3.5.2. Post Print Processing

Post print processing for CNT inks varies greatly based on the specific dispersants and polymers employed in the ink synthesis [136,139]. Generally, the processing is complex, which creates an incentive to remove as much of the polymer residue and dispersant before printing as possible [135]. For instance, sonication, centrifugation, washing and filtering before printing are typically essential measures to create an environment in which postprint processing is feasible [87]. In addition, careful selection of polymers and dispersants and effective processing can be employed to yield simple and effective processing [92,140]. Although several complicated polymer removal strategies have been studied, such as metal–chelation-assisted polymer removal (McAPR) and yttrium oxide coating, washing and annealing are still the most preferred because of simplicity, cost, and scalability [91]. For example, Yu et al. recently removed polycarbazole (PCz) from a CNT print via THF washing [140]. Although some PCz remained in ink, this method is an effective and simple mechanism for biocompatible post-print CNT processing [140]. Another common washing solvent is toluene which is often used with elevated temperatures to improve solubility. Annealing is also highly effective, but high-temperature restraints (above 300 ◦C) make it not suited for many flexible substrates, such as PET and TPU [83]. In a modified annealing process, one may exchange the polymer for a different material, and this process is both effective and suited to lower temperatures [139]. For instance, Sun et al. exchanged PFDD for P3ME4MT, as discussed previously, to create a high mobility electrophoretic deposition [136]. Overall, post-print processing for CNT inks is an area of high research interest, and novel advancements are greatly needed to implement CNT imprinting in high throughput fabrication processes fully.

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**Figure 8.** Graphene printing and functionalization for bioelectronics sensors. (**a**) Atomic force microscopy (AFM) images **Figure 8.** Graphene printing and functionalization for bioelectronics sensors. (**a**) Atomic force microscopy (AFM) images of screen-printed graphene (reprinted with permission from *J. Colloid Interface* Sci. (2021), 582(A), 15. Copyright 2021, Elsevier). (**b**,**c**) SEM images of an inkjet-printed graphene deposition (**b**) before and (**c**) after curing, with a minor coffee ring effect. (reprinted with permission from *Adv. Mater.* (2013), 25(29), 3985–3992. Copyright 2013, Wiley). (**d**) Examples of covalently bonded bioreceptors on a functionalized GO deposition. (reprinted with permission from *J. Nanobiotechnol.* (2018), 16,75. Copyright 2018, Springer Nature). (**e**) Graphical depiction of a FET biosensor with organo-functionalization. (reprinted with permission from *Biosens. Bioelectron.* (2017). 87, 7–17. Copyright 2017, Elsevier).
