“…While similarly designed crossed microfluidic arrays were recently demonstrated by Whitesides and co-workers, 41 these used passive diffusion through the pores of the polycarbonate membrane to mix the fluids, as opposed to the electrically driven flow demonstrated here. [42][43][44] A significant advantage of using electrically driven flow, by choosing the pore diameter, pore surface chemistry, channel surface charge, and solution ionic strength, one can select the direction that fluid flows through the pore for the same externally applied voltage. Interestingly, in the microfluidic-nanofluidic hybrid architecture, the flow is opposite to the direction based on the electroosmotic flow characteristics of the 200-nm pore diameter PCTE capillary array alone.…”
Section: Resultsmentioning
confidence: 99%
“…Figure b demonstrates the insensitivity to analyte charge state by comparing the transfer of the neutral fluorophore bodipy. While similarly designed crossed microfluidic arrays were recently demonstrated by Whitesides and co-workers, these used passive diffusion through the pores of the polycarbonate membrane to mix the fluids, as opposed to the electrically driven flow demonstrated here. − 2 Photograph of a separation/collection microchip showing the crossed microchannels and the nanofluidic capillary array membrane. 3 Fluorescence intensity (left ordinate, solid line) and applied bias, Δ V , (right ordinate, dashed line) as a function of time showing transport of 0.17 μM fluorescein in 5 mM pH 8 phosphate buffer (PB) across a 200-nm pore diameter PCTE membrane. The schematics below the respective graphs show the bias voltage application schemes.…”
The extension of microfluidic devices to include three-dimensional fluidic networks allows complex fluidic and chemical manipulations but requires innovative methods to interface fluidic layers. Externally controllable interconnects, employing nuclear track-etched polycarbonate membranes containing nanometer-diameter capillaries, are described that produce hybrid three-dimensional fluidic architectures. Controllable nanofluidic transfer is achieved by controlling applied bias, polarity, and density of the immobile nanopore surface charge and the impedance of the nanocapillary array relative to the microfluidic channels. Analyte transport between vertically separated microchannels has three stable transfer levels, corresponding to zero, reverse, and forward bias. The transfer can even depend on the properties of the analyte being transferred such as the molecular size, illustrating the flexible character of the analyte transfer. In a specific analysis implementation, nanochannel array gating is applied to capillary electrophoresis separations, allowing selected separated components to be isolated for further manipulation, thereby opening the way for preparative separations at attomole analyte mass levels.
“…While similarly designed crossed microfluidic arrays were recently demonstrated by Whitesides and co-workers, 41 these used passive diffusion through the pores of the polycarbonate membrane to mix the fluids, as opposed to the electrically driven flow demonstrated here. [42][43][44] A significant advantage of using electrically driven flow, by choosing the pore diameter, pore surface chemistry, channel surface charge, and solution ionic strength, one can select the direction that fluid flows through the pore for the same externally applied voltage. Interestingly, in the microfluidic-nanofluidic hybrid architecture, the flow is opposite to the direction based on the electroosmotic flow characteristics of the 200-nm pore diameter PCTE capillary array alone.…”
Section: Resultsmentioning
confidence: 99%
“…Figure b demonstrates the insensitivity to analyte charge state by comparing the transfer of the neutral fluorophore bodipy. While similarly designed crossed microfluidic arrays were recently demonstrated by Whitesides and co-workers, these used passive diffusion through the pores of the polycarbonate membrane to mix the fluids, as opposed to the electrically driven flow demonstrated here. − 2 Photograph of a separation/collection microchip showing the crossed microchannels and the nanofluidic capillary array membrane. 3 Fluorescence intensity (left ordinate, solid line) and applied bias, Δ V , (right ordinate, dashed line) as a function of time showing transport of 0.17 μM fluorescein in 5 mM pH 8 phosphate buffer (PB) across a 200-nm pore diameter PCTE membrane. The schematics below the respective graphs show the bias voltage application schemes.…”
The extension of microfluidic devices to include three-dimensional fluidic networks allows complex fluidic and chemical manipulations but requires innovative methods to interface fluidic layers. Externally controllable interconnects, employing nuclear track-etched polycarbonate membranes containing nanometer-diameter capillaries, are described that produce hybrid three-dimensional fluidic architectures. Controllable nanofluidic transfer is achieved by controlling applied bias, polarity, and density of the immobile nanopore surface charge and the impedance of the nanocapillary array relative to the microfluidic channels. Analyte transport between vertically separated microchannels has three stable transfer levels, corresponding to zero, reverse, and forward bias. The transfer can even depend on the properties of the analyte being transferred such as the molecular size, illustrating the flexible character of the analyte transfer. In a specific analysis implementation, nanochannel array gating is applied to capillary electrophoresis separations, allowing selected separated components to be isolated for further manipulation, thereby opening the way for preparative separations at attomole analyte mass levels.
“…Incorporating the DNAzyme into a microfluidic device offers a convenient package and the ability to include capillary ion analysis on selected analyte bands prior to the Pb determination for greatly improved selectivity. We expect that the combination of immobilized DNAzyme inside the nanopores of a hybrid nanofluidic/microfluidic device will offer a convenient method of accomplishing this. − Although all of the experiments discussed here were performed on planar Au, there is every reason to believe the molecular beacon chemistry can be ported to other Au-coated surfaces, such as the electrolessly deposited Au on the interior of nanocapillaries, to yield a flow-through device compatible with a preseparation. Since the rate-limiting step is diffusion to and away from the Au surface, incorporation into a flow-through device is expected to improve reaction times dramatically.…”
A Pb(II)-specific DNAzyme fluorescent sensor has been modified with a thiol moiety in order to immobilize it on a Au surface. Self-assembly of the DNAzyme is accomplished by first adsorbing the single-thiolated enzyme strand (HS-17E-Dy) followed by adsorption of mercaptohexanol, which serves to displace any Au-N interactions and ensure that DNA is bound only through the Sheadgroup. The preformed self-assembled monolayer is then hybridized with the complementary fluorophorecontaining substrate strand (17DS-Fl). Upon reaction with Pb(II), the substrate strand is cleaved, releasing a fluorescent fragment for detection. Fluorescence intensity may be correlated with original Pb(II) concentration, and a linear calibration was obtained over nearly four decades: 10 µM g [Pb(II)] g 1 nM. The immobilized DNAzyme is
“…Transport through pores is affected by steric hindrance or exclusion due to molecular entropy, hydrodynamic hindrance, caused by viscous forces associated with the walls of the pores, and charge interactions between the molecule and the surface of the nanopore or nanochannel. Three-dimensional systems using nanofluidic interconnects, which provide fluidic communication among microfluidic channels in vertically separated layers, have been of interest for the purpose of fluid handling in mass-transported limited samples [57,58]. Pore/channel size, surface chemistry (i.e., charge), applied potentials and multistep filtrations with different membranes can be used to perform highly efficient separations [2,12].…”
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