[10]-[12] However, these traditional methods have their limitations for point-of-care application. For instance, ELISA and many electrochemical assays relies on the secondary enzymatic reactions from the specifically labeled secondary antibody to translate and amplify the binding events of among the primary antibody and the analyte, e.g., HBsAg. These traditional methods have limited sensitivity and require complicated assay fabrication steps, which may not meet the growing demand for clinical practice at POC. Nowadays, carbon nanomaterials with excellent semiconducting properties are an important era of research to develop highly sensitive bioassays. - Among all, single-walled carbon nanotubes (SWCNTs) are one of the most promising 1-D nanostructures to fabricate nanoscale biosensor. The unique properties of SWCNTs offered great advantages such as their high surface area, high conductivity, high mechanical strength, and versatile chances of doping and biofunctionalization. Thus, SWCNTs are suitable materials for electrical immunoassay fabrication. - Nonetheless, current SWCNTs-based bioassays relied on firstly the deposition or patterning of the nanotubes, then immobilization of the bioreceptors, which requires multi-step biofunctionalization to achieve the specificity and sensitivity. - In this study, a simple method of prefunctionalized CNT-Ab bioink was developed. With the immobilization of the antibody against HBsAg and blocking steps done before sensing channel or working electrode patterning via inkjet printing, the fabrication process is much simplified and flexible for various biosensing applications. As a demonstration of the utility of the proposed bioink, this report presents the ink preparation, ink printing, and the biosensing of HBsAg at low but biological relevant concentrations.