In this work we will describe the fabrication of flexible, foldable, and wearable electronic/electrochemical devices using carbon-based materials. The first fabrication route is based on a direct, simple, and dry transfer method of graphite onto paper with unprecedented electrochemical features on paper. We have selected soft pencils to transfer graphite onto paper and achieved comparatively low sheet resistances. The sluggish electron transfer observed on bare pencil drawn surfaces was enhanced by two steps. The surface was first electrochemically oxidized and reduced. The origin of such unprecedented performance was characterizaed by atomic force microscopy, laser scanning confocal microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and contact angle measurements. We observed that the oxidation process causes the formation of a few microcracks on the electrode surface. Also, different chemical groups are formed and reduced due to the electrochemical treatment. Some of the weakly attached graphite particles and carbon nanodebris are detached from the electrode surface after the electrochemical treatment. Our results suggest that oxidation process leads to chemical and structural transformations on the electrode surface, and these transformations are responsible for the electrode response improvements.
The second route to fabricate carbon-based devices on paper is based on the use of sacrificial adhesive layers. It is extremelly challenging to fabricate carbon-based nanostructures on paper that has the potential to meet some of the recent demands of paper-based devices, namely: (i) low sheet resistance, (ii) high folding stability, (iii) flexible electrochemical cells with high performance and (iv) tunable electric properties to fabricate motion and wearable sensors. With this method it is possible to print different compositions of binder/carbon black with no extra care related to viscosity, particle size and solvent composition. The carbon black tracks have low sheet resistance and a high-record folding stability. I will also demonstrate the fabrication of a 3D paper-based electrochemical cell made from a single carbon-black track. Moreover, the ink was tailored in order to electrochemically detect biologically relevant molecules at low potentials. Flexible circuits can be fully crumpled and operated again with no significant response loss. Finally, we have created bioinspired motion and wearable devices by locally tuning the electrical properties of the conductive tracks.