Yujia Zhong

A Wearable and Highly Sensitive Graphene Strain Sensor for Precise Home-Based Pulse Wave Monitoring

Profuse medical information about cardiovascular properties can be gathered from pulse waveforms. Therefore, it is desirable to design a smart pulse monitoring device to achieve noninvasive and real-time acquisition of cardiovascular parameters. The majority of current pulse sensors are usually bulky or insufficient in sensitivity. In this work, a graphene-based skin-like sensor is explored for pulse wave sensing with features of easy use and wearing comfort. Moreover, the adjustment of the substrate stiffness and interfacial bonding accomplish the optimal balance between sensor linearity and signal sensitivity, as well as measurement of the beat-to-beat radial arterial pulse. Compared with the existing bulky and nonportable clinical instruments, this highly sensitive and soft sensing patch not only provides primary sensor interface to human skin, but also can objectively and accurately detect the subtle pulse signal variations in a real-time fashion, such as pulse waveforms with different ages, pre- and post-exercise, thus presenting a promising solution to home-based pulse monitoring.

Graphene oxide as a water transporter promoting germination of plants in soil

Graphene oxide (GO) is a graphene derivative bearing various oxygen-containing functional groups attached to the basal plane and to the edges of the graphene lattice and hence has a unique structure in which numerous hydrophobic sp2 clusters are isolated within the hydrophilic sp3 C–O matrix. In this study, the hydrophilic nature and water-transporting properties of GO were exploited to promote germination and growth of plants. It was found that a low dose of GO significantly promoted the germination of spinach and chive in soil. The oxygen-containing functional groups of GO collected water, and the hydrophobic sp2 domains transported water to the seeds to accelerate the germination of plants. The strong interaction between GO and the surfaces of soil grains stabilized GO in the soil and prevented dissipation of GO. In addition, no GO was detected either on the surface or inside the cells of plants; this finding confirmed that GO was not phytotoxic. Therefore, GO may serve as a promising nontoxic additive to increase a plant yield.

Formation of Uniform Water Microdroplets on Wrinkled Graphene for Ultrafast Humidity Sensing

Portable humidity sensors with ultrafast responses fabricated in wearable devices have promising application prospects in disease diagnostics, health status monitoring, and personal healthcare data collecting. However, prolonged exposures to high-humidity environments usually cause device degradation or failure due to excessive water adsorbed on the sensor surface. In the present work, a graphene film based humidity sensor with a hydrophobic surface and uniformly distributed ring-like wrinkles is designed and fabricated that exhibits excellent performance in breath sensing. The wrinkled morphology of the graphene sensor is able to effectively prevent the aggregation of water microdroplets and thus maximize the evaporation rate. The as-fabricated sensor responds to and recovers from humidity in 12.5 ms, the fastest response of humidity sensors reported so far, yet in a very stable manner. The sensor is fabricated into a mask and successfully applied to monitoring sudden changes in respiratory rate and depth, such as breathing disorder or arrest, as well as subtle changes in humidity level caused by talking, cough and skin evaporation. The sensor can potentially enable long-term daily monitoring of breath and skin evaporation with its ultrafast response and high sensitivity, as well as excellent stability in high-humidity environments.

In situ electrodeposition of polypyrrole onto TaSe2 nanobelts quasi-arrays for high-capacitance supercapacitor

Transition metal dichalcogenides have recently revealed interesting physical properties which lead to promising applications for functional devices. TaSe2, as a member of transition metal dichalcogenides, attracts a great deal of attention as a layered electric conductor with low dimension and metallic nature. Herein, we prepare a three-dimensional conductive quasi-array based on 2H-TaSe2 nanobelts, which are synthesized directly on a tantalum foil by one step surface-assisted chemical vapor transport method. The conductive quasi-arrays are used as substrate for in situ electrodeposition of polypyrrole to form cylinder-like composite nanostructures. It is shown that the TaSe2 nanobelts can improve conductivity and stability of polypyrrole by acting as conductive and robust skeleton. A symmetric supercapacitor constructed from the composites demonstrates high areal capacitance of 835 mF cm-2 at a scan rate of 2 mV s-1, wide potential window of 1.2 V, and excellent cycling stability with 98.7% capacitance retention after 10 000 cycles. Meanwhile, the assembly process of the supercapacitor is quite simple because it does not need any additional current collector, binder or conductive additive. The nanocomposites have been verified to be a very effective way to improve electrochemical performance of polypyrrole, and are promising to be applied as supercapacitors.

Synthetic Multifunctional Graphene Composites with Reshaping and Self-Healing Features via a Facile Biomineralization-Inspired Process

Since graphene is a type of 2D carbon material with excellent mechanical, electrical, thermal, and optical properties, the efficient preparation of graphene macroscopic assemblies is significant in the potentially large-scale application of graphene sheets. Conventional preparation methods of graphene macroscopic assemblies need strict conditions, and, once formed, the assemblies cannot be edited, reshaped, or recycled. Herein, inspired by the biomineralization process, a feasible approach of shapeable, multimanipulatable, and recyclable gel-like composite consisting of graphene oxide/poly(acrylic acid)/amorphous calcium carbonate (GO-PAA-ACC) is designed. This GO-PAA-ACC material can be facilely synthesized at room temperature with a cross-linking network structure formed during the preparation process. Remarkably, it is stretchable, malleable, self-healable, and easy to process in the wet state, but tough and rigid in the dried state. In addition, these two states can be readily switched by adjusting the water content, which shows recyclability and can be used for 3D printing to form varied architectures. Furthermore, GO-PAA-ACC can be functionalized or processed to meet a variety of specific application requirements (e.g., energy-storage, actuators). The preparation method of GO-PAA-ACC composite in this work also provides a novel strategy for the versatile macroscopic assembly of other materials, which is low-cost, efficient, and convenient for broad application.