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We propose a simple microfluidic device for protein preconcentration based on the electrokinetic trapping principle. It comprises a narrow Nation strip that is simply cut from a commercial membrane and is integrated into a molded poly(dimethylsiloxane) (PDMS) microfluidic structure using a guiding channel. Mechanically clamping the PDMS/Nation assembly with a glass substrate results in a rapid prototypable, leak-tight, and easily disposable device. Our device preconcentrates negatively charged fluorescent proteins located at the anodic microfluidic compartment side of the Nation strip within a few minutes and up to a concentration factor of [10.sup.4]. Moreover, we present a numerical study of the preconcentration effect by solving the coupled Poisson, Nernst-Planck, and Navier Stokes equations for our type of device, which provides microscopic insight into the mechanism of preconcentration. The electrical field across the ion-permselective Nation generates concentration polarization, i.e., ion depletion at the anodic side and ion enrichment at the cathodic side for both types of ions, with a local excess of mobile positive ions in the depleted concentration polarization zone, inducing a nonequilibrium electrical double layer in close proximity to the Nation membrane. A voltage difference applied over the anodic compartment is used to generate the electrophoretic flow velocity of the negatively charged tracer biomolecules. This, in combination with the electroosmotic flow in the opposite direction, which originates from the fixed charges on the channel walls and the induced space charge near the membrane, provides the basis for the local preconcentration of the negative tracer biomolecules. 10.1021/ac102149f

A spectroelectrochemical sensor was demonstrated for an organic compound whose oxidation proceeds through an electron transfer--chemical reaction-electron transfer (ECE) mechanism to generate new chemical species that are used for detection by fluorescence. The polycyclic aromatic hydrocarbon 1-hydroxypyrene (1-PyOH) served as a representative model analyte. The spectroelectro-chemical properties of 1-PyOH in solution were explored with an optically transparent thin layer electrode. Electrochemical oxidation of 1-PyOH under acidic conditions proceeds via the ECE mechanism to a diquinonepyrene, which shows reversible electrochemistry and fluoresces at 425 nm in its reduced form, dihydroxypyrene. The sensor consisted of a tin-doped indium optically transparent electrode coated with a Nation thin-film (20 nm) that rapidly preconcentrated the analyte at the sensor surface. Fluorescence in the film was excited by the evanescent wave from attenuated total reflection spectroscopy. Electrochemical modulation of dihydroxypyrene fluorescence at 425 nm in the 500 to -200 mV (vs Ag/AgCl) potential range was used for indirect detection of 1-PyOH. The spectroelectrochemical sensor calibration curve had a range of 5 x [10.sup.-9] to 1 x [10.sup.-6] M with a calculated detection limit of 1 x [10.sup.-9] M. 10.1021/ac101883a

The concept of triggered polycatenated DNA scaffolds has been elegantly introduced into ultrasensitive biosensing applications by a combination of rolling circle amplification (RCA) and DNAzyme amplification. As compared to traditional methods in which one target could only initiate the formation of one circular template for RCA reaction, in the present study two species of linear single-stranded DNA (ssDNA) monomers are self-assembled into mechanically interlocked polycatenated nanostructares on capture probe-tagged magnetic nanoparticles (MNPs) only upon the introduction of one base mutant DNA sequence as initiator for single-nucleotide polymorphisms (SNPs) analysis. The resultant topologically polycatenated DNA ladder is further available for RCA process by using the serially ligated circular DNA as template for the synthesis of hemin/G-quadruplex HRP-mimicking DNAzyme chains, which act as biocatalytic labels for the luminol-[H.sub.2][O.sub.2] chemiluminescence (CL) system. Notably, the problem of high background induced by excess heroin itself is circumvented by immobilizing the biotinylated RCA products on streptavidin-modified MNPs via biotin--streptavidin interaction. Similarly, a universal strategy is contrived by substitutedly employing aptamer as initiator for the construction of polycatenated DNA scaffolds to accomplish ultrasensitive detection of proteins based on structure-switching of aptamer upon target binding, which is demonstrated by using thrombin as a model analyte in this study. Overall, with two successive amplification steps and one magnetic separation procedure, this flexible biosensing system exhibits not only high sensitivity and specificity with the detection limits of SNPs and thrombin as low as 71 aM and 6.6 pM, respectively, but also excellent performance in real human serum assay with no PCR preamplification for SNPs assay. Given the unique and attractive characteristics, rids study illustrates the potential of DNA nanotechnology in bioanalytical applications for both fundamental and practical research. 10.1021/ac1021198

A portable surface-enhanced Raman scattering (SERS) sensor is developed and applied to simultaneous detection of aniline and phenol derivatives in a label-free way with an electrostatic preconcentration technique to amplify the signals. A SERS-active substrate, silver-electrodeposited screen-printed electrodes (Ag-SPEs), is used for qualification and quantification of polar organic pollutants. Observation of SERS spectra at different potentials indicates that polar pollutants are selectively adsorbed on the Ag-SPEs at a given potential, suggesting that Ag-SPEs could selectively attract polar pollutants to an oppositely charged electrode at different potentials. Optimum SERS-active substrate was obtained when a potential of-0.15 V vs Ag/AgC1 was applied on the SPEs in 0.1 M AgN[O.sub.3] solution for 10 min. Moreover, the effects of experimental variables such as the electrodeposition time and potential of Ag and preconcentration time of polar molecules on the SERS signals are presented. Under optimum conditions and with a 785 nm laser, the method is effective over a wide range of concentration (1 nM to 1 [micro]M) for aniline and phenol derivatives. The novel method described herein presents a new detection regime for environmental pollutant analysis and also demonstrates simultaneous multiplexed detection of polar organic pollutants using convenient Ag-SPEs. 10.1021/ac101812x

Electrochemical mapping of neurotransmitter concentrations on a chip promises to be an interesting technique for investigating synaptic release in cellular networks. In here, we present a novel chip-based device for the detection of ueurotransmitter fluctuations in real-time. The chip features an array of plane-parallel nanocavity sensors, which strongly amplify the electrochemical signal. This amplification is based on efficient redox cycling via confined diffusion between two electrodes inside the nanocavity sensors. We demonstrate the capability of resolving concentration fluctuations of redox-active species in a microfluidic mixing gradient on the chip. The results are explained by a simulated concentration profile that was calculated on the basis of the coupled Navier-Stokes and convection-diffusion equations using a finite element approach. 10.1021/ac1013871

A highly sensitive competitive immunosensor based on the electrochemiluminescence (ECL) of quantum dots (QDs) was proposed by coupling with an enzymatic amplification. The fabrication process of the immunosensor was traced with atomic force microscopic images and electrochemical impedance spectra. The strong cathodic ECL emission of the immobilized QDs could be detected at a relatively low emission potential. The reduction of dissolved oxygen during the cathodic process provided a self-produced coreactant, [H.sub.2][O.sub.2], for the ECL emission. Using human IgG (HIgG) as a model protein, upon the immuno-recognition of the immobilized HIgG to its antibody labeled simply with horseradish peroxidase, the ECL intensity decreased due to the steric hindrance of the proteins to electron Iransfer. The decrease could be greatly amplified by an enzymatic cycle to consume the self-produced coreactant, leading to a wide calibration range of 0.05 ng [mL.sup.-1] ~ 5 [micro]g [mL.sup.-1] and a low limit of detection for the competitive immunoassay of HIgG. This immunosensor showed good stability and fabrication reproducibility. The immunoassays of practical samples showed acceptable results. This facile immunosensing strategy opened a new avenue for detection of proteins and application of QDs in ECL biosensing. 10.1021/ac1013942

A ubiquitous electrochemical sensor which can detect pollutants in nonconducting aqueous solutions is prepared using a triple layer design, comprising a polyelectrolyte entrapped within micrometer-length nanochannels and sandwiched between two nanometer-thick electrode layers. Replacement of the polyelectrolyte with an enzyme-polyelectrolyte mixture within the nanochannels confers excellent biosensing characteristics. Its superior analytical performance of quantitating copper ions and formaldehyde at trace levels without additional sample treatment steps is demonstrated in freshwater samples derived from a local reservoir. 10.1021/ac100776p

We have designed fluorescent nanosensors based on ion-selective optodes capable of detecting small molecules. By localizing the sensor components in a hydrophobic core, these nanosensors are able to monitor dynamic changes in concentration of the model analyte, glucose. The nanosensors demonstrated this response in vitro and also when injected subcutaneously into mice. The response of the nanosensors tracked changes in blood glucose levels in vivo that were comparable to measurements taken using a glucometer. The development of these nanosensors offers an alternative, minimally invasive tool for monitoring glucose levels in such fields as diabetes research. Furthermore, the extension of the ion-selective optode sensor platform to small molecule detection will allow for enhanced monitoring of physiological processes. 10.1021/ac100042e

In this study, we demonstrated that an amplitude-sensitive paired surface plasma wave biosensor (PSPWB) is capable of real-time detection of prostate-specific antigen (PSA) in diluted human serum without labeling. Experimentally, the detection limit of PSPWB was 8.4 x [10.sup.-9] refractive index unit (RIU) and the PSPWB could measure PSA in a phosphate buffered saline solution from 10 fg/mL (~300 aM) to 100 pg/mL (~3 pM) successfully, with demonstration of a linear relationship between PSA concentrations and surface plasmon resonance (SPR) signals. Therefore, results were obtained over a wide dynamic range 5 orders of magnitude for analyte concentration. In addition, the PSPWB successfully detected PSA in diluted human serum as well. These experimental results indicate that the PSPWB is capable of detection with high sensitivity over a wide range by using SPR-based biosensors and has a capability of detecting biological analytes in clinical sample without complicated operating procedures. 10.1021/ac100071h

A novel strategy for the fabrication of electrochemical aptasensor is proposed in this work, and the strategy has been employed to develop an aptasensor for the assay of adenosine deaminase activity. While a well-designed oligonucleotide containing three functional regions (an adenosine aptamer region, a G-quadruplex halves region, and a linker region) is adopted in our strategy as the core element, the enzymatic reaction of adenosine catalyzed by adenosine deaminase plays a key role as well in the regulation of the binding of the G-quadruplex halves with heroin, the electroactive probe, which is to reflect the activity of the enzyme indirectly but accurately. The detection limit of the fabrication biosensor can be lowered to 0.2 U [mL.sup.-1] of adenosine deaminase, and 1 nM of the inhibitor erythro-9-(2-hydroxy-3-nonyl) adenine hydrochloride is enough to present distinguishable electrochemical response. Moreover, since the electroactive probe is not required to be bound with the oligonucleotide, this strategy may integrate the advantages of both the labeled and label-free strategies. 10.1021/ac902771k

A novel electrochemical immunosensor for sensitive detection of cancer biomarker [alpha]-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 immunosensot showed a 7-fold increase in detection signal compared to the immunosensor without graphene modification and CNSs labeling. The proposed method could respond to 0.02 ng [mL.sup.-1] AFP with a linear calibration range from 0.05 to 6 ng [mL.sup.-1]. This amplification strategy is a promising platform for clinical screening of cancer biomarkers and point-of-care diagnostics. 10.1021/ac100036p

A research element of the European Union (EU) sixth Framework project BioCop focused on the development of a surface plasmon resonance (SPR) biosensor assay for the detection of paralytic shellfish poisoning (PSP) toxins in shellfish as an alternative to the increasingly ethically unacceptable mouse bioassay. A biosensor assay was developed using both a saxitoxin binding protein and chip surface in tandem with a highly efficient simple extraction procedure. The present report describes the single laboratory validation of this immunological screening method, for this complex group of toxins with differing toxicities, according to the European Decision 2002/ 657/EC in conjunction with IUPAC and AOAC single laboratory validation guidelines. The different performance characteristics (detection capability CC[beta], specificity/selectivity, repeatability, reproducibility, stability, and applicability) were determined in relation to the EU regulatory limit of 800 [micro]g of saxitoxin equivalents (STX eq) per kg of shellfish meat. The detection capability CC[beta] was calculated to be 120 [micro]g/kg. intra-assay repeatability was found to be between 2.5 and 12.3% and interassay reproducibility was between 6.1 and 15.2% for different shellfish matrices. Natural samples were also evaluated and the resultant data displayed overall agreements of 96 and 92% with that of the existing AOAC approved methods of mouse bioassay (MBA) and high performance liquid chromatography (HPLC), respectively. 10.1021/ac1000338

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 those of fluorescent sensors based on carbon nanotubes. The excellent performance of FRET aptasensor based on graphene will also be aseribed to the unique structure and electronic properties of graphene. 10.1021/ac9025384

We demonstrate a highly sensitive nano aptasensor for anthrax toxin through the detection of its polypeptide entity, protective antigen (PA toxin) using a PA toxin ssDNA aptamer functionalized single-walled carbon nanotubes (SWNTs) device. The aptamer was developed inhouse by capillary electrophoresis systematic evolution of ligands by exponential enrichment (CE-SELEX) and had a dissociation constant ([K.sub.d]) of 112 nM. The aptasensor displayed a wide dynamic range spanning up to 800 nM with a detection limit of I nM. The sensitivity was 0.11 per nM, and it was reusable six times. The aptasensor was also highly selective for PA toxin with no interference from human and bovine serum albumin, demonstrating it as a potential tool for rapid and point-of-care diagnosis for anthrax. 10.1021/ac902791q

Owing to their unique optical properties, quantum dots (QDs) with different colors have been applied for simultaneous detection of multiple analytes. However, the use of single QD for multiplex detection of analytes with single-molecule detection has not been explored. Here we report a single QD-based nanosensor for multiplex detection of HIV-1 and HIV-2 at single-molecule level in a homogeneous format. In this single QD-based nanosensor, the QD functions not only as a fluorescence pair for coincidence detection and as a fluorescence-resonance-energy-transfer (FRET) donor for FRET detection but also as a local nanoconcentrator which significantly amplifies the coincidence-related fluorescence signals and the FRET signals. This single-QD-based nanosensor takes advantage of a simple 'mix and detection' assay with extremely low sample consumption, high sensitivity, and short analysis time and has the potential to be applied for rapid point-of-care testing, gene expression studies, high-throughput screening, and clinical diagnostics. 10.1021/ac9026675

The lead ion ([Pb.sup.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.sup.2+]-induced allosteric G-quadruplex DNAzyme to probe aqueous [Pb.sup.2+]. Here, we choose a common G-quadruplex DNAzyme named PS2.M to develop a novel [Pb.sup.2+] sensor with two detection means: colorimetry and chemiluminescence (CL). In the presence of [K.sup.+], PS2.M (with hemin as a cofactor) exhibits a superior DNAzyme activity and effectively catalyzes the [H.sub.2][O.sub.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.sup.2+], [K.sup.+]-stabilized PS2.M is induced to convert to the [Pb.sup.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.sup.2+] using the ABTS-[H.sub.2][O.sub.2] colorimetric system and luminol [H.sub.2][O.sub.2] CL system. In each case, the readout signal is linearly dependent on the logarithm of [Pb.sup.2+] concentration within a certain range. Nevertheless, two sensing systems provide different sensitivity for [Pb.sup.2+] analysis. With colorimetry, [Pb.sup.2+] can be detected at a level of 32 nM (~7 pph), whereas the detection limit of [Pb.sup.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.sup.2+] over other metal ions. These results demonstrate the facility and effectivity of our introduced DNAzyme-based sensor for quantitative [Pb.sup.2+] analysis. 10.1021/ac902638v

A new fluorescence method based on aptamer-target interactions has been developed for cocaine detection with target-induced strand displacement. Here we describe new probes, the hairpin-probe and the single strand-probe (ss-probe), that possess two recognition sequences of cocaine aptamer. In the presence of cocaine, both probes would associate with the target to form a tripartite complex. The conformational change in the hairpin-probe causes the opening of a hairpin structure and the hybridization to primer. With polymerase and the dNTPs, the replication of the single-stranded domain of hairpin-probe triggers the process of primer extension. When the hairpin-probe is converted into a fully double-stranded form, the ss-probe and cocaine are displaced to bind another hairpin-probe and initiate new amplification cycles. Fluorescence signal generation would be observed upon SYBR Green I intercalating into the new DNA double helix. The new protocol design permits detection of as low as 2 nM cocaine in a closed tube, offering a convenient approach for a homogeneous assay. Compared with previously reported cocaine aptameric sensors, our new method is highly sensitive, selective, and economical. 10.1021/ac902416u

In this paper, we present an innovative sensing nanomaterial for an interference localized surface plasmon resonance (iLSPR) sensor. The iLSPR is based on plasmonic gold nanoparticles with photonic thin-film muifilayers of porous aluminum oxide ([Al.sub.2][O.sub.3]) and aluminum (Al) on a substrate. With a controllable Wansparent [Al.sub.2][O.sub.3] layer and a highly reflective Al layer, our new nanomaterial was able to detect refractive index (RI) changes of the surrounding environment and the specific interaction of biomoleeules including biotin and avidin, 5-fluorouracil (5-FU) and its antibody, anti-5-fluorouracil (anti 5-FU), when the iLSPR surfaces were biologically functionalized. Our model nanostructure will open the way to display the plasmonic properties of other noble metal nanoparticles and to develop other functionally similar nanosensors, which could then be expanded into multiarrays. 10.1021/ac902008x

Optical fluorescence sol gel sensors have been developed for the detection of carbon dioxide gas in the 0.03-30% range with a detection limit of 0.008% (or 80 ppm) and a quantitation limit of 0.02% (or 200 ppm) C[O.sub.2]. Sol-gels were spin-coated on glass slides to create an organically modified silica-doped matrix with the 1-hydroxypyrene-3,6,8--trisulfonate (HPTS) fluorescent indicator. The luminescence intensity of the HPTS indicator (513 nm) is quenched by C[O.sub.2], which protonates the anionic form of HPTS. An ion pair technique was used to incorporate the lipophilic dye into the hydrophllic sol-gel matrix. Ti[O.sub.2] particles ( 10.1021/ac901890r

A novel tracer, glucose oxidase-functionalized nanocomposite, was designed to label the signal antibodies for ultrasensitive multiplexed measurement of tumor markers using a disposable immunosensor array. The immunosensor array was constructed by coating layer-by-layer colloidal Prussian blue (PB), gold nanoparticles, and capture antibodies on screen-printed carbon electrodes. The preparation of glucose oxidase-functionalized nanocomposites and the labeling of antibody were performed by one-pot assembly of glucose oxidase and antibody on gold nanoparticles attached carbon nanotubes. The PB immobilized on immunosensor surface acted as a mediator to catalyze the reduction of [H.sub.2][O.sub.2] produced in the enzymatic cycle. Both the high-content glucose oxidase and carbon nanotubes in the tracer amplified the detectable signal for the sandwich-type immunoassay. Using carcinoembryonic antigen and [alpha]-fetoprotein as model analytes, the simultaneous multiplexed immunoassay method using the immunosensor array and the designed tracer showed linear ranges of 3 orders of magnitude with the detection limits down to 1.4 and 2.2 pg/mL, respectively. The assay results of serum samples with the proposed method were in an acceptable agreement with the reference values. The dual signal amplification of glucose oxidase-functionalized nanocomposites provided a promising ultrasensitive simultaneous multiplexed immunoassay approach for clinical applications. 10.1021/ac901996a

Small RNA molecules are effective regulators of gene expression, and the expression signature of one subgroup of small RNA, the microRNA (miRNA), has been linked to disease development and progression. Therefore, detection of small RNA in biological samples will greatly improve the understanding of their functions and render effective tools to researchers for cellular process control and disease prevention. To solve the challenges in detecting the low-abundance and short strand-length of small RNA molecules, we designed a ligation-assisted binding assay and applied the cation exchange-based fluorescence amplification (CXFluoAmp) method developed in our group for detection. Nonfluorescent, ionic nanocrystals (NCs) of CdSe were conjugated to detection probes and immobilized onto the array surface via ligation with the target small RNA, miR21, which bound to the capture probe complimentarily. Each binding event induced by one target miR21 molecule was then amplified by the release of thousands of [Cd.sup.2+] from one NC. The free [Cd.sup.2+] immediately turned on the fluorescence of thousands of fluorogenic Rhod-5N molecules. With such a powerful signal amplification strategy, our assay achieved a limit of detection (LOD) of 35 fM and signals were detectible with analyte concentrations spanning over 7 orders of magnitude. We also identified the differential expression of miR21 in total RNA extracts from healthy breast tissue and diseased cells. Furthermore, our detection scheme demonstrated good specificity in small RNA detection, because significant signal intensity could be observed from small RNAs with one or two nucleotides difference in sequences. Thus, our assay has great application potential for disease diagnosis relying on miRNA biomarkers, or in small RNA expression profiling for now target discovery and functional study. 10.1021/ac901983s

A novel rolling circle amplification (RCA) immunoassay based on DNA-encapsulating liposomes, liposome-RCA immunoassay, was developed for ultrasensitive protein detection. This technique utilized antibody-modified liposomes with DNA prime probes encapsulated as the detection reagent in the sandwiched immunoassays. The DNA prime probes were released from liposomes and then initiated a linear RCA reaction, generating a long tandem repeated sequences that could be selectively and sensitively detected by a microbead-based fluorescence assay. The developed technique offered very high sensitivity due to primary amplification via releasing numerous DNA primers from a liposome followed by a secondary RCA amplification. A biobarcode design was incorporated in the technique, which allowed the strategy to be directly implemented for multiplex assay of multiple proteins. Also, the technique allowed easy preparation of the DNA-carrying antibody reagent and the implementation with simple instrumentation. The technique was demonstrated for the determination of prostate-specific antigen (PSA), a highly selective biomarker associated with prostate cancer. The results revealed that the technique exhibited a dynamic response to PSA over a 6-decade concentration range from 0.1 fg [mL.sup.-1] to 0.1 ng [mL.sup.-1] with a limit of detection as Iowas 0.08 fg mL 1 and a high dose-response sensitivity. The liposome-RCA immunoassay holds great promise as a versatile, sensitive, and robust platform to combine the nucleic acid amplification with immunoassay for ultrasensitive protein detection. 10.1021/ac901786m

Spectroelectrochemical sensors combine three modes of selectivity in a single device (electrochemistry, spectroscopy, and selective partitioning). A thin polymer film is coated onto the sensing platform in order to facilitate chemically selective transport to the electrode. The film is an essential part of the sensor because it provides an increase in selectivity and sensitivity by selectively pre-concentrating the analyte. Here, we report the next step in the characterization of partially sulfonated polystyrene-block-poly(ethylene-ran-butylene)block-polystyrene (SSEBS) films for the purpose of chemical sensing by examining the selectivity of the sensor fabricated with this novel thin film material. Binaw mixtures using model analytes were used to demonstrate the sensor's ability to detect an analyte in the presence of a direct interference. The binary mixtures consisted of Ru[(bpy).sub.3.sup.2+]/Fe[(CN).sub.6.sup.3-], Ru[(bpy).sub.3.sup.2+]/ Fe[(bpy).sub.3.sup.2+], and Ru[(bpy).sub.3.sup.2+]/Cu[(bpy).sub.2.sup.2+]. Demonstration of the selective partitioning mode using the Ru[(bpy).sub.3.sup.2+]/Fe[(CN).sub.6.sup.3-] mixture and absorption detection showed the SSEBS film's preference for Ru[(bpy).sub.3.sup.2+] over Fe[(CN).sub.6.sup.3-], and therefore, Fe[(CN).sub.6.sup.3-] did not interfere with the sensor's response to Ru[(bpy).sub.3.sup.2+]. Furthermore, the importance of the use of three modes together was demonstrated by analysis of the Ru[(bpy).sub.3.sup.2+]/Fe[(bpy).sub.3.sup.2+] and the Ru[(bpy).sub.3.sup.2+]/Cu[(bpy).sub.2.sup.2+] test mixtures, where both selection of a specific wavelength for absorption and selection of a specific potential window were required to reduce or eliminate the signal from the interference. Finally, analysis of the Ru[(bpy).sub.3.sup.2+]/Fe[(bpy).sub.3.sup.2+] test mixture was also demonstrated using fluorescence detection. 10.1021/ac901595b

We present the preparation, characterization, and analytical application of silica nanochannels in the size range of 5-100 nm. These cylindrical-shaped nanochannels are prepared using a simple laser-assisted mechanical pulling process, followed by partial enclosure into a glass micropipet. The nanochannels are characterized using a combination of optical microscopy, scanning electron microscopy (SEM), and resistance measurements in an electrolyte solution. The SEM results show that the nanochannel has circular geometry at the orifice. Ohmic response has been obtained from current--voltage measurements in KCl solutions using a silica nanochannel as small as 9 nm in diameter. These nanochannels have been utilized to sense single 40 nm polystyrene nanoparticles. A linear response has been observed between the detection rate and the concentration of nanoparticles in the range of 0-25 nM. The silica nanochannels have also been applied to the study of molecular transport of double-stranded DNA. Electroosmosis-driven molecular translocation has been observed for genomic-length [lambda]-DNA through a 9 nm nanochannel in a 3 M KCl solution.

Detailed compositional analyses of sedimentary organic matter can provide information on its biotic input, environment of deposition, and level of thermal maturation. Pyrolysis-gas chromatography (py-GC), often coupled with a mass spectrometer (py-GC/MS), is one technique used to provide this information. New developments in comprehensive two-dimensional gas chromatography (GC x GC or 2D-GC), coupled with pyrolysis (py-GC x GC), offer the prospect of providing more complete and quantitative compositional information of complex organic solids, such as kerogen and coals. This study will describe applications of pyrolysis-GC x GC to the characterization of petroleum source rocks using flame ionization detector (FID) and sulfur chemiluminescence detector (SCD). In the hydrocarbon analysis by FID, paraffins, naphthenes, and aromatics form distinct two-dimensional separated groups. In the analysis with SCD, sulfur-containing compounds can be distinguished as different classes, such as mer-captans, sulfides, thiophenes, benzothiophenes, and dibenzothiophenes. Single components or summed bands of homologous components can be analyzed qualitatively and quantitatively. With these detailed molecular fingerprints, the relations between kerogen composition and its biotic input, environment of deposition, and thermal maturation may be better understood.

Quantification of a chemical concentration in a pollution plume using a moving membrane-based sensor can be problematic. In many cases, the sensor passes through the plume faster than the time necessary to reach a steady-state signal, which is often used for quantification. Since the exposure time is typically not known, quantification based upon the flow injection analysis principle is also impractical. In this paper, we present a two-dimensional calibration model, exemplified by membrane inlet mass spectrometry, in which the concentration of a chemical can be determined using a simple algorithm. The concentration is given by a calibration factor, which is multiplied by the peak height and divided by the value of a polynomial, calculated at a normalized peak width. The model is demonstrated to give good quantitative estimates of concentrations for exposure times down to ~1/10 of the time it takes to reach steady-state diffusion through the membrane. Although the model is demonstrated using membrane inlet mass spectrometry and detection of volatile organic chemicals, it should be generally applicable to many membrane-covered sensors.