A 3D Composited Flexible Sensor Based on Percolative Nanoparticle Arrays to Discriminate Coupled Pressure and Strain.

Flexible mechanical sensors based on nanomaterials operate on a deformation-response mechanism, making it challenging to discern different types of mechanical stimuli such as pressure and strain. Therefore, these sensors are susceptible to significant mechanical interference. Here, we introduce a multifunctional flexible sensor capable of discriminating coupled pressure and strain without cross-interference. Our design involves an elastic cantilever fixed on the pillar of the flexible main substrate, creating a three-dimensional (3D) substrate, and two percolative nanoparticle (NP) arrays are deposited on the cantilever and main substrate, respectively, as the sensing materials. The 3D flexible substrate could confine pressure/strain loading exclusively on the cantilever or main substrate, resulting in independent responses of the two nanoparticle arrays with no cross-interference. Benefitting from the quantum transport in nanoparticle arrays, our sensors demonstrate an exceptional sensitivity, enabling discrimination of subtle strains down to 1.34 × 10-4. Furthermore, the suspended cantilever with one movable end can enhance the pressure perception of the NP array, exhibiting a high sensitivity of -0.223 kPa-1 and an ultrahigh resolution of 4.24 Pa. This flexible sensor with multifunctional design will provide inspiration for the development of flexible mechanical sensors and the advancement of decoupling strategies.

Metal Nanocluster-Metal Organic Framework-Polymer Hybrid Nanomaterials for Improved Hydrogen Detection.

The development of hydrogen sensors is of paramount importance for timely leak detection and remains a crucial unmet need. Palladium-based materials, well known as hydrogen sensors, still suffer from poisoning and deactivation. Here, a hybrid hydrogen sensor consisting of a Pd nanocluster (NC) film, a metal-organic framework (MOF), and a polymer, are proposed. The polymer coating, as a protection layer, endows the sensor with excellent H2 selectivity and CO-poisoning resistance. The MOF serves as an interface layer between the Pd NC film and the polymer layer, which alters the nature of the interaction with hydrogen and leads to significant sensing performance improvements, owing to the interfacial electronic coupling between Pd NCs and the MOF. The strategy overcomes the shortcomings of retarded response speed and degraded sensitivity induced by the polymer coating of a Pd NC film-polymer hybrid system. This is the first exhibition of a hydrogen-sensing enhancement mechanism achieved by engineering the electronic coupling between Pd and a MOF. The work establishes a deep understanding of the hydrogen-sensing enhancement mechanism at the nanoscale and provides a feasible strategy to engineer next-generation gas-sensing nanodevices with superior sensing figures of merit via hybrid material systems.

Clinical Characteristics and Outcomes of Acute Ischemic Stroke in Patients with Type 2 Diabetes: A Single-Center, Retrospective Study in Southern China.

OBJECTIVE: To explore the associations between type 2 diabetes mellitus (DM) and stroke by evaluating the clinical risk factors, characteristics, and outcomes of acute ischemic stroke (AIS) patients with and without type 2 DM. METHODS: A total of 1,156 AIS patients (including 410 with type 2 DM (AIS-DM group)) and 746 without type 2 DM (AIS-NDM group)) were included. Patients' demographics, auxiliary examinations, clinical manifestations, and treatment outcomes were recorded and analyzed. RESULTS: Among the included AIS patients, 35.46% had type 2 DM. The AIS-DM group had less males (59.76% versus 70.64%), less smokers (33.90% versus 41.96%), more patients with hypertension (72.93% versus 63.94%; p=0.002), higher triglyceride levels (42.93% versus 25.08%; p ≤ 0.01), and lower total cholesterol (147.06 mg/dl versus 175.31 mg/dl) than the AIS-NDM group. The proportion of patients with large artery atherosclerosis (LAA) in the AIS-DM group was lower (77.56% versus 85.92%; p < 0.05) than that in the AIS-NDM group, and the proportion of patients with small arterial occlusions (SAO) in the AIS-DM group was higher (27.07% versus 13.67%; p < 0.05) than that in the AIS-NDM group. The mean National Institutes of Health Stroke Scale (NIHSS) score at admission in the AIS-DM group was lower than that in the AIS-NDM group (4.39 versus 5.00; p=0.008), but there was no significant difference in the NIHSS score or the modified Rankin Scale score between the two groups at discharge. A total of 85 AIS patients underwent intravenous thrombolysis treatment with recombinant tissue plasminogen activator (rtPA). The door-to-needle time (DNT) did not differ significantly between the groups (49.39 ± 30.40 min versus 44.25 ± 15.24 min; p=0.433). In addition, there were no significant differences in the baseline NIHSS score, 7-day NIHSS score, and mRS score at discharge between the groups. After intravenous thrombolysis with rtPA, the AIS-NDM group had better recovery (44.30% versus 29.20%; p=0.017) and a higher ratio of good treatment outcome at discharge (65.60% versus 54.20%; p=0.762). CONCLUSIONS: Type 2 DM is associated with AIS and its risk factors, such as dyslipidemia and hypertension. Patients in the AIS-DM group had less LAA and smaller arterial occlusions, and DM could exacerbate the short-term clinical outcomes in AIS patients.

Effects of the COVID-19 pandemic on reperfusion therapy for acute ischemic stroke patients in Huizhou City, China.

BACKGROUND AND PURPOSE: The COVID-19 pandemic has impacted the reperfusion therapy for acute ischemic stroke (AIS) patients. Huizhou City utilized its experience with the SARS and MERS breakouts to establish a reperfusion treatment program for AIS patients. METHOD: This is a retrospective study on 8 certified stroke hospitals in Huizhou City from January 2020 to May 2020. We analyzed the number of AIS patients with reperfusion therapy, stroke type (anterior/posterior circulation stroke), modes of transport to hospital, NIHSS score, onset to door time (ODT), door to needle time (DNT), and door to puncture time (DPT). The analysis was compared with baseline data from the same time period in 2019. RESULT: In 2020, the number of AIS patients receiving reperfusion therapy decreased (315 vs. 377), NIHSS score increased [8 (4, 15) vs. 7 [ (1, 2)], P = 0.024], ODT increased [126 (67.5, 210.0) vs. 120.0 (64.0, 179.0), P = 0.032], and DNT decreased [40 (32.5, 55) vs. 48 (36, 59), P = 0.003]. DPT did not change. Seventy percent of AIS patients indicated self-visit as their main mode of transport to the hospital. In both periods, mild stroke patients were more likely to self-visit than utilize emergency systems [2019: 152 (57.6%) vs. 20 (45.6%), P = 0.034; 2020: 123 (56.9%) vs. 5 (14.7%), P < 0.001]. The NIHSS score for self-visiting patients was lower for patients who utilized the ambulance system in both years [self-visit: 6.00 (3.00, 12.00), ambulance: 14.00 (9.00, 19.00), P < 0.001]. The volume of reperfusion patients was lower in 2020; however, the decrease was only significant (P = 0.028) in February 2020. CONCLUSION: During the COVID-19 pandemic in 2020, the number of AIS patients receiving reperfusion therapy significantly decreased when compared to the same period in 2019. The patients' condition increased severity, ODT increased, and the DNT decreased. DPT was not significant for self-visiting and ambulance patients. Moderate to severe stroke patients were more likely to utilize ambulance services.

An ultrahigh resolution pressure sensor based on percolative metal nanoparticle arrays.

Tunneling conductance among nanoparticle arrays is extremely sensitive to the spacing of nanoparticles and might be applied to fabricate ultra-sensitive sensors. Such sensors are of paramount significance for various application, such as automotive systems and consumer electronics. Here, we represent a sensitive pressure sensor which is composed of a piezoresistive strain transducer fabricated from closely spaced nanoparticle films deposited on a flexible membrane. Benefited from this unique quantum transport mechanism, the thermal noise of the sensor decreases significantly, providing the opportunity for our devices to serve as high-performance pressure sensors with an ultrahigh resolution as fine as about 0.5 Pa and a high sensitivity of 0.13 kPa-1. Moreover, our sensor with such an unprecedented response capability can be operated as a barometric altimeter with an altitude resolution of about 1 m. The outstanding behaviors of our devices make nanoparticle arrays for use as actuation materials for pressure measurement.

Pd Nanoparticle Film on a Polymer Substrate for Transparent and Flexible Hydrogen Sensors.

Alongside the rise in fully automated equipment and wearable devices, there is currently a high demand for optically transparent and flexible gas sensors operating at room temperature. Nanoparticle films are ideal H2-sensing materials that can be coupled with flexible substrates because of their discrete nanogranular structure and unique interparticle electrical responsiveness. In this work, we present an optically transparent and flexible H2 sensor based on a Pd nanoparticle film, prepared on a polyethylene terephthalate sheet using a straightforward nanocluster deposition technique. Hundreds of bending cycles demonstrated that the sensor has good electrical stability and mechanical robustness without significant degradation in H2-sensing performance. The H2-sensing behaviors under bent state were systematically evaluated. The loading of tensile and compressive strains under bent state produced a positive and negative influence, respectively, on the sensing performances. The possible influence mechanism of the tensile and compressive strains on the H2-sensing performance was attributed to the changes in the percolation network topology and the interparticle space induced by the strains. The ability to detect a H2 concentration as low as 15 ppm, dynamic response range as wide as 0-10%, and sub-10 s response time was achieved. In addition, the sensor can be operated in the relative humidity range of 0-90% at room temperature. These results demonstrate that the sensor exhibits significant potential for next-generation transparent and flexible H2 detectors.

Response Characteristics of Hydrogen Sensors Based on PMMA-Membrane-Coated Palladium Nanoparticle Films.

Coating a polymeric membrane for gas separation is a feasible approach to fabricate gas sensors with selectivity. In this study, poly(methyl methacrylate)-(PMMA-)membrane-coated palladium (Pd) nanoparticle (NP) films were fabricated for high-performance hydrogen (H2) gas sensing by carrying out gas-phase cluster deposition and PMMA spin coating. No changes were induced by the PMMA spin coating in the electrical transport and H2-sensing mechanisms of the Pd NP films. Measurements of H2 sensing demonstrated that the devices were capable of detecting H2 gas within the concentration range 0-10% at room temperature and showed high selectivity to H2 due to the filtration effect of the PMMA membrane layer. Despite the presence of the PMMA matrix, the lower detection limit of the sensor is less than 50 ppm. A series of PMMA membrane layers with different thicknesses were spin coated onto the surface of Pd NP films for the selective filtration of H2. It was found that the device sensing kinetics were strongly affected by the thickness of the PMMA layer, with the devices with thicker PMMA membrane layers showing a slower response to H2 gas. Three mechanisms slowing down the sensing kinetics of the devices were demonstrated to be present: diffusion of H2 gas in the PMMA matrix, nucleation and growth of the ß phase in the α phase matrix of Pd hydride, and stress relaxation at the interface between Pd NPs and the PMMA matrix. The retardation effect caused by these three mechanisms on the sensing kinetics relied on the phase region of Pd hydride during the sensing reaction. Two simple strategies, minimizing the thickness of the PMMA membrane layer and reducing the size of the Pd NPs, were proposed to compensate for retardation of the sensing response.

Towards an all-in fiber photodetector by directly bonding few-layer molybdenum disulfide to a fiber facet.

Although photodetectors based on two dimensional (2D) materials have been intensively studied, there are few reports of optical fiber compatible devices. Herein we successfully fabricated an all-in fiber photodetector (FPD) based on an end-face bonded with few-layer molybdenum disulfide (MoS2). Our FPD has a considerably high photo-responsivity of ∼0.6 A W-1 at a bias voltage of 4 V and 0.01 A W-1 under the bias-free conditions. We believe that the proposed platform may provide a new strategy for the integration of 2D materials in fibers and realization of optoelectronic and sensing applications.

Mechanism for the photoreduction of poly(vinylpyrrolidone) to HAuCl4 and the dominating saturable absorption of Au colloids.

Both fabrication of Au nano-objects and the nonlinear optical properties of Au nano-objects are the focus of research. In the present work, Au nanoparticles with different mean sizes (18, 32, 42, and 70 nm) are controllably fabricated in ethanol by changing the concentration of poly(vinylpyrrolidone) (PVP) and HAuCl4, as well as the power of continuous wave UV light at 365 nm. PVP acts as both reducing and protective agent. The mechanism of photoreduction of PVP to HAuCl4 is proposed. PVP undergoes a series of chemical reactions which include the attack of the hydrogen atom on the tertiary carbon atom at the α-position of the nitrogen atom, production of a hydroxyl radical, and chain scission. The hydroxyl radical combines with the hydrogen atom produced through the dissociation of HAuCl4, which facilitates the decomposition of HAuCl4. The fabrication mechanism of Au nanoparticles is discussed. The nonlinear absorption of these Au nanoparticles is investigated; all of them exhibit saturable absorption, and the saturable absorption dominates the nonlinear absorption with the increase of laser energy. The dominance of saturable absorption in the nonlinear absorption is due to the stronger single-photon absorbed intraband absorption from the ground state to the first excited state in the conduction band, the weaker excited state absorption in the conduction band, and the weaker two-photon absorption from the d band to the conduction band.

Fabrication of Polystyrene/ZnO Micronano Hierarchical Structure Applied for Light Extraction of Light-Emitting Devices.

Polystyrene(PS)/ZnO micronano hierarchical structures were fabricated on a flat surface by depositing ZnO nanoparticles from a cluster beam at oblique incidence on the surface predeposited with PS microspheres. The hierarchical structure was composed of submicron-sized PS particle layers covered with dense films of columnar ZnO nanoparticle piles separated with nanoscale pores. It was demonstrated that the cooperative effect that combines the microlens function of the PS microspheres and the enhanced Rayleigh scattering of the ZnO nanoparticle porous layers can be used to greatly reduce the total internal reflection at the medium-air interface. The PS/ZnO hierarchical structures were fabricated on the surface of GaN-based light-emitting diode (LED) chips to enhance the light-extraction efficiency. A 77.7% improvement on the light-output power was realized, which was much greater than that obtained with the PS microstructures alone.