The prepared ink was a clear, transparent but half-black solution that was stable for at least 3 months. The ink surface tension was about 28 -33 mN/m due to the addition of surfactants; and the viscosity was regulated by CMC to be compatible with the printer at 0.88 cSt. Next, the ink was printed at 5mm×1cm rectangular channels which connected to the gold electrodes (source-drain). After inkjet printing, SWCNT-Ab formed a film and conveyed a certain level of conductance. Multiple layers were printed to achieve sufficient electrical conductivity. As seen in Figure , 1 layer of printing formed a thin layer of film which gave very sparse electron pathways and resulted in a high resistance at about 1 MΩ. Such low conductivity was unstable and not suitable for a sensor. Thus, by increasing the printing layers, the electrical film was thicker and provided more electron pathways. This resulted in a significantly higher conductivity. Evidently, after printing 5 layers of the SWCNTs-Ab ink, we've obtained sufficient electrical conductance. It was obvious that more than 5 layers wouldn't promote further improvement in electrical conductance. Therefore, 5 layers of printing was selected for fabricating the biosensors for HBsAg.