosensors and their employment for the detection of a number of biomolecules. In addition, recent developments in the fields of CNT-based chemiresistors and chemically sensitive field-effect transistors are presented. After a critical discussion of the factors that currently limit the practical use of CNT-based biosensors, the review concludes with an outline of potential future applications for CNTs in biology and medicine.      

High-throughput evaluation of quiescent hematopoietic progenitor cells using a micro-multiwell plate

Conventional assays for hematopoietic progenitor cells (HPCs) require long-term culturing, a labor-intensive procedure, and technique proficiency. We aimed to develop a high-throughput method to determine frequency of quiescent primitive HPCs by a combination of the micro-multiwell plate and 5-fluorouracil (5-FU) treatment. The micro-multiwell plate was made of a silicone sheet with a 6 × 6 array of 1-mm diameter holes and a glass substrate. To enrich primitive HPCs in a CD34 population, CD34 cells and stromal cells were applied to micro-multiwells and cultured in the presence of 5-FU for 2 days. The quiescent primitive HPCs that survived after 5-FU treatment were then expanded with cytokines in the absence of 5-FU for a further 10 days. After culturing, cells were immunostained and the number of primitive HPCs in inoculated CD34 cells was estimated from fluorescent intensity for each well under a stereoscopic fluorescent microscope. The frequencies of primitive HPCs correlated well with frequencies of cobblestone area-forming cells for two CD34 cell lots. Our method allows high-throughput screening for primitive HPCs in CD34 cells. Figure Representative image of a micro-multiwell plate fordetecting primitive hematopoietic stem cells     

Nanoscale organic and polymeric field-effect transistors as chemical sensors

This article reviews recently published work concerning improved understanding of, and advancements in, organic and polymer semiconductor vapor-phase chemical sensing. Thin-film transistor sensors ranging in size from hundreds of microns down to a few nanometers are discussed, with comparisons made of sensing responses recorded at these different channel-length scales. The vapor-sensing behavior of nanoscale organic transistors is different from that of large-scale devices, because electrical transport in a nanoscale organic thin-film transistor depends on its morphological structure and interface properties (for example injection barrier) which could be modulated by delivery of analyte. Materials used in nanoscale devices, for example nanoparticles, nanotubes, and nanowires, are also briefly summarized in an attempt to introduce other relevant nano-transducers.      

Critical evaluation of sample pretreatment techniques

Sample preparation before chromatographic separation is the most time-consuming and error-prone part of the analytical procedure. Therefore, selecting and optimizing an appropriate sample preparation scheme is a key factor in the final success of the analysis, and the judicious choice of an appropriate procedure greatly influences the reliability and accuracy of a given analysis. The main objective of this review is to critically evaluate the applicability, disadvantages, and advantages of various sample preparation techniques. Particular emphasis is placed on extraction techniques suitable for both liquid and solid samples. Figure Miniaturised extraction techniques allow sensitive analysis of also small sample volumes.     

Arsine and selenium hydride trapping in a novel quartz device for atomic-absorption spectrometry

A novel quartz device has been designed to trap arsine and selenium hydride and subsequently to volatilize the collected analyte and atomize it for atomic-absorption spectrometric detection. The device is actually the multiple microflame quartz-tube atomizer (multiatomizer) with inlet arm modified to serve as the trap and to accommodate the oxygen-delivery capillary used to combust hydrogen during the trapping step. The effect of relevant experimental conditions (trap temperature during trapping and hydrogen flow rate and trap temperature during volatilization) on collection and volatilization efficiency was investigated. Under the optimum conditions collection and volatilization efficiency for arsenic and selenium were 50 and 70%, respectively.      

Optical sensing in microfluidic lab-on-a-chip by femtosecond-laser-written waveguides

We use direct femtosecond laser writing to integrate optical waveguides into a commercial fused silica capillary electrophoresis chip. High-quality waveguides crossing the microfluidic channels are fabricated and used to optically address, with high spatial selectivity, their content. Fluorescence from the optically excited volume is efficiently collected at a 90° angle by a high numerical aperture fiber, resulting in a highly compact and portable device. To test the platform we performed electrophoresis and detection of a 23-mer oligonucleotide plug. Our approach is quite powerful because it allows the integration of photonic functionalities, by simple post-processing, into commercial LOCs fabricated with standard techniques. Figure Femtosecond laser written waveguides can selectively excite fluorescence in a microfluidic channel of a commercial lab-on-a-chip. A compact scheme for on-chip detection by laser induced fluorescence is applied to capillary electrophoresis of a 23-mer Cy3-labeled oligonucleotide     

Development of an SdFFF–ETAAS hyphenated technique for dimensional and elemental characterization of colloids

Direct hyphenation of electrothermal atomic-absorption spectroscopy (ETAAS) to sedimentation field-flow fractionation (SdFFF) has been developed to enable elemental characterization of submicron particles as a function of size. This hyphenation is particularly suitable for characterizing colloidal particles of environmental interest, for example water-borne particles. The interface is an automatic capillary injection device (CID) which enables direct introduction of large and variable volumes of colloidal particle suspensions into a hot graphite furnace, thus preconcentrating the colloidal particles on the furnace walls. The method was validated by determination of Fe in certified submicron Fe₂O₃. The procedure was set up by first optimizing the SdFFF fractionation under programmed field conditions, thus enabling optimum fractionation of particle size. The ETAAS procedure was then tested to determine whether it could be used for direct analysis of Fe₂O₃ slurries without the need for a mineralization step. CID coupled to ETAAS was subsequently exploited for its ability to enhance the sensitivity, because of the increased injection volume. Statistical tests and data handling were conducted to prove the suitability of the ETAAS-CID module. Finally, off-line and on-line ETAAS-CID-SdFFF hyphenation were investigated. These experiments emphasized the advantages of the on-line coupling, because it enables synchronized sampling, enrichment, and elemental analysis of the flowing eluate. The benefits of the proposed hyphenation are the high specificity of analytical detection, increased sensitivity, reduction of analysis time, and minimum sample handling and contamination.      

Electrophoresis microchips with sharp inlet tips, for contactless conductivity detection, fabricated by in-situ surface polymerization

A novel method based on in-situ surface polymerization of methyl methacrylate (MMA) has been developed for rapid fabrication of poly(methyl methacrylate) (PMMA) electrophoresis microchips with sharp inlet tips. Prepolymerized MMA containing an ultraviolet (UV) initiator was directly sandwiched between a nickel template and a PMMA plate. The image of the relief on the nickel template was precisely replicated in the synthesized PMMA layer on the surface of the commercially available PMMA plate during UV-initiated polymerization at room temperature. The chips were subsequently assembled by thermal bonding of channel plates and cover sheets. The sample was directly introduced into the separation channel through a sharp inlet tip, which was placed in the sample vial, without use of an injection cross. The attractive performance of the novel PMMA microchips has been demonstrated by using contactless conductivity detection for determination of several inorganic ions. Such rapid and simple sample introduction leads to highly reproducible signals with relative standard deviations of less than 5% for peak responses. These new approaches significantly simplify the process of fabricating PMMA devices and show great promise for high-speed microchip analysis.      

Electrospray mass spectrometry analysis of dendritic branches bearing peripheral fullerene subunits

The electrospray mass spectrometric characterization of neutral dendrons with a carboxylic acid function or a t-butyl ester moiety at the central point and up to eight peripheral C₆₀ subunits has been performed and is described in detail. Molecules bearing a carboxylic acid group at the center turned out to be preferentially ionized by deprotonation, whereas those with a t-butyl ester head group were ionized by reduction of the C₆₀ units in the infusion capillary of the electrospray source. Electronic supplementary material Supplementary material is available for this article at and is accessible for authorized users.     

Characterization and application of quantum dot nanocrystal–monoclonal antibody conjugates for the determination of sulfamethazine in milk by fluoroimmunoassay

Quantum dot (Qdot) nanocrystals have been increasingly used as fluorescence labels in fluoroimmunoassays recently because of their excellent optical characteristics. In this paper, a new monoclonal antibody (MAb) against sulfamethazine (SMZ) was successfully produced and linked to Qdot nanocrystals by covalent coupling. The Qdot–MAb conjugates were characterized by SDS-PAGE and high-performance capillary electrophoresis (HPCE). An enzyme-linked immunosorbent assay (ELISA) method was utilized to evaluate the antigen–antibody binding affinity and then a novel direct competitive fluorescence-linked immunosorbent assay (cFLISA) for the detection of SMZ in milk by using Qdots as fluorescent labels was evaluated. The results showed that the 50% inhibition values (IC₅₀) of the cFLISA were 4.3 ng/mL in milk and 5.2 ng/mL in PBS, and the limits of detection (LODs) were 0.6 ng/mL in milk and 0.4 ng/mL in PBS, respectively. The recoveries of SMZ from spiked milk samples at levels of 10–100 ng/mL ranged from 94 to 106%, with coefficients of variation (CVs) of 2.1–9.2%. Figure Shematic diagram of the direct cFLISA procedure Jianzhong Shen and Fei Xu contributed equally to this work.