Hydrophobic-Hydrophilic Block Copolymer Mediated Tuning of Halide Perovskite Photosensitive Device Stability and Efficiency.

The polymer additive strategy provides a facile and cost-effective way for passivating defects and trap sites at the grain boundaries and interfaces and acting as a barrier against the external degradation factors in perovskite-based devices. However, limited literature exists discussing the integration of hydrophobic and hydrophilic polymer additives in the form of a copolymer within the perovskite films. The inherent difference in the chemical structure of these polymers and their interaction with perovskite components and the environment leads to critical differences in the respective polymer-perovskite films. The current work utilizes both homopolymer and copolymer strategies to understand the effect of polystyrene (PS) and polyethylene glycol (PEG), two common commodity polymers, over the physicochemical and electro-optical properties of the as-fabricated devices and the distribution of polymer chains across the depth of perovskite films. The hydrophobic PS integrated perovskite devices PS-MAPbI3, 36 PS-b-1.4-PEG-MAPbI3, and 21.5 PS-b-20-PEG-MAPbI3 outperform hydrophilic PEG-MAPbI3 and pristine MAPbI3 devices and exhibit higher photocurrent, lower dark currents, and greater stability. A critical difference is also observed in the stability of devices, where rapid decay of performance is observed in the pristine MAPbI3 films. The deterioration in performance is highly limited for hydrophobic polymer-MAPbI3 films as they maintain 80% of their initial performance.

Au-Pt-Ni nanochains as dopamine catalysts: role of elements and their spatial distribution.

Multi-element materials can improve biosensing ability as each element can catalyze different steps in a reaction pathway. By combining Pt and Ni on self-assembled 1D gold nanochains and controlling their spatial distribution, a detailed understanding of each element's role in dopamine oxidation is developed. In addition, the developed synthesis process provides a simple way to fabricate multi-element composites for electrocatalytic applications based on electrical double-layer formation on the surface of charged nanoparticles. The performance parameters of the catalyst, such as its sensitivity, limit of detection, and range of operation for dopamine sensing, are optimized by changing the relative ratios of Pt : Ni and the morphology of the Pt and Ni domains, using the developed understanding. The morphology of the domains also affects the oxidation state of Ni, which is crucial to the performance of the electrocatalyst.

Soft Polymer-Organolead Halide Perovskite Films for Highly Stretchable and Durable Photodetectors with Pt-Au Nanochain-Based Electrodes.

The rigid and brittle nature of methylammonium lead iodide (MAPbI3) polycrystalline films limits their application in stretchable devices due to rapid deterioration in performance on cycling. By incorporation of polymer chains in the MAPbI3 films, a strategy to alter the mechanical modulus and the viscoelastic nature of the films has been developed. Combining this with flexible nanochain electrodes, highly stretchable and stable perovskite devices have been fabricated. The resultant polymer-MAPbI3 photodetector exhibits ultralow dark currents (∼10-11 A) and high light switching ratios (∼103) and maintains 75% of performance after 30 days. The viscoelastic nature and lower modulus of the polymer improve the energy dissipation in the polymer-MAPbI3 devices; as a result, they maintain 52% of the device performance after 10000 stretching cycles at 50% strain. The difference in the mechanical behavior is clearly observed in the failure mode of the two films. While rapid catastrophic cracking is observed in MAPbI3 films, the intensity and size of such crack formation are highly limited in polymer-MAPbI3 films, which prevent their failure.

Management of Left Staghorn Calculus With Colorenal Fistula.

Fistula formation between the kidney and the colon is a rare occurrence. Colorenal fistulas have been reported after renal cryoablation, calculous pyonephrosis, and renal cell carcinoma. Fistula formation is reported in as many as 35% of patients with Crohn's disease. Crohn's-related urinary fistulas may include enterovesical, enteroureteral, rectourethral, urethrocutaneous, and entero-urachal fistulas. Here, we report a rare case of a patient who was found to have a left colorenal fistula in the setting of a left staghorn calculus and recurrent urinary tract infections with a question about the eventual definitive management of the patient.

Nanoscale Architecture of Polymer-Organolead Halide Perovskite Films and the Effect of Polymer Chain Mobility on Device Performance.

The integration of polymer chains with organolead halide perovskite (MAPbI3) films, leading to enhanced stability and electro-optical performance, is critically affected by the molecular weight of chains. The molecular weight determines the mobility and volume of the chains, which affects the crystallization kinetics and, hence, perovskite grain size. The insulating nature of the chains is another critical factor that affects both ion migration and conduction of electronic charge. The combined effect of these factors leads to optimal performance with the use of medium-length chains. A simple model integrating the two effects accurately fits the response of the polymer-perovskite composite. Further characterization results show that the polymer-perovskite films have a three-layer architecture consisting of nanoscale polymer-rich top and bottom layers. These combined results show that the optimization of performance in polymer-perovskite devices depends critically on the size of the chains due to their multiple effects on the perovskite matrix.

Polymer-Controlled Growth and Wrapping of Perovskite Single Crystals Leading to Better Device Stability and Performance.

A commodity-scale polymer is used for controlling the nucleation and growth of single crystals of organolead halide perovskite. The polymer [polystyrene (PS)] cross-links and strongly interacts with PbI2 and MAI (MAPbI3 perovskite precursors) resulting in the control of the crystallization process. The PS concentration modulates the nucleation time, crystal size, and the number of perovskite single crystals. In addition, the PS-based MAPbI3 crystals show an enhanced performance as well as improved thermal and environmental stability. Specifically, the PS-MAPbI3 crystals show 3 times higher photocurrent than plain MAPbI3 crystals and maintain a stable structure for more than 50 days (1200 h) under continuous 0.1 sun illumination in the air with a relative humidity of 40-45%. The improved performance and stability are attributed to the direct interaction between the PS and perovskite, which greatly reduces the ion migration, defect traps, and charge recombination and improves the carrier mobility and lifetime.

Fluoride-capped nanoceria as a highly efficient oxidase-mimicking nanozyme: inhibiting product adsorption and increasing oxygen vacancies.

Nanozymes aim to mimic enzyme activities using nanomaterials. Nanoceria (CeO2 nanoparticles) is an important model nanozyme for its rich redox chemistry. In particular, its oxidase-like activity allows oxidation reactions without the need of unstable and toxic H2O2. Fluoride can significantly improve its oxidase-like activity, and this work aims to understand the mechanism of fluoride-promoted catalysis. First, fluoride can adsorb on CeO2 tighter than other halides, but not as strong as phosphate as characterized by isothermal titration calorimetry (ITC). FT-IR spectroscopy indicates adsorption of fluoride likely via exchange with surface hydroxide groups. Fluoride capping inverses the surface charge of CeO2, facilitating desorption of the ABTS oxidation product, significantly increasing the turnover number. The Raman, EPR and XPS spectroscopy results demonstrate that the concentration of Ce3+ and the accompanying oxygen vacancy significantly increased upon adding F-, which can explain the enhanced catalytic activity. Finally, the electron transfer properties of fluoride-capped CeO2 were more efficient than that of the bare CeO2 as determined by a direct electrochemical measurement on a glass carbon electrode. This study has provided new insight into nanoceria, and can also further confirm the role of nanoceria as a model for engineering the surface of nanozymes.

Magnetic nano-nets for capture of microbes in solution based on physical contact.

Self-assembly of Au nanoparticles with Fe ions is used to develop magnetic nano-nets similar to fishing nets for capture and removal of microbes in aqueous medium. The nano-nets have a high aspect ratio, span microns in length with openings of 80-300 nm. This allows them to sample the liquid medium even at low volume fraction and also entrap the microbes in the solution. The nets and the trapped microbes can be effectively pulled from the solution by using an off the shelf magnet. Since the capture is based on physical contact, the nano-nets overcome the ability of the microbes to develop resistance to the cytotoxic effects of chemical compounds and nanomaterials. Using the nano-nets an absolute inactivation of 0.9 is achieved in 5 min. in a non-deaerated solution with Escherichia coli (E. coli). Further the removal of the nano-nets along with the captured microbes also predominantly eliminates the nanomaterial from the aqueous medium for future use.

Long-acting intramuscular ACTH stimulation test for the diagnosis of secondary adrenal insufficiency in children.

Background The diagnosis of adrenal insufficiency (AI) is based on the basal and stimulated levels of serum cortisol in response to the short Synacthen test (SST). In patients with secondary AI (SAI) due to hypothalamic-pituitary-adrenal (HPA) axis defects, the SST has been validated against the insulin tolerance test (ITT), which is the gold standard. However, injection Synacthen is not easily available in some countries, and endocrinologists often use Acton-Prolongatum (intramuscular [IM] long-acting adrenocorticotropic hormone [ACTH]) in place of Synacthen. There are no studies validating the use of IM-ACTH in children with suspected AI. We evaluated the diagnostic value of the IM-ACTH test against the ITT for the diagnosis of SAI in children. Methods All children with suspected growth hormone deficiency (GHD) undergoing a routine ITT were evaluated using the IM-ACTH test within 1 week. Results Forty-eight patients (36 boys/12 girls, age range: 5-14 years) were evaluated using both the ITT and the IM-ACTH test. Twenty-eight patients had a normal cortisol response (≥18 µg/dL, 500 nmol/L) in the ITT and 20 had low values. In patients with a normal cortisol response on the ITT, the peak value obtained after the IM-ACTH test was higher than that on the ITT (28.7 µg/dL [± 8.8] vs. 23.8 µg/dL [± 4.54], respectively; p=0.0012). Compared to the ITT, the sensitivity and specificity of the IM-ACTH test for the diagnosis of SAI at cortisol cut-offs <18 µg/dL (500 nmol/L) and <22 µg/dL (600 nmol/L) were 57.1% and 92.8%, and 100% and 73.5%, respectively. Conclusions A peak cortisol value <18 µg/dL on the IM-ACTH test is highly suggestive of SAI, whereas a value >22 µg/dL rules out SAI.

Self-Powered Photodetector Based on Electric-Field-Induced Effects in MAPbI3 Perovskite with Improved Stability.

A monolith photodetector is presented that utilizes the material properties of MAPbI3 perovskite for self-powered operation and achieves improved stability by composting with polystyrene. The self-powered operation makes this device suitable for remote applications and in smart systems. Improved stability of more than 20 days, with performance maintained by over 80% under ambient conditions, is achieved by incorporating polystyrene without additional fabrication steps. A plain MAPbI3 device in comparison shows a performance degradation of 70-85% within 4 days of operation. The incorporation of polystyrene also improves the current detectivity of the device by over 70 times compared to plain perovskite.

A Light Harvesting, Self-Powered Monolith Tactile Sensor Based on Electric Field Induced Effects in MAPbI3 Perovskite.

Organolead trihalide perovskite MAPbI3 shows a distinctive combination of properties such as being ferroelectric and semiconducting, with ion migration effects under poling by electric fields. The combination of its ferroelectric and semiconducting nature is used to make a light harvesting, self-powered tactile sensor. This sensor interfaces ZnO nanosheets as a pressure-sensitive drain on the MAPbI3 film and once poled is operational for at least 72 h with just light illumination. The sensor is monolithic in structure, has linear response till 76 kPa, and is able to operate continuously as the energy harvesting mechanism is decoupled from its pressure sensing mechanism. It has a sensitivity of 0.57 kPa-1 , which can be modulated by the strength of the poling field. The understanding of these effects in perovskite materials and their application in power source free devices are of significance to a wide array of fields where these materials are being researched and applied.

Bio-inspired interlocking random 3-D structures for tactile and thermal sensing.

Hierarchical nanostructures are tailored and used routinely in nature to accomplish tasks with high performance. Their formation in nature is accomplished without the use of any patterning process. Inspired by the performance of such structures, we have combined 2-D nanosheets with 1-D nanorods for functioning as electronic skin. These structures made in high density without any patterning process can be easily assembled over large areas. They can sense pressures as low as 0.4 Pa, with a response time in milliseconds. Further, these structures can also detect temperature changes with a non-linear response in the 298-400 K range, which is similar to skins perception of thermal stimuli. We illustrate this effect by showing that the device can differentiate between two 10 µl water droplets which are at room temperature and 323 K respectively.

Nanoparticle chains as electrochemical sensors and electrodes.

With the advances in the field of nanotechnology, significant progress is being achieved in fabrication of nanoscale electrodes (nanoelectrodes) and using their properties for applications in multiple fields. Compared with conventional macroscale electrodes, nanoelectrodes offer many advantages that arise from their limited size. Self-assembled chains of metal nanoparticles in particular have drawn interest for fabrication of nanoelectrodes because of their unique electrical properties and geometric morphology. This article discusses the fabrication methods and potential applications of nanoparticle chains as nanoelectrodes in electrochemical systems and also as conductometric sensors. The challenges for such systems are also summarized.

Electrochemical synthesis on nanoparticle chains to couple semiconducting rods: coulomb blockade modulation using photoexcitation.

Hybrid nanostructures are made by coupling a room temperature coulomb blockade device with photoexcitable nano-rods. Direct electrochemical synthesis on nanoparticle chain arrays leads to the formation of semiconducting rods that are in direct contact with the nanoparticles and also spatial confined by them. This direct interfacing leads to mutual intermodulation between the two systems.

Electrochemical synthesis on single cells as templates.

The cell surface is made electrochemically active by interfacing with graphene sheets. The electrical and thermal properties of graphene allow the control of cell surface potential for electrochemical synthesis. Using this approach radially projecting ZnO nanorods are templated on the surface of single cells. This reported single cell photosensor has superior performance than similar devices made on planar surfaces.

Ultrasoft 100 nm thick zero Poisson's ratio film with 60% reversible compressibility.

About a 100 nm thick multilayer film of nanoparticle monolayers and polymer layers is shown to behave like cellular-foam with a modulus below 100 KPa. The 1.25 cm radius film adhered to a rigid surface can be compressed reversibly to 60% strain. The more than 4 orders of magnitude lower modulus compared to its constituents is explained by considering local bending in the (nano)cellular structure, similar to cork and wings of beetles. As the rigidity of the polymer backbone is increased in just four monolayers, the modulus of the composite increases by over 70%. Electro-optical map of the strain distribution over the area of compression and increase in modulus with thickness indicates the films have zero Poisson's ratio.

Graphene as membrane for encapsulation of yeast cells: protective and electrically conducting.

Graphene sheets (chemically reduced), a high modulus and high thermal and electrically conductive material are coupled with yeast cells to form an encapsulating inorganic functional layer. The coupling of the high modulus sheets with the cells increases their stability to osmotic stresses. The sheets also allow the direct visualization of the cells in an electron microscope.

Graphene as cellular interface: electromechanical coupling with cells.

Interfacing cells with nanomaterials such as graphene, nanowires, and carbon nanotubes is useful for the integration of cellular physiology with electrical read outs. Here we show the interfacing of graphene sheets on the surface of yeast cells, leading to electromechanical coupling between the sheets and the cells. The cells are viable after the interfacing. The response caused by physiologically stressing the cells by exposure to alcohols, which causes a change in cell volume, can be observed in the electrical signal through graphene. The change in the cell volume leads to straining of the sheets, forming wrinkles which reduce the electrical conductivity. As the dynamic response of the cell can be observed, it is possible to differentiate between ethanol, 2-propanol, and water. We believe this will lead to further development of cell-based electrical devices and sensors.

Adsorption and desorption of DNA on graphene oxide studied by fluorescently labeled oligonucleotides.

Being the newest member of the carbon materials family, graphene possesses many unique physical properties resulting is a wide range of applications. Recently, it was discovered that graphene oxide can effectively adsorb DNA, and at the same time, it can completely quench adsorbed fluorophores. These properties make it possible to prepare DNA-based optical sensors using graphene oxide. While practical analytical applications are being demonstrated, the fundamental understanding of binding between graphene oxide and DNA in solution received relatively less attention. In this work, we report that the adsorption of 12-, 18-, 24-, and 36-mer single-stranded DNA on graphene oxide is affected by several factors. For example, shorter DNAs are adsorbed more rapidly and bind more tightly to the surface of graphene. The adsorption is favored by a lower pH and a higher ionic strength. The presence of organic solvents such as ethanol can either increase or decrease adsorption depending on the ionic strength of the solution. By adding the cDNA, close to 100% desorption of the absorbed DNA on graphene can be achieved. On the other hand, if temperature is increased, only a small percentage of DNA is desorbed. Further, the adsorbed DNA can also be exchanged by free DNA in solution. These findings are important for further understanding of the interactions between DNA and graphene and for the optimization of DNA and graphene-based devices and sensors.

Ion mediated monolayer deposition of gold nanoparticles on microorganisms: discrimination by age.

A general strategy to target cells by nanoparticles for drug delivery, imaging, or diagnostics involves immunospecific binding between the probes and target molecules on the particles and on the cell surface, respectively. Usually, the macromolecular nature of the molecules requires a specific conformation to achieve the desired immunospecificity, and the extent of deposition of particles is limited by the number of receptor molecules present on the cell. In this report, we successfully obtain targeted binding by decorating the nanoparticle with simple ions, such as Ca(2+), without affecting the cell's vitality. The yeast cells for study, Saccharomyces cerevisiae, have no specific electrostatic affinity toward positive charge as confirmed by lysine-coated Au nanoparticles. The specificity of nanoparticle binding is found to be directly related to the metabolic vitality of the yeast cell (i.e., a significantly larger deposition occurs on a younger generation with higher metabolism than on older cells). The ion-mediated targeted deposition seems to be a general phenomenon for biologically important ions, as demonstrated by the contrast between Mg(2+) and (toxic) Cd(2+). The high density of (percolating) nanoparticle deposition as a monolayer on the cells, as a result of the large number of ion receptors on the cell surface, is shown to be a potential method for building bioelectronic devices. The use of ions as an interface to target cells can have possible applications in diagnosing diseases and making biosensors using live cells.