Electrochemical deposition of MnO2 onto carbon nanotube (CNT) yarn gives a high-performance, flexible yarn supercapacitor. The hybrid yarn's blended structure, resulting from trapping of MnO2 in its internal pores, effectively enlarges electrochemical area and reduces charge diffusion length. Accordingly, the yarn supercapacitor exhibits high values of capacitance, energy density, and average power density. Applications in wearable electronics can be envisaged.

Porous tungsten oxide films were deposited onto a sensor substrate with a Si bulk-micromachined hotplate, by drop-coating isopropyl alcohol solution of highly crystalline tungsten oxide (WO2.72) nanorods with average 75nm length and 4nm diameter. The temperature-dependent gas sensing characteristics of the films have been investigated over the mild temperature range from 20to250°C. While the sensing responses for ammonia vapor showed increase in electrical conductivity at temperatures above 150°C as expected for n-type metal oxide sensors, they exhibited the opposite behavior of unusual conductivity decrease below 100°C. Superb sensing ability of the sensors at room temperature in conjunction with their anomalous conductivity behavior might be attributed to unique nanostructural features of very thin, nonstoichiometric WO2.72.

We report electrochemically powered, all-solid-state torsional and tensile artificial yarn muscles using a spinnable carbon nanotube (CNT) sheet that provides attractive performance. Large torsional muscle stroke (53°/mm) with minor hysteresis loop was obtained for a low applied voltage (5 V) without the use of a relatively complex three-electrode electromechanical setup, liquid electrolyte, or packaging. Useful tensile muscle strokes were obtained (1.3% at 2.5 V and 0.52% at 1 V) when lifting loads that are ∼25 times heavier than can be lifted by the same diameter human skeletal muscle. Also, the tensile actuator maintained its contraction following charging and subsequent disconnection from the power supply because of its own supercapacitor property at the same time. Possible eventual applications for the individual tensile and torsional muscles are in micromechanical devices, such as for controlling valves and stirring liquids in microfluidic circuits, and in medical catheters.

Fiber and yarn supercapacitors that are elastomerically deformable without performance loss are sought for such applications as power sources for wearable electronics, micro-devices, and implantable medical devices. Previously reported yarn and fiber supercapacitors are expensive to fabricate, difficult to upscale, or non-stretchable, which limits possible use. The elastomeric electrodes of the present solid-state supercapacitors are made by using giant inserted twist to coil a nylon sewing thread that is helically wrapped with a carbon nanotube sheet, and then electrochemically depositing pseudocapacitive MnO2 nanofibers. These solid-state supercapacitors decrease capacitance by less than 15% when reversibly stretched by 150% in the fiber direction, and largely retain capacitance while being cyclically stretched during charge and discharge. The maximum linear and areal capacitances (based on active materials) and areal energy storage and power densities (based on overall supercapacitor dimensions) are high (5.4 mF/cm, 40.9 mF/cm2, 2.6 μWh/cm2 and 66.9 μW/cm2, respectively), despite the engineered superelasticity of the fiber supercapacitor. Retention of supercapacitor performance during large strain (50%) elastic deformation is demonstrated for supercapacitors incorporated into the wristband of a glove.

We have developed a sandwich-type enzyme-linked DNA sensor as a new electrochemical method to detect DNA hybridization. A partially ferrocenyl-tethered poly(amidoamine) dendrimer (Fc-D) was used as an electrocatalyst to enhance the electronic signals of DNA detection as well as a building block to immobilize capture probes. Fc-D was immobilized on a carboxylic acid-terminated self-assembled monolayer (SAM) by covalent coupling of unreacted amine in Fc-D to the acid. Thiolated capture probe was attached to the remaining amine groups of Fc-D on the SAM via a bifunctional linker. The target DNA was hybridized with the capture probe, and an extension in the DNA of the target was then hybridized with a biotinylated detection probe. Avidin-conjugated alkaline phosphatase was bound to the detection probe and allowed to generate the electroactive label, p-aminophenol, from p-aminophenyl phosphate enzymatically. p-Aminophenol diffuses into the Fc-D layer and is then electrocatalytically oxidized by the electronic mediation of the immobilized Fc-D, which leads to a great enhancement in signal. Consequently, the amount of hybridized target can be estimated using the intensity of electrocatalytic current. This DNA sensor exhibits a detection limit of 20 fmol. Our method was also successfully applied to the sequence-selective discrimination between perfectly matched and single-base mismatched target oligonucleotides.