As the major analytical model

AcknowledgmentsThe authors thank the financial support from the Key Program of Science and Technology of Beijing Municipal Education Commission (No. KZ201110005006) and the Doctoral Fund of China Education Ministry (No. 20131103110011).
Sandwich-type electrochemical immunosensor; Tissue polypeptide antigen; Ferriferrous oxide nanoparticles; Gold nanoparticles; Graphene
1. Introduction
Tissue polypeptide antigen (TPA) is a protein produced and released by proliferating G-749 that possesses several characteristics for an ideal tumor marker [1]. Evaluating the content of TPA in human serum is helpful to the monitoring the occurrence of cancer, such as breast cancer [2], ovarian carcinoma [3], squamous cell lung cancer [4] and oral squamous cell carcinoma [5]. Nowadays, electrochemical immunosensor based on specific interaction between antigens and antibodies has attracted extensive attentions and become a popular technique for the detection of tumor markers [6] and [7]. Because it has good portability, low cost, low power requirements, high sensitivity, and high compatibility with advance micromachining technologies [8].