A Magnetic Levitation System for Range/Sensitivity-Tunable Measurement of Density.

Magnetic levitation (MagLev) is a promising density-based analytical technique with numerous applications. Several MagLev structures with different levels of sensitivity and range have been studied. However, these MagLev structures can seldom satisfy the different performance requirements simultaneously, such as high sensitivity, wide measurement range, and easy operation, which have prevented them from being widely used. In this work, a tunable MagLev system was developed. It is confirmed by numerical simulation and experiments that this system possesses a high resolution down to 10-7 g/cm3 or even higher compared to the existing systems. Meanwhile, the resolution and range of this tunable system can be adjusted to meet different requirements of measurement. More importantly, this system can be operated simply and conveniently. This bundle of characteristics demonstrates that the novel tunable MagLev system could be handily applied in various density-based analyses on demand, which would greatly expand the ability of MagLev technology.

All Paper-Based Flexible and Wearable Piezoresistive Pressure Sensor.

Flexible and wearable pressure sensors are of paramount importance for the development of personalized medicine and electronic skin. However, the preparation of easily disposable pressure sensors is still facing pressing challenges. Herein, we have developed an all paper-based piezoresistive (APBP) pressure sensor through a facile, cost-effective, and environmentally friendly method. This pressure sensor was based on a tissue paper coated with silver nanowires (AgNWs) as a sensing material, a nanocellulose paper (NCP) as a bottom substrate for printing electrodes, and NCP as a top encapsulating layer. The APBP pressure sensor showed a high sensitivity of 1.5 kPa-1 in the range of 0.03-30.2 kPa and retained excellent performance in the bending state. Furthermore, the APBP sensor has been mounted on the human skin to monitor physiological signals (such as arterial heart pulse and pronunciation from throat) and successfully applied as a soft electronic skin to respond to the external pressure. Due to the use of the common tissue paper, NCP, AgNWs, and conductive nanosilver ink only, the pressure sensor has advantages of low cost, facile craft, and fast preparation and can be disposed off easily by incineration. We believe that the developed sensor will propel the advancement of easily disposable pressure sensors and green paper-based flexible electronic devices.

Revealing the Electrochemical Mechanism of Cationic/Anionic Redox on Li-Rich Layered Oxides via Controlling the Distribution of Primary Particle Size.

Lithium-manganese-rich layered oxides have sparked intense interest on high-energy-density lithium-ion batteries because of their unique anionic redox. While making efforts to adjust the primary particle size for the improved electrochemical kinetics, current research is insufficient to explain how the anionic/cationic interplay governs the electrochemical behavior except for ion diffusion. Here, fully ordered Li1.2Mn0.54Ni0.13Co0.13O2 spheres of shortened primary particle size were synthesized via the coprecipitation method for use as cathodes. A high discharge capacity of 303.2 mA h g-1 was achieved for the first cycle. Optimized nanostructures reduce the lithium ion diffusion length and increase electronic conductivity unsurprisingly, contributing to excellent electrochemical activity and rate capability. Furthermore, the decreased primary particle size accelerated the redox reactivity of cations and the reversibility of anionic redox on path dependence. This work clarifies the electrochemical mechanism of cationic/anionic redox of these Li-rich layered oxides and provides a new vision for a unique design of high-energy cathode materials with better application.

Paper-based fluorescent immunoassay for highly sensitive and selective detection of norfloxacin in milk at picogram level.

Norfloxacin (NOR) in milk may influence mammalian cell replication and bring about a decrease in the efficiency for treating infection in humans. However, current techniques for detecting NOR usually require expensive instruments and trained personnel. In this work, we have developed a low-cost and simple method via paper-based fluorescent immunoassay for highly sensitive and selective detection of NOR in milk at picogram level. The NOR monoclonal antibody labeled with quantum dots is used as a detection probe to recognize the corresponding NOR, which can quantitatively detect NOR on paper-based devices. The detection limits in aqueous solution and milk are 1 pg/mL and 10 pg/mL, respectively. The developed paper-based method provides a cheap, sensitive, eco-friendly, and rapid approach for quantitative detection of trace NOR in milk, which may find wide applications in food safety inspection. Noteworthy, the method is especially suitable for applications at resource-limited and on-site settings.

Using magnetic levitation for density-based detection of cooking oils.

Adulterated cooking oils and the repeated use of frying cooking oils are harmful to human health. Current techniques for the quality control of cooking oils such as gas chromatography and high performance liquid chromatography usually require expensive facilities, and they are complicated to operate. This paper describes a simple technique that uses magnetic levitation (MagLev) to analyse cooking oils based on density. We have demonstrated the application of MagLev to detect the quality of cooking oil by simulating adulterated sesame oil using peanut oil and frying soybean oil for different times. We have also demonstrated the use of MagLev to differentiate secondhand cooking oil from certified cooking oil. MagLev provides a portable and inexpensive method for the on-site inspection of cooking oils, and it may be extended to many other applications in food safety, environmental monitoring, medical diagnosis, and so on. The advantages of high sensitivity, low cost, and convenience of operation make MagLev especially useful for in situ applications in resource-limited settings.