Organic electrochemical transistors (OECTs) have been previously demonstrated in the sensing of cells and metabolic products. In this study, we report a novel approach on the universal detection of ...bacterial contamination in home liquid goods through the utilization of a microfluidic flow cell that has been integrated with OECT technology. The flow-cell device has been developed for the purpose of detecting minimal concentration (<inline-formula> <tex-math notation="LaTeX">\sim 10^{{3}} </tex-math></inline-formula> CFU/mL) of several bacterium types Escherichia coli (E. Coli), Pseudomonas fluorescens (P. flu), and Staphylococcus aureus (S. au) in various commercial household liquid product blends (see Air Febreze, Tide, and Old SPICE Bodywash). This process can be completed in a testing period of 1 h or less and does not require amplification or a designated binding agent. The flow-cell configuration uses a microporous filter membrane (Au-coated polyethylene terephthalate (PETE), 0.2-<inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula> pore diameter) designed to concentrate the bacteria within the chamber. The membrane also functions as a gate electrode for the operation of OECT. The presence of bacteria on the gate filter membrane leads to an increase in the total effective gate voltage (<inline-formula> <tex-math notation="LaTeX">{V}_{\text {eff}} </tex-math></inline-formula>), which in turn causes a decrease in the OECT source-drain channel current (<inline-formula> <tex-math notation="LaTeX">{I}_{\text {DS}} </tex-math></inline-formula>). Based on the shift of <inline-formula> <tex-math notation="LaTeX">{I}_{\text {DS}} </tex-math></inline-formula>, the OECT provides good discrimination between bacteria and sterile solutions (0.4-mA difference). The OECT transconductance (<inline-formula> <tex-math notation="LaTeX">{g}_{\text {m}} </tex-math></inline-formula>) exhibits a maximum value at different levels of <inline-formula> <tex-math notation="LaTeX">{V}_{\text {GS}} </tex-math></inline-formula> for sterile and bacteria solutions. This approach exhibits potential for biosensing systems that will enable real-time monitoring at the production line.
Naturally occurring biomolecules have increasingly found applications in organic electronics as a low cost, performance‐enhancing, environmentally safe alternative. Previous devices, which ...incorporated DNA in organic light emitting diodes (OLEDs), resulted in significant improvements in performance. In this work, nucleobases (NBs), constituents of DNA and RNA polymers, are investigated for integration into OLEDs. NB small molecules form excellent thin films by low‐temperature evaporation, enabling seamless integration into vacuum deposited OLED fabrication. Thin film properties of adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U) are investigated. Next, their incorporation as electron‐blocking (EBL) and hole‐blocking layers (HBL) in phosphorescent OLEDs is explored. NBs affect OLED performance through charge transport control, following their electron affinity trend: G < A < C < T < U. G and A have lower electron affinity (1.8–2.2 eV), blocking electrons but allowing hole transport. C, T, and U have higher electron affinities (2.6–3.0 eV), transporting electrons and blocking hole transport. A‐EBL‐based OLEDs achieve current and external quantum efficiencies of 52 cd A−1 and 14.3%, a ca. 50% performance increase over the baseline device with conventional EBL. The combination of enhanced performance, wide diversity of material properties, simplicity of use, and reduced cost indicate the promise of nucleobases for future OLED development.
Nucleic acid bases show promise as biomaterials for OLEDs due to a diverse range of properties. Guanine and adenine thin films are very good hole‐transporting materials while cytosine, thymine, and uracil are efficient electron‐transporting materials. The confluence of their diverse electronic properties, simple thin‐film fabrication, and renewable origins lays the groundwork for further development of bioelectronic devices.
Versatile electrowetting (EW) arrays were fabricated with small to large pixels, on fixed glass and flexible polymer substrates, for smart window applications. EW prototypes on glass substrates were ...constructed with pixel sizes ranging from 50μm×150μm to 2mm×2mm. The dosing of the array with colored oil was achieved by dip coating the substrate through an oil film suspended on a water bath. The arrays can be driven by either DC or AC voltage. Optical transmission of the prototypes can be modulated from ∼5% to >70% with a relatively low applied voltage of ∼15V. The switching speed of the prototype depends on oil properties and cell size, typically ∼10ms for 300μm×900μm pixel cells. Flexible color EW array prototypes have been fabricated on polymer polyethylene terephthalate (PET) substrates, which can be switched reversibly by applying a relatively low voltage difference between the water and bottom electrode. The EW specifications are maintained even when the prototype is mechanically flexed. These results indicate the promise of EW technology for smart window applications.
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•Electrowetting is used in the smart windows application.•Arrays with different pixel sizes are fabricated.•Optical transmission of the prototypes can be modulated from ∼5% to 70% with a low applied voltage.•The switching speed of the prototype is ∼10ms.•Flexible arrays have been fabricated and the EW operation is maintained when the prototype is mechanically flexed.
Electrospun polyacrylonitrile (PAN) based carbon nanofibers (CNFs) have attracted intense attention due to their easy processing, high carbon yield, and robust mechanical properties. In this work, a ...CNF modified glassy carbon (GC) electrode that was coated with Nafion polymer was evaluated as a new electrode material for the simultaneous determination of trace levels of heavy metal ions by anodic stripping voltammetry (ASV). Pb2+ and Cd2+ were used as a representative system for this initial study. Well-defined stripping voltammograms were obtained when Pb2+ and Cd2+ were determined individually and then simultaneously in a mixture. Compared to a bare GC electrode, the CNF/Nafion modified GC (CNF/Nafion/GC) electrode improved the sensitivity for lead detection by 8-fold. The interface properties of the CNF/Nafion/GC were characterized by electrochemical impedance spectroscopy (EIS), which showed the importance of the ratio of CNF/Nafion on electrode performance. Under optimized conditions, the detection limits are 0.9 and 1.5 nM for Pb2+ and Cd2+, respectively.
The first self-immolative polymer (SIP) nanofiber membrane is demonstrated in this report, in which the immolation can be triggered by external stimulus. Electrospun SIP/polyacrylonitrile (PAN) ...fibers provide depolymerization that is ∼25 times quicker and more responsive (i.e., immolation) than that of a cast film in the triggering condition. Depolymerization of SIP in the SIP/PAN blended fiber membrane results in the transition of the surface properties from hydrophobic (∼110°) to hygroscopic (∼0°). Triggered release of encapsulated functional molecules was demonstrated using coaxially electrospun fiber membrane made of a SIP/PAN blend sheath and polyvinylpyrrolidone/dye core. Coaxial fibers with the SIP/PAN sheath provide minimal release of the encapsulated material in nontriggering solution, while it releases the encapsulated material instantly when the triggering condition is met. Its versatility has been strengthened compared to that of non-SIP coaxial fibers that provide no triggering reaction by external stimulus.
A review is presented of the fabrication, operation, and applications of rare-earth-doped GaN electroluminescent devices (ELDs). GaN:RE ELDs emit light due to impact excitation of the rare earth (RE) ...ions by hot carriers followed by radiative RE relaxation. By appropriately choosing the RE dopant, narrow linewidth emission can be obtained at selected wavelengths from the ultraviolet to the infrared. The deposition of GaN:RE layers is carried out by solid-source molecular beam epitaxy, and a plasma N/sub 2/ source. Growth mechanisms and optimization of the GaN layers for RE emission are discussed based on RE concentration, growth temperature, and V/III ratio. The fabrication processes and electrical models for both dc- and ac-biased devices are discussed, along with techniques for multicolor integration. Visible emission at red, green, and blue wavelengths from GaN doped with Eu, Er, and Tm has led to the development of flat-panel display (FPD) devices. The brightness characteristics of thick dielectric EL (TDEL) display devices are reviewed as a function of bias, frequency, and time. High contrast TDEL devices using a black dielectric are presented. The fabrication and operation of FPD prototypes are described. Infrared emission at 1.5 /spl mu/m from GaN:Er ELDs has been applied to optical telecommunications devices. The fabrication of GaN channel waveguides by inductively coupled plasma etching is also reviewed, along with waveguide optical characterization.
Organic light-emitting diodes (OLED) were fabricated on flexible and transparent reconstituted cellulose obtained from wood pulp. Cellulose is naturally available, abundant, and biodegradable and ...offers a unique substrate alternative for the fabrication of flexible OLEDs. Transparent cellulose material was formed by dissolution of cellulose in an organic solvent (dimethyl acetamide) at elevated temperature (165 °C) in the presence of a salt (LiCl). The optical transmission of 40-μm thick transparent cellulose sheet averaged 85% over the visible spectrum. High brightness and high efficiency thin film OLEDs were fabricated on transparent cellulose films using phosphorescent Ir(ppy)3 as the emitter material. The OLEDs achieved current and luminous emission efficiencies as high as 47 cd A−1 and 20 lm W−1, respectively, and a maximum brightness of 10 000 cd m−2.
The integration of organic light emitting diodes (OLEDs) as excitation light sources for quantum dot-based fluorescent lateral flow immunoassay systems (LFIA) was investigated. This approach has the ...potential to deliver a sensitive visible detection scheme for low-cost, disposable lab-on-chip point-of-care (POC) diagnosis system. Thin film phosphorescent green OLEDs fabricated on plastic substrates were integrated on-chip to excite the test line of a quantum dot-based LFIA (QD-LFIA). OLEDs were fabricated by sequential deposition of organic thin films (total of ~100nm) onto ITO-coated PET substrates. CdSe/ZnS QDs emitting at 655nm and Au nanoparticles (NP – 10nm size) conjugated antibodies were used for the fluorescence QD-LFIA and conventional reflection-mode Au NP-LFIA, respectively. Thin plastic color light filters were integrated for filtering the excitation light source and, thereby, increasing the contrast of the emitted light for optimized visual detection. Integration of the OLED and color filters with the analytical membrane was achieved using adhesive techniques facilitated by the planar nature of the layers, which suggests possible large scale manufacturing using roll-to-roll processing. Gray scale analysis from digital images captured with a digital camera was used to quantify the visual sensitivity. The signal intensity, signal-to-noise ratio (SNR) and the limit of detection (LOD) of OLED integrated QD-LFIAs were compared to Au NP LFIAs. OLED QD-LFIA exhibited superior performance in all signal aspects: 7–8× higher signal intensity and SNR, and a 7× lower LOD of 3nM (measured at S/N=3). These results demonstrate the potential of OLED-integrated in LFIA devices for obtaining sensitive, fast and low-cost POC diagnostics.
•OLEDs were integrated as excitation for fluorescent lateral flow immunoassay.•Integration approach and fabrication method are described.•Photoemission from fluorescent quantum dot conjugated antibodies was measured.•Limit of detection of 3nM was obtained, 7× lower than conventional reflection LFIA.
Electrospun nanofibers are promising drug delivery systems for transdermal applications with a release rate of the drug depending on the host polymer used. However, it is still a challenge to control ...(i.e., reduce) the release rate for hydrophilic drugs in order to provide long-term sustained release. In this study, we aimed to produce controlled release nanofibers to achieve long term drug release for transdermal applications. Pramipexole, which requires multiple doses per day, was selected as a hydrophilic model drug molecule and was electrospun with hydrophobic polycaprolactone polymer. To prevent burst release of the drug and provide a long-term release profile, nanofibers were coated with Parylene C or N using a chemical vapor deposition process. The effective thickness of nanofibers increased with the amount of Parylene coating. Parylene coating also enhanced the mechanical properties and hydrophobicity but decreased the bioadhesion values. Drug release and diffusion studies showed that Parylene coating successfully prevents drug burst release. Uncoated nanofibers completely released pramipexole within 12 h. A relatively low amount of Parylene N and C coating provided 81% and 52% drug release over 10 days, while increased Parylene N and C coating resulted in 27% and 12.6% drug release over a 30-day period, respectively. Parylene coating process offers the possibility of long-term controlled release kinetics including hydrophilic drugs.
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•Chemical vapor deposition provides many advantages on nanofiber coating.•Parylene coating of nanofibers improved mechanical properties.•The thickness of parylene coating plays important role on nanofiber characteristics.•Burst release of hydrophilic drug molecules can be prevented by hydrophobic parylene coating.
Photocatalytic self-cleaning textile fibers have been created using coaxial electrospinning. This is accomplished by electrospinning cellulose acetate as the core phase and a dispersion of ...nanocrystalline TiO2, a well-known photocatalyst, in the sheath phase. A simple deacetylation step after the initial electrospinning yields self-cleaning textile fibers. Self-cleaning activity is exhibited at moderate power densities in indoor lighting conditions. Nanofibers created from coaxial electrospinning outperform TiO2 surface-loaded nanofibers obtained by conventional electrospinning. Surface-loaded fibers degrade blue dye stains only to a minimum of 20% of the initial concentration, whereas fibers created by coaxial electrospinning fully degrade stains (in 7−8 h).
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