Biodegradable polymers can be applied to a variety of implants for controlled and local drug delivery. The aim of this study is to develop a biodegradable and nanoporous polymeric platform for a wide spectrum of drug-eluting implants with special focus on stent-coating applications. It was synthesized by poly(DL-lactide-co-glycolide) (PLGA 65:35, PLGA 75:25) and polycaprolactone (PCL) in a multilayer configuration by means of a spin-coating technique. The antiplatelet drug dipyridamole was loaded into the surface nanopores of the platform. Surface characterization was made by atomic force microscopy (AFM) and spectroscopic ellipsometry (SE). Platelet adhesion and drug-release kinetic studies were then carried out. The study revealed that the multilayer films are highly nanoporous, whereas the single layers of PLGA are atomically smooth and spherulites are formed in PCL. Their nanoporosity (pore diameter, depth, density, surface roughness) can be tailored by tuning the growth parameters (eg, spinning speed, polymer concentration), essential for drug-delivery performance. The origin of pore formation may be attributed to the phase separation of polymer blends via the spinodal decomposition mechanism. SE studies revealed the structural characteristics, film thickness, and optical properties even of the single layers in the triple-layer construct, providing substantial information for drug loading and complement AFM findings. Platelet adhesion studies showed that the dipyridamole-loaded coatings inhibit platelet aggregation that is a prerequisite for clotting. Finally, the films exhibited sustained release profiles of dipyridamole over 70 days. These results indicate that the current multilayer phase therapeutic approach constitutes an effective drug-delivery platform for drug-eluting implants and especially for cardiovascular stent applications.
drug delivery; implants; stents; polymers; spin-coating; atomic force microscopy
Synthetic nanoporous materials have numerous potential biological and medical applications that involve sorting, sensing, isolating and releasing biological molecules. Nanoporous systems engineered to mimic natural filtration systems are actively being developed for use in smart implantable drug delivery systems, bioartificial organs, and other novel nano-enabled medical devices. Recent advances in nanoscience have made it possible to precisely control the morphology as well as physical and chemical properties of the pores in nanoporous materials that make them increasingly attractive for regulating and sensing transport at the molecular level. In this work, an overview of nanoporous membranes for biomedical applications is given. Various in vivo and in vitro membrane applications, including biosensing, biosorting, immunoisolation and drug delivery, are presented. Different types of nanoporous materials and their fabrication techniques are discussed with an emphasis on membranes with ordered pores. Desirable properties of membranes used in implantable devices, including biocompatibility and antibiofouling behavior, are discussed. The use of surface modification techniques to improve the function of nanoporous membranes is reviewed. Despite the extensive research carried out in fabrication, characterization, and modeling of nanoporous materials, there are still several challenges that must be overcome in order to create synthetic nanoporous systems that behave similarly to their biological counterparts.
Biosensing; Drug delivery; Implantable materials; Nanopores; Nano-scale membranes
The growth of known biologically-relevant mineral phases on semiconducting surfaces is one strategy to explicitly induce bioactivity in such materials, either for sensing or drug delivery applications. In this work, we describe the use of a spark ablation process to fabricate deliberate patterns of Ca10(PO4)6(OH)2 on crystalline Si (calcified nanoporous silicon). These patterns have been principally characterized by scanning electron microscopy in conjunction with elemental characterization by energy dispersive x-ray analysis. This is followed by a detailed comparison of the effects of fibroblast adhesion and proliferation onto calcified nanoporous Si, calcified nanoporous Si derivatized with alendronate, as well as control samples of an identical surface area containing porous SiO2. Fibroblast adhesion and proliferation assays demonstrate that a higher density of cells grow on the Ca3(PO4)2 /porous Si/ SiO2 structures relative to the alendronate-modified surfaces and porous Si/SiOM2 samples.
Calcium phosphate; silicon; fibroblasts; biosensor
Prototyping of nanoporous carbon membranes with three-dimensional microscale patterns is significant for integration of such multifunctional materials into various miniaturized systems. Incorporating nano material synthesis into microelectronics technology, we present a novel approach to direct prototyping of carbon membranes with highly nanoporous structures inside. Membranes with significant thicknesses (1 ~ 40 μm) are rapidly prototyped at wafer level by combining nano templating method with readily available microfabrication techniques, which include photolithography, high-temperature annealing and etching. In particular, the high-surface-area membranes are specified as three-dimensional electrodes for micro supercapacitors and show high performance compared to reported ones. Improvements in scalability, compatibility and cost make the general strategy promising for batch fabrication of operational on-chip devices or full integration of three-dimensional nanoporous membranes with existing micro systems.
We report here the synthesis and characterization of polydiacetylene (PDA) films and nanotubes using layer-by-layer (LBL) chemistry. 10,12-Docosadiyndioic acid (DCDA) monomer was self-assembled on flat surfaces and inside of nanoporous alumina templates. UV irradiation of DCDA provided polymerized-DCDA (PDCDA) films and nanotubes. We have used zirconium-carboxylate interlayer chemistry to synthesize PDCDA multilayers on flat surfaces and in nanoporous template. PDCDA multilayers were characterized using optical (UV–vis, fluorescence, ellipsometry, FTIR) spectroscopies, ionic current–voltage (I–V) analysis, and scanning electron microscopy. Ellipsometry, FTIR, electronic absorption and emission spectroscopies showed a uniform DCDA deposition at each deposition cycle. Our optical spectroscopic analysis indicates that carboxylate-zirconium interlinking chemistry is robust. To explain the disorganization in the alkyl portion of PDCDA multilayer films, we propose carboxylate-zirconium interlinkages act as “locks” in between PDCDA layers which restrict the movement of alkyl portion in the films. Because of this locking, the induced-stresses in the polymer chains can not be efficiently relieved. Our ionic resistance data from I–V analysis correlate well with calculated resistance at smaller number of PDCDA layers but significantly deviated for thicker PDCDA nanotubes. These differences were attributed to ion-blocking because some of the PDCDA nanotubes were totally closed and the nonohmic and permselective ionic behaviors when the diameter of the pores approaches the double-layer thickness of the solution inside of the nanotubes.
Self-aligned nanoporous TiO2templates synthesized via dc current electrochemical anodization have been carefully analyzed. The influence of environmental temperature during the anodization, ranging from 2 °C to ambient, on the structure and morphology of the nanoporous oxide formation has been investigated, as well as that of the HF electrolyte chemical composition, its concentration and their mixtures with other acids employed for the anodization. Arrays of self-assembled titania nanopores with inner pores diameter ranging between 50 and 100 nm, wall thickness around 20–60 nm and 300 nm in length, are grown in amorphous phase, vertical to the Ti substrate, parallel aligned to each other and uniformly disordering distributed over all the sample surface. Additional remarks about the photoluminiscence properties of the titania nanoporous templates and the magnetic behavior of the Ni filled nanoporous semiconductor Ti oxide template are also included.
Titanium oxides; Nanoporous materials; Electrochemical anodization
Using all-atom molecular dynamics and atomic-resolution Brownian dynamics, we simulate the translocation of single-stranded DNA through graphene nanopores and characterize the ionic current blockades produced by DNA nucleotides. We find that transport of single DNA strands through graphene nanopores may occur in single nucleotide steps. For certain pore geometries, hydrophobic interactions with the graphene membrane lead to a dramatic reduction in the conformational fluctuations of the nucleotides in the nanopores. Furthermore, we show that ionic current blockades produced by different DNA nucleotides are, in general, indicative of the nucleotide type, but very sensitive to the orientation of the nucleotides in the nanopore. Taken together, our simulations suggest that strand sequencing of DNA by measuring the ionic current blockades in graphene nanopores may be possible, given that the conformation of DNA nucleotides in the nanopore can be controlled through precise engineering of the nanopore surface.
Nanopore; graphene; molecular dynamics; biosensors; nucleic acids; ionic current
Here we present an optofluidic surface enhanced Raman spectroscopy (SERS) device for on-chip detection of vasopressin using an aptamer based binding assay. To create the SERS-active substrate, densely packed, 200 nm diameter, metal nanotube arrays were fabricated using an anodized alumina nanoporous membrane as a template for shadow evaporation. We explore the use of both single layer Au structures and multilayer Au/Ag/Au structures and also demonstrate a facile technique for integrating the membranes with all polydimethylsiloxane (PDMS) microfluidic devices. Using the integrated device, we demonstrate a linear response in the main detection peak intensity to solution phase concentration and a limit of detection on the order of 5.2 μU/mL. This low limit of detection is obtained with device containing the multilayer SERS substrate which we show exhibits a stronger Raman enhancement while maintaining biocompatibility and ease or surface reactivity with the capture probe.
SERS-active substrate; Nanotube array; Optofluidic device; Aptamer; Vasopressin
Meso- and nanoporous structures are adequate matrices for controlled drug delivery systems, due to their large surface areas and to their bioactive and biocompatibility properties. Mesoporous materials of type SBA-15, synthesized under different pH conditions, and zeolite beta were studied in order to compare the different intrinsic morphological characteristics as pore size, pore connectivity, and pore geometry on the drug loading and release process. These materials were characterized by X-ray diffraction, nitrogen adsorption, scanning and transmission electron microscopy, and calorimetric measurements. Ibuprofen (IBU) was chosen as a model drug for the formulation of controlled-release dosage forms; it was impregnated into these two types of materials by a soaking procedure during different periods. Drug loading and release studies were followed by UV-Vis spectrophotometry. All nano- and mesostructured materials showed a similar loading behavior. It was found that the pore size and Al content strongly influenced the release process. These results suggest that the framework structure and architecture affect the drug adsorption and release properties of these materials. Both materials offer a good potential for a controlled delivery system of ibuprofen.
Superhydrophobic nanoporous anodic aluminum oxide (alumina) surfaces were prepared using treatment with vapor-phase hexamethyldisilazane (HMDS). Nanoporous alumina substrates were first made using a two-step anodization process. Subsequently, a repeated modification procedure was employed for efficient incorporation of the terminal methyl groups of HMDS to the alumina surface. Morphology of the surfaces was characterized by scanning electron microscopy, showing hexagonally ordered circular nanopores with approximately 250 nm in diameter and 300 nm of interpore distances. Fourier transform infrared spectroscopy-attenuated total reflectance analysis showed the presence of chemically bound methyl groups on the HMDS-modified nanoporous alumina surfaces. Wetting properties of these surfaces were characterized by measurements of the water contact angle which was found to reach 153.2 ± 2°. The contact angle values on HMDS-modified nanoporous alumina surfaces were found to be significantly larger than the average water contact angle of 82.9 ± 3° on smooth thin film alumina surfaces that underwent the same HMDS modification steps. The difference between the two cases was explained by the Cassie-Baxter theory of rough surface wetting.
superhydrophobic surfaces; surface modification; hexamethyldisilazane; nanoporous alumina
Nanoporous alumina which was produced by a conventional direct current anodization [DCA] process at low temperatures has received much attention in various applications such as nanomaterial synthesis, sensors, and photonics. In this article, we employed a newly developed hybrid pulse anodization [HPA] method to fabricate the nanoporous alumina on a flat and curved surface of an aluminum [Al] foil at room temperature [RT]. We fabricate the nanopores to grow on a hemisphere curved surface and characterize their behavior along the normal vectors of the hemisphere curve. In a conventional DCA approach, the structures of branched nanopores were grown on a photolithography-and-etched low-curvature curved surface with large interpore distances. However, a high-curvature hemisphere curved surface can be obtained by the HPA technique. Such a curved surface by HPA is intrinsically induced by the high-resistivity impurities in the aluminum foil and leads to branching and bending of nanopore growth via the electric field mechanism rather than the interpore distance in conventional approaches. It is noted that by the HPA technique, the Joule heat during the RT process has been significantly suppressed globally on the material, and nanopores have been grown along the normal vectors of a hemisphere curve. The curvature is much larger than that in other literatures due to different fabrication methods. In theory, the number of nanopores on the hemisphere surface is two times of the conventional flat plane, which is potentially useful for photocatalyst or other applications.
PACS: 81.05.Rm; 81.07.-b; 82.45.Cc.
anodic aluminum oxide; porous alumina; nanoporous template
Nanoporous cobalt thin films were deposited on anodized aluminum oxide (AAO) membranes at room temperature using pulsed laser deposition. Scanning electron microscopy demonstrated that the nanoporous cobalt thin films retained the monodisperse pore size and high porosity of the anodized aluminum oxide substrates. Temperature- and field-dependent magnetic data obtained between 10 K and 350 K showed large hysteresis behavior in these materials. The increase of coercivity values was larger for nanoporous cobalt thin films than for multilayered cobalt/alumina thin films. The average diameter of the cobalt nanograins in the nanoporous cobalt thin films was estimated to be ~5 nm for blocking temperatures near room temperature. These results suggest that pulsed laser deposition may be used to fabricate nanoporous magnetic materials with unusual properties for biosensing, drug delivery, data storage, and other technological applications.
A. Magnetization curves; B. Epitaxial films; C. Magnetic nano-networks
Ordered CuIn(1−x)GaxSe2 (CIGS) nanopore films were prepared by one-step electrodeposition based on porous anodized aluminum oxide templates. The as-grown film shows a highly ordered morphology that reproduces the surface pattern of the substrate. Raman spectroscopy and X-ray diffraction pattern show that CIGS nanopore films had ideal chalcopyrite crystallization. Energy dispersive spectroscopy reveals the Cu-Se phases firstly formed in initial stage of growth. Then, indium and gallium were incorporated in the nanopore films in succession. Cu-Se phase is most likely to act as a growth promoter in the growth progress of CIGS nanopore films. Due to the high surface area and porous structure, this kind of CIGS films could have potential application in light-trapping CIGS solar cells and photoelectrochemical water splitting.
CuIn(1−x)GaxSe2; nanopore films; electrodeposition; anodic aluminumoxide; annealing; 82.45.Yz; 81.05.Rm; 81.15.Pq; 81.40.Ef
The goal of the present study was to compare the drug release properties and stability of the nanoporous silica with different pore architectures as a matrix for improved delivery of poorly soluble drugs. For this purpose, three dimensional ordered macroporous (3DOM) silica with 3D continuous and interconnected macropores of different sizes (200 nm and 500 nm) and classic mesoporous silica (ie, Mobil Composition of Matter [MCM]-41 and Santa Barbara Amorphous [SBA]-15) with well-ordered two dimensional (2D) cylindrical mesopores were successfully fabricated and then loaded with the model drug indomethacin (IMC) via the solvent deposition method. Scanning electron microscopy (SEM), N2 adsorption, differential scanning calorimetry (DSC), and X-ray diffraction (XRD) were applied to systematically characterize all IMC-loaded nanoporous silica formulations, evidencing the successful inclusion of IMC into nanopores, the reduced crystallinity, and finally accelerated dissolution of IMC. It was worth mentioning that, in comparison to 2D mesoporous silica, 3DOM silica displayed a more rapid release profile, which may be ascribed to the 3D interconnected pore networks and the highly accessible surface areas. The results obtained from the stability test indicated that the amorphous state of IMC entrapped in the 2D mesoporous silica (SBA-15 and MCM-41) has a better physical stability than in that of 3DOM silica. Moreover, the dissolution rate and stability of IMC loaded in 3DOM silica was closely related to the pore size of macroporous silica. The colorimetric 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and Cell Counting Kit (CCK)-8 assays in combination with direct morphology observations demonstrated the good biocompatibility of nanoporous silica, especially for 3DOM silica and SBA-15. The present work encourages further study of the drug release properties and stability of drug entrapped in different pore architecture of silica in order to realize their potential in oral drug delivery.
3D ordered macroporous silica; mesoporous silica; poorly soluble drugs; in vitro dissolution; stability test; in vitro cytotoxicity
Knowledge of nanopore size and shape is critical for many implementations of these single-molecule sensing elements. Geometry determination by fitting the electrolyte-concentration-dependence of the conductance of surface-charged, solid-state nanopores has been proposed to replace demanding electron microscope-based methods. The functional form of the conductance poses challenges for this method by restricting the number of free parameters used to characterize the nanopore. We calculated the electrolyte-dependent conductance of nanopores with an exponential-cylindrical radial profile using three free geometric parameters; this profile, itself, could not be uniquely geometry-optimized by the conductance. Several different structurally simplified models, however, generated quantitative agreement with the conductance, but with errors exceeding 40% for estimates of key geometrical parameters. A tractable conical-cylindrical model afforded a good characterization of the nanopore size and shape, with errors of less than 1% for the limiting radius. Understanding these performance limits provides a basis for using and extending analytical nanopore conductance models.
Electric double layer; nanopore surface charge; nanopore conductance; nanopore shape; silicon nitride nanopore; silicon oxide nanopore
We report on the fabrication, simulation, and characterization of insulated nanoelectrodes aligned with nanopores in low-capacitance silicon nitride membrane chips. We are exploring these devices for the transverse sensing of DNA molecules as they are electrophoretically driven through the nanopore in a linear fashion. While we are currently working with relatively large nanopores (6–12 nm in diameter) to demonstrate the transverse detection of DNA, our ultimate goal is to reduce the size sufficiently to resolve individual nucleotide bases, thus sequencing DNA as it passes through the pore. We present simulations and experiments that study the impact of insulating these electrodes, which is important to localize the sensing region. We test whether the presence of nanoelectrodes or insulation affects the stability of the ionic current flowing through the nanopore, or the characteristics of DNA translocation. Finally, we summarize the common device failures and challenges encountered during fabrication and experiments, explore the causes of these failures, and make suggestions on how to overcome them in the future.
Insulation; Nanoelectrodes; Nanogaps; Nanopore DNA sequencing; Transverse sensing
The ability to monitor DNA polymerase activity with single-nucleotide resolution has been the cornerstone of a number of advanced single-molecule DNA sequencing concepts. Toward this goal, we report the first spatially-resolved observation of DNA polymerase activity with single-base resolution at the single-molecule level. We describe the design and characterization of a single-species supramolecular nanopore device capable of detecting up to nine consecutive DNA polymerase-catalyzed single nucleotide primer extensions with high sensitivity and spatial resolution (≤ 2.4 Å). The device is assembled in a suspended lipid membrane by threading and mechanically capturing a single strand of DNA-PEG copolymer inside an α-hemolysin protein pore. Single nucleotide primer extensions result in successive displacements of the template DNA strand within the protein pore, which can be monitored by the corresponding stepped changes in the ion current flowing through the pore under an applied transmembrane potential. The system described thus represents a promising advance toward nanopore-mediated single-molecule DNA sequencing concept, and in addition might be applicable to studying a number of other biopolymer-protein interactions and dynamics.
Metallic nanopore arrays have emerged as optofluidic platforms with multifarious sensing and analytical capabilities such as label-free surface plasmon resonance (SPR) sensing of molecular binding interactions and surface-enhanced Raman spectroscopy (SERS). However, directed delivery of analytes through open nanopores using traditional methods such as external electric fields or pressure gradients still remains difficult. We demonstrate that nanopore arrays have an intrinsic ability to promote flow through them via capillary flow and evaporation. This passive “nano-drain” mechanism is utilized to concentrate biomolecules on the surface of nanopores for improved detection sensitivity or create ordered nanoscale arrays of beads and liposomes. Without using any external pump or fluidic interconnects, we can concentrate and detect the presence of less than a femtomole of streptavidin in 10 µL of sample using fluorescence imaging. Liposome nanoarrays are also prepared in less than 5 minutes and used to detect lipid-protein interactions. We also demonstrate label-free SPR detection of analytes using metallic nanopore arrays. This method provides a fast, simple, transportable and small-volume platform for labeled as well as label-free plasmonic analysis while improving the detection time and sensitivity.
Nanohole array; nanopore; microfluidics; nanofluidics; surface plasmon resonance; flow-through sensing; diffusion limits; optofluidics; plasmonics; liposome; fluidic self-assembly
A novel neural surface protein, Bravo, shows a pattern of topological restriction in the embryonic chick retinotectal system. Bravo is present on the developing optic fibers in the retina; however, retinal axons in the tectum do not display Bravo. The appearance of Bravo in vitro is modulated by environmental cues. Axons growing out from retinal explants on retinal basal lamina, their natural substrate, express Bravo, whereas such axons growing on collagen do not. Retinal explants provide a valuable system to characterize the mechanism of Bravo restriction, as well as the cellular signals controlling it. Bravo was identified with monoclonal antibodies from a collection generated against exposed molecules isolated by using a selective cell surface biotinylation procedure. The NH2-terminal sequence of Bravo shows similarity with L1, a neural surface molecule which is a member of the immunoglobulin superfamily. This possible relationship to L1, together with its restricted appearance, suggests an involvement of Bravo in axonal growth and guidance.
Solid state nanopores are emerging as robust single molecule electronic measurement devices and as platforms for confining biomolecules for further analysis. The first silicon nitride nanopore to detect individual DNA molecules were fabricated using ion beam sculpting (IBS), a method that uses broad, low energy ion beams to create nanopores with dimensions ranging from 2 to 20 nm. In this chapter, we discuss the fabrication, characterization, and use of IBS sculpted nanopores as well as efficient uses of pClamp and MATLAB software suites for data acquisition and analysis. The fabrication section will cover the repeatability and the pore size limits. The characterization discussion focuses on the geometric properties as measured by low and high resolution transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), and energy filtered TEM (EFTEM). The section on translocation experiments focuses on how to use tools commonly available to the nanopore experimenter to determine whether a pore will be useful for experimentation or if it should be abandoned. A memory efficient method of taking data using Clampex’s event-driven mode and dual channel recording will be presented, followed by an easy to implement multi-threshold event detection and classification method using MATLAB software.
Ion beam sculpting; silicon nitride nanopore; ionic current blockage; DNA size; DNA conformation
Polymeric nanopores show unique transport properties and have attracted a great deal of scientific interest as a test system to study ionic and molecular transport at the nanoscale. By means of all-atom molecular dynamics, we simulated the ion dynamics inside polymeric polyethylene terephthalate nanopores. For this purpose, we established a protocol to assemble atomic models of polymeric material into which we sculpted a nanopore model with the key features of experimental devices, namely a conical geometry and a negative surface charge density. Molecular dynamics simulations of ion currents through the pore show that the protonation state of the carboxyl group of exposed polyethylene terephthalate residues have a considerable effect on ion selectivity, by affecting ionic densities and electrostatic potentials inside the nanopores. The role of high concentrations of Ca2+ ions on charge inversion effects, earlier reported in experiments, were investigated in detail.
polymer nanopores; polyethylene terephthalate; ion current; charge inversion
Single nanopores attract a great deal of scientific interest as a basis for biosensors and as a system to study the interactions and behavior of molecules in a confined volume. Tuning the geometry and surface chemistry of nanopores helps create devices that control transport of ions and molecules in solution. Here, we present single conically shaped nanopores whose narrow opening of 8 or 12 nm is modified with single-stranded DNA molecules. We find that the DNA occludes the narrow opening of nanopores and that the blockade extent decreases with the ionic strength of the background electrolyte. The results are explained by the ionic strength dependence of the persistence length of DNA. At low KCl concentrations (10 mM) the molecules assume an extended and rigid conformation, thereby blocking the pore lumen and reducing the flow of ionic current to a greater extent than compacted DNA at high salt concentrations. Attaching flexible polymers to the pore walls hence creates a system with tunable opening diameters in order to regulate transport of both neutral and charged species.
DNA strand; Nanopore; Ion transport
Pyogenic granuloma is a reactive hyperplasia of connective tissue in response to local irritants. It is a tumourlike growth of the oral cavity, frequently located surrounding the anterior teeth or skin that is considered to be neoplastic in nature. It usually arises in response to various stimuli such as low-grade local irritation, traumatic injury, hormonal factors, or certain kinds of drugs. Histologically, the surface epithelium may be intact, or may show foci of ulcerations or even exhibiting hyperkeratosis. It overlies a mass of dense connective tissue composed of significant amounts of mature collagen. Gingiva is the most common site affected followed by buccal mucosa, tongue and lips. Pyogenic granuloma in general, does not occur when excised along with the base and its causative factors. This paper presents some cases of a pyogenic granuloma managed by surgical intervention.
Pyogenic granuloma; benign neoplasm; hyperplastic lesion.
A novel phenomenon has recently been reported in polymeric nanopores. This phenomenon, so-called nanoprecipitation, is characterized by the transient formation of precipitates in the nanopore lumen, producing a sequence of low and high conductance states in the ionic current through the pore. By means of all-atom molecular dynamics simulations, we studied nanoprecipitation for polyethylene terephthalate nanopore immersed in electrolytic solution containing calcium phosphate, covering a total simulation time of 1.24 microseconds. Our results suggest that protonable surface residues at the nanopore surface, namely carboxyl groups, trigger the formation of precipitates which strongly adhere to the surface, blocking the pore and producing the low conductance state. Based on the simulations, we propose a mechanism for the formation of the high conductance state; the mechanism involves detachment of the precipitate from the surface due to reprotonation of carboxyl groups and subsequent translocation of the precipitate out of the pore.
polymer nanopore; polyethylene terephthalate; nanoprecipitation; calcium phosphate; ionic current oscillations
A DNA sequencing device which integrates transverse conducting electrodes for the measurement of electrode currents during DNA translocation through a nanopore has been nanofabricated and characterized. A focused electron beam (FEB) milling technique, capable of creating features on the order of 1 nm in diameter, was used to create the nanopore. The device was characterized electrically using gold nanoparticles as an artificial analyte with both DC and AC measurement methods. Single nanoparticle/electrode interaction events were recorded. A low-noise, high-speed transimpedance current amplifier for the detection of nano to picoampere currents at microsecond time scales was designed, fabricated and tested for future integration with the nanopore device.
nanopore; nanoelectrodes; DNA sequencing; gold nanoparticles