Mass-amplifying quantum dots in a fluorescence polarization-based aptasensor for ATP

We report on a fluorescence polarization assay for the detection of the target analyte ATP by making use of an aptasensor and of mass-amplifying CdTe-CdS quantum dots. The ATP aptamer was modified with digoxin antigen and hybridized with its complementary DNA that was modified with the CdTe-CdS quantum dots. Following the addition of digoxin antibody, the mass-amplifying aptasensor probe is formed as a result of the immuno reaction. In the presence of ATP, the polarization of fluorescence decreases because the digoxin antibody becomes dissociated due to the recognition of the ATP by the ATP aptamer. Under optimized conditions, the method has a linear response to ATP in the 10 to 350 μM concentration range, and the limit of detection is 3.7 μM. The method combines the specific recognition capability of aptamers with the sensitivity of an immunoreaction. It has good selectivity and sensitivity, and can be used to detect ATP in serum samples.

Sensitive detection of tuberculosis using nanoparticle-enhanced surface plasmon resonance

We show that the antigen CFP-10 (found in tissue fluids of tuberculosis patients) can be used as a marker protein in a surface-plasmon resonance (SPR) based method for early and simplified diagnosis of tuberculosis. A sandwich SPR immunosensor was constructed by immobilizing the CFP-10 antibody on a self-assembled monolayer on a gold surface, this followed by blocking it with bovine serum albumin. Following exposure of the sensor surface to a sample containing CFP-10, secondary antibody immobilized on nickel oxide nanoparticles are injected which causes a large SPR signal change. The method has a dynamic range from 0.1 to around 150 ng per mL of CFP-10, and a detection limit as low as 0.1 ng per mL. This is assumed to be due to the high amplification power of the NiO nanoparticles.

Hybrid nanonet/nanoflake NiCo2O4 electrodes with an ultrahigh surface area for supercapacitors

An integrated electrode consisting of hybrid nanonet/nanoflake NiCo₂O₄ grown on stainless steel mesh substrates exhibits a high specific capacitance while maintaining high-rate capability and good cycling stability. The specific capacitance reaches a maximum of 911 F g^?1 at a current density of 10 A g^?1, which can still retain 864 F g^?1 (94.8 % retention) after 10,000 cycles. These much-improved electrochemical performances are attributed to the unique architecture of NiCo₂O₄ electrode. The interconnected nanonet NiCo₂O₄ with an ultrahigh surface area significantly facilitates the rapid ion/electron transport and guarantees good mechanical adhesion, while the ultrathin nanoflakes further extend the active sites for fast redox reactions for efficient energy storage. Figure

Hybrid nanonet/nanoflake NiCo₂O₄ grown on stainless steel mesh exhibits superior capacitive performance and long-life stability as an integrated electrode for high-performance supercapacitors.     

Real-time monitoring of immobilized single yeast cells through multifrequency electrical impedance spectroscopy

We present a microfluidic device, which enables single cells to be reliably trapped and cultivated while simultaneously being monitored by means of multifrequency electrical impedance spectroscopy (EIS) in the frequency range of 10 kHz–10 MHz. Polystyrene beads were employed to characterize the EIS performance inside the microfluidic device. The results demonstrate that EIS yields a low coefficient of variation in measuring the diameters of captured beads (~0.13 %). Budding yeast, Saccharomyces cerevisiae, was afterwards used as model organism. Single yeast cells were immobilized and measured by means of EIS. The bud growth was monitored through EIS at a temporal resolution of 1 min. The size increment of the bud, which is difficult to determine optically within a short time period, can be clearly detected through EIS signals. The impedance measurements also reflect the changes in position or motion of single yeast cells in the trap. By analyzing the multifrequency EIS data, cell motion could be qualitatively discerned from bud growth. The results demonstrate that single-cell EIS can be used to monitor cell growth, while also detecting potential cell motion in real-time and label-free approach, and that EIS constitutes a sensitive tool for dynamic single-cell analysis. Figure

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A micro-discharge photoionization detector for micro-gas chromatography

We report on a small (20?×?10 mm) micromachined device for the detection of gases in micro-gas chromatography (GC). It incorporates a micro-discharge across a 20-μm gap, and a remote electrode in the micro cavity that generates an electrical signal corresponding to the photo-ionization of gaseous analytes in a stream of carrier gas. Multi-component mixtures were detected and the results compared to those obtained with a flame ionization detector. The minimum detectable limit is 350 pg.μL^?1 of n-octane in air when applying a 1.4 mW discharge. The combination of wet etching of glass (as used for microfluidic channels) with a lift-off process for detector electrodes by a robust batch process results in a universal, non-destructive, and sensitive microdetector for micro-GC.

Detection of mismatched caspase-3 DNA oligonucleotides with an SPR biosensor following amplification by Taq polymerase

We demonstrate that base mismatches of caspase-3 DNA sequences can be detected by surface plasmon resonance (SPR) following signal amplification by polymerase from Thermus aquaticus (Taq). The concentration of magnesium ions and the respective dNTPs for polymerase binding to the oligonucleotides on the sensing surface were optimized. Taq polymerase binds to double-stranded DNA that is self-assembled on the gold surface of the biosensor to induce an SPR signal. Experiments are presented on the effect of Mg(II) and dNTP concentrations on the activity of the polymerase on the sensing surface. The detection limits are 50 pM, 0.1 nM, 0.7 nM, 7 nM, and 20 nM for correctly matched, single-base mismatched, two-base mismatched, three-base mismatched and four-base mismatched DNA of caspase-3, respectively. This is attributed to the optimized experimental conditions, with samples containing 2 μM of Mg(II) and 0.3 mM of dNTP.

An indium tin oxide electrode modified with gold nanorods for use in potential-controlled surface plasmon resonance studies

The modification of electrodes with gold nanoparticles results in an increased electrode surface area, enhanced mass transport, and improved catalytic properties. We have extended this approach to indium tin oxide (ITO) electrodes to obtain optically transparent gold nanorod-modified electrodes which display enhanced electrochemical capabilities and have the additional advantage of showing a tunable surface plasmon resonance. The procedures for attaining high surface coverage (15 gold nanorods per square µm) of such electrodes were optimized, and the potential-dependent surface plasmon resonance was studied under controlled electrical potential. In an exemplary sensor application, we demonstrate the detection of mercury via potential-dependent formation of an Au-Hg amalgam.

Improving surface plasmon resonance imaging of DNA by creating new gold and silver based surface nanostructures

The use of nanoparticles (NPs) can substantially improve the analytical performance of surface plasmon resonance imaging (SPRi) in general, and in DNA sensing in particular. In this work, we report on the modification of the gold surface of commercial biochips with gold nanospheres, silica-coated gold nanoshells, and silver nanoprisms, respectively. The NPs were tethered onto the surface of the chip and functionalized with a DNA probe. The effects of tethering conditions and varying nanostructures on the SPRi signals were evaluated via hybridization assays. The results showed that coupling between planar surface plasmons and electric fields, generated by localized surface plasmons of the NPs, is mandatory for signal enhancement. Silver nanoprisms gave the best results in improving the signal change at a target DNA concentration of <50 nM by +50 % (compared to a conventional SPRi chip). The limit of detection for the target DNA was 0.5 nM which is 5 times less than in conventional SPRi.

The use of gold-silver core-shell nanorods self-assembled on a glass substrate can substantially improve the performance of plasmonic affinity biosensors

We report on an effective strategy for the enhancement in the sensitivity of localized surface plasmon resonance (LSPR). It is based on the use of gold-silver core-shell nanorods (Au-Ag-cs-NRs) immobilized on a glass substrate. The nanorods arrange themselves by self-assembly, and the resulting LSPR band of the Au-Ag-cs-NRs becomes sharper and more intense. The sensitivity to refractive index (RI) of the Au-Ag-cs-NRs on the glass support is ~281 nm per RI unit, which is better by about 30 % compared to gold nanorods immobilized on glass substrate. The system was applied to study the streptavidin-biotin affinity system which is widely used in biosciences. It is found that the red-shift of the LSPR peak linearly increases with the concentration of streptavidin in the 95 pM to 1.7 μM concentration range. The detection limit (at an S/N ratio of 3) is at 35 pM. The results reveal the merits of this approach in terms of label-free optical affinity sensing. Figure

Au-Ag core-shell nanorods self-assembled on glass substrates. The refractive index sensitivity was enhanced obviously. A strategy to amplify the response and fabricate a label-free optical biosensor     

Sandwich immunoassay for alpha-fetoprotein in human sera using gold nanoparticle and magnetic bead labels along with resonance Rayleigh scattering readout

We describe a sensitive sandwich immunoassay for alpha-fetoprotein (AFP). It is making use of gold nanoparticles (GNPs) and magnetic beads (MBs) as labels, and of resonance Rayleigh scattering for detection. Two antibodies were labeled with GNPs and MBs, respectively, and MB-antigen-GNP complexes were formed in the presence of antigens. The MB labels also serve as solid phase carriers that can be used to magnetically separate the immuno complex. The GNP labels are used as optical probes, and Rayleigh scattering was used to determine the concentration of free GNPs-antibody after separation of the MB-antigen-GNP complexes. The concentration of AFP is related to the intensity of light scattered by free GNPs in the 13.6 pM to 436 pM concentration range, and the limit of detection is 13.6 pM. The method was applied to the determination of AFP in sera of cancer patients, and the results agree well with those obtained by conventional ELISA.

Capacitive sensing of microcystin variants of Microcystis aeruginosa using a gold immunoelectrode modified with antibodies,gold nanoparticles and polytyramine

We report on the application of an automated and easy-to-use device to directly measure the immunoreactions between adda-specific monoclonal antibodies and microcystins. The antibodies were immobilized on a gold electrode whose surface was modified first with polytyramine and then with gold nanoparticles. The immunoreaction leads to a change in the capacitance of the system. Under optimum conditions, the sensor is capable of performing stable regeneration-assay cycles and has a low detection limit at a concentration of 0.01 pM level of microcystin-leucine-arginine (MC-LR). The surface of the biosensor can be regenerated with pH 2.5 glycine buffer which dissociates the antibody-antigen complex. The biosensor was used to monitor the production of microcystins during batch cultivation of Microcystis aeruginosa (isolated from ponds in Botswana). Liquid chromatography coupled to MS/MS detection was used to identify three variants, viz. MC-LR (995.6 Da), DmMC-LR (981.2 Da) and MC-LA (910.5 Da).

Terahertz split-ring metamaterials as transducers for chemical sensors based on conducting polymers: a feasibility study with sensing of acidic and basic gases using polyaniline chemosensitive layer

We report on the first application of terahertz metamaterials acting as transducers for chemical sensors based on conducting polymers. In our feasibility study aimed at sensing of gaseous hydrochloric and ammonia, a two-dimensional sensor metamaterial consisting of an array of split-ring resonators on the surface of undoped silicon wafer was prepared. The surface of the resonator was coated with a 150-μm layer of polyaniline. Binding of hydrogen chloride to polyaniline leads to distinct changes in the resonance frequency of the metamaterial. Measurements can be performed both in the reflection and transmission mode. A numerical simulation of the response revealed an increase of both the real and the imaginary components of the dielectric function of the polyaniline film. These changes are attributed to the transition from emaraldine base to emeraldine salt. The results demonstrate a new approach for formation of highly sensitive transducers for chemical sensors.

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Electromechanical biosensors for pathogen detection

Rapid and sensitive detection of pathogen is critical for public health, defense and security. Methods such as culture and immunoassays, though highly selective and accurate, are time-consuming and not sufficient for fast decision-making in many situations. Biosensors have been developed to meet the challenges in pathogen detection. This article reviews the development and application of electromechanical biosensors for pathogen detection. It covers the most commonly used electromechanical biosensor systems, specifically quartz crystal microbalances, cantilever sensors and surface wave acoustic sensors. Sensing principles, immobilization of biorecognition elements, and applications to the detection of pathogens in food and water samples are sequentially discussed.

Highly selective piezoelectric sensor for lead(II) based on the lead-catalyzed release of gold nanoparticles from a self-assembled nanosurface

A novel quartz crystal microbalance (QCM) sensor has been developed for highly selective and sensitive detection of Pb²⁺ by exploiting the catalytic effect of Pb²⁺ ions on the leaching of gold nanoparticles from the surface of a QCM sensor. The use of self-assembled gold nanoparticles (AuNPs) strongly enlarges the size of the interface and thus amplifies the analytical response resulting from the loss of mass. This results in a very low detection limit for Pb²⁺ (30 nM). The high selectivity is demonstrated by studying the effect of potentially interfering ions both in the absence and presence of Pb²⁺ ions. This simple and well reproducible sensor was applied to the determination of lead in the spiked drinking water. This work provides a novel strategy for fabricating QCM sensors towards Pb²⁺ in real samples. Figure

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Streptavidin-enhanced surface plasmon resonance biosensor for highly sensitive and specific detection of microRNA

We are presenting a method for sensitive and specific detection of microRNA (miRNA) using surface plasmon resonance. A thiolated capture DNA probe with a short complete complementary sequence was immobilized on the gold surface of the sensor to recognize the part sequence of target miRNA, and then an oligonucleotide probe linked to streptavidin was employed to bind the another section of the target. The use of the streptavidin-oligonucleotide complex caused a ~5-fold increase in signal, improved the detection sensitivity by a factor of ~24, and lowered the detection limit to 1.7 fmol of miR-122. This specificity allowed a single mismatch in the target miRNA to be discriminated. The whole assay takes 30 min, and the surface of the sensor can be regenerated at least 30 times without loss in performance. The method was successfully applied to the determination of miRNA spiked into human total RNA samples.

Rapid extraction and preservation of genomic DNA from human samples

Simple and rapid extraction of human genomic DNA remains a bottleneck for genome analysis and disease diagnosis. Current methods using microfilters require cumbersome, multiple handling steps in part because salt conditions must be controlled for attraction and elution of DNA in porous silica. We report a novel extraction method of human genomic DNA from buccal swab and saliva samples. DNA is attracted onto a gold-coated microchip by an electric field and capillary action while the captured DNA is eluted by thermal heating at 70 °C. A prototype device was designed to handle four microchips, and a compatible protocol was developed. The extracted DNA using microchips was characterized by qPCR for different sample volumes, using different lengths of PCR amplicon, and nuclear and mitochondrial genes. In comparison with a commercial kit, an equivalent yield of DNA extraction was achieved with fewer steps. Room-temperature preservation for 1 month was demonstrated for captured DNA, facilitating straightforward collection, delivery, and handling of genomic DNA in an environment-friendly protocol.

A novel synthesis of (3,6-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-9-(4-vinylbenzyl)-9H-carbazole), alternating polymer formation, characterization, and capacitance measurements

In this work, (3,6-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-9-(4-vinylbenzyl)-9H-carbazole) (EDOTVBCz) comonomer was chemically synthesized and characterized by Fourier transform infrared (FTIR), proton nuclear magnetic resonance, and carbon nuclear magnetic resonance spectroscopy. EDOTVBCz was electrocoated on glassy carbon electrode (GCE) in various initial molar concentrations ([EDOTVBCz]₀?=?1.0, 1.5, 2.0, and 3.0) in 0.1 M lithium perchlorate (LiClO₄)/acetonitrile (CH₃CN). P(EDOTVBCz)/GCE was characterized by cyclic voltammetry, FTIR reflectance-attenuated total reflection spectroscopy, scanning electron microscopy–energy dispersive X-ray analysis, atomic force microscopy, and electrochemical impedance spectroscopy (EIS). EIS was used to determine the capacitive behaviors of modified GCE via Nyquist, Bode magnitude, Bode phase, and admittance plots. The highest low-frequency capacitance value was obtained as C _LF?=?～2.35 mF cm^?2 for [EDOTVBCz]₀?=?3.0 mM. Double-layer capacitance of the polymer/electrolyte system was calculated as C _dl?=?～2.78 mF cm^?2 for [EDOTVBCz]₀?=?1.0 and 3.0 mM. The maximum phase angle was obtained as θ?=?～76.7^o for [EDOTVBCz]₀?=?1.0, 1.5, 2.0, and 3.0 mM at the frequency of 20.6 Hz. AC impedance spectra of P(EDOTVBCz)/LiClO₄/CH₃CN was obtained by performing electrical equivalent circuit model of R(Q(R(CR))) with linear Kramers–Kronig test.

Determination of soy proteins in food samples by dispersive solid-phase immunoextraction and dynamic long-wavelength fluorometry

We report on a method for the determination of soy proteins in food samples via dispersive solid-phase immunoextraction using gold-coated magnetic nanoparticles (NPs) as a support. Soy proteins were first extracted using anti-soy protein antibodies immobilized on the NPs, and then quantified by measuring the increase in fluorescence of the long-wavelength fluorophore cresyl violet in the presence of the anionic surfactant sodium dodecyl sulfate at neutral pH in a flow system. The method involves the use of two standard or sample aliquots. The fluorescence intensity of one aliquot is directly measured whereas that of the other aliquot is measured after immunoextraction. The difference between the peak heights of both aliquots serves as the analytical information that is directly proportional to the protein concentration. The limit of detection is 0.35 mg L^?1, the linear range is from 1 to 15 mg L^?1, and the relative standard deviation is <?5 %. Proteins such as bovine serum albumin and globulins do not interfere at the same concentration level. The method was applied to the analysis of soy-based beverages and gave recoveries in the range between 80.0 and 107.3 %.

Ultrasensitive detection of Dynabeads protein A using the giant magnetoimpedance effect

We report on a biosensing system for ultrasensitive detection of Dynabeads protein A (DPA) that employs the magnetoimpedance (GMI) effect. The system is capable of detecting DPA via magnetic signals in the form of a magnetoimpedance change. The GMI ratio shows distinctive changes because of the induced fringe field produced by the superparamagnetic Dynabeads. The GMI ratio undergoes an overall downturn at high frequencies, but the drop becomes smaller with increasing DPA concentration. This phenomenon has not been observed so far. At a concentration of 0.1 μg mL^?1, the GMI ratio drops by 8.53 % at a frequency of 1.4 MHz. In other word: almost 90 Dynabeads can be detected. We believe that this novel scheme has a large potential in high-sensitivity and miniaturized immunoassays.

Mesoporous ZnO-NiO architectures for use in a high-performance nonenzymatic glucose sensor

Mesoporous ZnO-NiO architectures were prepared by thermal annealing of zinc-nickel hydroxycarbonate composites. The resulting architectures are shown to be assembled by many mesoporous nanosheets, and this results in a large surface area and a strong synergy between the ZnO and NiO nanoparticles. The material obtained by annealing at 400 °C was used as an electrode that responds to glucose over a wide concentration range (from 0.5 μM to 6.4 mM), with a detection limit as low as 0.5 μM, fast response time (<3 s), and good sensitivity (120.5 μA?·?mM^?1?·?cm^?2). Figure

The mesoporous ZnO-NiO architecture by annealing at 400 °C was used as an electrode that responds to glucose over a wide concentration range (from 0.5 μM to 6.4 mM), with a detection limit as low as 0.5 μM, fast response time (<3 s), and good sensitivity (120.5 μA?·?mM^?1?·?cm^?2