Nickel-Doped La_0.8Sr_0.2Mn_{1–<i><i>x</i></i>}Ni_<i>x</i>O₃ Nanoparticles Containing Abundant Oxygen Vacancies as an Optimized Bifunctional Catalyst for Oxygen Cathode in Rechargeable Lithium–Air Batteries

In this work, Ni-doped manganite perovskite oxides (La_0.8Sr_0.2Mn_1–<i>x</i>Ni_<i>x</i>O₃, <i>x</i> = 0.2 and 0.4) and undoped La_0.8Sr_0.2MnO₃ were synthesized via a general and facile sol–gel route and used as bifunctional catalysts for oxygen cathode in rechargeable lithium–air batteries. The structural and compositional characterization results showed that the obtained La_0.8Sr_0.2Mn_1–<i>x</i>Ni_<i>x</i>O₃ (<i>x</i> = 0.2 and 0.4) contained more oxygen vacancies than did the undoped La_0.8Sr_0.2MnO₃ as well as a certain amount of Ni³⁺ (<i>e</i>_g = 1) on their surface. The Ni-doped La_0.8Sr_0.2Mn_1–<i>x</i>Ni_<i>x</i>O₃ (<i>x</i> = 0.2 and 0.4) was provided with higher bifunctional catalytic activities than that of the undoped La_0.8Sr_0.2MnO₃. In particular, the La_0.8Sr_0.2Mn_0.6Ni_0.4O₃ had a lower total over potential between the oxygen evolution reaction and the oxygen reduction reaction than that of the La_0.8Sr_0.2MnO₃, and the value is even comparable to that of the commercial Pt/C yet is provided with a much reduced cost. In the lithium–air battery, oxygen cathodes containing the La_0.8Sr_0.2Mn_0.6Ni_0.4O₃ catalyst delivered the optimized electrochemical performance in terms of specific capacity and cycle life, and a reasonable reaction mechanism was given to explain the improved performance

An Ultrahigh Linear Sensitive Temperature Sensor Based on PANI:Graphene and PDMS Hybrid with Negative Temperature Compensation

The detection of human body temperature is one of the important indicators to reflect the physical condition. In order to accurately judge the state of the human body, a high-performance temperature sensor with fast response, high sensitivity, and good linearity characteristics is urgently needed. In this paper, the positive temperature characteristics of graphene–polydimethylsiloxane (PDMS) composite with high sensitivity were studied. Besides, doping polyaniline (PANI) with special negative temperature characteristics as the temperature compensation of the composite finally creatively solved the problem of sensor nonlinearity from the material level. Thus, the PANI:graphene and PDMS hybrid temperature sensor with extraordinary linearity and high sensitivity is realized by establishing the space-gap model and mathematical theoretical analysis. The prepared sensor exhibits high sensitivity (1.60%/°C), linearity (R2 = 0.99), accuracy (0.3 °C), and time response (0.7 s) in the temperature sensing range of 25–40 °C. Based on this, the fabricated temperature sensor can combine with the read-out circuit and filter circuit with a high-precision analog digital converter (ADC) to monitor real-time skin temperature, ambient temperature, and respiratory rate, et al. This high-performance temperature sensor reveals its great potential in electronic skin, disease diagnosis, medical monitoring, and other fields

Simultaneous Generation of Gradients with Gradually Changed Slope in a Microfluidic Device for Quantifying Axon Response

Over the past decades, various microfluidic devices have been developed to investigate the role of the molecular gradient in axonal development; however, there are very few devices providing quantitative information about the response of axons to molecular gradients with different slopes. Here, we propose a novel laminar-based microfluidic device enabling simultaneous generation of multiple gradients with gradually changed slope on a single chip. This device, with two asymmetrically designed peripheral channels and opposite flow direction, could generate gradients with gradually changed slope in the center channel, enabling us to investigate simultaneously the response of axons to multiple slope gradients with the same batch of neurons. We quantitatively investigated the response of axon growth rate and growth direction to substrate-bound laminin gradients with different slopes using this single-layer chip. Furthermore, we compartmented this gradient generation chip and a cell culture chip by a porous membrane to investigate quantitatively the response of axon growth rate to the gradient of soluble factor netrin-1. The results suggested that contacting with a molecular gradient would effectively accelerate neurites growth and enhance axonal formation, and the axon guidance ratio obviously increased with the increase of gradient slope in a proper range. The capability of generating a molecular gradient with continuously variable slopes on a single chip would open up opportunities for obtaining quantitative information about the sensitivity of axons and other types of cells in response to gradients of various proteins

Real-Time Monitoring of Nitric Oxide at Single-Cell Level with Porphyrin-Functionalized Graphene Field-Effect Transistor Biosensor

An ultrasensitive and highly efficient assay for real-time monitoring of nitric oxide (NO) at single-cell level based on a reduced graphene oxide (RGO) and iron–porphyrin-functionalized graphene (FGPCs) field-effect transistor (FET) biosensor is reported. A layer-to-layer assembly of RGO and FGPCs on a prefabricated FET sensor surface through π–π stacking interaction allowed superior electrical conductivity caused by RGO, and highly catalytic specificity induced by metalloporphyrin, ensuring the ultrasensitive and highly specific detection of NO. The results demonstrated that the RGO/FGPCs FET biosensor was capable of real-time monitoring of NO in the range from 1 pM to 100 nM with the limit of detection as low as 1 pM in phosphate-buffered saline (PBS) and 10 pM in the cell medium, respectively. Moreover, the developed biosensor could be used for real-time monitoring of NO released from human umbilical vein endothelial cells (HUVECs) at single-cell level. Along with its miniaturized sizes, ultrasensitive characteristics, and fast response, the FET biosensor is promising as a new platform for potential biological and diagnostic applications