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Among nerve agents, V-series nerve agents are some of the most toxic, making low-concentration detection critical for the protection of individuals, populations, and strategic resources. Electrochemical sensors are ideally suited for the real-time and in-field sensing of these agents. While V-series nerve agents are inherently nonelectroactive, they can be hydrolyzed to electroactive products compatible with electrochemical sensing. Zr(IV) MOFs are next-generation nanoporous materials that have been shown to rapidly catalyze the hydrolysis of nerve agents. This work makes use of these nanomaterials to develop, for the first time, an MOF-enabled electrochemical sensor for V-series nerve agents. Our work demonstrates that the VX thiol hydrolysis product can be electrochemically detected at low concentrations using commercially available gold electrodes. We demonstrate that low-concentration thiol oxidation is an irreversible reaction that is dependent on both mass transport and adsorption. Demeton-S-methylsulfon, a VX simulant, is used to demonstrate the full range of sensor operation that includes hydrolysis and electrochemical detection. We demonstrate that MOF-808 rapidly, selectively, and completely hydrolyzes demeton-S-methylsulfon to less-hazardous dimethyl phosphate and 2-ethylsulfonylethanethiol. Low-concentration measurements of 2-ethylsulfonylethanethiol are performed by using electrochemical techniques. This sensor has a limit of detection of 30 nM or 7.87 μg/L for 2-ethylsulfonylethanethiol, which is near the nerve agent exposure limit for water samples established by the United States military. Our work demonstrates the feasibility of rapid, robust electrochemical sensing of V-series nerve agents at low concentrations for in-field applications.

Directed placement of DNA origami could play a key role in future integrated nanoelectronic devices. Here we demonstrated the site-selective attachment of DNA origami on gold dots formed using a pattern transfer method through block copolymer self-assembly. First, a random copolymer brush layer is grafted on the Si surface and then poly (styrene- b -methylmethacrylate) block copolymer is spin-coated to give a hexagonal nanoarray after annealing. UV irradiation followed by acetic acid etching is used to remove the PMMA, creating cylindrical holes and then oxygen plasma etching removes the random copolymer layer inside those holes. Next, metal evaporation, followed by lift-off creates a gold dot array. We evaluated different ligand functionalization of Au dots, as well as DNA hybridization to attach DNA origami to the nanodots. DNA-coated Au nanorods are assembled on the DNA origami as a step towards creating nanowires and to facilitate electron microscopy characterization of the attachment of DNA origami on these Au nanodots. The DNA hybridization approach showed better DNA attachment to Au nanodots than localization by electrostatic interaction. This work contributes to the understanding of DNA-templated assembly, nanomaterials, and block copolymer nanolithography. Furthermore, the work shows potential for creating DNA-templated nanodevices and their placement in ordered arrays in future nanoelectronics.

Bottom-up fabrication using DNA is a promising approach for the creation of nanoarchitectures. Accordingly, nanomaterials with specific electronic, photonic, or other functions are precisely and programmably positioned on DNA nanostructures from a disordered collection of smaller parts. These self-assembled structures offer significant potential in many domains such as sensing, drug delivery, and electronic device manufacturing. This review describes recent progress in organizing nanoscale morphologies of metals, semiconductors, and carbon nanotubes using DNA templates. We describe common substrates, DNA templates, seeding, plating, nanomaterial placement, and methods for structural and electrical characterization. Finally, our outlook for DNA-enabled bottom-up nanofabrication of materials is presented.

Self-assembly nanofabrication is increasingly appealing in complex nanostructures, as it requires fewer materials and has potential to reduce feature sizes. The use of DNA to control nanoscale and microscale features is promising but not fully developed. In this work, we study self-assembled DNA nanotubes to fabricate gold nanowires for use as interconnects in future nanoelectronic devices. We evaluate two approaches for seeding, gold and palladium, both using gold electroless plating to connect the seeds. These gold nanowires are characterized electrically utilizing electron beam induced deposition of tungsten and four-point probe techniques. Measured resistivity values for 15 successfully studied wires are between 9.3 × 10 -6 and 1.2 × 10 -3 Ωm. Our work yields new insights into reproducible formation and characterization of metal nanowires on DNA nanotubes, making them promising templates for future nanowires in complex electronic circuitry.

DNA origami-templated fabrication enables bottom-up fabrication of nanoscale structures from a variety of functional materials, including metal nanowires. We studied the impact of low-temperature annealing on the morphology and conductance of DNA-templated nanowires. Nanowires were formed by selective seeding of gold nanorods on DNA origami and gold electroless plating of the seeded structures. At low annealing temperatures (160 °C for seeded-only and 180 °C for plated), the wires broke up and separated into multiple, isolated islands. Through the use of polymer-constrained annealing, the island formation in plated wires was suppressed up to annealing temperatures of 210 °C. Four-point electrical measurements showed that the wires remained conductive after a polymer-constrained annealing at 200 °C.

Background: Currently, dermatology residency training requires minimal experience in cosmetic procedures which can be achieved through observation. Objective: To assess education in and expectations for cosmetic procedures during dermatology residency. Materials and Methods: A 20-question survey was electronically distributed to 138 Accreditation Council for Graduate Medical Education-accredited dermatology residency training programs. Results: One hundred fifty surveys were returned. While 74 percent of the responding residents reported plans to integrate cosmetic procedures into their future practice, only 36 percent felt adequately trained. Forty-eight percent of residents received one or less didactic lectures annually. Over 95 percent of residents felt that a more formal curriculum in cosmetic procedures would benefit residency education. Conclusion: There appears to be insufficient didactic and clinical training in cosmetic procedures during dermatology residency to meet resident expectations and future practice habits., Competing Interests: FUNDING:No funding was provided for this study. DISCLOSURES:The authors have no conflicts of interest relevant to the content of this article. An abstract reflecting this work was presented previously at the Dermatology Teacher Exchange Group at the Annual Meeting of the Association of Professors of Dermatology on October 5th, 2018.

A 72-year-old white man presented to the clinic with a tender, pruritic lesion on the upper part of his left arm that had progressively worsened over 4 months. Physical examination revealed an erythematous to violaceous, indurated, and sclerotic plaque with multiple foci of crusting and erosions (Figure 1). The patient denied any recent trauma, travel, fever, chills, weight loss, or constitutional symptoms. Before presentation, he had undergone treatment with cephalexin, prednisone, and doxycycline without reported improvement. Laboratory studies were negative for antinuclear antibody and SCL70 antibody; however, an absolute eosinophilia of 1478/uL was noted.

Bottom-up nanofabrication is increasingly making use of self-assembled DNA to fabricate nanowires and potential integrated circuits, although yields of such electronic nanostructures are inadequate, as is the ability to reliably make electrical measurements on them. In this paper, we report improved yields and unprecedented conductivity measurements for Au nanowires created on DNA origami tile substrates. We created several different self-assembled Au nanowire arrangements on DNA origami tiles that are approximately 70 nm × 90 nm, through anisotropic growth of Au nanorods attached to specific sites. Modifications to the tile design increased yields of the final desired nanostructures as much as 6-fold. In addition, we measured the conductivity of Au nanowires created on these DNA tiles (∼130 nm long, 10 nm diameter, and 40 nm spacing between measurement points) with a four-point measurement technique that utilized electron beam induced metal deposition to form probe electrodes. These nanowires formed on single DNA origami tiles were electrically conductive, having resistivities as low as 4.24 × 10 -5 Ω m. This work demonstrates the creation and measurement of inorganic nanowires on single DNA origami tiles as a promising path toward future bottom-up fabrication of nanoelectronics.

Actinic granuloma (AG) manifests as annular plaques on sun-damaged skin. There remains no universal consensus on the nosology, etiology, or clinicopathologic criteria of AG as a distinct entity. Broadly, AG is characterized by granulomatous inflammation, multinucleated giant cells, elastophagocytosis, and the absence of mucin and necrobiosis. It is not uncommon, however, to encounter overlapping histological features of other granulomas, such as granuloma annulare and necrobiosis lipoidica, confounding the diagnosis of this controversial entity. Herein, we describe 2 cases of AG with features of granuloma annulare and necrobiosis lipoidica, supporting the concept of AG as a histologic spectrum. These 2 cases displayed dilated follicular infundibula and pseudoepitheliomatous hyperplasia analogous to changes in keratoacanthomas. These unique epithelial changes, in tandem with characteristic elastin alterations and clinical findings, are helpful and unifying features that permit accurate diagnosis of this controversial entity.

Freestanding, vertically aligned carbon nanotubes (VACNTs) were patterned into 16 μm diameter microchannel arrays for flow-through electrochemical glucose sensing. Non-enzymatic sensing of glucose was achieved by the chemical reaction of glucose with methyl viologen (MV) at an elevated temperature and pH (0.1 M NaOH), followed by the electrochemical reaction of reduced-MV with the VACNT surface. The MV sensor required no functionalization (including no metal) and was able to produce on average 3.4 electrons per glucose molecule. The current density of the MV sensor was linear with both flow rate and glucose concentration. Challenges with interference chemicals were mitigated by operating at a low potential of -0.2 V vs Ag/AgCl. As a comparison, enzymatic VACNT sensors with platinum nano-urchins were functionalized with glucose oxidase by covalent binding (1-ethyl-3-(-3-dimethylaminopropyl)carbodiimide/ N-hydroxysuccinimide) or by polymer entrapment [poly(3,4-ethylene-dioxythiophene)] and operated in phosphate buffered saline. With normalization by the overall cross-sectional area of the flow (0.713 cm 2 ), the sensitivity of the MV, enzyme-in-solution, and covalent sensors were 45.93, 18.77, and 1.815 mA cm -2 mM -1 , respectively. Corresponding limits of detection were 100, 194, and 311 nM glucose. The linear sensing ranges for the sensors were 250 nM to 200 μM glucose for the MV sensor, 500 nM to 200 μM glucose for the enzyme-in-solution sensor, and 1 μM to 6 mM glucose for the covalent sensor. The flow cell and sensor cross-sectional area were scaled down (0.020 cm 2 ) to enable detection from 200 μL of glucose with MV by flow injection analysis. The sensitivity of the small MV sensor was 5.002 mA cm -2 mM -1 , with a limit of detection of 360 nM glucose and a linear range up to at least 150 μM glucose. The small MV sensor has the potential to measure glucose levels found in 200 μL of saliva.

Microelectrode arrays of carbon nanotube (CNT)/carbon composite posts with high aspect ratio and millimeter-length were fabricated using carbon-nanotube-templated microfabrication with a sacrificial "hedge". The high aspect ratio, mechanical robustness, and electrical conductivity of these electrodes make them a potential candidate for next-generation neural interfacing. Electrochemical measurements were also demonstrated using an individual CNT post microelectrode with a diameter of 25 μm and a length of 1 mm to perform cyclic voltammetry on both methyl viologen and dopamine in a phosphate-buffered saline solution. In addition to detection of the characteristic peaks, the CNT post microelectrodes show a fast electrochemical response, which may be enabling for in vivo and/or in vitro measurements. The CNT post electrode fabrication process was also integrated with other microfabrication techniques, resulting in individually addressable electrodes.

This work examines the anisotropic electroless plating of DNA-functionalized gold nanorods attached to a DNA origami template to fabricate continuous metal structures of rectanglar, square, and T shapes. DNA origami, a versatile method for assembling a variety of 2- and 3-D nanostructures, is utilized to construct the DNA breadboard template used for this study. Staple strands on selective sites of the breadboard template are extended with an additional nucleotide sequence for the attachment of DNA-functionalized gold nanorods to the template via base pairing. The nanorod-seeded DNA templates are then introduced into an electroless gold plating solution to determine the extent to which the anisotropic growth of the nanorods is able to fill the gaps between seeds to create continuous structures. Our results show that the DNA-functionalized nanorods grow anisotropically during plating at a rate that is approximately 4 times faster in the length direction than in the width direction to effectively fill gaps of up to 11-13 nm in length. The feasibility of using this directional growth at specific sites to enable the fabrication of continuous metal nanostructures with diameters as thin as 10 nm is demonstrated and represents important progress toward the creation of devices and systems based on self-assembled biological templates.

An improved method for the metallization of DNA origami is examined in this work. DNA origami, a simple and robust method for creating a wide variety of nanostructured shapes and patterns, provides an enabling template for bottom-up fabrication of next-generation nanodevices. Selective metallization of these DNA templates is needed to make nanoelectronic devices. Here, we demonstrate a metallization process that uses gold nanorod seeds followed by anisotropic plating to provide improved morphology and greater control of the final metallized width of the structure. In our approach, gold nanorods are attached to an origami template to create a seed layer. Electroless gold deposition is then used to fill the gaps between seeds in order to create continuous, conductive nanowires. Importantly, growth during electroless deposition occurs preferentially in the length direction at a rate that is approximately 4 times the growth rate in the width direction, which enables fabrication of narrow, continuous wires. The electrical properties of 49 nanowires with widths ranging from 13 to 29 nm were characterized, and resistivity values as low as 8.9 × 10 -7 Ω·m were measured. The anisotropic metallization process presented here represents important progress toward the creation of nanoelectronic devices by molecularly directed placement of functional components onto self-assembled biological templates.

Cutaneous squamous cell carcinoma (cSCC) is the most common skin cancer diagnosed in African Americans. 1 Twenty to forty percent of cSCCs reported in African Americans are related to chronic scarring processes or areas of in ammation. 2 Risk factors for developing cSCCs in patients of color include chronic scars resulting from burns, skin ulcers, and radiation sites; and chronic inflammatory diseases such as discoid lupus and hidradenitis suppuritiva. 1 Although skin cancer only accounts for 1% to 2% of cancers diagnosed within African Americans, it is associated with increased morbidity and mortality in this population. 1,3 Significant delays in diagnosis and treatment are largely thought to be responsible for this prognostic incongruity. The rate of metastasis in patients of color is 31%, compared with only 4% in Caucasians. 4,5 Early recognition by physicians and increased awareness resulting in preventative measures by patients may decrease this noted disparity. J Drugs Dermatol. 2016;16(1):81-84..

A previously healthy man aged 50 years presented with malaise, anorexia, abdominal pain, nausea, vomiting, generalised jaundice, scleral icterus and dark urine. He was not on any prescription or over-the-counter medications, but reported drinking 4-5 energy drinks daily for 3 weeks prior to presentation. Physical examination revealed jaundice and right upper quadrant abdominal tenderness. Laboratory studies were remarkable for transaminitis and evidence of chronic hepatitis C infection. Ultrasound scan demonstrated an echogenic liver and diffuse gallbladder wall thickening. Liver biopsy showed severe acute hepatitis with bridging necrosis and marked cholestasis. The patient was treated supportively with complete resolution of his symptoms and marked improvement in his laboratory abnormalities. The development of acute hepatitis in this patient was likely secondary to excessive energy drink consumption. Energy drinks as well as other herbal/over-the-counter supplements should be considered by clinicians in the workup of patients with acute hepatitis, particularly once other aetiologies have been excluded., Competing Interests: Conflicts of Interest: None declared., (2016 BMJ Publishing Group Ltd.)

Background: The current NCCN recommendation for resection margins in patients with melanomas between 1.01 and 2 mm deep is a 1-2 cm radial margin. We sought to determine whether margin width had an impact on local recurrence (LR), disease-specific survival (DSS), and type of wound closure., Methods: Melanomas measuring 1.01-2.0 mm were evaluated at a single institution between 2008 and 2013. All patients had a 1 or 2 cm margin., Results: We identified 965 patients who had a 1 cm (n = 302, 31.3 %) or 2 cm margin (n = 663, 68.7 %). Median age was 64 years, and 592 (61.3 %) were male; 32.5 and 48.7 % of head and neck and extremity patients had a 1 cm margin versus 18.9 % of trunk patients (p < 0.001). LR was 2.0 and  2.1 % for a 1 and 2 cm margin, respectively (p = not significant). Five-year DSS was 87 % for a 1 cm margin and 85 % for a 2 cm margin (p = not significant). Breslow thickness, melanoma on the head and neck, lymphovascular invasion, and sentinel lymph node biopsy (SLNB) status significantly predicted LR on univariate analysis; however, only location and SLNB status were associated with LR on multivariate analysis. Margin width was not significant for LR or DSS. Wider margins were associated with more frequent graft or flap use only on the head and neck (p = 0.025)., Conclusions: Our data show that selectively using a narrower margin of 1 cm did not increase the risk of LR or decrease DSS. Avoiding a 2 cm margin may decrease the need for graft/flap use on the head and neck.

Introduction: Historically dermal melanoma (DM) has been labeled as either stage IIIB (in-transit) or stage IV (M1a) disease. We sought to investigate the natural history of DM and the utility and prognostic significance of sentinel lymph node biopsy (SLNB)., Methods: Patients with DM undergoing SLNB at a single center from 1998 to 2009 were identified., Results: Eighty-three patients met criteria, 10 (12%) patients had a positive SLNB. Of those, 5 (50%) recurred (all with distant disease). Twenty-one (29%) of the 73 SLNB negative patients recurred and of those, 15 (71%) developed distant metastases, whereas 6 (29%) developed local or regional recurrence, including two false-negative regional nodal recurrences. No in-transit recurrences were recorded. Five-year recurrence-free and disease-specific survival was significantly better for patients with a negative SLNB versus positive SLNB (56.8% vs. 22.2% P = 0.02, 81.1% vs. 61.0%, P = 0.05, respectively)., Conclusion: SLNB has prognostic significance for RFS and DSS, and should be utilized in the management of DM based on a >10% yield and low false-negative rate. Our data demonstrate patients with DM do not recur in an in-transit fashion, which along with the survival outcomes suggest the behavior of DM is consistent with primary cutaneous melanoma of similar thickness rather than an isolated in-transit or distant dermal metastasis from a regressed cutaneous primary., (© 2015 Wiley Periodicals, Inc.)

This work examines the selective deposition of two different metals on a single DNA origami template that was designed and assembled to direct the deposition. As a result, we were able to direct copper and gold to predesignated locations on the template, as verified by both compositional and morphological data, to form a heterogeneous Cu-Au junction. Seeding and deposition were performed in sequential steps. An enabling aspect of this work was the use of an organic layer or "chemical mask" to prevent unwanted deposition during the deposition of the second metal. In light of recent efforts in the field, the ability to localize components of different composition and structure to specific sections of a DNA template represents an important step forward in the fabrication of nanostructures based on DNA templates.

This paper demonstrates the use of galvanic displacement to form continuous tellurium-based nanowires on DNA templates, enabling the conversion of metals, which can be deposited site-specifically, into other materials needed for device fabrication. Specifically, galvanic displacement reaction of copper and nickel nanowires is used to fabricate tellurium and bismuth telluride nanowires on λ-DNA templates. The method is simple, rapid, highly selective, and applicable to a number of different materials. In this study, continuous Ni and Cu nanowires are formed on DNA templates by seeding with Ag followed by electroless plating of the desired metal. These wires are then displaced by a galvanic displacement reaction where either Te or Bi2Te3 is deposited from an acidic solution containing HTeO2(+) ions or a combination of HTeO2(+) and Bi(3+) ions, and the metal wire is simultaneously dissolved due to oxidation. Both tellurium and bismuth telluride wires can be formed from nickel templates. In contrast, copper templates only form tellurium nanowires under the conditions considered. Therefore, the composition of the metal being displaced can be used to influence the chemistry of the resulting nanowire. Galvanic displacement of metals deposited on DNA templates has the potential to enable site-specific fabrication of a variety of materials and, thereby, make an important contribution to the advancement of useful devices via self-assembled nanotemplates.

We show the controllable patterning of palladium nanoparticles in both one and two dimensions using electron-beam lithography and reactive ion etching of a thin film of poly(acrylic acid) (PAA). After the initial patterning of the PAA, a monolayer of polystyrene-b-poly-2-vinylpyridine micelles is spun cast onto the surface. A short reactive ion etch is then used to transfer the micelle pattern into the patterned poly(acrylic acid). Finally, PdCl2 is loaded from solution into the patterned poly(acrylic acid) features, and a reactive-ion etching process is used to remove the remaining polymer and form Pd nanoparticles. This method yields location-controlled patches of nanoparticles, including single- and double-file lines and nanoparticle pairs. A locational accuracy of 9 nm or less in one direction was achieved by optimizing the size of the PAA features.

This work demonstrates the use of a circuit-like DNA origami structure as a template to fabricate conductive gold and copper nanostructures on Si surfaces. We improved over previous results by using multiple Pd seeding steps to increase seed uniformity and density. Our process has also been characterized through atomic force microscopy, particle size distribution analysis, and scanning electron microscopy. We found that four successive Pd seeding steps yielded the best results for electroless metal plating on DNA origami. Electrical resistance measurements were done on both Au- and Cu-metallized nanostructures, with each showing ohmic behavior. Gold-plated DNA origami structures made under optimal conditions had an average resistivity of 7.0 × 10(-5) Ω·m, whereas copper-metallized structures had a resistivity as low as 3.6 × 10(-4) Ω·m. Importantly, this is the first demonstration of electrically conductive Cu nanostructures fabricated on either DNA or DNA origami templates. Although resistivities for both gold and copper samples were larger than those of the bulk metal, these metal nanostructures have the potential for use in electrically connecting small structures. In addition, these metallized objects might find use in surface-enhanced Raman scattering experiments.

DNA origami is a promising tool for use as a template in the design and fabrication of nanoscale structures. The ability to engineer selected staple strands on a DNA origami structure provides a high density of addressable locations across the structure. Here we report a method using site-specific attachment of gold nanoparticles to modified staple strands and subsequent metallization to fabricate conductive wires from DNA origami templates. We have modified DNA origami structures by lengthening each staple strand in select regions with a 10-base nucleotide sequence and have attached DNA-modified gold nanoparticles to the lengthened staple strands via complementary base-pairing. The high density of extended staple strands allowed the gold nanoparticles to pack tightly in the modified regions of the DNA origami, where the measured median gap size between neighboring particles was 4.1 nm. Gold metallization processes were optimized so that the attached gold nanoparticles grew until gaps between particles were filled and uniform continuous nanowires were formed. Finally, electron beam lithography was used to pattern electrodes in order to measure the electrical conductivity of metallized DNA origami, which showed an average resistance of 2.4 kΩ per metallized structure.

Dielectrophoresis has been used as a technique for the parallel localization and alignment of both semiconducting and metallic carbon nanotubes (CNTs) at junctions between electrodes. A variation of this technique known as floating potential dielectrophoresis (FPD) allows for a self-limiting number of CNTs to be localized at each junction, on a massively parallel scale. However, the smallest FPD geometries to date are restricted to conductive substrates and have a lower limit on floating electrode size. We present a geometry which eliminates this lower limit and enables FPD to be performed on non-conducting substrates. We also discuss experiments clarifying the self-limiting mechanism of CNT localization and how it can be used advantageously as devices are scaled downwards to smaller sizes.

We have used block copolymer patterned arrays of 5 nm gold nanoparticles (AuNPs) for chemically aligned surface attachment of DNA origami. Addition of single-stranded DNA-thiol to AuNPs allowed a base paired attachment of sticky end modified DNA origami. Results indicate a stable, selective attachment between the DNA origami and ssDNA modified AuNPs. Yield data showed 74% of AuNP binding sites forming an attachment with a DNA origami rectangle, and control surfaces showed less than 0.5% nonspecific adsorption.

This work examines the metallization of folded DNA, known as DNA origami, as an enabling step toward the use of such DNA as templates for nanoelectronic circuits. DNA origami, a simple and robust method for creating a wide variety of shapes and patterns, makes possible the increased complexity and flexibility needed for both the design and assembly of useful circuit templates. In addition, selective metallization of the DNA template is essential for circuit fabrication. Metallization of DNA origami presents several challenges over and above those associated with the metallization of other DNA templates such as λ-DNA. These challenges include (1) the stability of the origami in the processes used for metallization, (2) the enhanced selectivity required to metallize small origami structures, (3) the increased difficulty of adhering small structures to the surface so that they will not be removed when subject to multiple metallization steps, and (4) the influence of excess staple strands present with the origami. This paper describes our efforts to understand and address these challenges. Specifically, the influence of experimental conditions on template stability and on the selectivity of metal deposition was investigated for small DNA origami templates. These templates were seeded with Ag and then plated with Au via an electroless deposition process. Both staple strand concentration and the concentration of ions in solution were found to have a significant impact. Selective continuous metal deposition was achieved, with an average metallized height as small as 32 nm. The shape of branched origami was also retained after metallization. These results represent important progress toward the realization of DNA-templated nanocircuits.

In superconformal filling of copper-chip interconnects, organic additives are used to fill high-aspect-ratio trenches or vias from the bottom up. In this study we report on the development of intermolecular potentials and use molecular dynamics simulations to provide insight into the molecular function of an organic additive (3-mercaptopropanesulfonic acid or MPSA) important in superconformal electrodeposition. We also investigate how the presence of sodium chloride affects the surface adsorption and surface action of MPSA as well as the charge distribution in the system. We find that NaCl addition decreases the adsorption strength of MPSA at a simulated copper surface and attenuates the copper-ion association with MPSA. The model also was used to simulate induced-charge effects and adsorption on a nonplanar electrode surface.

Miniaturized devices for electric field gradient focusing (EFGF) were developed that consist of a cylindrical separation channel surrounded by an acrylic-based polymer hydrogel. The ionic transport properties of the hydrogel enable the manipulation of the electric field inside the separation channel. A changing cross-section design was used in which the hydrogel is shaped such that an electric field gradient is established in the separation channel. One of the challenges with this type of EFGF device has been that experimental resolution between protein analytes is lower than theoretically predicted. In order to investigate this phenomenon, a mathematical transport model was developed using FEMLAB. Model results and experimental observations showed that the reduced performance was caused by concentration gradients formed in the EFGF channel, and that these concentration gradients were the result of an imbalance in cation transport between the open separation channel and the hydrogel. Removing acidic impurities from the monomers that form the hydrogel reduced this tendency and improved the resolution. These transport-induced concentration gradients can be used to establish electric field gradients that may be useful for sample pre-concentration. Both the results of simulation and experiments demonstrate how transport-induced concentration gradients lead to the establishment of electric field gradients.

Azotobacter vinelandii bacterioferritin (AvBF) containing 800-1500 Co or Mn atoms as Co(III) and Mn(III) oxyhydroxide cores (Co-AvBF, Mn-AvBF) was synthesized by the same procedure used previously for horse spleen ferritin (HoSF). The kinetics of reduction of Co-AvBF and Mn-AvBF by ascorbic acid are first-order in each reactant. The rate constant for the reduction of Mn-AvBF (8.52 M(-1) min(-1)) is approximately 12 times larger than that for Co-AvBF (0.72 M(-1) min(-1)), which is consistent with a previous observation that Mn-HoSF is reduced approximately 10-fold faster than Co-HoSF [Zhang, B. et al. (2005) Inorg. Chem. 44, 3738-3745]. The rates of reduction of M-AvBF (M = Co and Mn) are more than twice that for the reduction of the corresponding M-HoSF. HoSF containing reduced Fe(II) cores (Fe(II)-HoSF), prepared by methyl viologen and CO, also reduces M-HoSF and M-AvBF species, with both cores remaining within ferritin, suggesting that electrons transfer through the ferritin shell. Electron transfer from Fe(II)-HoSF to Co-AvBF occurs at a rate approximately 3 times faster than that to Co-HoSF, indicating that the Co cores in AvBF are more accessible to reduction than the Co cores in HoSF. The presence of nonconductive (SiO2) or conductive (gold) surfaces known to bind ferritins enhances the rate of electron transfer. A more than approximately 4-fold increase in the apparent reaction rate is observed in the presence of gold. Although both surfaces (SiO2 and gold) enhance reaction by providing binding sites for molecular interaction, results show that ferritins with different mineral cores bound to a gold surface transfer electrons through the gold substrate so that direct contact of the reacting molecules is not required.

Horse spleen ferritin (HoSF) containing 800-1500 cobalt or 250-1200 manganese atoms as Co(O)OH and Mn(O)OH mineral cores within the HoSF interior (Co-HoSF and Mn-HoSF) was synthesized, and the chemical reactivity, kinetics of reduction, and the reduction potentials were measured. Microcoulometric and chemical reduction of HoSF containing the M(O)OH mineral core (M = Co or Mn) was rapid and quantitative with a reduction stoichiometry of 1.05 +/- 0.10 e/M forming a stable M(OH)(2) mineral core. At pH 9.0, ascorbic acid (AH(2)), a two-electron reductant, effectively reduced the mineral cores; however, the reaction was incomplete and rapidly reached equilibrium. The addition of excess AH(2) shifted the reaction to completion with a M(3+)/AH(2) stoichiometry of 1.9-2.1, consistent with a single electron per metal atom reduction. The rate of reaction between M(O)OH and excess AH(2) was measured by monitoring the decrease in mineral core absorbance with time. The reaction was first order in each reactant with second-order rate constants of 0.53 and 4.74 M(-1) min(-1), respectively, for Co- and Mn-HoSF at pH 9.0. From the variation of absorbance with increasing AH(2) concentration, equilibrium constants at pH 9.0 of 5.0 +/- 1.9 for Co-HoSF and 2.9 +/- 0.9 for Mn-HoSF were calculated for 2M(O)OH + AH(2) = 2M(OH)(2) + D, where AH(2) and D are ascorbic acid and dehydroascorbic acid, respectively. Consistent with these equilibrium constants, the standard potential for the reduction of Co(III)-HoSF is 42 mV more positive than that of the ascorbic acid reaction, while the standard potential of Mn(III)-HoSF is 27 mV positive relative to AH(2). Fe(2+) in solution with Co- and Mn-HoSF under anaerobic conditions was oxidized to form Fe(O)OH within the HoSF interior, resulting in partial displacement of the Co or Mn by iron.

Electrical conductivity measurements were performed on single apoferritin and holoferritin molecules by conductive atomic force microscopy. Conductivity of self-assembled monolayer films of ferritin molecules on gold surfaces was also measured. Holoferritin was 5-15 times more conductive than apoferritin, indicating that for holoferritin most electron-transfer goes through the ferrihydrite core. With 1 V applied, the average electrical currents through single holoferritin and apoferritin molecules were 2.6 pA and 0.19 pA, respectively.

Three-branched DNA molecules have been designed and assembled from oligonucleotide components. These nucleic acid constructs contain double- and single-stranded regions that control the hybridization behavior of the assembly. Specific localization of a single streptavidin molecule at the center of the DNA complex has been investigated as a model system for the directed placement of nanostructures. Highly selective silver and copper metallization of the DNA template has also been characterized. Specific hybridization of these DNA complexes to oligonucleotide-coupled nanostructures followed by metallization should provide a bottom-up self-assembly route for the fabrication and characterization of discrete three-terminal nanodevices.