Showing papers in "Analytical Chemistry in 2010"

Diagnostics for the Developing World: Microfluidic Paper-Based Analytical Devices

Abstract: Microfluidic paper-based analytical devices (μPADs) are a new class of point-of-care diagnostic devices that are inexpensive, easy to use, and designed specifically for use in developing countries. (To listen to a podcast about this feature, please go to the Analytical Chemistry multimedia page at pubs.acs.org/page/ancham/audio/index.html.)

Graphene Fluorescence Resonance Energy Transfer Aptasensor for the Thrombin Detection

Abstract: Combining nanomaterials and biomolecule recognition units is promising in developing novel clinic diagnostic and protein analysis techniques. In this work, a highly sensitive and specific fluorescence resonance energy transfer (FRET) aptasensor for thrombin detection is developed based on the dye labeled aptamer assembled graphene. Due to the noncovalent assembly between aptamer and graphene, fluorescence quenching of the dye takes place because of FRET. The addition of thrombin leads to the fluorescence recovery due to the formation of quadruplex−thrombin complexes which have weak affinity to graphene and keep the dyes away from graphene surface. Because of the high fluorescence quenching efficiency, unique structure, and electronic properties of graphene, the graphene aptasensor exhibits extraordinarily high sensitivity and excellent specificity in both buffer and blood serum. A detection limit as low as 31.3 pM is obtained based on the graphene FRET aptasensor, which is two orders magnitude lower than ...

Fluorescence Resonance Energy Transfer between Quantum Dots and Graphene Oxide for Sensing Biomolecules

Abstract: This work designed a novel platform for effective sensing of biomolecules by fluorescence resonance energy transfer (FRET) from quantum dots (QDs) to graphene oxide (GO). The QDs were first modified with a molecular beacon (MB) as a probe to recognize the target analyte. The strong interaction between MB and GO led to the fluorescent quenching of QDs. Upon the recognition of the target, the distance between the QDs and GO increased, and the interaction between target-bound MB and GO became weaker, which significantly hindered the FRET and, thus, increased the fluorescence of QDs. The change in fluorescent intensity produced a novel method for detection of the target. The GO-quenching approach could be used for detection of DNA sequences, with advantages such as less labor for synthesis of the MB-based fluorescent probe, high quenching efficiency and sensitivity, and good specificity. By substituting the MB with aptamer, this strategy could be conveniently extended for detection of other biomolecules, whic...

Collision Cross Sections of Proteins and Their Complexes: A Calibration Framework and Database for Gas-Phase Structural Biology

Abstract: Collision cross sections in both helium and nitrogen gases were measured directly using a drift cell with RF ion confinement inserted within a quadrupole/ion mobility/time-of-flight hybrid mass spectrometer (Waters Synapt HDMS, Manchester, U.K.). Collision cross sections for a large set of denatured peptide, denatured protein, native-like protein, and native-like protein complex ions are reported here, forming a database of collision cross sections that spans over 2 orders of magnitude. The average effective density of the native-like ions is 0.6 g cm−3, which is significantly lower than that for the solvent-excluded regions of proteins and suggests that these ions can retain significant memory of their solution-phase structures rather than collapse to globular structures. Because the measurements are acquired using an instrument that mimics the geometry of the commercial Synapt HDMS instrument, this database enables the determination of highly accurate collision cross sections from traveling-wave ion mob...

mMass 3: a cross-platform software environment for precise analysis of mass spectrometric data

Abstract: While tools for the automated analysis of MS and LC-MS/MS data are continuously improving, it is still often the case that at the end of an experiment, the mass spectrometrist will spend time carefully examining individual spectra. Current software support is mostly provided only by the instrument vendors, and the available software tools are often instrument-dependent. Here we present a new generation of mMass, a cross-platform environment for the precise analysis of individual mass spectra. The software covers a wide range of processing tasks such as import from various data formats, smoothing, baseline correction, peak picking, deisotoping, charge determination, and recalibration. Functions presented in the earlier versions such as in silico digestion and fragmentation were redesigned and improved. In addition to Mascot, an interface for ProFound has been implemented. A specific tool is available for isotopic pattern modeling to enable precise data validation. The largest available lipid database (from...

Development, characterization, and application of paper spray ionization.

Abstract: Paper spray is developed as a direct sampling ionization method for mass spectrometric analysis of complex mixtures. Ions of analyte are generated by applying a high voltage to a paper triangle wetted with a small volume (<10 μL) of solution. Samples can be preloaded onto the paper, added with the wetting solution, or transferred from surfaces using the paper as a wipe. It is demonstrated that paper spray is applicable to the analysis of a wide variety of compounds, including small organic compounds, peptides, and proteins. Procedures are developed for analysis of dried biofluid spots and applied to therapeutic drug monitoring with whole blood samples and to illicit drug detection in raw urine samples. Limits of detection of 50 ng/mL (or 20 pg absolute) are achieved for atenolol in bovine blood. The combination of sample collection from surfaces and paper spray ionization also enables fast chemical screening at high sensitivity, for example 100 pg of heroin distributed on a surface and agrochemicals on fr...

Experimental methods for quantifying the activity of platinum electrocatalysts for the oxygen reduction reaction.

Abstract: A tutorial is provided for methods to accurately and reproducibly determine the activity of Pt-based electrocatalysts for the oxygen reduction reaction in proton exchange membrane fuel cells and other applications. The impact of various experimental parameters on electrocatalyst activity is demonstrated, and explicit experimental procedures and measurement protocols are given for comparison of electrocatalyst activity to fuel cell standards. (To listen to a podcast about this article, please go to the Analytical Chemistry multimedia page at pubs.acs.org/page/ancham/audio/index.html.)

Si:WO3 Sensors for Highly Selective Detection of Acetone for Easy Diagnosis of Diabetes by Breath Analysis

Abstract: Acetone in the human breath is an important marker for noninvasive diagnosis of diabetes. Here, novel chemo-resistive detectors have been developed that allow rapid measurement of ultralow acetone concentrations (down to 20 ppb) with high signal-to-noise ratio in ideal (dry air) and realistic (up to 90% RH) conditions. The detector films consist of (highly sensitive) pure and Si-doped WO3 nanoparticles (10−13 nm in diameter) made in the gas phase and directly deposited onto interdigitated electrodes. Their sensing properties (selectivity, limit of detection, response, and recovery times) have been investigated as a function of operating temperature (325−500 °C), relative humidity (RH), and interfering analyte (ethanol or water vapor) concentration. It was found that Si-doping increases and stabilizes the acetone-selective e-WO3 phase while increasing its thermal stability and, thus, results in superior sensing performance with an optimum at about 10 mol % Si content. Furthermore, increasing the operation ...

Metabolomic analysis and visualization engine for LC-MS data.

Abstract: Metabolomic analysis by liquid chromatography−high-resolution mass spectrometry results in data sets with thousands of features arising from metabolites, fragments, isotopes, and adducts. Here we describe a software package, Metabolomic Analysis and Visualization ENgine (MAVEN), designed for efficient interactive analysis of LC−MS data, including in the presence of isotope labeling. The software contains tools for all aspects of the data analysis process, from feature extraction to pathway-based graphical data display. To facilitate data validation, a machine learning algorithm automatically assesses peak quality. Users interact with raw data primarily in the form of extracted ion chromatograms, which are displayed with overlaid circles indicating peak quality, and bar graphs of peak intensities for both unlabeled and isotope-labeled metabolite forms. Click-based navigation leads to additional information, such as raw data for specific isotopic forms or for metabolites changing significantly between condi...

Metabolomic Analysis via Reversed-Phase Ion-Pairing Liquid Chromatography Coupled to a Stand Alone Orbitrap Mass Spectrometer

Abstract: We present a liquid chromatography−mass spectrometry (LC−MS) method that capitalizes on the mass-resolving power of the orbitrap to enable sensitive and specific measurement of known and unanticipated metabolites in parallel, with a focus on water-soluble species involved in core metabolism. The reversed phase LC method, with a cycle time 25 min, involves a water−methanol gradient on a C18 column with tributylamine as the ion pairing agent. The MS portion involves full scans from 85 to 1000 m/z at 1 Hz and 100 000 resolution in negative ion mode on a stand alone orbitrap (“Exactive”). The median limit of detection, across 80 metabolite standards, was 5 ng/mL with the linear range typically ≥100-fold. For both standards and a cellular extract from Saccharomyces cerevisiae (Baker’s yeast), the median inter-run relative standard deviation in peak intensity was 8%. In yeast exact, we detected 137 known compounds, whose 13C-labeling patterns could also be tracked to probe metabolic flux. In yeast engineered to...

Sensitive Immunosensor for Cancer Biomarker Based on Dual Signal Amplification Strategy of Graphene Sheets and Multienzyme Functionalized Carbon Nanospheres

Abstract: A novel electrochemical immunosensor for sensitive detection of cancer biomarker α-fetoprotein (AFP) is described that uses a graphene sheet sensor platform and functionalized carbon nanospheres (CNSs) labeled with horseradish peroxidase-secondary antibodies (HRP-Ab2). Greatly enhanced sensitivity for the cancer biomarker is based on a dual signal amplification strategy: first, the synthesized CNSs yielded a homogeneous and narrow size distribution, which allowed several binding events of HRP-Ab2 on each nanosphere. Enhanced sensitivity was achieved by introducing the multibioconjugates of HRP-Ab2-CNSs onto the electrode surface through “sandwich” immunoreactions. Second, functionalized graphene sheets used for the biosensor platform increased the surface area to capture a large amount of primary antibodies (Ab1), thus amplifying the detection response. On the basis of the dual signal amplification strategy of graphene sheets and the multienzyme labeling, the developed immunosensor showed a 7-fold increas...

Colorimetric Sensing of Silver(I) and Mercury(II) Ions Based on an Assembly of Tween 20-Stabilized Gold Nanoparticles

Abstract: We have developed a rapid and homogeneous method for the highly selective detection of Hg2+ and Ag+ using Tween 20-modified gold nanoparticles (AuNPs). Citrate ions were found to still be adsorbed on the Au surface when citrate-capped AuNPs were modified with Tween 20, which stabilizes the citrate-capped AuNPs against conditions of high ionic strength. When citrate ions had reduced Hg2+ and Ag+ to form Hg−Au alloys and Ag on the surface of the AuNPs, Tween 20 was removed from the NP surface. As a result, the AuNPs were unstable under a high-ionic-strength solution, resulting in NP aggregation. The formation of Hg−Au alloys or Ag on the surface of the AuNPs was demonstrated by means of inductively coupled plasma mass spectroscopy and energy-dispersive X-ray spectroscopy. Tween 20-AuNPs could selectively detect Hg2+ and Ag+ at concentrations as low as 0.1 and 0.1 μM in the presence of NaCl and EDTA, respectively. Moreover, the probe enables the analysis of AgNPs with a minimum detectable concentration that ...

Rapid and sensitive detection of protein biomarker using a portable fluorescence biosensor based on quantum dots and a lateral flow test strip.

Abstract: A portable fluorescence biosensor with rapid and ultrasensitive response for protein biomarker has been built up with quantum dots and a lateral flow test strip. The superior signal brightness and high photostability of quantum dots are combined with the promising advantages of a lateral flow test strip and result in high sensitivity and selectivity and speed for protein detection. Nitrated ceruloplasmin, a significant biomarker for cardiovascular disease, lung cancer, and stress response to smoking, was used as model protein biomarker to demonstrate the good performances of this proposed quantum dot-based lateral flow test strip. Quantitative detection of nitrated ceruloplasmin was realized by recording the fluorescence intensity of quantum dots captured on the test line. Under optimal conditions, this portable fluorescence biosensor displays rapid responses for nitrated ceruloplasmin with the concentration as low as 1 ng/mL. Furthermore, the biosensor was successfully utilized for spiked human plasma sa...

Graphene as a Novel Matrix for the Analysis of Small Molecules by MALDI-TOF MS

Abstract: Graphene was utilized for the first time as a matrix for the analysis of low molecular weight compounds using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Polar compounds including amino acids, polyamines, anticancer drugs, and nucleosides could be successfully analyzed. Additionally, nonpolar compounds including steroids could be detected with high resolution and sensitivity. Compared with a conventional matrix, graphene exhibited a high desorption/ionization efficiency for nonpolar compounds. The graphene matrix functions as a substrate to trap analytes, and it transfers energy to the analytes upon laser irradiation, which allows for the analytes to be readily desorbed/ionized and interference of intrinsic matrix ions to be eliminated. The use of graphene as a matrix avoided the fragmentation of analytes and provided good reproducibility and a high salt tolerance, underscoring the potential application of graphene as a matrix for MALDI MS analysis of pract...

Refinements to label free proteome quantitation: how to deal with peptides shared by multiple proteins.

Abstract: Quantitative shotgun proteomics is dependent on the detection, identification, and quantitative analysis of peptides. An issue arises with peptides that are shared between multiple proteins. What protein did they originate from and how should these shared peptides be used in a quantitative proteomics workflow? To systematically evaluate shared peptides in label-free quantitative proteomics, we devised a well-defined protein sample consisting of known concentrations of six albumins from different species, which we added to a highly complex yeast lysate. We used the spectral counts based normalized spectral abundance factor (NSAF) as the starting point for our analysis and compared an exhaustive list of possible combinations of parameters to determine what was the optimal approach for dealing with shared peptides and shared spectral counts. We showed that distributing shared spectral counts based on the number of unique spectral counts led to the most accurate and reproducible results.

Fabrication and Characterization of Paper-Based Microfluidics Prepared in Nitrocellulose Membrane By Wax Printing

Abstract: Paper-based microfluidics is a promising technology to develop a simple, low-cost, portable, and disposable diagnostic platform for resource-limited settings. Here we report the fabrication of paper-based microfluidic devices in nitrocellulose membrane by wax printing for protein immobilization related applications. The fabrication process, which can be finished within 10 min, includes mainly printing and baking steps. Wax patterning will form hydrophobic regions in the membrane, which can be used to direct the flow path or separate reaction zones. The fabrication parameters like printing mode and baking time were optimized, and performances of the wax-patterned nitrocellulose membrane such as printing resolution, protein immobilization, and sample purification capabilities were also characterized in this report. We believe the wax-patterned nitrocellulose membrane will enhance the capabilities of paper microfluidic devices and bring new applications in this field.

Enhanced gold nanoparticle based ELISA for a breast cancer biomarker.

Abstract: In this work, we developed an optical enzyme-linked immunosorbent assay (ELISA) immunoassay for the analysis of CA15-3 antigen, an important biomarker present in blood samples and useful for the follow-up of the medical treatment of breast cancer. Gold nanoparticles (AuNPs) were used as carriers of the signaling antibody anti-CA15-3−HRP (horseradish peroxidase) in order to achieve an amplification of the optical signal. In the range between 0 and 60 U/mL, the assay adopting AuNPs as an enhancer resulted in higher sensitivity and shorter assay time when compared to classical ELISA procedures. The application of AuNPs to the commercially available ELISA test can be useful to improve important immunoanalysis procedures where a more confident result is needed.

Ultrasensitive Electrochemical Immunosensor for Oral Cancer Biomarker IL-6 Using Carbon Nanotube Forest Electrodes and Multilabel Amplification

Abstract: Squamous cell carcinomas of head and neck (HNSCC) are associated with immune, inflammatory, and angiogenic responses involving interleukin-6 (IL-6). This article reports an ultrasensitive electrochemical immunosensor for human IL-6 and proof-of-concept studies of IL-6 detection in HNSCC cells. Single wall carbon nanotube (SWNT) forests with attached capture antibodies (Ab1) for IL-6 were used in an electrochemical sandwich immunoassay protocol using enzyme label horseradish peroxidase (HRP) to measure very low (≤30 pg mL−1) and elevated levels of IL-6. Two levels of multienzyme labeling were used to measure a broad concentration range of IL-6 in a representative panel of HNSCC cells. Secondary antibodies (Ab2) attached to carboxylated multiwall carbon nanotubes with 106 HRP labels per 100 nm gave the highest sensitivity of 19.3 nA mL (pg IL-6)−1 cm−2 and the best detection limit (DL) of 0.5 pg mL−1 (25 fM) for IL-6 in 10 μL of calf serum. For more concentrated samples, biotinylated Ab2 bound to streptavid...

Lead(II)-Induced Allosteric G-Quadruplex DNAzyme as a Colorimetric and Chemiluminescence Sensor for Highly Sensitive and Selective Pb2+ Detection

Abstract: The lead ion (Pb(2+)) has been proven to induce a conformational change of K(+)-stabilized G-quadruplex DNAzyme and inhibit the peroxidase-like activity [Li, T.; Wang, E.; Dong, S. J. Am. Chem. Soc. 2009, 131, 15082-15083]. This provides a rationale for utilizing Pb(2+)-induced allosteric G-quadruplex DNAzyme to probe aqueous Pb(2+). Here, we choose a common G-quadruplex DNAzyme named PS2.M to develop a novel Pb(2+) sensor with two detection means: colorimetry and chemiluminescence (CL). In the presence of K(+), PS2.M (with hemin as a cofactor) exhibits a superior DNAzyme activity and effectively catalyzes the H(2)O(2)-mediated oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) or luminol, which results in a color change or generates CL emission. Upon the addition of Pb(2+), K(+)-stabilized PS2.M is induced to convert to the Pb(2+)-stabilized structure with higher stability but lower DNAzyme activity, which is reflected by an obvious increase in DNA melting temperature but a sharp decrease in readout signal. This allows us to utilize PS2.M for quantitative analysis of aqueous Pb(2+) using the ABTS-H(2)O(2) colorimetric system and luminol-H(2)O(2) CL system. In each case, the readout signal is linearly dependent on the logarithm of Pb(2+) concentration within a certain range. Nevertheless, two sensing systems provide different sensitivity for Pb(2+) analysis. With colorimetry, Pb(2+) can be detected at a level of 32 nM (approximately 7 ppb), whereas the detection limit of Pb(2+) is 1 nM (0.2 ppb) when utilizing the CL method. In addition to high sensitivity, the above sensing systems exhibit good selectivity for Pb(2+) over other metal ions. These results demonstrate the facility and effectivity of our introduced DNAzyme-based sensor for quantitative Pb(2+) analysis.

Conjugation of glucose oxidase onto Mn-doped ZnS quantum dots for phosphorescent sensing of glucose in biological fluids.

Abstract: Integrating various enzymes with nanomaterials provides various nanohybrids with new possibilities in biosensor applications. Furthermore, the enzymatic activity and stability are also improved due to the large surface area of nanomaterials. Here we report the conjugation of glucose oxidase (GOD) onto phosphorescent Mn-doped ZnS quantum dots (QDs) using 1-ethyl-3-(3-dimethylaminopropy)carbodiimide (EDC)/N-hydroxysuccinimide (NHS) as coupling reagents for glucose biosensing based on the effective quenching of the room temperature phosphorescence (RTP) of Mn-doped ZnS QDs by the H2O2 generated from GOD-catalyzed oxidation of glucose. The obtained bioconjugate not only provided improved enzymatic performance with Michaelis−Menten constant of 0.70 mM but also favored biological applications because the phosphorescent detection mode avoided the interference from autofluorescence and scattering light from the biological matrix. In addition, the GOD-conjugated Mn-doped ZnS QDs showed better thermal stability in ...

Size-Selective Microcavity Array for Rapid and Efficient Detection of Circulating Tumor Cells

Abstract: Circulating tumor cells (CTCs) are tumor cells circulating in the peripheral blood of patients with metastatic cancer. Detection of CTCs has clinical significance in cancer therapy because it would enable earlier diagnosis of metastasis. In this research, a microfluidic device equipped with a size-selective microcavity array for highly efficient and rapid detection of tumor cells from whole blood was developed. The microcavity array can specifically separate tumor cells from whole blood on the basis of differences in the size and deformability between tumor and hematologic cells. Furthermore, the cells recovered on the microcavity array were continuously processed for image-based immunophenotypic analysis using a fluorescence microscope. Our device successfully detected approximately 97% of lung carcinoma NCI-H358 cells in 1 mL whole blood spiked with 10-100 NCI-H358 cells. In addition, breast, gastric, and colon tumor cells lines that include EpCAM-negative tumor cells, which cannot be isolated by conventional immunomagnetic separation, were successfully recovered on the microcavity array with high efficiency (more than 80%). On an average, approximately 98% of recovered cells were viable. Our microfluidic device has high potential as a tool for the rapid detection of CTCs and can be used to study CTCs in detail.

Metal−Organic Framework Thin Film for Enhanced Localized Surface Plasmon Resonance Gas Sensing

Abstract: Despite its high refractive index sensitivity, localized surface plasmon resonance (LSPR) spectroscopy has been generally restricted to large biological analytes. Sensing of smaller molecules is a compelling target for this technique; in particular, LSPR spectroscopy could be utilized to detect hazardous or toxic gases and manage industrial processes involving gaseous chemicals. Here, we report sensing of pure gases over Ag nanoparticles using LSPR spectroscopy, where the detected changes in bulk refractive index are <5 × 10−4 refractive index units (RIU). We further demonstrate a novel strategy for amplifying the sensing signal by coating the plasmonic substrate with a metal−organic framework (MOF) material. Cu3(BTC)2(H2O)3, BTC = benzenetricarboxylate, was grown on Ag nanoparticles using a layer-by-layer method in order to control the MOF thickness, which we show greatly affects the sensor response. Preferential concentration of CO2 within the MOF pores produces a 14-fold signal enhancement for CO2 sens...

Ultrahigh performance liquid chromatography-tandem mass spectrometry method for fast and robust quantification of anionic and aromatic metabolites.

Abstract: Quantification of metabolites is of pivotal relevance in biology, where it complements more established omics techniques such as transcriptomics and proteomics. Here, we present a 25 min ion-pairing ultrahigh performance liquid chromatography−tandem mass spectrometry method that was developed for comprehensive coverage of central metabolism (glycolysis, pentose phosphate pathway, and tricarboxylic acid cycle) and closely related biosynthetic reactions. We demonstrate quantification of 138 compounds, including carboxylic acids, amino acids, sugar phosphates, nucleotides, and functionalized aromatics. Biologically relevant isomers such as sugar phosphates are individually quantified by combining chromatographic separation and fragmentation. The obtained sensitivity and robustness enabled the detection of more than half all tested compounds in each of eight diverse biological samples of 0.5−50 mg dry cell weight. We recommend this method for routine and yet comprehensive quantification of primary metabolites...

Highly Sensitive, Colorimetric Detection of Mercury(II) in Aqueous Media by Quaternary Ammonium Group-Capped Gold Nanoparticles at Room Temperature

Abstract: We provide a highly sensitive and selective assay to detect Hg2+ in aqueous solutions using gold nanoparticles modified with quaternary ammonium group-terminated thiols at room temperature. The mechanism is the abstraction of thiols by Hg2+ that led to the aggregation of nanoparticles. With the assistance of solar light irradiation, the detection limit can be as low as 30 nM, which satisfies the guideline concentration of Hg2+ in drinking water set by the WHO. In addition, the dynamic range of detection is wide (3 × 10−8−1 × 10−2 M). This range, to our best knowledge, is the widest one that has been reported so far in gold nanoparticle (AuNP)-based assays for Hg2+.

High-Performance Single Cell Genetic Analysis Using Microfluidic Emulsion Generator Arrays

Abstract: High-throughput genetic and phenotypic analysis at the single cell level is critical to advance our understanding of the molecular mechanisms underlying cellular function and dysfunction. Here we describe a high-performance single cell genetic analysis (SCGA) technique that combines high-throughput microfluidic emulsion generation with single cell multiplex polymerase chain reaction (PCR). Microfabricated emulsion generator array (MEGA) devices containing 4, 32, and 96 channels are developed to confer a flexible capability of generating up to 3.4 × 106 nanoliter-volume droplets per hour. Hybrid glass-polydimethylsiloxane diaphragm micropumps integrated into the MEGA chips afford uniform droplet formation, controlled generation frequency, and effective transportation and encapsulation of primer functionalized microbeads and cells. A multiplex single cell PCR method is developed to detect and quantify both wild type and mutant/pathogenic cells. In this method, microbeads functionalized with multiple forward...

Ultrasensitive sensing of Hg2+ and CH3Hg+ based on the fluorescence quenching of lysozyme type VI-stabilized gold nanoclusters.

Abstract: This study presents a one-step approach to prepare lysozyme type VI-stabilized gold nanoclusters (Lys VI-AuNCs) for the ultrasensitive detection of Hg2+ and CH3Hg+ based on fluorescence quenching. The optical properties and size of Lys VI-AuNCs are highly dependent on the concentration of Lys VI, which acts as both a reducing and a stabilizing agent. With an increase in the concentration of Lys VI, we observed a systematic blue shift in the fluorescence maxima, an increase in the quantum yields, and a reduction in the particle size. When using 25 mg/mL Lys VI as a reducing agent, the formed Lys VI-AuNCs (denoted as Au-631) were found to be highly stable in a high-concentration glutathione or NaCl. Additionally, the Au-631 were capable of sensing Hg2+ and CH3Hg+ through the interaction between Hg2+/CH3Hg+ and Au+ on the Au surface; the limits of detection (LODs) for Hg2+ and CH3Hg+ were 3 pM and 4 nM, respectively. The selectivity of this probe is more than 500-fold for Hg2+ over any metal ions. As compare...

Flexographically Printed Fluidic Structures in Paper

Abstract: This Technical Note demonstrates a simple method based on flexographic printing of polystyrene to form liquid guiding boundaries and layers on paper substrates. The method allows formation of hydrophobic barrier structures that partially or completely penetrate through the substrate. This unique property enables one to form very thin fluidic channels on paper, leading to reduced sample volumes required in point-of-care diagnostic devices. The described method is compatible with roll-to-roll flexography units found in many printing houses, making it an ideal method for large-scale production of paper-based fluidic structures.

Aptamer-based electrochemical biosensor for interferon gamma detection

Abstract: In this paper, we describe the development of an electrochemical DNA aptamer-based biosensor for detection of interferon (IFN)-γ. A DNA hairpin containing IFN-γ−binding aptamer was thiolated, conjugated with methylene blue (MB) redox tag, and immobilized on a gold electrode by self-assembly. Binding of IFN-γ caused the aptamer hairpin to unfold, pushing MB redox molecules away from the electrode and decreasing electron-transfer efficiency. The change in redox current was quantified using square wave voltammetry (SWV) and was found to be highly sensitive to IFN-γ concentration. The limit of detection for optimized biosensor was 0.06 nM with linear response extending to 10 nM. This aptasensor was specific to IFN-γ in the presence of overabundant serum proteins. Importantly, the same aptasensor could be regenerated by disrupting aptamer−IFN-γ complex in urea buffer and reused multiple times. Unlike standard sandwich immunoassays, the aptasensor described here allowed one to detect IFN-γ binding directly with...

Bipolar Electrodes: A Useful Tool for Concentration, Separation, and Detection of Analytes in Microelectrochemical Systems

Abstract: Over the past decade, bipolar electrochemistry has emerged from relative obscurity to provide a promising new means for integrating electrochemistry into lab-on-a-chip systems. This article describes the fundamental operating principles of bipolar electrodes, as well as several interesting applications.