As the ink possessed proper fluidic properties, including the particle size, low surface tension, medium viscosity, and good ink stability, the droplet was formed by wetting the nozzle and perturbated out to form the ligand drop and main drop. With the optimal ink formulation, the ink had a Z value between 1-14, meaning the secondary ligand did not evolve into the satellite, rather, the ligand and the main drop re-joined to form the final droplet to deposit on the substrate. The droplets were then connected on the film by repeated printing process. Since the ink contains ethyl cellulose, the coffee ring effect was significantly reduced. Therefore, a uniform film of rGO was formed. rGO ink was printed in lines to fill the gaps between the IDEs to contact the source-drain electrode. After annealing at 210C for 1 h, the film was fully annealed and achieved high conductivity at 25 kΩ/sqr. Therefore, for each sensor, after thermal annealing, the rGO-gold contacts were firmly connected with excellent conductivity with a final roughness of about 90 nm and an initial resistance at 0.99 kΩ. With the UV-Vis spectrum scan, the ink adsorption showed a peak at around 340 nm in the UV region which indicated the van Hove singularity of rGO. Other WLs did not show obvious peaks due to the linear dispersion of Dirac electrons. In addition, the Raman spectrum showed classical D and G peaks for rGO.