Allergy diagnosis, conducted to determine whether a specific syndrome is attributable to allergy, plays a significant role in the overall health examination. In this paper we report that the detection of allergy-associated protein, immunoglobulin E (IgE), was achieved by using field effect transistors (FETs) immobilized with an antigen as a receptor, which is smaller in size than the conventional receptor (antibody). The antigen-immobilized FETs exhibit a higher response to IgE than the antibody-immobilized FETs, suggesting that the smaller receptor not only makes the more effective use of the charge-detectable region for the PET-based detection in terms of Debye length, but also provides more recognition sites for target molecules and greater ability to block nonspecific adsorption of non-related proteins because of the closely-packed immobilized receptors. In addition, the application of the antigen to FET biosensor gives an advantage in the identification of the specific allergen. These results show that the small receptor of antigen is more effective than the antibody in the allergy detection using PET biosensors. (C) 2013 Elsevier Ltd. All rights reserved.