 In this study we will use an atomic force microscopy AFM to probe the surface nanostructure of beta human chorionic gonadotropin. The conformational change of the beta human chorionic gonadotropin which is secreted by persistent gestational trophoblastic tumors during chemotherapy will be studied. We will also want to directly visualize a single molecular structure of beta human chorionic gonadotropin, and quantitative measurements of the dimensions of the glycoprotein will be provided. The average height calculated for each hCG beta particle will be measured and compared subsequently during chemotherapy. Moreover, a experiment using dual polarization interferometric DPI as a biosensor will also be performed, and the average monolayer thickness value will also be calculated. To investigate further the surface ultrastructure of a hCG beta molecule, a hCG beta sample at very low concentration will be scanned in vacuum by AFM. The higher-resolution images will clearly reveal the shape of hCG beta molecules. In addition, phase images of hCG beta molecules will be captured simultaneously with their height images, and the lateral dimensions of the shape of hCG beta molecules will then be measured and calculated. The average values calculated for the outside diameter and pore diameter will thus be obtained. This study will represent the first direct characterization of the surface ultrastructure of the hCG beta molecule at a nanometer scale. The physical measurements of the outer diameter, pore diameter, and protomer diameter in the hCG beta by AFM and DPI may suggest how to recognize hCG beta molecules, which constitute an important tumor marker during chemotherapy for persistent gestational trophoblastic tumors. Unraveling the molecular structure and measuring the dimensions of hCG beta may provide new directions for future application in clinical hCG beta sensor chips. In can also be likely that the dimensional change of hCG beta molecules may also have some clinical implications for persistent gestational trophoblastic tumors. 