A new wearable nanoporous organic electrochemical device used as a medical diagnostics tool for noninvasive hormone sensing.

Aerogels are solid materials with desirable properties, including very low densities, thermal conductivities, and high specific surface areas. These properties offer numerous possibilities for aerogels as functional materials. A number of mesoscopic materials have been used as building blocks for aerogels, including carbon nanotubes [1] and graphene. [2] The true potential of aerogels may be realized when functional materials are added to achieve more advanced usability. Some examples include the demonstration of oxygen-reduction reactions in graphene aerogels, [3] mechanoresponsive nanocellulose aerogels, [4] and magnetic aerogels. [5] In these examples, the active aerogels were designed from the bottom up for each specific application. However the bottom-up approach presents challenges and shortcomings, including: -The necessity of adding the active materials to the aerogel building block prior to making the aerogel. This may demand complex chemistry, and the functional materials may not be compatible with the building-block dispersion or the aerogel process. -The inability to control the thickness of the active material at the nanoscale, and the inability to construct multiple layers of different materials. -The need to design completely new aerogel building blocks and preparation procedures for each desired function.Layer by layer (LbL) assembly is a generic technique for coating functional materials onto surfaces, [6] and a large number of applications based on this technique have been accomplished. [7] It is therefore easy to envision a diversity of advanced materials that can be made using the LbL method for the self-assembly of functional materials onto aerogels. However, no aerogel material suitable for LbL and no feasible method for the LbL assembly onto aerogels have been found to date. Examples of LbL assemblies onto porous structures include the nanotube-assembly on macroporous carbon paper, [8] fire-resistant three-layer structures on a polyurethane foam, [9] and an LbL nanosheath on a polymer-blend porous structure.[10]Herein, we report a robust and rapid method for the LbL assembly of functional polymers and nanoparticles on crosslinked nanocellulose aerogels with a porosity close to 99 %, high strength, and nanoscale shape integrity in water. We show that the LbL assembly of thin films of biomolecules, conducting polymers, and carbon nanotubes can be used for adding electronic and mechanical properties. Furthermore, we demonstrate that aerogels with dry-strength and elastic wet strength enhancement, elastic mechanoresponsive resistance, and supercapacitor properties with specific capacitance values exceeding 400 F g À1 have been developed. In this study, we have chosen to work with nanofibrillated cellulose (NFC) as the aerogel building block. NFC is a rapidly emerging class of bio-friendly bulk nanomaterial that offers tremendous possibilities for the aqueous selfassembly of a range of advanced micro-and nano-structures.[11] By blending functional materials in NFC dispersions, active composites ...

Traditional thin-film energy-storage devices consist of stacked layers of active films on two-dimensional substrates and do not exploit the third dimension. Fully three-dimensional thin-film devices would allow energy storage in bulk materials with arbitrary form factors and with mechanical properties unique to bulk materials such as compressibility. Here we show three-dimensional energy-storage devices based on layer-by-layer self-assembly of interdigitated thin films on the surface of an open-cell aerogel substrate. We demonstrate a reversibly compressible three-dimensional supercapacitor with carbon nanotube electrodes and a three-dimensional hybrid battery with a copper hexacyanoferrate ion intercalating cathode and a carbon nanotube anode. The three-dimensional supercapacitor shows stable operation over 400 cycles with a capacitance of 25 F g−1 and is fully functional even at compressions up to 75%. Our results demonstrate that layer-by-layer self-assembly inside aerogels is a rapid, precise and scalable route for building high-surface-area 3D thin-film devices.