Co-reporter:Roholah Sharifi ; Milinda Samaraweera ; José A. Gascón
Journal of the American Chemical Society 2014 Volume 136(Issue 20) pp:7452-7463
Publication Date(Web):May 12, 2014
DOI:10.1021/ja502714z
Establishing methods to accurately assess and model the binding strength of surfactants around a given-chirality single-walled carbon nanotube (SWNT) are crucial for selective enrichment, targeted functionalization, and spectrally sharp nanodevices. Unlike surfactant exchange, which is subject to interferences from the second surfactant, we herein introduce a thermal dissociation method based on reversible H+/O2 doping to determine SWNT/surfactant thermodynamic stability values with greater fidelity. Thermodynamic values were reproduced using molecular mechanics augmented by ab initio calculations in order to better assess π–π interactions. This afforded detailed quantification of the flavin binding strength in terms of π–π stacking (55–58%), with the remaining portion roughly split 3:1 between electrostatic plus van der Waals flavin mononucleotide (FMN) interdigitation and H-bonding interactions, respectively. Quasi-epitaxial π–π alignment between the near-armchair FMN helix and the underlying nanotube lattice plays a crucial role in stabilizing these assemblies. The close resemblance of the thermal dissociation method to helix–coil and ligand-binding transitions of DNA opens up a unique insight into the molecular engineering of self-organizing surfactants around various-chirality nanotubes.
Co-reporter:Yan Wang, Fotios Papadimitrakopoulos, Diane J. Burgess
Journal of Controlled Release 2013 Volume 169(Issue 3) pp:341-347
Publication Date(Web):10 August 2013
DOI:10.1016/j.jconrel.2012.12.028
Application of implantable glucose biosensors for “real-time” monitoring is reliant on controlling the negative tissue reaction at the sensor tissue interphase. A novel polymer coating consisting of poly(lactic-co-glycolic) acid (PLGA) microsphere dispersed in poly(vinyl alcohol) (PVA) hydrogels was evaluated in combination with dummy sensors as a “smart” drug eluting biocompatible coating for implantable biosensors to prevent the foreign body response, and thus enhance sensor performance in vivo. The polymeric microspheres slowly release tissue-modifying drugs at the implantation sites to control the inflammation and fibrous encapsulation, while the hydrogel allows rapid analyte diffusion to the sensing elements. Dummy sensors with identical dimensions to that of the functional glucose sensors (0.5 × 0.5 × 5 mm) were coated with the PLGA/PVA composites using a mold fabrication process. Both normal and diabetic rats were used in the current study to investigate the effect of the diabetic state on tissue sensor interactions. It was evident that the PLGA/PVA hydrogel composite was able to form a uniform coating around the dummy sensor and stayed intact throughout the course of the study (one month). Tissue samples containing dummy sensors that were coated with dexamethasone free composites exhibited acute and chronic inflammation as well as fibrous encapsulation in both normal and diabetic rats. However, the diabetic rats exhibited decreased intensity and delayed onset of the foreign body response following implantation of drug free dummy sensors in comparison to those of normal rats. On the other hand, tissues containing dummy sensors that were coated with dexamethasone containing composites remained normal (i.e. similar to untreated tissues), with no inflammatory reaction or fibrous encapsulation occurring over the one-month period in both the normal and diabetic rats. The feasibility of utilizing PLGA microsphere/PVA hydrogel composites as coatings for implantable biosensors was demonstrated. This polymeric composite is an innovative approach to control the foreign body reaction at the tissue–device interface to prolong biosensor lifetime.
Co-reporter:Robert A. Croce Jr;SanthiSagar Vaddiraju;Jun Kondo;Yan Wang
Biomedical Microdevices 2013 Volume 15( Issue 1) pp:151-160
Publication Date(Web):2013 February
DOI:10.1007/s10544-012-9708-x
Implantable sensors for continuous glucose monitoring hold great potential for optimal diabetes management. This is often undermined by a variety of issues associated with: (1) negative tissue response; (2) poor sensor performance; and (3) lack of device miniaturization needed to reduce implantation trauma. Herein, we report our initial results towards constructing an implantable device that simultaneously address all three aforementioned issues. In terms of device miniaturization, a highly miniaturized CMOS (complementary metal-oxide-semiconductor) potentiostat and signal processing unit was employed (with a combined area of 0.665 mm2). The signal processing unit converts the current generated by a transcutaneous, Clark-type amperometric sensor to output frequency in a linear fashion. The Clark-type amperometric sensor employs stratification of five functional layers to attain a well-balanced mass transfer which in turn yields a linear sensor response from 0 to 25 mM of glucose concentration, well beyond the physiologically observed (2 to 22 mM) range. In addition, it is coated with a thick polyvinyl alcohol (PVA) hydrogel with embedded poly(lactic-co-glycolic acid) (PLGA) microspheres intended to provide continuous, localized delivery of dexamethasone to suppress inflammation and fibrosis. In vivo evaluation in rat model has shown that the transcutaneous sensor system reproducibly tracks repeated glycemic events. Clarke’s error grid analysis on the as—obtained glycemic data has indicated that all of the measured glucose readings fell in the desired Zones A & B and none fell in the erroneous Zones C, D and E. Such reproducible operation of the transcutaneous sensor system, together with low power (140 μW) consumption and capability for current-to-frequency conversion renders this a versatile platform for continuous glucose monitoring and other biomedical sensing devices.
Co-reporter:R. Sharifi, D. C. Abanulo, and F. Papadimitrakopoulos
Langmuir 2013 Volume 29(Issue 24) pp:7209-7215
Publication Date(Web):February 12, 2013
DOI:10.1021/la304615g
Isotopic, hydrogen-to-deuterium substitution has been an invaluable tool in the characterization of small molecules and biological nanostructures. The natural variability of most inorganic nanomaterials has hindered the use of isotopic substitution in gaining meaningful insights into their structure. The ideal helical wrapping of a flavin mononucleotide (FMN) around (8,6)-SWNTs (single-walled carbon nanotubes) is presently utilized to probe isotopically dependent intermolecular interactions. The facile proton-to-deuterium exchange of the imide group of FMN enabled us to alter the intermolecular stability of the helix depending on the surrounding solvent (i.e., H2O vs D2O). Our studies show that FMN-dispersed (8,6)-SWNTs exhibit greater stability in D2O than in H2O. The higher complex stability in D2O was verified on the basis of (i) FMN helix replacement with SDBS (sodium dodecylbenzenesulfate) and (ii) thermal- and (iii) pH-induced helix dissociation. This is in agreement with the previously observed stronger amide H-bonding of proteins in D2O, and to the best of our knowledge, it demonstrates the architectural fidelity of FMN-wrapped SWNTs, which is expected to enhance the assembly repertoire of carbon nanotubes further.
Co-reporter:Sang-Yong Ju ; Darlington C. Abanulo ; Christopher A. Badalucco ; José A. Gascón
Journal of the American Chemical Society 2012 Volume 134(Issue 32) pp:13196-13199
Publication Date(Web):August 7, 2012
DOI:10.1021/ja305250g
In order to truly unlock advanced applications of single-walled carbon nanotubes (SWNTs), one needs to separate them according to both chirality and handedness. Here we show that the chiral d-ribityl phosphate chain of flavin mononucleotide (FMN) induces a right-handed helix that enriches the left-handed SWNTs for all suspended (n,m) species. Such enantioselectivity stems from the sp3 hybridization of the N atom anchoring the sugar moiety to the flavin ring. This produces two FMN conformations (syn and anti) analogous to DNA. Electrostatic interactions between the neighboring uracil moiety and the 2′-OH group of the side chain provide greater stability to the anti-FMN conformation that leads to a right-handed FMN helix. The right-handed twist that the FMN helix imposes to the underlying nanotube, similar to “Indian burn”, causes diameter dilation of only the left-handed SWNTs, whose improved intermolecular interactions with the overlaying FMN helix, impart enantioselection.
Co-reporter:Jonathan D. Doll, Bin Hu, and Fotios Papadimitrakopoulos
Chemistry of Materials 2012 Volume 24(Issue 21) pp:4043
Publication Date(Web):September 13, 2012
DOI:10.1021/cm3012809
It was recently shown that, by controlling the O2 concentration, the seeded-growth of CdSe nanocrystals (NC) can be manipulated to proceed either unidirectionally (from the (0001) facet) or three-dimensionally. In this contribution, we investigate two new Se precursors (i.e., SeO2 and NaHSe) and compare them with Se obtained from etching of smaller NC seeds. Under anaerobic conditions, both precursors led to successful three-dimensional (3D) NC growth. At high O2 concentrations, the seeded growth of rods was enhanced by the NaHSe precursor, while impeded by the use of SeO2. Mechanistic studies showed that the reduction of SeO2 to Se2– produces an excessive amount of O2. This leads to rod fragmentation due to etching as well as the production of deep traps that quench their luminescence. These new precursors, along with a heightened understanding of oxygen’s role, expand the synthetic repertoire of the redox-assisted, seeded-growth of CdSe and better position this low temperature (125 °C) methodology toward realizing advanced NC heterostructures.Keywords: nanocrystals; oxygen; quantum rods; seeded growth; unidirectional;
Co-reporter:S. Vaddiraju, Y. Wang, L. Qiang, D. J. Burgess, and F. Papadimitrakopoulos
Analytical Chemistry 2012 Volume 84(Issue 20) pp:8837
Publication Date(Web):October 5, 2012
DOI:10.1021/ac3022423
Biofouling and tissue inflammation present major challenges toward the realization of long-term implantable glucose sensors. Following sensor implantation, proteins and cells adsorb on sensor surfaces to not only inhibit glucose flux but also signal a cascade of inflammatory events that eventually lead to permeability-reducing fibrotic encapsulation. The use of drug-eluting hydrogels as outer sensor coatings has shown considerable promise to mitigate these problems via the localized delivery of tissue response modifiers to suppress inflammation and fibrosis, along with reducing protein and cell absorption. Biodegradable poly (lactic-co-glycolic) acid (PLGA) microspheres, encapsulated within a poly (vinyl alcohol) (PVA) hydrogel matrix, present a model coating where the localized delivery of the potent anti-inflammatory drug dexamethasone has been shown to suppress inflammation over a period of 1–3 months. Here, it is shown that the degradation of the PLGA microspheres provides an auxiliary venue to offset the negative effects of protein adsorption. This was realized by: (1) the creation of fresh porosity within the PVA hydrogel following microsphere degradation (which is sustained until the complete microsphere degradation) and (2) rigidification of the PVA hydrogel to prevent its complete collapse onto the newly created void space. Incubation of the coated sensors in phosphate buffered saline (PBS) led to a monotonic increase in glucose permeability (50%), with a corresponding enhancement in sensor sensitivity over a 1 month period. Incubation in serum resulted in biofouling and consequent clogging of the hydrogel microporosity. This, however, was partially offset by the generated macroscopic porosity following microsphere degradation. As a result of this, a 2-fold recovery in sensor sensitivity for devices with microsphere/hydrogel composite coatings was observed as opposed to similar devices with blank hydrogel coatings. These findings suggest that the use of macroscopic porosity can reduce sensitivity drifts resulting from biofouling, and this can be achieved synergistically with current efforts to mitigate negative tissue responses through localized and sustained drug delivery.
Co-reporter:Sejong Kim, Ramazan Asmatulu, Harris L. Marcus, Fotios Papadimitrakopoulos
Journal of Colloid and Interface Science 2011 Volume 354(Issue 2) pp:448-454
Publication Date(Web):15 February 2011
DOI:10.1016/j.jcis.2010.11.023
Dielectrophoresis (DEP) force-assisted assembly of a colloidal single photonic-crystal monolayer in a microfluidic chamber was demonstrated. Negative DEP force with a high-frequency AC electric field induced the compression of colloidal microspheres to form a colloidal crystal domain at the center of a hexapolar-shaped electrode. While typical assembly by monotonic DEP force forms multicrystalline domains containing crystal defects, repetitions of the DEP/relaxation cycle significantly facilitated crystal growth of 10 μm monodispersed polystyrene microspheres, allowing a grain-boundary-free single-crystal monolayer domain of ca. 200 μm in size. Microsphere size as well as size distribution affected the formation of the single-crystal domain. A simple method was used to immobilize the single-crystal domain on the glass substrate without losing its crystallinity.Graphical abstractThe present study deals with a dielectrophoresis (DEP) force-assisted assembly of 2D colloidal photonic crystal (PC) fabrication in a microfluidic device. In this process, negative DEP force with high-frequency electric field was used to form a colloidal crystal domain at the center of an hexapolar shape electrode without any boundary. A simple method was utilized to immobilize the single-crystal domain on the glass substrate without losing its crystallinity. This study may open up new possibilities to fabricate the simple, rapid, and high efficient colloidal PCs for various applications. Colloidal crystal growth process of 10 μm microsphere (left) and its crystallinity profile (right) by DEP compression/relaxation cycles.Research highlights► The grain-boundary-free 2D colloidal single crystalline monolayer domains with colloidal microspheres were fabricated using dielectrophoretic forces associated with hexapolar electrodes in a microfluidics. ► By appropriate manipulation of DEP/relaxation cycle, crystal growth of colloidal microspheres was facilitated to follow formation of a grain-boundary-free, single crystalline, monolayer domain of ca. 200 μm in size. ► This result may open up new possibilities on colloidal photonic crystals and their manipulation in the near future.
Co-reporter:Liangliang Qiang, Santhisagar Vaddiraju, Dipesh Patel, Fotios Papadimitrakopoulos
Biosensors and Bioelectronics 2011 Volume 26(Issue 9) pp:3755-3760
Publication Date(Web):15 May 2011
DOI:10.1016/j.bios.2011.02.021
The promise of implantable electrochemical sensors is often undermined by the critical requirement of device miniaturization that inadvertently degrades sensor performance in terms of sensitivity and selectivity. Herein, we report a novel miniaturized and flexible amperometric sensor grown at the ‘edge plane’ of a 25-μm gold wire. Such geometry affords extreme miniaturization along with ease of fabrication, minimal iR drop and 3-D diffusion for effective mass transfer. This together with electrochemical rebuilding of the Au working electrode and subsequent Pt nanoparticles deposition resulted in the highest H2O2 sensitivity (33 mA mM−1 cm−2), reported thus far. Concurrent electrodeposition of o-phenylenediamine with glucose oxidase afforded glucose detection at these edge-plane microsensors with a six fold improvement in sensitivity (1.2 mA mM−1 cm−2) over previous reports. In addition, these sensors exhibit low operation potential (0.3 V), high selectivity (more than 95%) against in vivo interferences, and an apparent Michealis–Menten constant (Kmapp) of 17 and 75 mM of glucose in the absence and presence of an outer polyurethane coating, respectively. These features render the edge-plane sensor architecture as a powerful platform for next-generation implantable biosensors.
Co-reporter:Jonathan D. Doll, Ghanshyam Pilania, Ramamurthy Ramprasad and Fotios Papadimitrakopoulos
Nano Letters 2010 Volume 10(Issue 2) pp:680-685
Publication Date(Web):January 22, 2010
DOI:10.1021/nl903843g
The role of oxygen in directing the low temperature (125 °C), redox-assisted, unidimensional and unidirectional growth of CdSe nanocrystals (NCs) was investigated. In the presence of oxygen, CdSe quantum dots grow selectively along their c axis with little to no change in their width. Reduction of oxygen in the growth medium results in three-dimensional growth. Moreover the one-dimensional growth was found to occur only from one of the two inequivalent polar (0001) facets, as supported by the seeded growth of CdxHg1−xSe onto CdSe seeds. This is in agreement with density functional theory simulations, which indicate that due to selective oxygen passivation growth can occur only along the [0001] direction. The ability to control seeded NC growth with respect to morphology and directionality opens new possibilities toward the low temperature synthesis of complex nanostructures.
Co-reporter:Liangliang Qiang, Santhisagar Vaddiraju, James F. Rusling, Fotios Papadimitrakopoulos
Biosensors and Bioelectronics 2010 Volume 26(Issue 2) pp:682-688
Publication Date(Web):15 October 2010
DOI:10.1016/j.bios.2010.06.064
Highly sensitive, long-term stable and reusable microfluidics electrodes have been fabricated and evaluated using H2O2 and hydroquinone as model analytes. These electrodes composed of a 300 nm Pt-black layer situated on a 5 μm thick electrodeposited Au layer, provide effective protection against electrooxidation of an underlying chromium adhesion layer. Using repeated cyclic voltammetric (CV) sweeps in flowing buffer solution, highly sensitive Pt-black working electrodes were realized with five- (four-) decade linear dynamic range for H2O2 (hydroquinone) and low detection limit of 10 nM for H2O2 and 100 nM for hydroquinone. Moreover, high sensitivity for H2O2 was demonstrated at low (0.3 V vs. Ag/AgCl) oxidation potentials, together with long-term stability and reusability for at least 30 days. Microfluidic flow was employed for desorption and reactivation of the nominally planar Pt-black electrodes. Such electrocatalytic surface architecture should be appropriate for long-term electrochemical detection of various molecules and biomolecules as well as in reusable immunoassay configurations.
Co-reporter:Santhisagar Vaddiraju, Ioannis Tomazos, Diane J. Burgess, Faquir C. Jain, Fotios Papadimitrakopoulos
Biosensors and Bioelectronics 2010 Volume 25(Issue 7) pp:1553-1565
Publication Date(Web):15 March 2010
DOI:10.1016/j.bios.2009.12.001
The development of implantable biosensors for continuous monitoring of metabolites is an area of sustained scientific and technological interests. On the other hand, nanotechnology, a discipline which deals with the properties of materials at the nanoscale, is developing as a potent tool to enhance the performance of these biosensors. This article reviews the current state of implantable biosensors, highlighting the synergy between nanotechnology and sensor performance. Emphasis is placed on the electrochemical method of detection in light of its widespread usage and substantial nanotechnology based improvements in various aspects of electrochemical biosensor performance. Finally, issues regarding toxicity and biocompatibility of nanomaterials, along with future prospects for the application of nanotechnology in implantable biosensors, are discussed.
Co-reporter:Sang-Yong Ju ; Marcel Utz
Journal of the American Chemical Society 2009 Volume 131(Issue 19) pp:6775-6784
Publication Date(Web):April 27, 2009
DOI:10.1021/ja809054c
Utilization of single-walled carbon nanotubes (SWNTs) in high-end applications hinges on separating metallic (met-) from semiconducting (sem-) SWNTs. Surfactant amines, like octadecylamine (ODA) have proven instrumental for the selective extraction of sem-SWNTs from tetrahydrofuran (THF) nanotube suspensions. The chemical shift differences along the tail of an asymmetric, diacetylenic surfactant amine were used to probe the molecular dynamics in the presence and absence of nanotubes via NMR. The results suggest that the surfactant amine head is firmly immobilized onto the nanotube surface together with acidic water, while the aliphatic tail progressively gains larger mobility as it gets farther from the SWNT. X-ray and high-resolution TEM studies indicate that the sem-enriched sample is populated mainly by small nanotube bundles containing ca. three SWNTs. Molecular simulations in conjunction with previously determined HNO3/H2SO4 oxidation depths for met- and sem-SWNTs indicate that the strong pinning of the amine surfactants on the sem-enriched SWNTs bundles is a result of a well-ordered arrangement of nitrate/amine salts separated with a monomolecular layer of H2O. Such continuous 2D arrangement of nitrate/amine salts shields the local environment adjacent to sem-enriched SWNTs bundles and maintains an acidic pH that preserves nanotube oxidation (i.e., SWNTn+). This, in turn, results in strong interactions with charge-balancing NO3− counterions that through their association with neutralized surfactant amines provide effective THF dispersion and consequent sem enrichment.
Co-reporter:S. Vaddiraju, D.J. Burgess, F.C. Jain, F. Papadimitrakopoulos
Biosensors and Bioelectronics 2009 Volume 24(Issue 6) pp:1557-1562
Publication Date(Web):15 February 2009
DOI:10.1016/j.bios.2008.08.015
The performance of an implantable glucose sensor is strongly dependent on the ability of their outer membrane to govern the diffusion of the various participating species. In this contribution, using a series of layer-by-layer (LBL) assembled outer membranes, the role of outwards of H2O2 diffusion through the outer membrane of glucose sensors has been correlated to sensor sensitivity. Glucose sensors with highly permeable humic acids/ferric cations (HAs/Fe3+) outer membranes displayed a combination of lower sensitivities and better linearities when compared with sensors coated with lesser permeable outer membranes (namely HAs/poly(diallyldimethylammonium chloride) (PDDA) and poly(styrene sulfonate) (PSS)/PDDA). On the basis of a comprehensive evaluation of the oxygen dependence of these sensors in conjunction with the permeability of H2O2 through these membranes, it was concluded that the outer diffusion of H2O2 is crucial to attain optimized sensor performance. This finding has important implications to the design of various bio-sensing elements employing perm-selective membranes.
Co-reporter:Sang-Yong Ju;William P. Kopcha
Science 2009 Volume 323(Issue 5919) pp:1319-1323
Publication Date(Web):06 Mar 2009
DOI:10.1126/science.1166265
Abstract
Attaining high photoluminescence quantum yields for single-walled carbon nanotubes (SWNTs) in order to broaden their optoelectronics and sensing applications has been a challenging task. Among various nonradiative pathways, sidewall chemisorption of oxygen provides a known defect for exciton quenching through nanotube hole doping. We found that an aliphatic (dodecyl) analog of flavin mononucleotide, FC12, leads to high dispersion of SWNTs, which tend to aggregate into bundles. Unlike other surfactants, the surface organization of FC12 is sufficiently tight to exclude oxygen from the SWNT surface, which led to quantum yields as high as 20%. Toluene-dispersed, FC12-wrapped nanotubes exhibited an absorption spectrum with ultrasharp peaks (widths of 12 to 25 milli–electron volts) devoid of the characteristic background absorption of most nanotube dispersions.
Co-reporter:Haoyan Wei, Sang Nyon Kim, Minhua Zhao, Sang-Yong Ju, Bryan D. Huey, Harris L. Marcus and Fotios Papadimitrakopoulos
Chemistry of Materials 2008 Volume 20(Issue 8) pp:2793
Publication Date(Web):March 28, 2008
DOI:10.1021/cm7031465
Single-wall carbon nanotube (SWNT) nanofibrils were assembled onto conductive atomic force microscopy (AFM) probes with the help of dielectrophoresis (DEP). This process involved the application of a 10 V, 2 MHz, AC bias between a metal-coated AFM probe and a dilute suspension of SWNTs. This exerted a positive dielectrophoretic force onto the nanotubes that caused them to align while precipitating out onto the probe. The gradual removal of the AFM probe away from the SWNT suspension consolidated these nanotubes into nanofibrils with a high degree of alignment as demonstrated with polarization Raman experiments. By varying the pulling speed, immersion time, and concentration of the SWNT suspension, one can tailor the diameter and thus the stiffness of these probes. Precise length trimming of these nanofibrils was also performed by their gradual immersion and dissolution into a liquid that strongly interacted with nanotubes, (i.e., sodium dodecyl sulfate (SDS) solution). Vacuum annealing these nanoprobes at temperature up to 450 °C further increased their stiffness and rendered them insoluble to SDS and all other aqueous media. Regrowth of a new SWNT nanofibril from the side or at the end of a previously grown SWNT nanofibril was also demonstrated by a repeated dielectrophoretic assembly at the desired immersion depth. These SWNT nanofibril-equipped AFM probes are electrically conductive and mechanically robust for use as high-aspect-ratio electrochemical nanoprobes.
Co-reporter:S. N. Kim;F. Papadimitrakopoulos;J. F. Rusling
Advanced Materials 2007 Volume 19(Issue 20) pp:3214-3228
Publication Date(Web):21 SEP 2007
DOI:10.1002/adma.200700665
The unique electronic and optical properties of carbon nanotubes, in conjunction with their size and mechanically robust nature, make these nanomaterials crucial to the development of next-generation biosensing platforms. In this Review, we present recent innovations in carbon nanotube-assisted biosensing technologies, such as DNA-hybridization, protein-binding, antibody-antigen and aptamers. Following a brief introduction on the diameter- and chirality-derived electronic characteristics of single-walled carbon nanotubes, the discussion is focused on the two major schemes for electronic biodetection, namely biotransistor- and electrochemistry-based sensors. Key fabrication methodologies are contrasted in light of device operation and performance, along with strategies for amplifying the signal while minimizing nonspecific binding. This Review is concluded with a perspective on future optimization based on array integration as well as exercising a better control in nanotube structure and biomolecular integration.
Co-reporter:Haoyan Wei, Sejong Kim, Sang Nyon Kim, Bryan D. Huey, Fotios Papadimitrakopoulos and Harris L. Marcus
Journal of Materials Chemistry A 2007 vol. 17(Issue 43) pp:4577-4585
Publication Date(Web):07 Sep 2007
DOI:10.1039/B710854K
An approach for non-thiol functionalization of single-wall carbon nanotubes (SWNTs) on gold was demonstrated via an Fe3+-assisted self-assembly technique. Upon immersion of gold into a pH 2.2 aqueous FeCl3 solution, FeCl3 oxidized the gold surface, due to the aqua regia effect, resulting in the formation of films of FeO(OH)–FeOCl crystallites. Subsequent immersion into a SWNT dimethylformamide (DMF) dispersion led to needle-like forest assemblies of SWNTs based on metal-assisted chelation and electrostatic interactions. Two approaches for surface patterning of these SWNT forests were investigated based on shadow-mask evaporation and conventional photolithographic lift-off to localize FeO(OH)–FeOCl/Au composite pads on Si substrates. The strong adhesion of Fe3+ ions onto silica surfaces can be partially overcome by repeated washes in aqueous HCl solution (pH < 4), and completely overcome by photoresist-assisted protection which prevents unwanted Fe3+ ions from complexing with the unexposed silica surfaces. Such patterned Fe3+-functionalized Au structures provided the basis for the site-specific forest-assembly of SWNTs as characterized by atomic force microscopy (AFM) and resonance Raman spectroscopy.
Co-reporter:R. Li;J. Lee;D. Kang;Z. Luo;M. Aindow;F. Papadimitrakopoulos
Advanced Functional Materials 2006 Volume 16(Issue 3) pp:
Publication Date(Web):14 DEC 2005
DOI:10.1002/adfm.200500319
Low-cost, large-scale production of highly photoluminescent semiconductor nanocrystals (NCs) is desirable for a variety of applications. In this paper we report the realization of highly photoluminescent zinc-blende CdSe nanocrystals from room-temperature water-phase synthesis, followed by low-temperature (80 ± 5 °C) chemical etching in a solution of 3-amino-1-propanol/H2O (v/v = 10/1). X-ray diffraction (XRD) and transmission electron microscopy (TEM) data indicate that these CdSe NCs exhibit a cubic, zinc-blende crystal structure. After etching, these CdSe nanocrystals show strong band-edge photoluminescence (with quantum efficiency as high as 50 %) and lack of deep-trap emissions. A high-resolution TEM investigation suggests that this etching not only removes surface irregularities, but also attacks grain boundaries. Moreover, the size distribution reduces upon progressive etching to allow photoluminescence full-width-at-half-maximum (FWHM) values as low as 30 nm.
Co-reporter:S. Kim;B. Yang;S. Hou;J. Lee;F. Papadimitrakopoulos
Advanced Functional Materials 2006 Volume 16(Issue 12) pp:
Publication Date(Web):27 JUN 2006
DOI:10.1002/adfm.200500782
DNA supramolecular recognition is employed for the immobilization of 2D photonic crystals of monodisperse colloidal microspheres. Amine-terminated DNA oligomers are covalently attached to carboxy-decorated microspheres and substrates while preserving their colloidal stability and organization properties. Following a capillary-force-assisted organization of DNA-decorated microspheres into close-packed 2D opaline arrays, the first monolayer is immobilized by DNA hybridization. Various parameters affecting the long-range order of such opaline arrays are investigated, including surface hydrophobicity and the relative strengths of the specific versus nonspecific interactions. The type and concentration of salt and the process temperature are also optimized for the hybridization between microspheres and substrate. The selective removal of non-specifically bound multilayers is accomplished by carefully passing an air/liquid interface over these arrays. DNA hybridization was found to play an important role in immobilizing the first monolayer of 2D opaline arrays while preserving its long-range order, with an approximate binding strength three times higher than that of non-specific interactions.
Co-reporter:Xin Yu, Debjit Chattopadhyay, Izabela Galeska, Fotios Papadimitrakopoulos, James F. Rusling
Electrochemistry Communications 2003 Volume 5(Issue 5) pp:408-411
Publication Date(Web):May 2003
DOI:10.1016/S1388-2481(03)00076-6
This communication reports the first example, to our knowledge, of enzymes covalently attached onto the ends of vertically oriented single-wall carbon nanotube (SWNT) forest arrays used as electrodes. Quasi-reversible FeIII/FeII voltammetry was observed for the iron heme enzymes myoglobin and horseradish peroxidase coupled to carboxylated ends of the nanotube forests by amide linkages. Results suggest that the “trees” in the nanotube forest behaved electrically similar to a metal, conducting electrons from the external circuit to the redox sites of the enzymes. Electrochemically manifested peroxidase activity of myoglobin and horseradish peroxidase attached to the SWNT forests was demonstrated, with detection limits for hydrogen peroxide in buffer solutions of ∼100 nM. These prototype SWNT-forest biosensors are easy to prepare, and enzyme layers were stable for weeks.
Co-reporter:Haoyan Wei, Sejong Kim, Sang Nyon Kim, Bryan D. Huey, Fotios Papadimitrakopoulos and Harris L. Marcus
Journal of Materials Chemistry A 2007 - vol. 17(Issue 43) pp:NaN4585-4585
Publication Date(Web):2007/09/07
DOI:10.1039/B710854K
An approach for non-thiol functionalization of single-wall carbon nanotubes (SWNTs) on gold was demonstrated via an Fe3+-assisted self-assembly technique. Upon immersion of gold into a pH 2.2 aqueous FeCl3 solution, FeCl3 oxidized the gold surface, due to the aqua regia effect, resulting in the formation of films of FeO(OH)–FeOCl crystallites. Subsequent immersion into a SWNT dimethylformamide (DMF) dispersion led to needle-like forest assemblies of SWNTs based on metal-assisted chelation and electrostatic interactions. Two approaches for surface patterning of these SWNT forests were investigated based on shadow-mask evaporation and conventional photolithographic lift-off to localize FeO(OH)–FeOCl/Au composite pads on Si substrates. The strong adhesion of Fe3+ ions onto silica surfaces can be partially overcome by repeated washes in aqueous HCl solution (pH < 4), and completely overcome by photoresist-assisted protection which prevents unwanted Fe3+ ions from complexing with the unexposed silica surfaces. Such patterned Fe3+-functionalized Au structures provided the basis for the site-specific forest-assembly of SWNTs as characterized by atomic force microscopy (AFM) and resonance Raman spectroscopy.
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