Empirical Administration of Doxycycline for Rocky Mountain Spotted Fever: A Case Report.

Rocky Mountain spotted fever (RMSF) is a tick-borne illness that can cause extreme sickness, even death, in otherwise healthy individuals. Sometimes, it is difficult to confirm the diagnosis as the rash often lags behind other symptoms of the illness and may not occur at all. Other symptoms of RMSF are nonspecific, such as fever, headache, and malaise. Besides the confirmatory serology test, antibody titers remain negative in the early phase of the illness. Here, we reported a case of a 21-year-old male who presented with fever, mild headache, body aches, joint pain, dry cough, and characteristic maculopapular rash after visiting a tick-prone area. Doxycycline was started because symptoms and laboratory values heightened our suspicion for the diagnosis of RMSF. His condition improved gradually, and his labs became normal. Our study supports the empirical use of doxycycline in suspected RMSF cases.

Difference in presentation, outcomes, and hospital epidemiologic trend of COVID-19 among first, second, and third waves: a review of hospital records and prospective cohort study.

This study aimed to examine the differences in epidemiologic and disease aspects among patients with coronavirus disease-19 (COVID-19). Methods: The authors reviewed the hospital records between April 2020 and September 2021 and followed up on the patients for post-COVID complications. Findings: Older adult patients were predominantly affected during the third wave, and middle-aged patients were predominantly affected during the first and second waves. Men were predominantly admitted, considering the three waves, although more women were admitted in the second wave. Cough was more common in the second and third waves than in the first wave 522 (59.7%). Respiratory distress was the most common in the third wave, 251(67.1%), and least common in the first wave, 403 (46.1%). Anosmia was more common in the third wave 116 (31.2%). In the third wave, patients presenting in a critical state 23 (6.2%) and with severe disease 152 (40.8%) were more common. The hospital admission median (IQR) was longer in the first wave, 12 (8-20), than in other waves. More patients were admitted in the first wave (52%) than in the other waves, and patients received more oxygen in the third wave (75%) than in the other waves. Death occurred more commonly in the first wave (51%) than in the other waves. The positivity rate was higher in the third wave (22.8%) than in the other waves. In the third wave, the positivity rate was higher in women (24.3%) than in men. Post-COVID cough increased in the second wave, and fatigue was higher in the third wave than in the other waves. Tiredness and memory loss were greater during the second wave than in other waves. Conclusion: The authors found differences in the presentation, outcomes, and hospital epidemiologic trend of COVID-19 among the three waves.

Drastically Enhancing Moduli of Graphene-Coated Carbon Nanotube Aerogels via Densification while Retaining Temperature-Invariant Superelasticity and Ultrahigh Efficiency.

Lightweight open-cell foams that are simultaneously superelastic, possess exceptionally high Young's moduli (Y), exhibit ultrahigh efficiency, and resist fatigue as well as creep are particularly desirable as structural frameworks. Unfortunately, many of these features are orthogonal in foams of metals, ceramics, and polymers, particularly under large temperature variations. In contrast, foams of carbon allotropes including carbon nanotubes and graphene developed over the past few years exhibit these desired properties but have low Y due to low density, ρ = 0.5-10 mg/mL. Densification of these foams enhances Y although below expectation and also dramatically degrades other properties because of drastic changes in microstructure. We have recently developed size- and shape-tunable graphene-coated single-walled carbon nanotube (SWCNT) aerogels that display superelasticity at least up to a compressive strain (ε) = 80%, fatigue and creep resistance, and ultrahigh efficiency over -100-500 °C. Unfortunately, Y of these aerogels is only ∼0.75 MPa due to low ρ ≈ 14 mg/mL, limiting their competitiveness as structural foams. We report fabrication of similar aerogels but with ρ spanning more than an order of magnitude from 16-400 mg/mL through controlled isostatic compression in the presence of a polymer coating circumventing any microstructural changes in stark contrast to other foams of carbon allotropes. The compressive stress (σ) versus ε measurements show that the densification of aerogels from ρ ≈ 16 to 400 mg/mL dramatically enhances Y from 0.9 to 400 MPa while maintaining superelasticity at least up to ε = 10% even at the highest ρ. The storage (E') and loss (E″) moduli measured in the linear regime show ultralow loss coefficient, tan δ = E″/E' ≈ 0.02, that remains constant over three decades of frequencies (0.628-628 rad/s), suggesting unusually high frequency-invariant efficiency. Furthermore, these aerogels retain exceptional fatigue resistance for 106 loading-unloading cycles to ε = 2% and creep resistance for at least 30 min under σ = 0.02 MPa with ρ = 16 mg/mL and σ = 2.5 MPa with higher ρ = 400 mg/mL. Lastly, these robust mechanical properties are stable over a broad temperature range of -100-500 °C, motivating their use as highly efficient structural components in environments with extreme temperature variations.

Superelastic Pseudocapacitors from Freestanding MnO2-Decorated Graphene-Coated Carbon Nanotube Aerogels.

In recent years, the demand for emerging electronic devices has driven efforts to develop electrochemical capacitors with high power and energy densities that can preserve capacitance under and after recovery from mechanical deformation. We have developed superelastic pseudocapacitors using ∼1.5 mm thick graphene-coated single-walled carbon nanotube (SWCNT) aerogels decorated with manganese oxide (MnO2) as freestanding electrodes that retain high volumetric capacitance and electrochemical stability before, under, and after recovery from 50% compression. Graphene-coated SWCNT aerogels are superelastic and fatigue-resistant with high specific surface area and electrical conductivity. Electrodeposition of MnO2 onto these aerogels does not alter their superelasticity, with full shape recovery even after 10 000 compression-release cycles to 50% strain. Total (utilized) gravimetric capacitances of these aerogels before compression are similar to those under and after recovery from 50% compression over a wide range of scan rates with capacitances reaching 98 (468), 106 (522), and 128 F/g (626 F/g) at a scan rate of 2 mV/s, respectively. These gravimetric capacitances are preserved even after 10 000 compression-release cycles to 50% strain. Further, 50% compression of these aerogels increases the volumetric capacitance from 1.5 to 3.3 F/cm3. Before compression, the lifetime performances of these aerogels remain largely stable, with capacitance degrading by only ∼14% over the first 2000 charge-discharge cycles and remains constant for further 8000 cycles. Under 50% compression, capacitance displays a similar trend over 10 000 charge-discharge cycles. After recovery from 10 000 compression-release cycles to 50% strain, the aerogels show slightly greater capacitance loss of ∼28% over the first 2000 charge-discharge cycles and an additional ∼10% loss over the subsequent 8000 charge-discharge cycles. Finally, substantially higher gravimetric capacitance is achieved through greater MnO2 deposition, facilitated by the large porosity of these aerogels, albeit at a loss of capacitance retention upon compression. These capacitors display the feasibility of coating graphene-coated SWCNT aerogels with various pseudocapacitive materials to create superelastic energy-storage devices.

Nano-Photoelectrochemical Cell Arrays with Spatially Isolated Oxidation and Reduction Channels.

Photoelectrochemical conversion of solar energy is explored for many diverse applications but suffers from poor efficiencies due to limited solar absorption, inadequate charge carrier separation, redox half-reactions occurring in close proximity, and/or long ion diffusion lengths. We have taken a drastically different approach to the design of photoelectrochemical cells (PECs) to spatially isolate reaction sites at the nanoscale to different materials and flow channels, suppressing carrier recombination and back-reaction of intermediates while shortening ion diffusion paths and, importantly, avoiding mixed product generation. We developed massively parallel nano-PECs composed of an array of open-ended carbon nanotubes (CNTs) with photoanodic reactions occurring on the outer walls, uniformly coated with titanium dioxide (TiO2), and photocathodic reactions occurring on the inner walls, decorated with platinum (Pt). We verified the redox reaction isolation by demonstrating selective photodeposition of manganese oxide on the outside and silver on the inside of the TiO2/CNT/Pt nanotubes. Further, the nano-PECs exhibit improved solar absorption and efficient charge transfer of photogenerated carriers to their respective redox sites, leading to a 1.8% photon-to-current conversion efficiency (a current density of 4.2 mA/cm2) under white-light irradiation. The design principles demonstrated can be readily adapted to myriads of photocatalysts for cost-effective solar utilization.

Dispersed single wall carbon nanotubes do not impact mitochondria structure or function, but technical issues during analysis could yield incorrect results.

Mitochondria are the organelles of cells that generate a majority of the cell's energy through ATP and are involved in programmed cell death through apoptosis. An understanding of non-specific targeting of nanomaterials, including single wall carbon nanotubes (SWCNTs), to organelles is important in trying to modulate cell function or determine the cellular toxicity with long term exposure. Here, we examine the impact of SWCNTs dispersed with Pluronic F127 and protein on mitochondria using a battery of standard tests. Seahorse XF24 analysis suggests complete loss of mitochondiral function, but this data is artifactual due to SWCNTs adsorbing onto the Seahorse probes. Imaging using the mitochondrial functional dye JC-1 gives inconclusive results owing to fluorescence quenching by SWCNTs. We observe no co-localization or reorganization of mitochondria in the presence of SWCNTs, although the results could have been misinterpreted had we not been correcting for significant fluorescence quenching by SWCNTs. In sum, the surface activity and fluorescence quenching of SWCNTs alter many traditional cellular assays. However, light emitting (luciferase) assays show that ATP levels are not altered with SWCNT treatment suggesting that mitochondiral function is not impacted as well as that light-emitting assays are an essential complimentary approach for quantitative, unambiguous cellular study of nanomaterials.

Length-dependent intracellular bundling of single-walled carbon nanotubes influences retention.

Single-walled carbon nanotubes (SWCNTs) are increasingly being investigated for biomedical imaging, sensing, and drug delivery. Cell types, cellular entry mechanisms, and SWCNT lengths dictate SWCNT uptake, subsequent intracellular trafficking, and retention. Specialized immune cells known as macrophages are capable of two size-dependent entry mechanisms: endocytosis of small particles (diameter < 200 nm) and phagocytosis of large particles (diameter > 500 nm). In comparison, fibroblasts uptake particles predominantly through endocytosis. We report dependence of cellular processing including uptake, subcellular distribution, and retention on the SWCNT length and immune cell-specific processes. We chose SWCNTs of three different average lengths: 50 nm (ultrashort, US), 150 nm (short) and 500 nm (long) to encompass two different entry mechanisms, and noncovalently dispersed them in water, cell culture media, and phosphate buffer (pH 5) with bovine serum albumin, which maintains the SWCNT optical properties and promotes their cellular uptake. Using confocal Raman imaging and spectroscopy, we quantified cellular uptake, tracked the intracellular dispersion state (i.e., individualized versus bundled), and monitored recovery as a function of SWCNT lengths in macrophages. Cellular uptake of SWCNTs increases with decreasing SWCNT length. Interestingly, short-SWCNTs become highly bundled in concentrated phase dense regions of macrophages after uptake and most of these SWCNTs are retained for at least 24 h. On the other hand, both US- and long-SWCNTs remain largely individualized after uptake into macrophages and are lost over a similar elapsed time. After uptake into fibroblasts, however, short-SWCNTs remain individualized and are exocytosed over 24 h. We hypothesize that aggregation of SWCNTs within macrophages but not fibroblasts may facilitate the retention of SWCNTs within the former cell type. Furthermore, the differential length-dependent cellular processing suggests potential applications of macrophages as live cell carriers of SWCNTs into tumors and regions of inflammation for therapy and imaging.

Creep- and fatigue-resistant, rapid piezoresistive responses of elastomeric graphene-coated carbon nanotube aerogels over a wide pressure range.

Lightweight, flexible piezoresistive materials with wide operational pressure ranges are in demand for applications such as human physical activity and health monitoring, robotics, and for functional interfacing between living systems and wearable electronics. Piezoresistivity of many elastomeric foams of polymers and carbon allotropes satisfies much of the required characteristics for these applications except creep and fatigue resistance due to their viscoelasticity, critically limiting the reliability and lifetime of integrated devices. We report the piezoresistive responses from aerogels of graphene-coated single-walled carbon nanotubes (SWCNTs), made using a facile and versatile sol-gel method. Graphene crosslinks the junctions of the underlying random network of SWCNTs, generating lightweight elastomeric aerogels with a mass density of ≈11 mg mL-1 (volume fraction ≈7.7 × 10-3) and a Young's modulus of ≈0.4 MPa. The piezoresistivity of these aerogels spans wide compressive pressures up to at least 120 kPa with sensitivity that exhibit ultrafast temporal responses of <27 ms and <3% delay ratio over 104 compressive loading-unloading cycles at rates between 0.1-10 Hz. Most importantly, the piezoresistive responses do not show any creep at least for 1 hour and 80 kPa of compressive static loading. We suggest that the fatigue- and creep-resistant, ultrafast piezoresistive responses of these elastomeric aerogels are highly attractive for use in dynamic and static lightweight, pressure sensing applications such as human activity monitoring and soft robotics.

Polymer-based protein engineering grown ferrocene-containing redox polymers improve current generation in an enzymatic biofuel cell.

Enzymatic biofuel cells (EBFCs) are capable of generating electricity from physiologically present fuels making them promising power sources for the future of implantable devices. The potential application of such systems is limited, however, by inefficient current generation. Polymer-based protein engineering (PBPE) offers a unique method to tailor enzyme function through tunable modification of the enzyme surface with functional polymers. In this study, we report on the modification of glucose oxidase (GOX) with ferrocene-containing redox polymers to increase current generation efficiency in an enzyme-modified anode. Poly(N-(3-dimethyl(ferrocenyl)methylammonium bromide)propyl acrylamide) (pFcAc) was grown from covalently attached, water-soluble initiator molecules on the surface of GOX in a "grafting-from" approach using atom transfer radical polymerization (ATRP). The covalently-coupled ferrocene-containing polymers on the enzyme surface promoted the effective "wiring" of the GOX active site to an external electrode. The resulting GOX-pFcAc conjugates generated over an order of magnitude increase in current generation efficiency and a 4-fold increase in maximum EBFC power density (≈1.7µWcm(-2)) with similar open circuit voltage (0.27V) compared to native GOX when physically adsorbed onto paddle-shaped electrodes made up of electrospun polyacrylonitrile fibers coated with gold nanoparticles and multi-wall carbon nanotubes. The formation of electroactive enzyme-redox polymer conjugates using PBPE represents a powerful new tool for the improvement of mediated enzyme-based bioelectronics without the need for free redox mediators or anode/cathode compartmentalization.

Delivering Single-Walled Carbon Nanotubes to the Nucleus Using Engineered Nuclear Protein Domains.

Single-walled carbon nanotubes (SWCNTs) have great potential for cell-based therapies due to their unique intrinsic optical and physical characteristics. Consequently, broad classes of dispersants have been identified that individually suspend SWCNTs in water and cell media in addition to reducing nanotube toxicity to cells. Unambiguous control and verification of the localization and distribution of SWCNTs within cells, particularly to the nucleus, is needed to advance subcellular technologies utilizing nanotubes. Here we report delivery of SWCNTs to the nucleus by noncovalently attaching the tail domain of the nuclear protein lamin B1 (LB1), which we engineer from the full-length LMNB1 cDNA. More than half of this low molecular weight globular protein is intrinsically disordered but has an immunoglobulin-fold composed of a central hydrophobic core, which is highly suitable for associating with SWCNTs, stably suspending SWCNTs in water and cell media. In addition, LB1 has an exposed nuclear localization sequence to promote active nuclear import of SWCNTs. These SWCNTs-LB1 dispersions in water and cell media display near-infrared (NIR) absorption spectra with sharp van Hove peaks and an NIR fluorescence spectra, suggesting that LB1 individually disperses nanotubes. The dispersing capability of SWCNTs by LB1 is similar to that by albumin proteins. The SWCNTs-LB1 dispersions with concentrations ≥150 µg/mL (≥30 µg/mL) in water (cell media) remain stable for ≥75 days (≥3 days) at 4 °C (37 °C). Further, molecular dynamics modeling of association of LB1 with SWCNTs reveal that the exposure of the nuclear localization sequence is independent of LB1 binding conformation. Measurements from confocal Raman spectroscopy and microscopy, NIR fluorescence imaging of SWCNTs, and fluorescence lifetime imaging microscopy show that millions of these SWCNTs-LB1 complexes enter HeLa cells, localize to the nucleus of cells, and interact with DNA. We postulate that the modification of native cellular proteins as noncovalent dispersing agents to provide specific transport will open new possibilities to utilize both SWCNT and protein properties for multifunctional subcellular targeting applications. Specifically, nuclear targeting could allow delivery of anticancer therapies, genetic treatments, or DNA to the nucleus.

Distribution of single wall carbon nanotubes in the Xenopus laevis embryo after microinjection.

Single wall carbon nanotubes (SWCNTs) are advanced materials with the potential for a myriad of diverse applications, including biological technologies and large-scale usage with the potential for environmental impacts. SWCNTs have been exposed to developing organisms to determine their effects on embryogenesis, and results have been inconsistent arising, in part, from differing material quality, dispersion status, material size, impurity from catalysts and stability. For this study, we utilized highly purified SWCNT samples with short, uniform lengths (145 ± 17 nm) well dispersed in solution. To test high exposure doses, we microinjected > 500 µg ml(-1) SWCNT concentrations into the well-established embryogenesis model, Xenopus laevis, and determined embryo compatibility and subcellular localization during development. SWCNTs localized within cellular progeny of the microinjected cells, but were heterogeneously distributed throughout the target-injected tissue. Co-registering unique Raman spectral intensity of SWCNTs with images of fluorescently labeled subcellular compartments demonstrated that even at regions of highest SWCNT concentration, there were no gross alterations to subcellular microstructures, including filamentous actin, endoplasmic reticulum and vesicles. Furthermore, SWCNTs did not aggregate and localized to the perinuclear subcellular region. Combined, these results suggest that purified and dispersed SWCNTs are not toxic to X. laevis animal cap ectoderm and may be suitable candidate materials for biological applications.

Developing Xenopus embryos recover by compacting and expelling single wall carbon nanotubes.

Single wall carbon nanotubes are high aspect ratio nanomaterials being developed for use in materials, technological and biological applications due to their high mechanical stiffness, optical properties and chemical inertness. Because of their prevalence, it is inevitable that biological systems will be exposed to nanotubes, yet studies of the effects of nanotubes on developing embryos have been inconclusive and are lacking for single wall carbon nanotubes exposed to the widely studied model organism Xenopus laevis (African clawed frog). Microinjection of experimental substances into the Xenopus embryo is a standard technique for toxicology studies and cellular lineage tracing. Here we report the surprising finding that superficial (12.5 ± 7.5 µm below the membrane) microinjection of nanotubes dispersed with Pluronic F127 into one- to two-cell Xenopus embryos resulted in the formation and expulsion of compacted, nanotube-filled, punctate masses, at the blastula to mid-gastrula developmental stages, which we call "boluses." Such expulsion of microinjected materials by Xenopus embryos has not been reported before and is dramatically different from the typical distribution of the materials throughout the progeny of the microinjected cells. Previous studies of microinjections of nanomaterials such as nanodiamonds, quantum dots or spherical nanoparticles report that nanomaterials often induce toxicity and remain localized within the embryos. In contrast, our results demonstrate an active recovery pathway for embryos after exposure to Pluronic F127-coated nanotubes, which we speculate is due to a combined effect of the membrane activity of the dispersing agent, Pluronic F127, and the large aspect ratio of nanotubes.

Enhanced intracellular delivery of small molecules and drugs via non-covalent ternary dispersions of single-wall carbon nanotubes.

Albumins are used biologically and pharmacologically as transport proteins to deliver molecules to cells. Albumins also efficiently coat single-wall carbon nanotubes (SWCNTs) and promote their entry into mammalian and immune cells by the millions. Here, we show SWCNTs dispersed with bovine serum albumin (BSA) that are pre-loaded with rhodamine B (RB), small hydrophobic dye molecules that we consider here as models for drugs, drastically increase delivery of RB to HeLa cells and macrophages in culture. We determine spatial and concentration distribution of RB by independently visualizing SWCNTs and RB within the cells using unique SWCNT NIR fluorescence and fluorescence lifetime imaging of RB. The SWCNTs-BSA-RB ternary complexes are stable in water for days, and RB is only released when BSA is thermally or enzymatically denatured. We demonstrate efficacy of this approach by delivering daunomycin, a fluorescent chemotherapeutic drug that reduces proliferation in HeLa cells. Furthermore, we use molecular dynamics simulations to identify separate regions in BSA for drug loading and binding to SWCNTs. Together, our results demonstrate a pathway to enhance the delivery of a wide variety of drugs to cells through SWCNTs coated with albumin pre-loaded with drug molecules.

Compressible elastomeric aerogels of hexagonal boron nitride and single-walled carbon nanotubes.

Lightweight porous ceramic materials that can recover their shapes after mechanical deformation have numerous applications. However, these types of materials tend to be highly fragile and often crack when compressed. Here, we report on the fabrication and characterization of highly porous, freestanding composites of hexagonal boron nitride (h-BN) and single-walled carbon nanotubes (SWCNTs) of density 13-15 mg mL(-1), which corresponds to a volume fraction of 0.009, that were mechanically robust and recovered their original shape even after uniaxially compressing them by more than 50%. We made these porous elastomeric composites using a solution based assembly process that involved first shaping SWCNTs into porous networks of density ∼7 mg mL(-1) (volume fraction ∼0.005) followed by coatings of SWCNT networks with 6-8 mg mL(-1) of h-BN (volume fraction ∼0.003-0.004). The h-BN coating strengthened the underlying SWCNT networks, likely via reinforcement of the nodes between the SWCNTs, resulting in an increase in Young's modulus by ∼100% compared to that of SWCNT networks alone. Surprisingly, SWCNT networks, which were initially highly fragile, became elastomeric after h-BN coating, even though porous structures solely from h-BN are very brittle. Our fabrication approach preserves the morphology of the underlying networks, allowing for fabrication of various shapes and sizes of porous composites of h-BN and SWCNTs. Finally, our fabrication scheme is robust and facile for the preparation of porous composites of diverse ceramic materials and SWCNTs using the appropriate ceramic-precursor.

Subcellular Partitioning and Analysis of Gd3+-Loaded Ultrashort Single-Walled Carbon Nanotubes.

Magnetic resonance imaging (MRI) is of vast clinical utility, with tens of millions of scans performed annually. Chemical contrast agents (CAs) can greatly enhance the diagnostic potential of MRI, and ∼50% of MRI scans use CAs. However, CAs have significant limitations such as low contrast enhancement, lack of specificity, and potential toxicity. Recently developed, Gd3+-loaded ultrashort single-walled carbon nanotubes, also referred to as gadonanotubes or GNTs, exhibit ∼40 times the relaxivities of clinical CAs, representing a potential major advance in clinically relevant MRI CA materials. Although initial cytotoxicity and MRI studies have suggested great promise for GNTs, relatively little is known regarding their subcellular interactions, which are crucial for further, safe development of GNTs as CAs. In this work, we administered GNTs to a well-established human cell line (HeLa) and to murine macrophage-like cells (J774A.1). GNTs were not acutely cytotoxic and did not reduce proliferation, except for the highest exposure concentration of 27 µg/mL for J774A.1 macrophages, yet bulk uptake of GNTs occurred in minutes at picogram quantities, or millions of GNTs per cell. J774A.1 macrophages internalized substantially more GNTs than HeLa cells in a dose-dependent manner, and Raman imaging of the subcellular distribution of GNTs revealed perinuclear localization. Fluorescence intensity and lifetime imaging demonstrated that GNTs did not grossly alter subcellular compartments, including filamentous-actin structures. Together, these results provide subcellular evidence necessary to establish GNTs as a new MRI CA material.

Preformed nanoporous carbon nanotube scaffold-based multifunctional polymer composites.

Multifunctional polymer nanocomposites that simultaneously possess high modulus and strength, high thermal stability, novel optical responses, and high electrical and thermal conductivity have been actively researched. Carbon nanotubes are considered an ideal additive for composites because of their superlative physical, electronic and optical properties. While nanotubes have successfully added electrical conductivity, thermal stability, and novel optical responses to polymers, mechanical reinforcements, although substantial, have been well below any theoretical estimations. Here, we integrated preformed hydrogels and aerogels of individually dispersed nanotubes with polymer to increase elastic modulus of composites according to Halpin-Tsai model up to at least 25 vol % of nanotubes. Our solution-based fabrication method allowed us to create bulk composites with tunable form-factors, and with polymers that were incompatible with nanotubes. Further, in this approach, nanotubes were not covalently linked among themselves and to the polymer, so intrinsic optical, electrical, and thermal properties of nanotubes could be exploited. The optically active nanotubes, for example, added a strain-dependent, spatially resolved fluorescence to these composites. Finally, the nanoporous nanotube networks suppressed the polymer glass transition and extended the mechanical integrity of polymer well above its polymer melting point, and both the nanotubes and polymer remained thermally stable above their decomposition temperatures.

Membrane/mediator-free rechargeable enzymatic biofuel cell utilizing graphene/single-wall carbon nanotube cogel electrodes.

Enzymatic biofuel cells (EBFCs) utilize enzymes to convert chemical energy present in renewable biofuels into electrical energy and have shown much promise in the continuous powering of implantable devices. Currently, however, EBFCs are greatly limited in terms of power and operational stability with a majority of reported improvements requiring the inclusion of potentially toxic and unstable electron transfer mediators or multicompartment systems separated by a semipermeable membrane resulting in complicated setups. We report on the development of a simple, membrane/mediator-free EBFC utilizing novel electrodes of graphene and single-wall carbon nanotube cogel. These cogel electrodes had large surface area (∼ 800 m(2) g(-1)) that enabled high enzyme loading, large porosity for unhindered glucose transport and moderate electrical conductivity (∼ 0.2 S cm(-1)) for efficient charge collection. Glucose oxidase and bilirubin oxidase were physically adsorbed onto these electrodes to form anodes and cathodes, respectively, and the EBFC produced power densities up to 0.19 mW cm(-2) that correlated to 0.65 mW mL(-1) or 140 mW g(-1) of GOX with an open circuit voltage of 0.61 V. Further, the electrodes were rejuvenated by a simple wash and reloading procedure. We postulate these porous and ultrahigh surface area electrodes will be useful for biosensing applications, and will allow reuse of EBFCs.

Ultracompressible, high-rate supercapacitors from graphene-coated carbon nanotube aerogels.

Emerging applications for electrochemical energy storage require devices that not only possess high power and energy, but also are capable of withstanding mechanical deformation without degradation of performance. To this end, we have constructed electric double layer capacitors (EDLCs), also referred to as supercapacitors, using thick, ultracompressible graphene-coated carbon nanotube aerogels as electrodes. These electrodes showed a high capacitance in both aqueous and room-temperature ionic liquid (RTIL) electrolytes, achieving between 60 and100 F/g, respectively, with the performance stable over hundreds of charge/discharge cycles and at high rates exceeding 1 V/s. This performance was retained fully under 90% compression of the systems, allowing us to construct cells with high volumetric capacitances of ∼5-18 F/cm(3) in aqueous and RTIL electrolytes, respectively, which are 50-100 times higher than comparable compressible EDLCs (∼0.1 F/cm(3)). Further, the volumetric capacitances approach values reported for compressible pseudocapacitors (∼15-30 F/cm(3)) but without the degraded lifetime and reversibility that typically plague compressible pseudocapacitors. The electrodes demonstrated largely strain-invariant ion transport with no change in capacitance and high-rate performance even at 90% compressive strain. This material serves as an excellent platform for exploring the possibility for use of extremely compressible EDLCs with negligible degradation in capacitance in applications such as electric vehicles and wearable electronics.

Differential sub-cellular processing of single-wall carbon nanotubes via interfacial modifications.

Strategies for cell-specific targeting and delivery of carbon nanotubes have made significant advancements over recent years. However, control of sub-cellular localization, an important criterion for many biomedical applications, remains largely unexplored. In this work, we experimentally demonstrate how different molecules that are used to non-covalently suspend hydrophobic SWCNTs in aqueous conditions also influence cellular processing and localization. We utilized complementary imaging modalities to show that SWCNTs dispersed using the membrane active tri-block copolymer Pluronic® F-127 (PF127) were endocytosed into cells by the millions but eventually escaped endosomes and altered F-actin structures. In contrast, SWCNTs dispersed with the protein bovine serum albumin (BSA) were endocytosed into cells at similarly high levels but remained in the endosomal pathway, ultimately co-registering with endoplasmic reticulum and vesicles. Interestingly, cellular exposure to SWCNTs-BSA in the presence of the endosome disrupter, chloroquine, led to altered F-actin structures that were similar to the alterations induced by cellular exposure to SWCNTs-PF127. These results suggest that PF127 facilitated endosome escape and that SWCNTs might have an energetically favorable interaction with stiff, filamentous structures inside the cell. Thus, our results provide a design principle for non-covalent surface modifications of SWCNTs that do not degrade the desirable, intrinsic SWCNT properties but provide differential trafficking to intracellular compartments for sub-cellular biomedical applications.