In order to solve issues of air pollution, to monitor human health, and to promote agricultural production, gas sensors have been used widely. Metal oxide semiconductor (MOS) gas sensors have become an important area of research in the field of gas sensing due to their high sensitivity, quick response time, and short recovery time for NO₂, CO₂, acetone, etc. In our article, we mainly focus on the gas-sensing properties of MOS gas sensors and summarize the methods that are based on the interface effect of MOS materials and micro–nanostructures to improve their performance. These methods include noble metal modification, doping, and core-shell (C-S) nanostructure. Moreover, we also describe the mechanism of these methods to analyze the advantages and disadvantages of energy barrier modulation and electron transfer for gas adsorption. Finally, we put forward a variety of research ideas based on the above methods to improve the gas-sensing properties. Some perspectives for the development of MOS gas sensors are also discussed.

The release of chemicals and microorganisms from various sources, such as industry, agriculture, animal farming, wastewater treatment plants, and flooding, into water systems have caused water pollution in several parts of our world, endangering aquatic ecosystems and individual health. World Health Organization (WHO) has introduced strict standards for the maximum concentration limits for nutrients and chemicals in drinking water, surface water, and groundwater. It is crucial to have rapid, sensitive, and reliable analytical detection systems to monitor the pollution level regularly and meet the standard limit. Electrochemical biosensors are advantageous analytical devices or tools that convert a bio-signal by biorecognition elements into a significant electrical response. Thanks to the micro/nano fabrication techniques, electrochemical biosensors for sensitive, continuous, and real-time detection have attracted increasing attention among researchers and users worldwide. These devices take advantage of easy operation, portability, and rapid response. They can also be miniaturized, have a long-life span and a quick response time, and possess high sensitivity and selectivity and can be considered as portable biosensing assays. They are of special importance due to their great advantages such as affordability, simplicity, portability, and ability to detect at on-site. This review paper is concerned with the basic concepts of electrochemical biosensors and their applications in various water quality monitoring, such as inorganic chemicals, nutrients, microorganisms’ pollution, and organic pollutants, especially for developing real-time/online detection systems. The basic concepts of electrochemical biosensors, different surface modification techniques, bio-recognition elements (BRE), detection methods, and specific real-time water quality monitoring applications are reviewed thoroughly in this article.

Implantable electrodes represent a groundbreaking advancement in nervous system research, providing a pivotal tool for recording and stimulating human neural activity. This capability is integral for unraveling the intricacies of the nervous system’s functionality and for devising innovative treatments for various neurological disorders. Implantable electrodes offer distinct advantages compared to conventional recording and stimulating neural activity methods. They deliver heightened precision, fewer associated side effects, and the ability to gather data from diverse neural sources. Crucially, the development of implantable electrodes necessitates key attributes: flexibility, stability, and high resolution. Graphene emerges as a highly promising material for fabricating such electrodes due to its exceptional properties. It boasts remarkable flexibility, ensuring seamless integration with the complex and contoured surfaces of neural tissues. Additionally, graphene exhibits low electrical resistance, enabling efficient transmission of neural signals. Its transparency further extends its utility, facilitating compatibility with various imaging techniques and optogenetics. This paper showcases noteworthy endeavors in utilizing graphene in its pure form and as composites to create and deploy implantable devices tailored for neural recordings and stimulations. It underscores the potential for significant advancements in this field. Furthermore, this paper delves into prospective avenues for refining existing graphene-based electrodes, enhancing their suitability for neural recording applications in in vitro and in vivo settings. These future steps promise to revolutionize further our capacity to understand and interact with the neural research landscape.

Polydopamine (PDA)-based biomimetic materials have attracted much attention due to the outstanding adhesion and biocompatibility, etc. However, developing a generalized and simple approach for the patternable polymer coatings in a liquid environment and the secondary modification for high-resolution electrodes are challengeable. Herein, A high-performance flexible microelectrode arrays (fMEAs) for biomedical applications based on novel platinum nanowire (PtNW) was proposed using PDA as the bioinspired adhesive buffer layer between the polymer substrate and the nanowire layer. The PDA film was patternable and selectively grafted on the flexible PI substrate using the micro-contact printing ( $\mu $ CP) technique, followed by the reduction of PtNW on patterned PDA in chloroplatinic acid (H ₂ PtCl ₆ ) by in situ electroless deposition. The as-fabricated PI-PDA/PtNW electrode has greatly reduced the electrochemical impedance at 1 kHz by 99.54% compared with that of PI-Ti/Pt using the conventional sputtering method, and also increased the charge storage capacity (CSCc) by 27 times. At the same time, the adhesion between the metal layer (PDA/PtNW or Ti/Pt) and the PI substrate was evaluated using both intense ultrasonic bath and torsion fatigue test. The results showed that PDA was very effective as the adhesive layer by significantly enhancing both mechanical adhesion and impedance stability when suffering mechanical stress. These achievements are of great interest for robust flexible electronics for implantable or wearable biomedical applications.

In this study, Sn0.3Ag0.7Cu solder paste reinforced with different mass fractions (0, 0.02, 0.05, 0.1, 0.3, 0.5 wt%) of Ni-modified carbon nanotubes (CNTs) was fabricated by mechanical mixing method to improve the properties of Sn0.3Ag0.7Cu low-Ag solder alloys. The effects of CNTs on the melting characteristics, wettability, interfacial reaction and shear property of ball grid array (BGA) structure Cu/Sn0.3Ag0.7Cu- x CNTs/Cu solder joints were comprehensively investigated. Results show that adding CNTs do not change the melting temperature of the composite solder. The melting temperature of all samples is 217.1-217.5 °C. With the addition of CNTs, the undercooling increases significantly, and the wettability of the composite solder firstly increases and subsequently decreases. When the CNTs content is 0.02 wt%, the wetting angle is lowest (23.3°). In addition, CNTs addition could decrease the thickness and grain diameter of interfacial intermetallic compounds (IMCs) in composite solder joints. When the CNTs content reaches 0.05 wt% or higher, the surface of interfacial Cu ₆ Sn ₅ grains of Sn0.3Ag0.7Cu- x CNTs/Cu solder joints become very rough after four reflow times due to the good bonding between CNTs and interfacial Cu ₆ Sn ₅ grains. Besides, it is also found that the shear strength of the Cu/Sn0.3Ag0.7Cu- x CNTs/Cu solder joints increases and then decreases with the increase of CNTs content. When CNTs content reaches 0.1 wt%, the shear strength of joint is highest. Moreover, the shear fracture of the Cu/Sn0.3Ag0.7Cu- x CNTs/Cu solder joints mainly occurs near the twice reflow interface between the solder and Cu substrate. In general, adding a proper amount of CNTs is conducive to the improvement of reliability of low-Ag solder joints.