Picomolar detection of mercury (II) using a three-dimensional porous graphene/polypyrrole composite electrode.

A polypyrrole (PPy)-functionalized three-dimensional (3D) porous electrode of electrochemically reduced graphene oxide (ErGO) has been prepared by electrochemical deposition. This PPy-modified 3D-ErGO electrode was used for the electrochemical detection of Hg(2+) ions, and it exhibited high sensitivity and selectivity. Furthermore, the limit of detection (LOD) was measured to be as low as 0.03 nM (30 ppt), and this value is much lower than the guideline value of 2 ppb for drinking water given by the World Health Organization.

Conducting polymer nanomaterials: electrosynthesis and applications.

Conducting polymers (CPs) have been extensively studied and widely applied in various organic devices. To improve the performances or extend the functions of the devices, CPs usually have to be nanostructured. Electrosynthesis provides an effective and convenient one-step approach to CP nanomaterials. The resulting materials are usually oriented on the electrode surfaces and their properties are easy to be controlled. This critical review focuses on the syntheses of CP nanostructures and nanocomposites by electrochemical polymerization. The applications of the nanomaterials in organic devices such as sensors, actuators and memory devices also will be discussed (111 references).

Transparent Polymeric Strain Sensors for Monitoring Vital Signs and Beyond.

Wearable sensors that can precisely detect vital signs are highly desirable for monitoring personal health conditions and medical diagnosis. In this paper, we report an ultrasensitive strain sensor consisting of a 150 nm thick highly conductive dimethylsulfoxide-doped poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) sensing layer and an elastic fluorosilicone rubber substrate. This sensor exhibits a high sensitivity at small strains (e.g., gauge factor at 0.6% strain = 280), low limit of detection (<0.2% strain), and excellent repeatability and cycling stability. Therefore, it is promising for practically detecting vital signs, tiny human motions, and sounds. Furthermore, the semitransparent shallow blue color and the soft rubbery substrate make the strain sensor beautiful and comfortable to the human body.

Fibrous strain sensor with ultra-sensitivity, wide sensing range, and large linearity for full-range detection of human motion.

It is challenging to construct exquisite microstructures for integrating extraordinary sensitivity, wide strain range detectability, low hysteresis, good linearity, and excellent reliability and stability in a single type of strain sensor. In this paper, we report a high-performance fibrous strain sensor with ultrahigh sensitivity (gauge factor up to 350), wide sensing range (0.1% to 150% strain), low hysteresis, good linearity over a large strain range (up to 50%), and excellent reliability and stability (>2000 cycles). Our fibrous strain sensor exhibits superior comprehensive properties to previous strain sensors, attributed to its hierarchical microstructure composed of twisted polyurethane fibers and microcracked poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) sensing layer on each fiber, bridged by carbon nanotube agglomerates. This sensor is attractive and promising for the full-range detection of human motion from subtle deformations to large movements. In addition, the spatial extensional strain distribution of human skin can also be detected by the sensing fabric woven by this fibrous sensor due to its knittability.

Electrochemical fabrication of two-dimensional palladium nanostructures as substrates for surface enhanced Raman scattering.

Two-dimensional palladium (Pd) nanostructures have been fabricated by electrochemical deposition of Pd onto an indium tin oxide glass substrate modified with a thin flat film of polypyrrole or a nanofibril film of polyaniline. The experimental results demonstrated that the morphology of Pd nanoparticles strongly depended on the properties of conducting polymers and the conditions of electrochemical deposition. Two-dimensional nanostructures composed of flower-like (consisting of staggered nanosheets) or pinecone-like Pd nanoparticles were successfully synthesized. They can be used as substrates for surface-enhanced Raman scattering after partly decomposing the polymer components by heating in air, and the enhancement factor of the substrate composed of flower-like Pd nanoparticles was measured to be as high as 105 for 4-mercaptopyridine.

Graphene-Based Membranes for Molecular Separation.

In comparison with traditional chemical separation processes, membrane separation is much simpler and more efficient. An ideal membrane for molecular separation should be as thin as possible to maximize its solvent flux, be mechanically robust to prevent it from fracture, and have well-defined pore sizes to guarantee its selectivity. Graphene is an excellent platform for developing size-selective membranes because of its atomic thickness, high mechanical strength, and chemical inertness. In this Perspective, we review the recent advancements on the fabrication of nanoporous graphene membranes and graphene oxide membranes (GOMs) for molecular separation. The methods of fabricating these membranes are summarized, and the mechanisms of molecular separation based on these two types of graphene membranes are compared. The challenges of synthesizing and transferring large-area nanoporous graphene membranes and engineering the performances of GOMs are discussed.

Polythiophene-based optical sensors for small molecules.

Water-soluble, regioregular polythiophene (PT) derivatives are conformational sensitive to external stimuli, and their spectral responses are determined by conformation changes, π-π interactions and scattering of visible lights originated from PT aggregates. In this paper, we review the synthesis of water-soluble PTs and their photophysical properties, and then highlight our efforts toward the development of PT-based optical sensors for small molecules. Mechanism studies indicate that the interplay between side-chain steric/electrostatic repulsive and interchain attractive interactions is responsible for the assembly and disassembly of water-soluble PTs in aqueous media. Consequently, the planarization/deplanarization of PT backbones provides the possibility for colorimetric and fluorescent dual detection of small bioanalytes and chemical species.

Strong composite films with layered structures prepared by casting silk fibroin-graphene oxide hydrogels.

Composite films of graphene oxide (GO) sheets and silk fibroin (SF) with layered structures have been prepared by facile solution casting of SF-GO hydrogels. The as-prepared composite film containing 15% (by weight, wt%) of SF shows a high tensile strength of 221 ± 16 MPa and a failure strain of 1.8 ± 0.4%, which partially surpass those of natural nacre. Particularly, this composite film also has a high modulus of 17.2 ± 1.9 GPa. The high mechanical properties of this composite film can be attributed to its high content of GO (85 wt%), compact layered structure and the strong hydrogen bonding interaction between SF chains and GO sheets.

Facile fabrication of light, flexible and multifunctional graphene fibers.

Macroscopic graphene fibers with strength comparable to carbon nanotube yarns have been fabricated with a facile dimensionally-confined hydrothermal strategy from low-cost, aqueous graphite oxide suspensions, which is shapable, weavable, and has a density of less than 1/7 conventional carbon fibers. In combination with the easy in situ and post-synthesis functionalization, the highly flexible graphene fibers can be woven into smart textiles.

Colorimetric assays for acetylcholinesterase activity and inhibitor screening based on the disassembly-assembly of a water-soluble polythiophene derivative.

A complex between an anionic polythiophene derivative (PT-COO(-)) and a cationic surfactant, myristoylcholine, has been prepared and applied to be colorimetric probe for acetylcholinesterase (AChE) assays. The complex formation process, AChE activity assay and inhibitor screening has been studied by absorption spectroscopy. It was confirmed that the introduction of myristoylcholine into PT-COO(-) phosphate buffer solution resulted in the disassembly of PT-COO(-) aggregates, and further addition of AChE into the above solution led to the reassembly of PT-COO(-) due to the catalyzed hydrolysis of myristoylcholine and the collapse of the complex. The colorimetric assay for AChE can be readily realized with the concentration of AChE as low as 0.2 U/mL. The results also demonstrate that the colorimetric approach can be applied for screening inhibitors of AChE.

Colorimetric and fluorescent dual probe based on a polythiophene derivative for the detection of cysteine and homocysteine.

Colorimetric and fluorescent dual detection of cysteine (Cys) and homocysteine (Hcy) has been realized based on the ionic self-assembly of a cationic polythiophene derivative with aromatic derivatives of Cys and Hcy formed in situ.

A pH-sensitive graphene oxide composite hydrogel.

Graphene oxide/poly(vinyl alcohol) (GO/PVA) composite hydrogel was prepared and utilized for selective drug release at physiological pH.

Chemically converted graphene as substrate for immobilizing and enhancing the activity of a polymeric catalyst.

Graphitic carbon nitride, a polymeric catalyst, was immobilized on the surfaces of chemically converted graphene sheets to form a layered composite, which exhibited greatly improved conductivity and electrocatalytic performance on oxygen reduction reaction.

Polypyrrole actuator with a bioadhesive surface for accumulating bacteria from physiological media.

A gold/polypyrrole (Au/PPy) bilayer actuator was fabricated by electrochemical deposition, and its surface was modified with a bioadhesive polymer, polydopamine. The actuator exhibited high performances of actuation in physiological media. Furthermore, the surface of the actuator is sticky in water and thus can seize bacteria from their aqueous solutions. Actuation greatly increased the efficiency of adhering bacteria on the actuator surface, and this technique provides a cheap and convenient approach for accumulating bacteria from physiological media.

A simple approach for the discrimination of nucleotides based on a water-soluble polythiophene derivative.

A sensor based on an array of wavelengths of a cationic poythiophene derivative was applied to discriminate fifteen nucleotides along with monophosphate and pyrophosphate with 100% confidence limits.

Optically active supramolecular complexes of water-soluble achiral polythiophenes and folic acid: spectroscopic studies and sensing applications.

Optically active supramolecular complexes of water-soluble achiral polythiophene (PT) derivatives, PMTPA or PMTEA (Chart 1), and folic acid have been prepared; and the complex formation processes have been studied by absorption, emission, and circular dichroism (CD) spectroscopies. The complexes exhibited unique split-type induced CDs in the pi-pi* transition region of PTs, indicating that the molecular chirality of the glutamic acid moiety in folic acid was expressed in PT backbones. The influences of temperature, solvent composition, and the structures of the inducing molecules on the chirality induction to PTs were also investigated, and a possible mechanism for the formation of chiral superstructures was proposed. Furthermore, it was found that, upon addition of folic acid into aqueous solution of PTs (PMTPA or PMTEA), a dramatic color change from yellow to purple along with the emission quenching of PT derivatives was observed. PMTEA, having one fewer carbon in the hydrophobic side chain relative to PMTPA, showed better selectivity toward folic acid sensing over ATP because of its higher solubility in water and the appropriate hydrophilic/hydrophobic balance in the complex. Therefore, it can be applied as a colorimetric and fluorescent probe for detecting folic acid with high selectivity and sensitivity. Besides naked-eye detection of folic acid, the detection limit can be extended to be 10 (-8) M by using fluorometry and PMTEA as the probing molecule.

Drying enhanced adhesion of polythiophene nanotubule arrays on smooth surfaces.

Polythiophene (Pth) films with aligned nanotubule arrays were adhered strongly on various smooth surfaces such as glass, mica, and GaAs after drying from their wet states under ambient condition. The normal and shear dry adhesion forces of the films on glass with contact areas of 0.5-1.0 cm(2) were measured to be 80 +/- 8 and 174 +/- 10 N cm(-2), respectively. These extraordinary strong adhesion forces are attributed to the high strength and stiffness of Pth and the high contact fraction (approximately 79%) of Pth nanotips on the smooth surfaces induced by drying. During the drying process, there is little controlled preload, suggesting a real gecko-like adhesion of Pth nanotubule arrays.