Abstract
This work describes a facile, mild and general wet chemical method to change the material and the geometry of inkjet-printed interdigitated electrodes (IDEs) thus drastically enhancing the sensitivity of chemiresistive sensors. A novel layer-by-layer chemical method was developed and used to uniformly deposit semiconducting single-wall carbon nanotube (SWCNT)-based sensing elements on a Kapton® substrate. Flexible chemiresistive sensors were then fabricated by inkjet-printing fine-featured silver IDEs on top of the sensing elements. A mild and facile two-step process was employed to convert the inkjet-printed dense silver IDEs into their highly porous gold counterparts under ambient conditions without losing the IDE-substrate adhesion. A proof-of-concept gas sensor equipped with the resulting porous gold IDEs featured a sensitivity to diethyl ethylphosphonate (DEEP, a simulant of the nerve agent sarin) of at least 5 times higher than a similar sensor equipped with the original dense silver IDEs, which suggested that the electrode material and/or the Schottky contacts between the electrodes and the SWCNTs might have played an important role in the gas sensing process.
Highlights
This work describes a facile, mild and general wet chemical method to change the material and the geometry of inkjet-printed interdigitated electrodes (IDEs) drastically enhancing the sensitivity of chemiresistive sensors
A proof-of-concept gas sensor equipped with the resulting porous gold IDEs featured a sensitivity to diethyl ethylphosphonate (DEEP, a simulant of the nerve agent sarin) of at least 5 times higher than a similar sensor equipped with the original dense silver IDEs, which suggested that the electrode material and/or the Schottky contacts between the electrodes and the single-wall carbon nanotube (SWCNT) might have played an important role in the gas sensing process
Based on the energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analyses of the IDEs at different stages, we believe that the reaction responsible for our room temperature conversion process is as follows: 3Ag(s) + HAuCl4(aq) => Au(s) + 3AgCl(s) + HCl(aq)
Summary
® Conversion of inkjet-printed Ag IDEs into porous Au counterparts. A piece of Kapton HN substrate was cleaned and functionalized with SWCNT-based sensing elements, and an array of flexible sensor prototypes was fabricated on the substrate by inkjet-printing Ag IDEs with an SNP ink on top of the sensing elements. When combining the X-ray diffraction patterns (Fig. 4) with the EDX patterns of the IDEs at different stages (Figs 2d and 3c,d), it can be concluded that (1) the IDEs before the Ag-to-Au conversion were made of Ag (Figs 2d and 4b), (2) the incubation with the HAuCl4 solution led to the conversion of Ag into Au and AgCl (Figs 3c and 4c), and (3) another incubation with the saturated NaCl solution resulted in the selective dissolution of AgCl leaving only Au behind (Figs 3d and 4d) Based on these results, we can conclude that our two-step room temperature process has converted the starting inkjet-printed dense Ag IDEs into their porous Au counterparts. The conversion of the original inkjet-printed Ag IDEs into their porous Au counterparts increased the sensor sensitivity by more than 5 times
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