Eu(III)-Functionalized MOF-Based Dual-Emission Ratiometric Sensor Integrated with Logic Gate Operation for Efficient Detection of Hippuric Acid in Urine and Serum.

With the introduction of Eu3+ ions as the secondary fluorescent signal reporter and sensing active sites, a dual-emission ratiometric sensor of Eu3+@NiMOF (Eu3+ functional NiMOF) for hippuric acid (HA) detection in urine and serum was fabricated via the postsynthetic encapsulating strategy. Based on the two emission signals at 441 nm (turn-on) and 628 nm (turn-off), the produced Eu3+@NiMOF ratiometric sensor provided enhanced sensitivity, higher selectivity, and 9.7 times lower limits of detection (LOD) for the detection of HA (2.38 µM, 0.42 µg·mL-1) than that of the pristine NiMOF. Considering the high sensitivity and visualization results, further exploration of intelligent applications in the HA sensing process was carried out by constructing a tandem combinational logic gate to improve the practicability and convenience with the help of a smartphone. This work provides a promising approach for developing MOF-based ratiometric sensors to detect biomarkers.

A composite triboelectric nanogenerator based on flexible and transparent film impregnated with ZIF-8 nanocrystals.

The triboelectric nanogenerator (TENG), based on the triboelectrification coupled with electrostatic induction, can directly convert ambient mechanical energy into electric energy. However, the output performance of TENG is still low and demands further improvement to speed up the commercial application. In this work, we demonstrate a TENG based on a flexible and transparent composite film made of PDMS and ZIF-8. When the amount of the ZIF-8 is 4 wt%, the generated output current and voltage of the TENG are gradually increased up to 16.3µA and 176 V, which are 210% and 230% higher than that of TENG without ZIF-8, respectively. Impregnated ZIF-8 which exhibits a positive polarity lowers the effective work function of the PDMS and enhance the surface charge density, verified by Kelvin probe force microscope measurement.

Crystalline capsules: metal-organic frameworks locked by size-matching ligand bolts.

Metal-organic frameworks (MOFs) are shown to be good examples of a new class of crystalline porous materials for guest encapsulation. Since the encapsulation/release of guest molecules in MOF hosts is a reversible process in nature, how to prevent the leaching of guests from the open pores with minimal and nondestructive modifications of the structure is a critical issue. To address this issue, we herein propose a novel strategy of encapsulating guests by introducing size-matching organic ligands as bolts to lock the pores of the MOFs through deliberately anchoring onto the open metal sites in the pores. Our proposed strategy provides a mechanical way to prevent the leaching of guests and thereby has less dependence on the specific chemical environment of the hosts, thus making it applicable for a wide variety of existing MOFs once the size-matching ligands are employed.

Chemorobust dye-encapsulated framework as dual-emission self-calibrating ratiometric sensor for intelligent detection of toluene exposure biomarker in urine.

By taking advantages of confinement effect can effectively prevent dye aggregation caused luminescent quenching, Eosin Y (EY) was encapsulated into a chemorobust porous CoMOF as secondary fluorescent signal to construct the dual-emitting sensor of EY@CoMOF. And the photo-induced electron transfer from CoMOF to EY molecules induced EY@CoMOF presenting a weak blue emission at 421 nm and a strong yellow emission at 565 nm. Those dual-emission features also endow EY@CoMOF itself great potentials as a self-calibrating ratiometric sensor in visually and efficiently monitoring hippuric acid (HA) in urine, with fast response, high sensitivity and selectivity, excellent recyclable, and low LOD (0.24 µg/mL). Furthermore, based on a tandem combinational logic gate, an intelligent detection system was designed to improve the practicability and convenience of HA detection in urine. To the best of our knowledge, this is the first example of dye@MOF based sensor for HA detection. And this work provides a promising approach for developing dye@MOF based sensors to intelligent detect bioactive molecules.

Enhanced NO2 gas sensing of a single-layer MoS2 by photogating and piezo-phototronic effects.

NO2 sensors with ultrahigh sensitivity are demanded for future electronic sensing systems. However, traditional sensors are considerably limited by the relative low sensitivity, high cost and complicated process. Here, we report a simply and reliable flexible NO2 sensor based on single-layer MoS2. The flexible sensor exhibits high sensitivity to NO2 gas due to ultra-large specific surface area and the nature of two-dimensional (2D) semiconductor. When the NO2 is 400 ppb (parts per billion), compared with the dark and strain-free conditions, the sensitivity of the single-layer sensor is enhanced to 671% with a 625 nm red light-emitting diode (LED) illumination of 4 mW/cm2 power under 0.67% tensile strain. More important, the response time is dramatically reduced to ∼16 s and it only needs ∼65 s to complete 90% recovery. A theoretical model is proposed to discuss the microscopic mechanisms. We find that the remarkable sensing characteristics are the result of coupling among piezoelectricity, photoelectricity and adsorption-desorption induced charges transfer in the single-layer MoS2 Schottky junction based device. Our work opens up the way to further enhancements in the sensitivity of gas sensor based on single-layer MoS2 by introducing photogating and piezo-phototronic effects in mesoscopic systems.

Piezotronic Effect Enhanced Flexible Humidity Sensing of Monolayer MoS2.

We report the piezotronic effect on the performance of humidity detection based on a back-to-back Schottky contacted monolayer MoS2 device. By introducing an upswept mechanical strain, the in-plane electrical polarization can be induced at the MoS2/metal junction region. The polarization charges can modify the Schottky barrier height at the interface of MoS2/metal junction, subsequently improving the sensitivity of the humidity sensing. An energy band diagram is proposed to explain the experiment phenomenon of the humidity sensor. This work provides a simple way to enhance the sensitivity of ultrathin two-dimensional-materials-based sensors by the piezotronic effect, which has great potential applications in electronic skin, human-computer interfacing, gas sensing, and environment monitoring.

Magnetic-Induced-Piezopotential Gated MoS2 Field-Effect Transistor at Room Temperature.

Utilizing magnetic field directly modulating/turning the charge carrier transport behavior of field-effect transistor (FET) at ambient conditions is an enormous challenge in the field of micro-nanoelectronics. Here, a new type of magnetic-induced-piezopotential gated field-effect-transistor (MIPG-FET) base on laminate composites is proposed, which consists of Terfenol-D, a ferroelectric single crystal (PMNPT), and MoS2 flake. When applying an external magnetic field to the MIPG-FET, the piezopotential of PMNPT triggered by magnetostriction of the Terfenol-D can serve as the gate voltage to effectively modulate/control the carrier transport process and the corresponding drain current at room temperature. Considering the two polarization states of PMNPT, the drain current is diminished from 9.56 to 2.9 µA in the Pup state under a magnetic field of 33 mT, and increases from 1.41 to 4.93 µA in the Pdown state under a magnetic field of 42 mT and at a drain voltage of 3 V. The current on/off ratios in these states are 330% and 432%, respectively. This work provides a novel noncontact coupling method among magnetism, piezoelectricity, and semiconductor properties, which may have extremely important applications in magnetic sensors, memory and logic devices, micro-electromechanical systems, and human-machine interfacing.

Core-Shell-Yarn-Based Triboelectric Nanogenerator Textiles as Power Cloths.

Although textile-based triboelectric nanogenerators (TENGs) are highly promising because they scavenge energy from their working environment to sustainably power wearable/mobile electronics, the challenge of simultaneously possessing the qualities of cloth remains. In this work, we propose a strategy for TENG textiles as power cloths in which core-shell yarns with core conductive fibers as the electrode and artificial polymer fibers or natural fibrous materials tightly twined around core conductive fibers are applied as the building blocks. The resulting TENG textiles are comfortable, flexible, and fashionable, and their production processes are compatible with industrial, large-scale textile manufacturing. More importantly, the comfortable TENG textiles demonstrate excellent washability and tailorability and can be fully applied in further garment processing. TENG textiles worn under the arm or foot have also been demonstrated to scavenge various types of energy from human motion, such as patting, walking, and running. All of these merits of proposed TENG textiles for clothing uses suggest their great potentials for viable applications in wearable electronics or smart textiles in the near future.

A flexible zwitterion ligand based lanthanide metal-organic framework for luminescence sensing of metal ions and small molecules.

A new lanthanide metal-organic framework was constructed using a tripodal flexible zwitterion ligand (H3LBr3) which takes a chair-shaped configuration. The luminescence of the compound displays highly selective sensing of the Fe(3+) ion and nitrobenzene.

Chiral uranyl-organic compounds assembled with achiral furandicarboxylic acid by spontaneous resolution.

Influenced by different cations in the self-assembly of chiral units, achiral (UOC-NH4, UOC-Ca) and chiral (UOC-Na) uranyl-organic compounds were obtained from achiral reactants. The photocatalytic activity of UOC-Na was also investigated.

In vitro controlled release of theophylline from metal-drug complexes.

Two new metal-drug complexes constructed from non-toxic zinc and theophylline (TPL), an anti-asthmatic active drug, have been introduced into a release system based on matrices of hydroxypropylmethylcellulose (HPMC) and microcrystalline cellulose (MC). The release rate of TPL from the metal-drug complexes could be controlled by the amount of MC added, and the release mechanism changed from anomalous transport to Fickian diffusion.