No abstract

Lightweight, compressible and highly sensitive pressure/strain sensing materials are highly desirable for the development of health monitoring, wearable devices and artificial intelligence. Herein, a very simple, low-cost and solution-based approach is presented to fabricate versatile piezoresistive sensors based on conductive polyurethane (PU) sponges coated with synergistic multiwalled carbon nanotubes (MWCNTs) and graphene. These sensor materials are fabricated by convenient dip-coating layer-by-layer (LBL) electrostatic assembly followed by in situ reduction without using any complicated microfabrication processes. The resultant conductive MWCNT/RGO@PU sponges exhibit very low densities (0.027-0.064 g cm-3), outstanding compressibility (up to 75%) and high electrical conductivity benefiting from the porous PU sponges and synergistic conductive MWCNT/RGO structures. In addition, the MWCNT/RGO@PU sponges present larger relative resistance changes and superior sensing performances under external applied pressures (0-5.6 kPa) and a wide range of strains (0-75%) compared with the RGO@PU and MWCNT@PU sponges, due to the synergistic effect of multiple mechanisms: "disconnect-connect" transition of nanogaps, microcracks and fractured skeletons at low compression strain and compressive contact of the conductive skeletons at high compression strain. The electrical and piezoresistive properties of MWCNT/RGO@PU sponges are strongly associated with the dip-coating cycle, suspension concentration, and the applied pressure and strain. Fully functional applications of MWCNT/RGO@PU sponge-based piezoresistive sensors in lighting LED lamps and detecting human body movements are demonstrated, indicating their excellent potential for emerging applications such as health monitoring, wearable devices and artificial intelligence.

It is a challenge to fabricate low-cost and flexible electronic devices with degradable materials. In this work, a flexible and degradable strain sensor was fabricated on a paper substrate by dip-coating in an aqueous suspension of carbon black (CB) and carboxymethyl cellulose (CMC). The composition of CB and CMC in the suspension was first studied for producing a uniform conducting layer on the paper. Then the strain sensor was obtained by assembling the coated paper and wires with silver paste. The sensor exhibits gauge factor of 4.3 and responsive time of approximately 240 ms, demonstrating the capability of monitoring various human motions with high stability >1000 cycles. The microgaps between CB particles and cracks on the surface of the CB layer can account for this resistive-type sensitivity. The degradation test shows that the sensor can be degraded soon under gentle rubbing in wet state, implying it is an environmentally friendly “green” electronic device. Furthermore, the cost of the sensor is quite low (<$0.001/sensor) due to the cheap raw materials used, which provides an opportunity for its future utilization in various intelligent systems.

A highly sensitive and selective fluorescent probe for inorganic and organic mercury species displays colorimetric and ratiometric response in a buffer solution via mercury promoted cleavage reaction. The probe is demonstrated to detect CH(3)HgCl in living cells.

A colorimetric and ratiometric fluorescent probe for the palladium species has been developed based on the Pd(0)-catalyzed cleavage of an allyoxycarbonyl group of amines under mild conditions. The probe displays a highly sensitive and selective response with significant changes in both color (from colorless to jade-green) and fluorescence (from blue to green), through the ICT process.