of capacitive proximity sensing. We further demonstrate the capability of this method in the fabrication of multi-layered devices by printing graphene/polyurethane(PU)/graphene parallel-plate capacitors on arbitrarily shaped objects.

Experimental section
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Graphene ink formulation
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![Graphene ink formulation **a** Photographs of the graphene ink as it is passed through the three-roll mill and corresponding SEM images. Scale bar 5 $\mu$m. **b** Effect of three-roll milling on the R$_s$ of the ink. **c** Graph showing the influence of graphene ink on the final ink’s viscosity after 6 passes through the three-roll mill. **d** Rheogram of the graphene screen printable ink, showing shear thinning behaviour. **e** Log-log plot of viscosity and shear rate of the power law region of a flow curve. **f** Ternary plot of the interaction of different loadings of IPA, EC binder and graphene as determined by DOE. Experiments are indicated with black dots. []{data-label="panel1"}](panel1){width="90.00000%"}

Like the majority of the graphics inks [@R.H.Leach1993; @Goldschmidt2003; @Flick1999], the main components of the functional graphene ink is typically made up of a functional material (in this case, graphene), a binder system (a polymeric film former to provide mechanical integrity after curing) and appropriate solvents (ink carrier). Due to the need for the graphene 