Surface Modification of Hetero-phase Nanoparticles for Low-Cost Solution-Processable High-k Dielectric Polymer Nanocomposites.

The surface modification of nanoparticles (NPs) is crucial for fabricating polymer nanocomposites (NCs) with high dielectric permittivity. Here, we systematically studied the effect of surface functionalization of TiO2 and BaTiO3 NPs to enhance the dielectric permittivity of polyvinylidene fluoride (PVDF) NCs by 23 and 74%, respectively, measured at a frequency of 1 kHz. To further increase the dielectric permittivity of PVDF/NPs-based NCs, we developed a new hetero-phase filler-based approach that is cost-effective and easy to implement. At a 1:3 mixing ratio of TiO2:BaTiO3 NPs, the dielectric constant of the ensuing NC is found to be 50.2, which is comparable with the functionalized BaTiO3-based NC. The highest dielectric constant value of 76.1 measured at 1 kHz was achieved using the (3-aminopropyl)triethoxysilane (APTES)-modified hetero-phase-based PVDF composite at a volume concentration of 5%. This work is an important step toward inexpensive and easy-to-process high-k nanocomposite dielectrics.

The optical spectra of DMAC-based molecules for organic light-emitting diodes: Hybrid-exchange density functional theory study.

Organic light-emitting diodes (OLED) have considerable advantages over the conventional counterpart. Molecular design by simulations is important for the discovery of new material candidate to improve the performance of OLED. Recently, thermally assisted delayed fluorescence OLED based on DMAC (9,9-dimethyl-9,10-dihydroacridine)-related molecules have been found to have superior performance. In this work, a series of first-principles calculations are performed on DMAC-DPS (diphenylsulfone, emission of blue-color light), DMAC-BP (benzophenone, green), DMAC-DCPP (dicyclohexylphosphonium, red), and the newly designed DMAC-BF (enaminone difluoroboron complexes, red) molecules, based on time-dependent density-functional theory, the hybrid-exchange density functional, and the long-range corrected hybrid-exchange density functional. By varying the percentage of Hartree-Fock (HF) exchange in the hybrid-exchange functional, the emission spectra can be over 97% fitted to the experimental results. We found that the fitted proportion of HF will increase as the wavelengths of the molecules decrease (30% for DPS, 20% for BP, and 10% for DCPP). By contrast, the long-range corrected hybrid-exchange density functional can lead to a good estimate on the absorption spectra. In addition, we have also applied our fitting computational procedure to the newly designed molecule. The molecular orbitals involved in the related excited states have also been investigated for these molecules, which show a common charge-transfer characteristic between the acceptor part (DPS/BP/DCPP/BF) and the donor (DMAC).

A graphene nanoplatelet-polydopamine molecularly imprinted biosensor for Ultratrace creatinine detection.

Accurate and reliable analysis of creatinine is clinically important for the early detection and monitoring of patients with kidney disease. We report a novel graphene nanoplatelet (GNP)/polydopamine (PDA)-molecularly imprinted polymer (MIP) biosensor for the ultra-trace detection of creatinine in a range of body fluids. Dopamine hydrochloride (DA) monomers were polymerized using a simple one-pot method to form a thin PDA-MIP layer on the surface of GNP with high density of creatinine recognition sites. This novel surface-MIP strategy resulted in a record low limit-of-detection (LOD) of 2 × 10-2 pg/ml with a wide dynamic detection range between 1 × 10-1-1 × 109 pg/ml. The practical application of this GNP/PDA-MIP biosensor has been tested by measuring creatinine in human serum, urine, and peritoneal dialysis (PD) fluids. The average recovery rate was 93.7-109.2% with relative standard deviation (RSD) below 4.1% compared to measurements made using standard clinical laboratory methods. Our GNP/PDA-MIP biosensor holds high promise for further development as a rapid, accurate, point-of-care diagnostic platform for detecting and monitoring patients with kidney disease.

Density-functional-theory simulations of the water and ice adhesion on silicene quantum dots.

The absorption of water and ice on silicon is important to understand for many applications and safety concerns for electronic devices as most of them are fabricated using silicon. Meanwhile, recently silicene nanostructures have attracted much attention due to their potential applications in electronic devices such as gas or humidity sensors. However, for the moment, the theoretical study of the interaction between water molecules and silicene nanostructures is still rare although there is already theoretical work on the effect of water molecules on the silicene periodic structure. The specific conditions such as the finite size effect, the edge saturation of the silicene nanostructure, and the distance between the water/ice and the silicene at the initial onset of the contact have not been carefully considered before. Here we have modelled the absorption of a water molecule and a square ice on the silicene nanodot by using hybrid-exchange density-functional theory, complemented by the Van der Waals forces correction. Three different sizes of silicene nanodots have been chosen for simulations, namely [Formula: see text], [Formula: see text], and [Formula: see text], with and without the hydrogen saturation on the edge. Our calculations suggest that the silicene nanodots chosen here are both hydrophilic and ice-philic. The water molecule and the square ice have tilted angles towards the silicene nanodot plane at ~ 70º and ~ 45º, respectively, which could be owing to the zig-zag structure on silicene. The absorption energies are size dependent for unsaturated silicene nanodots, whereas almost size independent for the hydrogen saturated cases. Our work on the single water molecule absorption energy on silicene nanodots is qualitatively in agreement with the previous theoretical and experimental work. However, the ice structure on silicene is yet to be validated by the relevant experiments. Our calculation results not only further complement the current paucity of water-to-silicene-nanostructure contact mechanisms, but also lead to the first study of square-ice contact mechanisms for silicene. Our findings presented here could be useful for the future design of semiconducting devices based on silicene nanostructures, especially in the humid and low-temperature environments.

Design, Regulation, and Applications of Soft Actuators Based on Liquid-Crystalline Polymers and Their Composites.

Soft actuators designed from stimuli-responsive polymers often possess a certain amount of bionic functionality because of their versatile deformation. Liquid-crystalline polymers (LCPs) and their composites are among the most fascinating materials for soft actuators due to their great advantages of flexible structure design and easy regulation. In this Spotlight on Applications, we mainly focus on our group's latest research progress in soft actuators based on LCPs and their composites. Some representative research findings from other groups are also included for a better understanding of this research field. Above all, the essential principles for the responsive behavior and reconfigurable performance of the soft actuators are discussed, from the perspective of material morphology and structure design. Further on, we analyze recent work on how to precisely regulate the responsive modes and quantify the operating parameters of soft actuators. Finally, some application examples are given to demonstrate well-designed soft actuators with different functions under varied working environments, which is expected to provide inspiration for future research in developing more intelligent and multifunctional integrated soft actuators.

Multiplexed immunosensors for point-of-care diagnostic applications.

Accurate, reliable, and cost-effective immunosensors are clinically important for the early diagnosis and monitoring of progressive diseases, and multiplexed sensing is a promising strategy for the next generation of diagnostics. This strategy allows for the simultaneous detection and quantification of multiple biomarkers with significantly enhanced reproducibility and reliability, whilst requiring smaller sample volumes, fewer materials, and shorter average analysis time for individual biomarkers than individual tests. In this opinionated review, we compare different techniques for the development of multiplexed immunosensors. We review the state-of-the-art approaches in the field of multiplexed immunosensors using electrical, electrochemical, and optical methods. The barriers that prevent translating this sensing strategy into clinics are outlined together with the potential solutions. We also share our vision on how multiplexed immunosensors will continue their evolution in the coming years.

Impact of hybrid plasmonic nanoparticles on the charge carrier mobility of P3HT:PCBM polymer solar cells.

The solution processable polymer solar cells have shown a great promise as a cost-effective photovoltaic technology. Here, the effect of carrier mobility changes has been comprehensively investigated on the performance of P3HT:PCBM polymer solar cells using electro-optical coupled simulation regimes, which may result from the embedding of SiO2@Ag@SiO2 plasmonic nanoparticles (NPs) in the active layer. Firstly, the active layer thickness, stemmed from the low mobility of the charge carriers, is optimized. The device with 80 nm thick active layer provided maximum power conversion efficiency (PCE) of 3.47%. Subsequently, the PCE has increased to 6.75% and 6.5%, respectively, along with the benefit of light scattering, near-fields and interparticle hotspots produced by embedded spherical and cubic nanoparticles. The PCE of the devices with incorporated plasmonic nanoparticles are remarkably enhanced up to 7.61% (for spherical NPs) and 7.35% (for cubic NPs) owing to the increase of the electron and hole mobilities to [Formula: see text] and [Formula: see text], respectively (in the optimum case). Furthermore, SiO2@Ag@SiO2 NPs have been successfully synthesized by introducing and utilizing a simple and eco-friendly approach based on electroless pre-treatment deposition and Stober methods. Our findings represent a new facile approach in the fabrication of novel plasmonic NPs for efficient polymer solar cells.

Sponge-like Chitosan Based Porous Monolith for Uraemic Toxins Sorption.

More than three million patients are treated for kidney failure world-wide. Haemodialysis, the most commonly used treatment, requires large amounts of water and generates mountains of non-recyclable plastic waste. To improve the environmental footprint, dialysis treatments need to develop absorbents to regenerate the waste dialysate. Whereas conventional dialysis clears water-soluble toxins, it is not so effective in clearing protein-bound uraemic toxins (PBUTs), such as indoxyl sulfate (IS). Thus, developing absorption devices to remove both water-soluble toxins and PBUTs would be advantageous. Vapour induced phase separation (VIPS) has been used in this work to produce polycaprolactone/chitosan (PCL/CS) composite symmetric porous monoliths with extra porous carbon additives to increase creatinine and albumin-bound IS absorption. Moreover, these easy-to-fabricate porous monoliths can be formed into the required geometry. The PCL/CS porous monoliths absorbed 436 µg/g of albumin-bound IS and 2865 µg/g of creatinine in a single-pass perfusion model within 1 h. This porous PCL/CS monolith could potentially be used to absorb uraemic toxins, including PBUTs, and thus allow the regeneration of waste dialysate and the development of a new generation of environmentally sustainable dialysis treatments, including wearable devices.

Machine-Learning Approach for Predicting the Discharging Capacities of Doped Lithium Nickel-Cobalt-Manganese Cathode Materials in Li-Ion Batteries.

Understanding the governing dopant feature for cyclic discharge capacity is vital for the design and discovery of new doped lithium nickel-cobalt-manganese (NCM) oxide cathodes for lithium-ion battery applications. We herein apply six machine-learning regression algorithms to study the correlations of the structural, elemental features of 168 distinct doped NCM systems with their respective initial discharge capacity (IC) and 50th cycle discharge capacity (EC). First, a Pearson correlation coefficient study suggests that the lithium content ratio is highly correlated to both discharge capacity variables. Among all six regression algorithms, gradient boosting models have demonstrated the best prediction power for both IC and EC, with the root-mean-square errors calculated to be 16.66 mAhg-1 and 18.59 mAhg-1, respectively, against a hold-out test set. Furthermore, a game-theory-based variable-importance analysis reveals that doped NCM materials with higher lithium content, smaller dopant content, and lower-electronegativity atoms as the dopant are more likely to possess higher IC and EC. This study has demonstrated the exciting potentials of applying cutting-edge machine-learning techniques to accurately capture the complex structure-property relationship of doped NCM systems, and the models can be used as fast screening tools for new doped NCM structures with more superior electrochemical discharging properties.

Femtosecond Laser-Induced Crystallization of Amorphous Silicon Thin Films under a Thin Molybdenum Layer.

A new process to crystallize amorphous silicon without melting and the generation of excessive heating of nearby components is presented. We propose the addition of a molybdenum layer to improve the quality of the laser-induced crystallization over that achieved by direct irradiation of silicon alone. The advantages are that it allows the control of crystallite size by varying the applied fluence of a near-infrared femtosecond laser. It offers two fluence regimes for nanocrystallization and polycrystallization with small and large crystallite sizes, respectively. The high repetition rate of the compact femtosecond laser source enables high-quality crystallization over large areas. In this proposed method, a multilayer structure is irradiated with a single femtosecond laser pulse. The multilayer structure includes a substrate, a target amorphous Si layer coated with an additional molybdenum thin film. The Si layer is crystallized by irradiating the Mo layer at different fluence regimes. The transfer of energy from the irradiated Mo layer to the Si film causes the crystallization of amorphous Si at low temperatures (∼700 K). Numerical simulations were carried out to estimate the electron and lattice temperatures for different fluence regimes using a two-temperature model. The roles of direct phonon transport and inelastic electron scattering at the Mo-Si interface were considered in the transfer of energy from the Mo to the Si film. The simulations confirm the experimental evidence that amorphous Si was crystallized in an all-solid-state process at temperatures lower than the melting point of Si, which is consistent with the results from transmission electron microscopy (TEM) and Raman. The formation of crystallized Si with controlled crystallite size after laser treatment can lead to longer mean free paths for carriers and increased electrical conductivity.

Robust Protection of III-V Nanowires in Water Splitting by a Thin Compact TiO2 Layer.

Narrow-band-gap III-V semiconductor nanowires (NWs) with a suitable band structure and strong light-trapping ability are ideal for high-efficiency low-cost solar water-splitting systems. However, due to their nanoscale dimension, they suffer more severe corrosion by the electrolyte solution than the thin-film counterparts. Thus, short-term durability is the major obstacle for using these NWs for practical water-splitting applications. Here, we demonstrated for the first time that a thin layer (∼7 nm thick) of compact TiO2 deposited by atomic layer deposition can provide robust protection to III-V NWs. The protected GaAs NWs maintain 91.4% of its photoluminescence intensity after 14 months of storage in ambient atmosphere, which suggests the TiO2 layer is pinhole-free. Working as a photocathode for water splitting, they exhibited a 45% larger photocurrent density compared with unprotected counterparts and a high Faraday efficiency of 91% and can also maintain a record-long highly stable performance among narrow-band-gap III-V NW photoelectrodes; after 67 h photoelectrochemical stability test reaction in a strong acid electrolyte solution (pH = 1), they show no apparent indication of corrosion, which is in stark contrast to the unprotected NWs that fully failed after 35 h. These findings provide an effective way to enhance both stability and performance of III-V NW-based photoelectrodes, which are highly important for practical applications in solar-energy-based water-splitting systems.

Integration of an Aerosol-Assisted Deposition Technique for the Deposition of Functional Biomaterials Applied to the Fabrication of Miniaturised Ion Sensors.

Ion-selective electrodes are at the forefront of research nowadays, with applications in healthcare, agriculture and water quality analysis among others. Despite multiple attempts of miniaturization of these polyvinyl chloride (PVC) gel-based ion sensors, no ion-sensing devices with a thickness below the micrometer range, and operating using open circuit potential, have been developed so far. This work reports the causes of this thickness limitation in potassium-selective sensors. Highly homogeneous ion-sensing films were fabricated by a method based on aerosol assisted chemical vapour deposition, leading to smooth surfaces with 27 ± 11 nm of roughness. Such homogeneity allowed the systematic study of the performance and ionic diffusion properties of the sensing films at sub-micrometer scales. Sensitivities below the Nernst response were found at low thicknesses. The nature of this reduction in sensitivity was studied, and a difference in the superficial and bulk compositions of the films was measured. An optimal configuration was found at 15 µm, with a good selectivity against Na+ (KK+, Na+ = -1.8) a limit of detection in the range of 10-4 M and esponse time below 40 s. The stability of sensors was improved by the deposition of protective layers, which expanded the lifespan of the ion sensors up to 5 weeks while preserving the Nernst sensitivity.

Rapid detection of free and bound toxins using molecularly imprinted silica/graphene oxide hybrids.

Rapid, selective detection of biological analytes is necessary for early diagnosis, but is often complicated by the analytes being bound to proteins and the lack of fast and reliable systems available for their direct assessment. Here, a cheap, easily-assembled molecularly imprinted silica/graphene oxide hybrid is developed, which can selectively detect toxins linked to early-stage chronic kidney disease, down to femtomolar concentrations within 5 minutes. The hybrid material is capable of simultaneously and separately measuring free and bound analytes using with an ultra-low limit of detection in the femtomolar range, and uses processes intrinsically adaptable to any charged molecular analyte.

Nature-Inspired Bacterial Cellulose/Methylglyoxal (BC/MGO) Nanocomposite for Broad-Spectrum Antimicrobial Wound Dressing.

Bacterial cellulose (BC) is a natural material produced by Acetobacter xylinum, widely used in wound dressings due to the high water-holding capacity and great mechanical strength. In this paper, a novel antimicrobial dressing made from BC/methylglyoxal (MGO) composite with a dip-coating method inspired by naturally antimicrobial Manuka honey is proposed, which to our best knowledge, has not yet to be reported. Characterizations by scanning electron microscope and atomic force microscopy show the interconnected nanostructure of BC and MGO and increase surface roughness of the BC/MGO composite. Thermal analysis indicates high temperature stability of both BC and BC/MGO, while compared with BC, BC/MGO exhibits slightly weaker thermal stability possibly due to reduction of hydrogen bonding and increase of crystallinity. Mechanical test confirms the strong mechanical property of BC and BC/MGO nanocomposite. From the disk diffusion antimicrobial test, the BC/MGO nanocomposite with highest MGO concentration (4%) shows great zone inhibition diameter (around 14.3, 12.3, 17.1, and 15.5 mm against Micrococcus luteus, Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli). Compared with other antimicrobial wound dressing composite materials, the proposed BC/MGO nanocomposite has among the greatest antimicrobial property against broad-spectrum bacteria, making it a promising antimicrobial dressing in chronic wounds care.

Flexible and Self-Powered Photodetector Arrays Based on All-Inorganic CsPbBr3 Quantum Dots.

Flexible devices are garnering substantial interest owing to their potential for wearable and portable applications. Here, flexible and self-powered photodetector arrays based on all-inorganic perovskite quantum dots (QDs) are reported. CsBr/KBr-mediated CsPbBr3 QDs possess improved surface morphology and crystallinity with reduced defect densities, in comparison with the pristine ones. Systematic material characterizations reveal enhanced carrier transport, photoluminescence efficiency, and carrier lifetime of the CsBr/KBr-mediated CsPbBr3 QDs. Flexible photodetector arrays fabricated with an optimum CsBr/KBr treatment demonstrate a high open-circuit voltage of 1.3 V, responsivity of 10.1 A W-1 , specific detectivity of 9.35 × 1013 Jones, and on/off ratio up to ≈104 . Particularly, such performance is achieved under the self-powered operation mode. Furthermore, outstanding flexibility and electrical stability with negligible degradation after 1600 bending cycles (up to 60°) are demonstrated. More importantly, the flexible detector arrays exhibit uniform photoresponse distribution, which is of much significance for practical imaging systems, and thus promotes the practical deployment of perovskite products.

Shining Emitter in a Stable Host: Design of Halide Perovskite Scintillators for X-ray Imaging from Commercial Concept.

Halide perovskite (HP) nanocrystals (NCs) have recently shown great potential for X-ray detection and imaging. However, the practical application still has a long way to go with many technical requirements waiting to be fulfilled, including structure optimization, stability enhancement, and cost reduction. A design principle in this beginning stage is urgently needed but still lacking. Herein, with an "emitter-in-matrix" principle refined from commercial scintillators, CsPbBr3@Cs4PbBr6 with emissive CsPbBr3 NCs embedded inside a solid-state Cs4PbBr6 host is subjected to X-ray sensing and imaging. The Cs4PbBr6 matrix not only enhances the attenuation of X-rays but also dramatically improves the stability of CsPbBr3 NCs. A favorable optical design with the Cs4PbBr6 matrix being transparent to the emission from CsPbBr3 NCs enables efficient light output. As a result, stable and sensitive scintillation response to X-ray signals is demonstrated with superior linearity and ultrahigh time resolution. In order to show the huge potential for practical applications, X-ray imaging using a large-area film (360 mm × 240 mm) by the blade-coating technique is carried out to obtain a high-quality image of interior structures invisible to the human eye. In addition to the above advantages in optics, CsPbBr3@Cs4PbBr6 also enjoys facile solution synthesis with large scalability, excellent repeatability, and low cost.

Bionic Detectors Based on Low-Bandgap Inorganic Perovskite for Selective NIR-I Photon Detection and Imaging.

Fluorescence imaging with photodetectors (PDs) toward near-infrared I (NIR-I) photons (700-900 nm), the so-called "optical window" in organisms, has provided an important path for tracing biological processes in vivo. With both excitation photons and fluorescence photons in this narrow range, a stringent requirement arises that the fluorescence signal should be efficiently differentiated for effective sensing, which cannot be fulfilled by common PDs with a broadband response such as Si-based PDs. In this work, delicate optical microcavities are designed to develop a series of bionic PDs with selective response to NIR-I photons, the merits of a narrowband response with a full width at half maximum (FWHM) of <50 nm, and tunability to cover the NIR-I range are highlighted. Inorganic halide perovskite CsPb0.5 Sn0.5 I3 is chosen as the photoactive layer with comprehensive bandgap and film engineering. As a result, these bionic PDs offer a signal/noise ratio of ≈106 , a large bandwidth of 543 kHz and an ultralow detection limit of 0.33 nW. Meanwhile, the peak responsivity (R) and detectivity (D*) reach up to 270 mA W-1 and 5.4 × 1014 Jones, respectively. Finally, proof-of-concept NIR-I imaging using the PDs is demonstrated to show great promise in real-life application.

The Role of Thickness Control and Interface Modification in Assembling Efficient Planar Perovskite Solar Cells.

Perovskite solar cells (PSCs) have achieved tremendous success within just a decade. This success is critically dependent upon compositional engineering, morphology control of perovskite layer, or contingent upon high-temperature annealed mesoporous TiO2, but quantitative analysis of the role of facile TiCl4 treatment and thickness control of the compact TiO2 layer has not been satisfactorily undertaken. Herein, we report the facile thickness control and post-treatment of the electron transport TiO2 layer to produce highly efficient planar PSCs. TiCl4 treatment of TiO2 layer could remove the surface trap and decrease the charge recombination in the prepared solar cells. Introduction of ethanol into the TiCl4 aqueous solution led to further improved open-circuit voltage and short-circuit current density of the related devices, thus giving rise to enhanced power conversion efficiency (PCE). After the optimal TiCl4 treatment, PCE of 16.42% was achieved for PSCs with TiCl4 aqueous solution-treated TiO2 and 19.24% for PSCs with TiCl4 aqueous/ethanol solution-treated TiO2, respectively. This work sheds light on the promising potential of simple planar PSCs without complicated compositional engineering and avoiding the deposition and optimization of the mesoporous scaffold layer.

Enhanced photoelectrochemical hydrogen generation in neutral electrolyte using non-vacuum processed CIGS photocathodes with an earth-abundant cobalt sulfide catalyst.

This work reports the novelty of using eco-friendly and cost-effective non-vacuum Electrostatic Spray-Assisted Vapour Deposited Cu(In,Ga)SSe (CIGS) thin films as photocathodes, combined with the earth abundant cobalt sulfide (Co-S) as a catalyst to accelerate the kinetics of photogenerated electron transfer and hydrogen generation for photoelectrochemical water splitting. CdS and ZnO layers were subsequently deposited on top of the selenised CIGS films to increase the charge separation and lower the charge recombination for the photocathodes. In order to improve the lifetime and scalability of the CIGS photocathode and the other cell components, a photoelectrochemical test was conducted in a neutral electrolyte of 0.5 M Na2SO4 under simulated sunlight (AM 1.5G). Both the photocurrent densities and the onset potentials of the photocathodes were significantly improved by the electrodeposition of the low cost and earth-abundant Co-S catalyst, with a photocurrent density as high as 19.1 mA cm-2 at -0.34 V vs. reversible hydrogen electrode (RHE), comparable with and even higher than that of the control photocathode using rare and precious Pt as a catalyst.

Perfluoroalkane wax infused gels for effective, regenerating, anti-icing surfaces.

Infusion of solid perfluoroalkanes into polydimethylsiloxane gels provides a simple route to regenerating deicing surfaces, with low adhesion strength from the lower inherent cohesive energy of the perfluoroalkanes. Further, these surfaces are more hydrophobic and environmentally stable than their alkane analogues. The result is a robust, regenerating surface which demonstrates low energy ice adhesion (19.6 kPa), hydrophobicity (water contact angle, CA, >100°), and high environmental stability.