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1.
Davalos RV McGraw GJ Wallow TI Morales AM Krafcik KL Fintschenko Y Cummings EB Simmons BA 《Analytical and bioanalytical chemistry》2008,390(3):847-855
Efficient and robust particle separation and enrichment techniques are critical for a diverse range of lab-on-a-chip analytical
devices including pathogen detection, sample preparation, high-throughput particle sorting, and biomedical diagnostics. Previously,
using insulator-based dielectrophoresis (iDEP) in microfluidic glass devices, we demonstrated simultaneous particle separation
and concentration of various biological organisms, polymer microbeads, and viruses. As an alternative to glass, we evaluate
the performance of similar iDEP structures produced in polymer-based microfluidic devices. There are numerous processing and
operational advantages that motivate our transition to polymers such as the availability of numerous innate chemical compositions
for tailoring performance, mechanical robustness, economy of scale, and ease of thermoforming and mass manufacturing. The
polymer chips we have evaluated are fabricated through an injection molding process of the commercially available cyclic olefin
copolymer Zeonor 1060R. This publication is the first to demonstrate insulator-based dielectrophoretic biological particle
differentiation in a polymeric device injection molded from a silicon master. The results demonstrate that the polymer devices
achieve the same performance metrics as glass devices. We also demonstrate an effective means of enhancing performance of
these microsystems in terms of system power demand through the use of a dynamic surface coating. We demonstrate that the commercially
available nonionic block copolymer surfactant, Pluronic F127, has a strong interaction with the cyclic olefin copolymer at
very low concentrations, positively impacting performance by decreasing the electric field necessary to achieve particle trapping
by an order of magnitude. The presence of this dynamic surface coating, therefore, lowers the power required to operate such
devices and minimizes Joule heating. The results of this study demonstrate that iDEP polymeric microfluidic devices with surfactant
coatings provide an affordable engineering strategy for selective particle enrichment and sorting.
Figure Model generated image (COMSOL) depicting the electric field gradient divided by the electric field that occurs within an array
of insulating posts 相似文献
2.
Wang D Kvetny M Liu J Brown W Li Y Wang G 《Journal of the American Chemical Society》2012,134(8):3651-3654
Memristive and memcapacitive behaviors are observed from ion transport through single conical nanopores in SiO(2) substrate. In i-V measurements, current is found to depend on not just the applied bias potential but also previous conditions in the transport-limiting region inside the nanopore (history-dependent, or memory effect). At different scan rates, a constant cross-point potential separates normal and negative hysteresis loops at low and high conductivity states, respectively. Memory effects are attributed to the finite mobility of ions as they redistribute within the negatively charged nanopore under applied potentials. A quantative correlation between the cross-point potential and electrolyte concentration is established. 相似文献
3.
Christina L. Randall Aubri Gillespie Siddarth Singh Timothy G. Leong David H. Gracias 《Analytical and bioanalytical chemistry》2009,393(4):1217-1224
We describe the fabrication of 3D membranes with precisely patterned surface nanoporosity and their utilization in size selective
sampling. The membranes were self-assembled as porous cubes from lithographically fabricated 2D templates (Leong et al., Langmuir 23:8747–8751, 2007) with face dimensions of 200 μm, volumes of 8 nL, and monodisperse pores ranging in size from approximately 10 μm to 100 nm.
As opposed to conventional sampling and filtration schemes where fluid is moved across a static membrane, we demonstrate sampling
by instead moving the 3D nanoporous membrane through the fluid. This new scheme allows for straightforward sampling in small
volumes, with little to no loss. Membranes with five porous faces and one open face were moved through fluids to sample and
retain nanoscale beads and cells based on pore size. Additionally, cells retained within the membranes were subsequently cultured
and multiplied using standard cell culture protocols upon retrieval.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
4.
Here we report on the unprecedentedly high resolution imaging of ion transport through single nanopores by scanning electrochemical microscopy (SECM). The quantitative SECM image of single nanopores allows for the determination of their structural properties, including their density, shape, and size, which are essential for understanding the permeability of the entire nanoporous membrane. Nanoscale spatial resolution was achieved by scanning a 17 nm radius pipet tip at a distance as low as 1.3 nm from a highly porous nanocrystalline silicon membrane in order to obtain the peak current response controlled by the nanopore-mediated diffusional transport of tetrabutylammonium ions to the nanopipet-supported liquid-liquid interface. A 280 nm × 500 nm image resolved 13 nanopores, which corresponds to a high density of 93 nanopores/μm(2). A finite element simulation of the SECM image was performed to assess quantitatively the spatial resolution limited by the tip diameter in resolving two adjacent pores and to determine the actual size of a nanopore, which was approximated as an elliptical cylinder with a depth of 30 nm and major and minor axes of 53 and 41 nm, respectively. These structural parameters were consistent with those determined by transmission electron microscopy, thereby confirming the reliability of quantitative SECM imaging at the nanoscale level. 相似文献
5.
The language that cells use to communicate consists of the small molecules, peptides, and proteins that are released into
the extracellular environment. To decipher this language, analytical assays are needed that have high selectivity, high sensitivity,
and fast temporal resolution. Affinity assays are a group of analytical methodologies that are adept at studying this communication.
In this overview, we highlight several examples from the literature on various types of affinity assays used in different
platforms to monitor biological communication of peptides and proteins. 相似文献
6.
Ion‐ion electrostatic correlations are recognized to play a significant role in the presence of concentrated multivalent electrolytes. To account for their impact on ionic current rectification phenomenon in conical nanopores, we use the modified continuum Poisson‐Nernst‐Planck (PNP) equations by Bazant et al. Coupled with the Stokes equations, the effects of the EOF are also included. We thoroughly investigate the dependence of the ionic current rectification ratios as a function of the double layer thickness and the electrostatic correlation length. By considering the electrostatic correlations, the modified PNP model successfully captures the ionic current rectification reversal in nanopores filled with lanthanum chloride LaCl3. This finding qualitatively agrees with the experimental observations that cannot be explained by the standard PNP model, suggesting that ion‐ion electrostatic correlations are responsible for this reversal behavior. The modified PNP model not only can be used to explain the experiments, but also go beyond to provide a design tool for nanopore applications involving multivalent electrolytes. 相似文献
7.
The use of polymers in microchip fabrication affords new opportunities for the development of powerful, miniaturized separation
techniques. One method in particular, the use of phase-changing sacrificial layers, allows for simplified designs and many
additional features to the now standard fabrication of microchips. With the possibility of adding a third dimension to the
design of separation devices, various means of enhancing analysis now become possible. The application of phase-changing sacrificial
layers in microchip analysis systems is discussed, both in terms of current uses and future possibilities.
Figure Phase-changing sacrificial materials enable multilayer microfluidic device layouts 相似文献
8.
Hoegger D Morier P Vollet C Heini D Reymond F Rossier JS 《Analytical and bioanalytical chemistry》2007,387(1):267-275
A micro-analytical system for rapid and quantitative analysis by inhibition immunoassay is presented and applied to the detection of folic acid. Eight polymer microchannels of 65-nL volume each and containing microelectrodes are embedded in a cartridge so that they can be operated simultaneously. All fluidic steps as well as the amperometric detection in the channels are operated by an instrument and software developed in-house. The fluidic steps of the immunoassay occur through hydrodynamic loading of the different solutions through the channels. The speed and duration of the flow and incubation parameters can thus be adapted to the biological and testing requirements. The effectiveness of the system was demonstrated by analysing folic acid concentrations in real infant formula samples within 5 min. In an effort to get a fully monitored assay, each fluidic step is monitored thanks to continuous amperometric detection of oxygen in the microchannel. 相似文献
9.
Liu J Kvetny M Feng J Wang D Wu B Brown W Wang G 《Langmuir : the ACS journal of surfaces and colloids》2012,28(2):1588-1595
Current rectification is well known in ion transport through nanoscale pores and channel devices. The measured current is affected by both the geometry and fixed interfacial charges of the nanodevices. In this article, an interesting trend is observed in steady-state current-potential measurements using single conical nanopores. A threshold low-conductivity state is observed upon the dilution of electrolyte concentration. Correspondingly, the normalized current at positive bias potentials drastically increases and contributes to different degrees of rectification. This novel trend at opposite bias polarities is employed to differentiate the ion flux affected by the fixed charges at the substrate-solution interface (surface effect), with respect to the constant asymmetric geometry (volume effect). The surface charge density (SCD) of individual nanopores, an important physical parameter that is challenging to measure experimentally and is known to vary from one nanopore to another, is directly quantified by solving Poisson and Nernst-Planck equations in the simulation of the experimental results. The flux distribution inside the nanopore and the SCD of individual nanopores are reported. The respective diffusion and migration translocations are found to vary at different positions inside the nanopore. This knowledge is believed to be important for resistive pulse sensing applications because the detection signal is determined by the perturbation of the ion current by the analytes. 相似文献
10.
Microfluidic-based electrochemical genosensor coupled to magnetic beads for hybridization detection 总被引:1,自引:0,他引:1
This paper describes the development of a rapid and sensitive enzyme-linked electrochemical genosensor using a novel microfluidic-based platform. In this work, hybridization was performed on streptavidin-coated paramagnetic micro-beads functionalized with a biotinylated capture probe. The complementary sequence was then recognized via sandwich hybridization with a capture probe and a biotinylated signaling probe. After labeling the biotinylated hybrid with a streptavidin-alkaline phosphatase conjugate, the beads were introduced in a disposable cartridge composed of eight parallel microchannels etched in a polyimide substrate. The modified beads were trapped with a magnet addressing each microchannel individually. The presence of microelectrodes in each channel allowed direct electrochemical detection of the enzymatic product within the microchannel. Detection was performed in parallel within the eight microchannels, giving rise to the possibility of performing a multiparameter assay. Quantitative determinations of the analyte concentrations were obtained by following the kinetics of the enzymatic reaction in each channel. The chip was regenerated after each assay by removing the magnet and thus releasing the magnetic beads. The system was applied to the analytical detection of PCR amplified samples with a RSD% = 6. A detection limit of 0.2 nM was evaluated. 相似文献
11.
In situ Raman spectra of chemisorbed azobenzene (AB) monolayers on glassy carbon (GC) electrodes were observed under potentiostatic
conditions in acetonitrile (ACN) with tetrabutyl-ammonium tetrafluoroborate (TBA-BF4). The Raman intensities of these spectra were high below −1000 mV, and this is attributed to the change in absorbance of
AB on GC. In this paper, we describe chemisorbed AB molecules on GC electrode surfaces under potentiostatic conditions. 相似文献
12.
The electrochemical redox-induced contact angle changes of hemoglobin droplets in the absence and presence of tetraheptylammonium-capped
Fe3O4 nanoparticles have been explored by using in situ electrochemical contact angle measurements. The results indicate that the
electrochemical redox process may lead to some structure changes of hemoglobin (Hb), which could further induce the hydrophobic-to-hydrophilic
changes of the relative droplets. Our observations demonstrate that hemoglobin could self-assemble on the surface of the functionalized
Fe3O4 nanoparticles as Hb–Fe3O4 nanocomposites, which may contribute to much more significant change of the electrochemical redox-induced contact angle values
than that with free nano-Fe3O4. These results suggest that in situ electrochemical contact angle measurements could be readily applied as a new and convenient
method to detect some specific biological process.
Figure Schematic drawing of the possible process and contact angle changes for the self-assembly of hemoglobin on the tetraheptylammonium-capped
Fe3O4 nanoparticles
Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. 相似文献
13.
This review describes voltammetric studies on ion transport from one aqueous phase (W1) to another (W2) across a bilayer lipid
membrane (BLM) containing a hydrophobic ion, valinomycin (Val) or gramicidin A (GA). In particular, the ion transport mechanisms
are discussed in terms of the distribution of a pair of ions between aqueous and BLM phases. By addition of a small amount
of hydrophobic ion into W1 and/or W2 containing a hydrophilic salt as a supporting electrolyte, the hydrophobic ion was distributed
into the BLM with the counter ion to maintain electroneutrality within the BLM phase. It was found that the counter ion was
transferred between W1 and W2 across the BLM by applying a membrane potential. Facilitated transport of alkali ions across
a BLM containing Val as an ion carrier compound, could be interpreted by considering not only the formation of the alkali
metal ion–Val complex but also the distribution of both the objective cation and the counter ion. In the case of addition
of GA as a channel-forming compound into the BLM, the facilitated transport of alkali ions across the BLM depended on the
ionic species of the counter ions. It was discovered that the influence of the counter ion on the facilitated transport of
alkali ions across the BLM could be explained in terms of the hydrophobicity and the ionic radius of the counter ion. 相似文献
14.
For disposable microfluidic devices, easy and inexpensive fabrication is essential. Consequently, replication of microfluidic devices, using injection molding or hot embossing, from a master-mold is widely used. However, the conventional master-mold fabrication technique is unsatisfactory in terms of time and costs. In this regard, direct Ni growth (electroplating) from a back plate is promising when the photoresist is well-defined. Here, we demonstrate the use of SU-8 as a photoresist to define the Ni-growth region. We accomplish this application by focusing on the adhesion, the sidewall profile, and the removal of SU-8: the adhesion is enhanced by controlling the exposure dose, the soft-baking time, and by choosing the adhesion-promoting layer; the sidewall profile is regulated by selecting the intensity of each exposed wavelength, showing an aspect ratio of up to 20.9; and, easy removal is achieved by choosing a proper photoresist-stripper. Using the master-mold fabricated by this method, we test the mechanical stability of the features according to the aspect ratio and length; in the hot embossing process, the features are stable in the aspect ratio of up to 5.8 at a length of 200 microm. In addition, the plastic devices fabricated from this method are applied to the passive stop valves, showing a capillary pressure (-0.2 to -7.2 kPa). 相似文献
15.
Derveaux S Stubbe BG Braeckmans K Roelant C Sato K Demeester J De Smedt SC 《Analytical and bioanalytical chemistry》2008,391(7):2453-2467
In the field of medical diagnostics there is a growing need for inexpensive, accurate, and quick high-throughput assays. On
the one hand, recent progress in microfluidics technologies is expected to strongly support the development of miniaturized
analytical devices, which will speed up (bio)analytical assays. On the other hand, a higher throughput can be obtained by
the simultaneous screening of one sample for multiple targets (multiplexing) by means of encoded particle-based assays. Multiplexing
at the macro level is now common in research labs and is expected to become part of clinical diagnostics. This review aims
to debate on the “added value” we can expect from (bio)analysis with particles in microfluidic devices. Technologies to (a)
decode, (b) analyze, and (c) manipulate the particles are described. Special emphasis is placed on the challenges of integrating
currently existing detection platforms for encoded microparticles into microdevices and on promising microtechnologies that
could be used to down-scale the detection units in order to obtain compact miniaturized particle-based multiplexing platforms.
S. Derveaux and B. G. Stubbe contributed equally to this work. 相似文献
16.
We have evaluated five bioconjugation chemistries for immobilizing DNA onto silicon substrates for microfluidic biosensing
applications. Conjugation by organosilanes is compared with linkage by carbonyldiimidazole (CDI) activation of silanol groups
and utilization of dendrimers. Chemistries were compared in terms of immobilization and hybridization density, stability under
microfluidic flow-induced shear stress, and stability after extended storage in aqueous solutions. Conjugation by dendrimer
tether provided the greatest hybridization efficiency; however, conjugation by aminosilane treated with glutaraldehyde yielded
the greatest immobilization and hybridization densities, as well as enhanced stability to both shear stress and extended storage
in an aqueous environment. Direct linkage by CDI activation provided sufficient immobilization and hybridization density and
represents a novel DNA bioconjugation strategy. Although these chemistries were evaluated for use in microfluidic biosensors,
the results provide meaningful insight to a number of nanobiotechnology applications for which microfluidic devices require
surface biofunctionalization, for example vascular prostheses and implanted devices.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
17.
Recent applications of scanning electrochemical microscopy (SECM) to studies of single biological cells are reviewed. This
scanning probe microscopic technique allows the imaging of an individual cell on the basis of not only its surface topography
but also such cellular activities as photosynthesis, respiration, electron transfer, single vesicular exocytosis and membrane
transport. The operational principles of SECM are also introduced in the context of these biological applications. Recent
progress in techniques for high-resolution SECM imaging are also reviewed. Future directions, such as single-channel detection
by SECM, high-resolution imaging with nanometer-sized probes, and combined SECM techniques for multidimensional imaging are
also discussed. 相似文献
18.
Attila Gáspár István Bácsi Erika F. Garcia Mihály Braun Frank A. Gomez 《Analytical and bioanalytical chemistry》2009,395(2):473-478
The goal of this work was to increase the sensitivity of a UV–Vis spectrophotometer by decreasing the background noise and
lengthening the optical path. A microphotometer has been modified to precisely select very small parts of a microfluidic channel
pattern of a chip and to measure light absorbance on a magnified area of the selected part of the channel. The viability of
combining a projection microscope and a spectrophotometer for external absorbance measurements on disposable PDMS chips was
studied. Besides the external direct detection above a microfluidic channel, the optical pathlength was lengthened by detecting
in the region of the perpendicular exit port. Increasing the cross-sectional area of the zone of irradiation improved the
signal-to-noise ratio and the limits of detection (LOD). 相似文献
19.
20.
Study of a toxin–alkaline phosphatase conjugate for the development of an immunosensor for tetrodotoxin determination 总被引:2,自引:0,他引:2
This paper describes a direct competitive immunoenzymatic spectrophotometric assay (ELISA) for tetrodotoxin (TTX) determination
and the adaptation of this method for use in an electrochemical assay format. The novelty of this work involves the use of
the antigen labelled with alkaline phosphatase (AP); this conjugate was prepared in our laboratory as there is no commercially
available conjugate of any kind for TTX. The new conjugate was characterized in terms of its affinity for the specific antibody
as well as the residual concentration and the residual activity of the enzyme (AP) incorporated as label. The proposed method
based on the new conjugate showed satisfactory results for TTX determination: for the spectrophotometric method the dynamic
range was 4–15 ng mL−1 with a limit of detection (LOD) of 2 ng mL−1 (R=0.9247), whereas for the electrochemical protocol the dynamic range was 2–50 ng mL−1 and the LOD was1 ng mL−1. 相似文献