Wearable strain sensors for human motion detection are being highlighted in various fields such as medical, entertainment and sports industry. In this paper, we propose a new type of stretchable strain sensor that can detect both tensile and compressive strains and can be fabricated by a very simple process. A silver nanoparticle (Ag NP) thin film patterned on the polydimethylsiloxane (PDMS) stamp by a single-step direct transfer process is used as the strain sensing material. The working principle is the change in the electrical resistance caused by the opening/closure of micro-cracks under mechanical deformation. The fabricated stretchable strain sensor shows highly sensitive and durable sensing performances in various tensile/compressive strains, long-term cyclic loading and relaxation tests. We demonstrate the applications of our stretchable strain sensors such as flexible pressure sensors and wearable human motion detection devices with high sensitivity, response speed and mechanical robustness.

This work presents a new route to suppress grain growth and tune the sensitivity and selectivity of nanocrystalline SnO2 fibers. Unloaded and Pd‐loaded SnO2 nanofiber mats are synthesized by electrospinning followed by hot‐pressing at 80 °C and calcination at 450 or 600 °C. The chemical composition and microstructure evolution as a function of Pd‐loading and calcination temperature are examined using EDS, XPS, XRD, SEM, and HRTEM. Highly porous fibrillar morphology with nanocrystalline fibers comprising SnO2 crystallites decorated with tiny PdO crystallites is observed. The grain size of the SnO2 crystallites in the layers that are calcined at 600 °C decreases with increasing Pd concentration from about 15 nm in the unloaded specimen to about 7 nm in the 40 mol% Pd‐loaded specimen, indicating that Pd‐loading could effectively suppress the SnO2 grain growth during the calcination step. The Pd‐loaded SnO2 sensors have 4 orders of magnitude higher resistivity and exhibit significantly enhanced sensitivity to H2 and lower sensitivity to NO2 compared to their unloaded counterparts. These observations are attributed to enhanced electron depletion at the surface of the PdO‐decorated SnO2 crystallites and catalytic effect of PdO in promoting the oxidation of H2 into H2O. These phenomena appear to have a much larger effect on the sensitivity of the Pd‐loaded sensors than the reduction in grain size.

The development of gas sensors with innovative designs and advanced functional materials has attracted considerable scientific interest given their potential for addressing important technological challenges. This work presents new insight towards the development of high‐performance p‐type semiconductor gas sensors. Gas sensor test devices, based on copper (II) oxide (CuO) with innovative and unique designs (urchin‐like, fiber‐like, and nanorods), are prepared by a microwave‐assisted synthesis method. The crystalline composition, surface area, porosity, and morphological characteristics are studied by X‐ray powder diffraction, nitrogen adsorption isotherms, field‐emission scanning electron microscopy and high‐resolution transmission electron microscopy. Gas sensor measurements, performed simultaneously on multiple samples, show that morphology can have a substantial influence on gas sensor performance. An assembly of urchin‐like structures is found to be most effective for hydrogen detection in the range of parts‐per‐million at 200 °C with 300‐fold larger response than the previously best reported values for semiconducting CuO hydrogen gas sensors. These results show that morphology plays an important role in the gas sensing performance of CuO and can be effectively applied in the further development of gas sensors based on p‐type semiconductors.

Most of the reported mitochondria-targeting molecules are lipophilic and cationic, and thus they may become cytotoxic with accumulation. Here we show enzymatic cleavage of branched peptides that carry negative charges for targeting mitochondria. Conjugating a well-established protein tag (i.e., FLAG-tag) to self-assembling motifs affords the precursors that form micelles. Enzymatic cleavage of the hydrophilic FLAG motif (DDDDK) by enterokinase (ENTK) turns the micelles to nanofibers. After being taken up by cells, the micelles, upon the action of intracellular ENTK, turn into nanofibers to locate mainly at mitochondria. The micelles of the precursors are able to deliver cargos (either small molecules or proteins) into cells, largely to mitochondria and within 2 h. Preventing ENTK proteolysis diminishes mitochondria targeting. As the first report of using enzymatic self-assembly for targeting mitochondria and delivery cargos to mitochondria, this work illustrates a fundamentally new way to target subcellular organelles for biomedicine.

Significant progress has been achieved recently in developing dye-sensitized solar cells (DSSCs) [1] for low-cost solarpower devices using typical thick (∼ 12 lm) films of TiO 2 nanoparticles. [1][2][3] However, in TiO 2 nanoparticle-based DSSCs, the photoconverison efficiency is often limited by the disordered electrode morphology, which gives rise to interfacial interferences for electron transport. [4][5][6][7] To overcome this limitation, wide bandgap semiconducting oxides comprising 1D and 2D nanostructures have been proposed as promising solutions. [8][9][10][11][12][13][14] These include oriented single-crystalline ZnO nanowires, [8] quasi-ordered arrays of TiO 2 nanotubes, [15][16][17][18] core/shell nanostructures, [19][20][21][22] and 2D hollow structures assembled by colloidal templates.[23]In conjunction with these efforts, growing attention has also been paid to the importance of thin-film devices for use in DSSCs.[24] The key challenge here has been to enhance the surface area of thin-film electrodes. A TiO 2 electrode with a high surface area is necessary to effectively adsorb the dye and achieve a high photocurrent.[1] So far, however, there have been only a few reports on processing strategies designed to provide markedly enhanced surface activities and photocurrent efficiency for thin-film photoelectrodes (≤ 1-2 lm).[15] In particular, there are very few studies on TiO 2 electrodes prepared by physical vapor deposition (PVD), i.e., sputtering, which is a conventional method used in preparing thin films. [25,26] The sputtered film shows a dense columnar microstructure that provides efficient electron paths, a large internal surface area, and mitigates recombination processes. [25,27] Even though sputtered films give rise to a faster electron diffusion coefficient, the amount of dye they adsorbs is still small compared to nanoparticle-based TiO 2 electrodes because the sputtered films typically exhibit densely packed or pore-free morphologies. [25,26] In order to satisfy the requirements for fast electron transport and high surface area in thin-film photoelectrodes, we have combined colloidal templates and rf-sputtering to deposit quasi-ordered hollow TiO 2 hemispheres [28] on conducting glass substrates. This fabrication route produced monolayer-dispersed colloidal templates, providing flexible dimensional control over such features as colloidal diameter (hemisphere size) and shell thickness. Enhanced photoconversion efficiency was obtained due to the predominant role of the hollow structure in promoting electron transport [29] as well as a large surface area for enhanced dye loading. Moreover, the macroporous structure with hollow hemispheres allowed even viscous electrolytes to easily penetrate up to the glass substrate. In this work, the suitability of ordered hollow TiO 2 hemisphere films for highefficiency photoelectrodes in DSSCs was examined further. The scheme in Figure 1 illustrates the procedure used to fabricate the DSSCs used in this study. Detailed processing procedures are described...