Stretchable and conformal humidity sensors that can be attached to the human body for continuously monitoring the humidity of the environment around the human body or the moisture level of the human skin can play an important role in electronic skin and personal healthcare applications. However, most stretchable humidity sensors are based on the geometric engineering of non-stretchable components and only a few detailed studies are available on stretchable humidity sensors under applied mechanical deformations. In this paper, we propose a transparent, stretchable humidity sensor with a simple fabrication process, having intrinsically stretchable components that provide high stretchability, sensitivity, and stability along with fast response and relaxation time. Composed of reduced graphene oxide-polyurethane composites and an elastomeric conductive electrode, this device exhibits impressive response and relaxation time as fast as 3.5 and 7 s, respectively. The responsivity and the response and relaxation time of the device in the presence of humidity remain almost unchanged under stretching up to a strain of 60% and after 10, 000 stretching cycles at a 40% strain. Further, these stretchable humidity sensors can be easily and conformally attached to a finger for monitoring the humidity levels of the environment around the human body, wet objects, or human skin.

Flexible magnetoelectric (ME) materials have been studied for new applications such as memory, energy harvesters, and magnetic field sensors. Herein, with the widely studied and progressive advantages of ME phenomena in the multiferroic field, we demonstrate a new approach for utilizing flexible ME materials as gate dielectric layers in ME organic field-effect transistors (ME-OFET) that can be used for sensing a magnetic field and extracting the ME properties of the gate dielectric itself. The magnetoelectric nanohybrid gate dielectric layer comprises sandwiched stacks of magnetostrictive CoFe₂O₄ nanoparticles and a highly piezoelectric poly(vinylidene fluoride-co-trifluoroethylene) layer. While varying the magnetic field applied to the ME gate dielectric, the ME effect in the functional gate dielectric modulates the channel conductance of the ME-OFET owing to a change in the effective gate field. The clear separation of the ME responses in the gate dielectric layer of ME-OFET from those of the other parameters was demonstrated using the AC gate biasing method and enabled the extraction of the ME coefficient of ME materials. Additionally, the device shows high stability after cyclic bending of 10, 000 cycles at a banding radius of 1.2 cm. The device has significant potential for not only the extraction of the intrinsic characterization of ME materials but also the sensing of a magnetic field in integrated flexible electronic systems.

A field-effect transistor (FET) with two-dimensional (2D) few-layer MoS₂ as a sensing-channel material was investigated for label-free electrical detection of the hybridization of deoxyribonucleic acid (DNA) molecules. The high-quality MoS₂-channel pattern was selectively formedthrough the chemical reaction of the Mo layer with H₂S gas. The MoS2 FET was very stable in an electrolyte and inert to pH changes due to the lack of oxygen-containing functionalities on the MoS2 surface. Hybridization of single-stranded target DNA molecules with single-stranded probe DNA molecules physically adsorbed on the MoS₂ channel resulted in a shift of the threshold voltage (V_th) in the negative direction and an increase in the drain current. The negative shift in V_th is attributed to electrostatic gating effects induced by the detachment of negatively charged probe DNA molecules from the channel surface after hybridization. A detection limit of 10 fM, high sensitivity of 17 mV/dec, and high dynamic range of 10⁶ were achieved. The results showed that a bio-FET with an ultrathin 2D MoS₂ channel can be used to detect very small concentrations of target DNA molecules specifically hybridized with the probe DNA molecules.