Current electrocatalysts for oxygen evolution reaction (OER) are either expensive (such as IrO2, RuO2) or/and exhibit high overpotential as well as sluggish kinetics. This article reports mesoporous earth-abundant iron (Fe)-nitrogen (N) doped carbon electrocatalysts with iron clusters and closely surrounding Fe-N4 active sites. Unique to this work is that the mechanically stable mesoporous carbon-matrix structure (79 nm in pore size) with well-dispersed nitrogen-coordinated Fe single atom-cluster is synthesized via rapid thermal annealing (RTA) within only minutes using a self-assembled bottlebrush block copolymer (BBCP) melamine-formaldehyde resin composite template. The resulting porous structure and domain size can be tuned with the degree of polymerization of the BBCP backbone, which increases the electrochemically active surface area and improves electron transfer and mass transport for an effective OER process. The optimized electrocatalyst shows a required potential of 1.48 V (versus RHE) to obtain the current density of 10 mA/cm2 in 1 M KOH aqueous electrolyte and a small Tafel slope of 55 mV/decade at a given overpotential of 250 mV, which is significantly lower than recently reported earth-abundant electrocatalysts. Importantly, the Fe single-atom nitrogen coordination environment facilitates the surface reconstruction into a highly active oxyhydroxide under OER conditions, as revealed by X-ray photoelectron spectroscopy and in situ Raman spectroscopy, while the atomic clusters boost the single atoms reactive sites to prevent demetalation during the OER process. Density functional theory (DFT) calculations support that the iron nitrogen environment and reconstructed oxyhydroxides are electrocatalytically active sites as the kinetics barrier is largely reduced. This work has opened a new avenue for simple, rapid synthesis of inexpensive, earth-abundant, tailorable, mechanically stable, mesoporous carbon-coordinated single-atom electrocatalysts that can be used for renewable energy production.
Wearable sweat biosensors offer compelling opportunities for improved personal health monitoring and non-invasive measurements of key biomarkers. Inexpensive device fabrication methods are necessary for scalable manufacturing of portable, disposable, and flexible sweat sensors. Furthermore, real-time sweat assessment must be analyzed to validate measurement reliability at various sweating rates. Here, we demonstrate a "smart bandage" microfluidic platform for cortisol detection and continuous glucose monitoring integrated with a synthetic skin. The low-cost, laser-cut microfluidic device is composed of an adhesive-based microchannel and solution-processed electrochemical sensors fabricated from inkjet-printed graphene and silver solutions. An antibody-derived cortisol sensor achieved a limit of detection of 10 pM and included a low-voltage electrowetting valve, validating the microfluidic sensor design under typical physiological conditions. To understand effects of perspiration rate on sensor performance, a synthetic skin was developed using soft lithography to mimic human sweat pores and sweating rates. The enzymatic glucose sensor exhibited a range of 0.2 to 1.0 mM, a limit of detection of 10 µM, and reproducible response curves at flow rates of 2.0 µL min-1 and higher when integrated with the synthetic skin, validating its relevance for human health monitoring. These results demonstrate the potential of using printed microfluidic sweat sensors as a low-cost, real-time, multi-diagnostic device for human health monitoring.
Biosensing Techniques , Sweat , Blood Glucose , Blood Glucose Self-Monitoring , Glucose , Humans , Hydrocortisone , Microfluidics , Reproducibility of Results , Sweating
A series of rubrene derivatives were synthesized and the influence of the side group in enhancing photo-oxidative stability was evaluated. Photo-oxidation half-lives were determined via UV-vis absorption spectroscopy, which revealed thiophene containing derivatives to be the most stable species. The electron affinity of the compounds did not correlate with stability as previously reported in literature. Our work shows that shorter excited-state lifetimes result in increased photo-oxidative stability in these rubrene derivatives. These results confirm that faster relaxation kinetics out-compete the formation of reactive oxygen species that ultimately degrade linear oligoacenes. This report highlights the importance of using molecular design to tune excited-state lifetimes in order to generate more stable oligoacenes.
Carborane-containing poly(dihexylfluorene)s experience drastic solvatochromism in both the solution and solid states, a characteristic that is advantageous for use in environmental and biological sensing applications. Understanding the intrinsic decay mechanisms that give rise to such sensitive emission properties is important for designing responsive sensors. The solution-state photophysical properties of homopolymer, poly(9,9-dihexyl(bisfluorenyl)carborane) (PFCY), and alternating copolymer, poly(9,9-dihexyl-2,7-fluorene- alt-9,9-dihexyl(bisfluorenyl)carborane) (PFCS), were deciphered using steady-state, electrochemical, spectroelectrochemical, and time-resolved spectroscopic methods. From these techniques, it was discovered that following excitation the conjugated fluorene local excited state (LES) donates an electron to the carborane molecule, forming an intramolecular charge transfer (ICT) state between a radical cation on the fluorene moiety and a radical anion on the carborane moiety. From the global analysis of transient absorption data, it was discovered that the rate of electron transfer from the fluorene to the carborane is heavily influenced by solvent polarity and is significantly faster in more polar solvents. Once formed, the ICT state can decay through radiative or nonradiative mechanisms and is more likely to undergo radiative decay in nonpolar solvents, due to an intramolecular restriction of the polar ICT state. This study elucidates the effects that polarity has on the excited-state formation and subsequent decay mechanisms of fluorene-carborane systems, conclusively explaining the solvatochromism and steady-state emission properties exhibited by this system.
Fabrication of detection elements with ultrahigh surface area is essential for improving the sensitivity of analyte detection. Here, we report a direct patterning technique to fabricate three-dimensional CeO2 nanoelectrode arrays for biosensor application over relatively large areas. The fabrication approach, which employs nanoimprint lithography and a CeO2 nanoparticle-based ink, enables the direct, high-throughput patterning of nanostructures and is scalable, integrable, and of low cost. With the convenience of sequential imprinting, multilayered woodpile nanostructures with prescribed numbers of layers were achieved in a "stacked-up" architecture and were successfully fabricated over large areas. To demonstrate application as a biosensor, an enzymatic glucose sensor was developed. The sensitivity of glucose sensors can be enhanced simply by increasing the number of layers, which multiplies surface area while maintaining a constant footprint. The four-layer woodpile nanostructure of CeO2 glucose sensor exhibited enhanced sensitivity (42.8 µA mM-1 cm-2) and good selectivity. This direct imprinting strategy for three-dimensional sensing architectures is potentially extendable to other electroactive materials and other sensing applications.
Biosensing Techniques/methods , Cerium/chemistry , Electrochemical Techniques/methods , Glucose Oxidase/chemistry , Glucose/analysis , Nanoparticles/chemistry
A self-aligned double patterning approach using a dopamine chemistry-inspired coating technique has been developed for the fabrication of sub-20 nm patterns. Poly(methyl methacrylate) (PMMA) films were patterned by nanoimprint lithography to form relief features. A thin layer of polydopamine (PDA) was conformally deposited on the surface of the PMMA pattern sidewalls to form a spacer layer. After etching the surface of the PDA layer from the horizontal surfaces and subsequently removing the PMMA template, free-standing PDA sidewall patterns remained that essentially doubled the original PMMA pattern density with decreased feature dimensions as compared to the initial PMMA template structures. The critical dimension of the PDA patterns can be tuned to â¼20 nm by controlling the PDA deposition conditions and further reduced to â¼13 nm by thermal carbonization of the PDA. Both simple lines and more complex rhombic ring features were fabricated by this technique to demonstrate its capacity for replicating arbitrary patterns. This work represents a simple and scalable strategy for preparing well-defined nanostructures with feature sizes usually only accessible via complex leading edge lithographic methods.
Three-dimensional (3D) nanofabrication using the directed self-assembly of block copolymers (BCPs) holds great promise for the nanoscale device fabrication and integration into 3D architectures over large areas with high element densities. In this work, a robust platform is developed for building 3D BCP architectures with tailored functionality using 3D micron-scale woodpile structures (WPSs), fabricated by a multiphoton polymerization technique. By completely filling the spaces of the WPSs and using the interactions of the blocks of the BCPs with the struts of the WPS, well-developed 3D nanoscopic morphologies are produced. Metal ion complexation with one block of the copolymer affords a convenient stain to highlight one of the microdomains of the copolymer for electron microscopy studies but also, with the reduction of the complexing salt to the corresponding metal, a simple strategy is shown to produce 3D constructs with nanoscopic domain resolution.
We demonstrate the generation of block copolymer (BCP) line patterns oriented orthogonal to a very small (minimal) topographic trench pattern over arbitrarily large areas using solvent-vapor annealing. Increasing the thickness of BCP films induced an orthogonal alignment of the BCP cylindrical microdomains, where full orthogonal alignment of the cylindrical microdomains with respect to the trench direction was obtained at a film thickness corresponding to 1.70 L0. A capillary flow of the solvent across the trenches was a critical factor in the alignment of the cylindrical microdomains. Grazing incidence small-angle X-ray scattering was used to determine the orientation function of the microdomains, with a value of 0.997 being found reflecting a nearly perfect orientation. This approach to produce orthogonally aligned BCP line patterns could be extended to the nanomanufacturing and fabrication of hierarchical nanostructures.
The trend of device downscaling drives a corresponding need for power source miniaturization. Though numerous microfabrication methods lead to successful creation of submillimeter-scale electrodes, scalable approaches that provide cost-effective nanoscale resolution for energy storage devices such as on-chip batteries remain elusive. Here, we report nanoimprint lithography (NIL) as a direct patterning technique to fabricate high-performance TiO2 nanoelectrode arrays for lithium-ion batteries (LIBs) over relatively large areas. The critical electrode dimension is below 200 nm, which enables the structure to possess favorable rate capability even under discharging current densities as high as 5000 mA g-1. In addition, by sequential imprinting, electrodes with three-dimensional (3D) woodpile architecture were readily made in a "stack-up" manner. The height of architecture can be easily controlled by the number of stacked layers while maintaining nearly constant surface-to-volume ratios. The result is a proportional increase of areal capacity with the number of layers. The structure-processing combination leads to efficient use of the material, and the resultant specific capacity (250.9 mAh g-1) is among the highest reported. This work provides a simple yet effective strategy to fabricate nanobatteries and can be potentially extended to other electroactive materials.
A simple and robust method has been developed for the generation of macroscopically ordered hexagonal arrays from the directed self-assembly (DSA) of cylinder-forming block copolymers (BCPs) based on minimal trench patterns with solvent vapor annealing. The use of minimal trench patterns allows us to probe the guided hexagonal arrays of cylindrical microdomains using grazing incidence small angle X-ray scattering (GISAXS), where the sample stage is rotated on the basis of the six-fold symmetry of a hexagonal system. It is found that the (10) planes of hexagonal arrays of cylindrical microdomains are oriented parallel to the underlying trench direction over macroscopic length scales (â¼1 × 1 cm2). However, there are misorientations of the hexagonal arrays with short-range ordering. GISAXS patterns show that the hexagonal arrays on the minimal trench pattern are distorted, deviating from a perfect hexagonal lattice. This distortion has been attributed to the absence of topographic constraints in the unconfined direction on the 1-D minimal trench pattern. Also, the frustration of BCP microdomains, arising from the incommensurability between the trench pitch and natural period of the BCP at the base of the trench, influences the distortion of the hexagonal arrays.
Regioregular poly[(3-hexylthiophene)-ran-(3-undecenylthiophene)] (pP3HT) and vinyl terminated poly(3-hexylthiophene) (xP3HT) were synthesized by the McCullough method and surface grafted to thiol modified silicon dioxide wafers using thiol-ene click chemistry. Utilizing this method, semiconducting, solvent impervious films were easily generated. Thiol-ene click chemistry is convenient for film stabilization in electronics because it does not produce side products that could be inimical to charge transport in the active layer. It was found through grazing incidence wide-angle X-ray scattering (GIWAXS) that there is no change in microstructure between as-spun films and thiol-ene grafted films, while there was a change after the thiol-ene grafted film was exposed to solvent. Organic field-effect transistors (oFETs) were fabricated from grafted films that had been swelled with chloroform, and these devices had mobilities on the order of 10-6 cm2 V-1 s-1, which are consistent with poly(thiophene) monolayer devices.
Hydration is central to mitigating surface fouling by oil and microorganisms. Immobilization of hydrophilic polymers on surfaces promotes retention of water and a reduction of direct interactions with potential foulants. While conventional surface modification techniques are surface-specific, mussel-inspired adhesives based on dopamine effectively coat many types of surfaces and thus hold potential as a universal solution to surface modification. Here, we describe a facile, one-step surface modification strategy that affords hydrophilic, and underwater superoleophobic, coatings by the simultaneous deposition of polydopamine (PDA) with poly(methacryloyloxyethyl phosphorylcholine) (polyMPC). The resultant composite coating features enhanced hydrophilicity (i.e., water contact angle of ~10° in air) and antifouling performance relative to PDA coatings. PolyMPC affords control over coating thickness and surface roughness, and results in a nearly 10 fold reduction in Escherichia coli adhesion relative to unmodified glass. The substrate-independent nature of PDA coatings further promotes facile surface modification without tedious surface pretreatment, and offers a robust template for codepositing polyMPC to enhance biocompatibility, hydrophilicity and fouling resistance.
We demonstrate that a minimal topographic pattern with a confinement depth (D) much less than the domain spacing of block copolymers (L0) can be used to achieve highly ordered hexagonal arrays or unidirectionally aligned line patterns over large areas. Cylinder-forming poly(styrene-b-ethylene oxide) (PS-b-PEO) thin films were prepared on a series of minimal single trench patterns with different widths (W) and D. Upon thermal annealing, hexagonal arrays of cylindrical microdomains propagated away from the edges of a single trench, providing insight into the minimum pitch (P) of the trench necessary to fully order hexagonal arrays. The confinement trench D of 0.30L0, the W in the range of 1.26L0 to 2.16L0, and the P as long as 18.84L0 were found to be effective for the generation of laterally ordered hexagonal arrays with the density amplification up by a factor of 17, within the minimally patterned trench surfaces of 100 µm by 100 µm. Furthermore, we produced line patterns of cylindrical microdomains by using solvent vapor annealing on the minimally patterned trench surfaces. However, highly aligned line patterns could be achieved only on the patterned surface with P = 5.75L0, W = 1.26L0, and D = 0.30L0 because the influence of the minimally patterned trench surface on the lateral ordering decreased as the P and W increase at the fixed D, resulting in poor ordering. These findings suggest that the minimal topographic pattern is more effective in guiding hexagonal arrays than in guiding line patterns.
The fabrication and advanced function of large area biomimetic superhydrophobic surfaces (SHS) and slippery lubricant-infused porous surfaces (SLIPS) are reported. The use of roll-to-roll nanoimprinting techniques enabled the continuous fabrication of SHS and SLIPS based on hierarchically wrinkled surfaces. Perfluoropolyether hybrid molds were used as flexible molds for roll-to-roll imprinting into a newly designed thiol-ene based photopolymer resin coated on flexible polyethylene terephthalate films. The patterned surfaces exhibit feasible superhydrophobicity with a water contact angle around 160° without any further surface modification. The SHS can be easily converted into SLIPS by roll-to-roll coating of a fluorinated lubricant, and these surfaces have outstanding repellence to a variety of liquids. Furthermore, both SHS and SLIPS display antibiofouling properties when challenged with Escherichia coli K12 MG1655. The current article describes the transformation of artificial biomimetic structures from small, lab-scale coupons to low-cost, large area platforms.
Biomimetic Materials/chemistry , Lubricants/chemistry , Nanostructures/chemistry , Hydrophobic and Hydrophilic Interactions , Surface Properties , Water/chemistry
A pragmatic method to deposit silver nanoparticles on polydopamine-coated nanoimprinted pillars for use as surface-enhanced Raman scattering (SERS) substrates was developed. Pillar arrays consisting of poly(methyl methacrylate) (PMMA) that ranged in diameter from 300 to 500 nm were fabricated using nanoimprint lithography. The arrays had periodicities from 0.6 to 4.0 µm. A polydopamine layer was coated on the pillars in order to facilitate the reduction of silver ions to create silver nucleation sites during the electroless deposition of sliver nanoparticles. The size and density of silver nanoparticles were controlled by adjusting the growth time for the optimization of the SERS performance. The size of the surface-adhered nanoparticles ranged between 75 and 175 nm, and the average particle density was â¼30 particles per µm(2). These functionalized arrays had a high sensitivity and excellent signal reproducibility for the SERS-based detection of 4-methoxybenzoic acid. The substrates were also able to allow the SERS-based differentiation of three types of bacteriophages (λ, T3, and T7).
Metal Nanoparticles/chemistry , Nanostructures/chemistry , Nanotechnology/methods , Silver/chemistry , Spectrum Analysis, Raman/instrumentation , Bacteriophages/chemistry , Bacteriophages/isolation & purification , Hydroxybenzoate Ethers/analysis , Surface Properties
Research in microfluidic biosensors has led to dramatic improvements in sensitivities. Very few examples of these devices have been commercially successful, keeping this methodology out of the hands of potential users. In this study, we developed a method to fabricate a flexible microfluidic device containing electrowetting valves and electrochemical transduction. The device was designed to be amenable to a roll-to-roll manufacturing system, allowing a low manufacturing cost. Microchannels with high fidelity were structured on a PET film using UV-NanoImprint Lithography (UV-NIL). The electrodes were inkjet-printed and photonically sintered on second flexible PET film. The film containing electrodes was bonded directly to the channel-containing layer to form sealed fluidic device. Actuation of the multivalve system with food dye in PBS buffer was performed to demonstrate automated fluid delivery. The device was then used to detect Salmonella in a liquid sample.
Electrochemical Techniques , Microfluidic Analytical Techniques , Nanotechnology , Salmonella enterica/isolation & purification , Ultraviolet Rays , Electrochemical Techniques/instrumentation , Electrodes , Ink , Microfluidic Analytical Techniques/instrumentation , Nanotechnology/instrumentation , Polyethylene Terephthalates/chemistry , Printing/instrumentation , Printing/methods , Wettability
The most efficient architecture for achieving high donor/acceptor interfacial area in organic photovoltaics (OPVs) would employ arrays of vertically interdigitated p- and n- type semiconductor nanopillars (NPs). Such morphology could have an advantage in bulk heterojunction systems; however, precise control of the dimension morphology in a crystalline, interpenetrating architecture has not yet been realized. Here we present a simple, yet facile, crystallization technique for the growth of vertically oriented NPs utilizing a modified thermal evaporation technique that hinges on a fast deposition rate, short substrate-source distance, and ballistic mass transport. A broad range of organic semiconductor materials is beneficial from the technique to generate NP geometries. Moreover, this technique can also be generalized to various substrates, namely, graphene, PEDOT-PSS, ZnO, CuI, MoO3, and MoS2. The advantage of the NP architecture over the conventional thin film counterpart is demonstrated with an increase of power conversion efficiency of 32% in photovoltaics. This technique will advance the knowledge of organic semiconductor crystallization and create opportunities for the fabrication and processing of NPs for applications that include solar cells, charge storage devices, sensors, and vertical transistors.
Charge-modulated optical spectroscopy is used to achieve dynamic two-dimensional mapping of the charge-carrier distribution in poly(3-hexylthiophene) thin-film transistors. The resulting in-channel distributions evolve from uniformly symmetric to asymmetrically saturated as the devices are increasingly biased. Furthermore, physical, chemical, and electrical defects are spatially resolved in cases where their presence is not obvious from the device performance.
Thiol-ene chemistry is used for the surface grafting of vinyl-functionalized poly(fluorene) derivatives onto substrates containing free surface thiol groups. The grafting reaction proceeds in a matter of minutes under UV irradiation without photoinitiator, and the resulting surface-bound, solvent-impervious conjugated polymers retain their characteristic optoelectronic properties. End-chain grafted poly(fluorene)s reach greater surface densities than their side-chain grafted counterparts and show less blue-shifting of photoluminescence upon grafting, suggesting that chain end-grafted conjugated polymers experience less disruption of their extended conjugation and adopt a more brush-like surface conformation. Surface grafted poly(fluorene)s showed facile photopatterning, and thin film transistors with semiconducting polymers directly grafted to the dielectric layer showed performances directly comparable to conventional self-assembled layers of performance-improving alkylsilanes.
