Currently, organic field effect transistors (OFETs) are widely used in the field of biodetection because of their inherent gain amplification function and good biocompatibility. However, the vast majority of OFET biosensors have disadvantages including a long preparation cycle, complicated processing and expensive materials. Thus, this paper proposes a simple and inexpensive preparation method for label-free detection of immunoglobulin G (IgG). In this work an active dielectric bilayer field effect transistor with 3D-printed silver source and drain electrodes was used. The active layer was modified by physically adsorbing an anti-IgG antibody on P3HT as a recognition element and then sealed with bovine serum albumin (BSA) to prevent nonspecific adsorption. The carrier mobility of the bilayer dielectric layer active field effect transistor reached 4.6 × 10 cm/Vs, and the dynamic detection range for IgG spanned 6 orders of magnitude with a detection limit of 2.9 Picomolar (pM). Controlled experiments demonstrated that the developed sensor has high selectivity for IgG. Overall, this easy-to-operate and low-cost OFET biosensor has broad commercialization prospects and lays the foundation for the early clinical detection of disease-causing biomolecules.