Reduced graphene oxide (RGO) has proved to be a promising candidate in high-performance gas sensing in ambient conditions. However, trace detection of different kinds of gases with simultaneously high sensitivity and selectivity is challenging. Here, a chemiresistor-type sensor based on 3D sulfonated RGO hydrogel (S-RGOH) is reported, which can detect a variety of important gases with high sensitivity, boosted selectivity, fast response, and good reversibility. The NaHSO3 functionalized RGOH displays remarkable 118.6 and 58.9 times higher responses to NO2 and NH3, respectively, compared with its unmodified RGOH counterpart. In addition, the S-RGOH sensor is highly responsive to volatile organic compounds. More importantly, the characteristic patterns on the linearly fitted response-temperature curves are employed to distinguish various gases for the first time. The temperature of the sensor is elevated rapidly by an imbedded microheater with little power consumption. The 3D S-RGOH is characterized and the sensing mechanisms are proposed. This work gains new insights into boosting the sensitivity of detecting various gases by combining chemical modification and 3D structural engineering of RGO, and improving the selectivity of gas sensing by employing temperature dependent response characteristics of RGO for different gases.

A 3D Chemically Modified Graphene Hydrogel for Fast, Highly Sensitive, and Selective Gas Sensor

Thermal chemical vapour deposition techniques for graphene fabrication, while promising, are thus far limited by resource-consuming and energy-intensive principles. In particular, purified gases and extensive vacuum processing are necessary for creating a highly controlled environment, isolated from ambient air, to enable the growth of graphene films. Here we exploit the ambient-air environment to enable the growth of graphene films, without the need for compressed gases. A renewable natural precursor, soybean oil, is transformed into continuous graphene films, composed of single-to-few layers, in a single step. The enabling parameters for controlled synthesis and tailored properties of the graphene film are discussed, and a mechanism for the ambient-air growth is proposed. Furthermore, the functionality of the graphene is demonstrated through direct utilization as an electrode to realize an effective electrochemical genosensor. Our method is applicable to other types of renewable precursors and may open a new avenue for low-cost synthesis of graphene films.

Single-step ambient-air synthesis of graphene from renewable precursors as electrochemical genosensor

Microwave reduction of graphene oxide

Graphene, a two-dimensional single layered carbon atoms crystal lattice has grabbed much attention due to its unique electronic, surface, mechanical and optoelectronic characteristics. Owing to its unique structure and properties, graphene has opened new opportunities for the future systems and devices, which has led to increase its demand in numerous applications. However, scaling up its production is still a challenging job. Although there is a huge body of literature on the graphene synthesis using various techniques but eco-friendly and cost–effective processes for mass scale production are still needed. In order to conceptualize and develop the processes fulfilling the growing concerns, it is important to overview the existing literature. The current review summarizes the production of graphene using several approaches as well as the potential of various waste materials as graphene precursors. The methods used for graphene synthesis have been categorized into top down techniques such as chemical exfoliation, mechanical exfoliation and chemical fabrication processes, and bottom up techniques including pyrolysis, plasma synthesis, epitaxial growth and chemical vapor deposition (CVD) processes. Conversely, several limitations are considerate for an individual procedure such as toxicity of chemicals, high-cost, time consumption or inadequate quality of the product. Furthermore, mass production of graphene derivatives under low-cost can also be considered by utilizing a variety of wastes precursors such as plastic and batteries waste, newspaper, biomass, chitosan, coal, insects waste etc. This review designates the current advances in wastes-derived graphene synthesis to relief synthetic difficulties as well as predicts the future development in this area.

Advances in synthesis of graphene derivatives using industrial wastes precursors; prospects and challenges

A review on advances in graphene-derivative/polysaccharide bionanocomposites: Therapeutics, pharmacogenomics and toxicity.

Recently, graphene has been extensively researched in fundamental science and engineering fields and has been developed for various electronic applications in emerging technologies owing to its outstanding material properties, including superior electronic, thermal, optical and mechanical properties. Thus, graphene has enabled substantial progress in the development of the current electronic systems. Here, we introduce the most important electronic and thermal properties of graphene, including its high conductivity, quantum Hall effect, Dirac fermions, high Seebeck coefficient and thermoelectric effects. We also present up-to-date graphene-based applications: optical devices, electronic and thermal sensors, and energy management systems. These applications pave the way for advanced biomedical engineering, reliable human therapy, and environmental protection. In this review, we show that the development of graphene suggests substantial improvements in current electronic technologies and applications in healthcare systems.

Electronic and Thermal Properties of Graphene and Recent Advances in Graphene Based Electronics Applications

Monitoring the body temperature with high accuracy provides a fast, facile, yet powerful route about the human body in a wide range of health information standards. Here, the first ever ultrasensitive and stretchable gold-doped silicon nanomembrane (Au-doped SiNM) epidermal temperature sensor array is introduced. The ultrasensitivity is achieved by shifting freeze-out region to intrinsic region in carrier density and modulation of fermi energy level of p-type SiNM through the development of a novel gold-doping strategy. The Au-doped SiNM is readily transferred onto an ultrathin polymer layer with a well-designed serpentine mesh structure, capable of being utilized as an epidermal temperature sensor array. Measurements in vivo and in vitro show temperature coefficient of resistance as high as -37270.72 ppm °C-1 , 22 times higher than existing metal-based temperature sensors with similar structures, and one of the highest thermal sensitivity among the inorganic material based temperature sensors. Applications in the continuous monitoring of body temperature and respiration rate during exercising are demonstrated with a successful capture of information. This work lays a foundation for monitoring body temperature, potentially useful for precision diagnosis (e.g., continuous monitoring body temperature in coronavirus disease 2019 cases) and management of disease relevance to body temperature in healthcare.

Ultrahigh Sensitive Au-Doped Silicon Nanomembrane Based Wearable Sensor Arrays for Continuous Skin Temperature Monitoring with High Precision.

Due to the absence of thin-film barriers to biofluids with multidecade lifetimes, the penetration of biofluids into the devices and any ensuing electrochemical reactions pose significant safety risks. Here, we overcome these challenges by combining pristine thermal SiO2 layers with processing steps for their integration onto flexible electronics. We showed that an ultrathin, leakage-free, biocompatible dielectric layer which can completely seal the device. The resulting current-leakage levels and operational lifetimes have been improved significantly.

Mingyu Sang

Papers

Electronic and Thermal Properties of Graphene and Recent Advances in Graphene Based Electronics Applications

Ultrahigh Sensitive Au-Doped Silicon Nanomembrane Based Wearable Sensor Arrays for Continuous Skin Temperature Monitoring with High Precision.

Flexible Water-proof Bio-Integrated Electronics