ABSTRACT
Early detection of cancer biomarkers plays an important role in early diagnosis and treatment of cancers [1-3]. Prostate-specic antigen (PSA) is a protein produced by cells of the prostate gland [4]. The PSA test measures the level of PSA in the blood. It is normal for men to have a low level of PSA in their blood; however, prostate cancer can lead to a high level of serum PSA. The serum PSA concentration ranges from 1 to 4 ng/mL and 4 to 10 ng/mL for normal person and cancer patient, respectively [5]. Hence, developing rapid, simple, and sensitive detection methods to accurately quantify the serum PSA concentration in clinic can signicantly facilitate the early diagnosis of prostate cancer. Due to the specic binding of antibody to its antigen, immunosensors based on antibody-antigen interaction are one of the most widely used analytical techniques in quantitative detection of cancer biomarkers [6-8]. Immunosensors are biosensors based on specic antigen-antibody interactions. The transducers used in the immunosensors can detect the immunochemical reactions either directly or indirectly. Some of the common transducers used in immunosensors include optical, electrochemical, thermometric, piezoelectric, magnetic, or micromechanical. In recent years, various methods, such as enzyme-linked immunosorbent assays (ELISA) [9], •uorescence immunoassay [10], chemiluminescent assay [11], and time-resolved immuno•uorometric assay [12], have been developed for PSA detection. Compared to these methods, electrochemical immunosensors have gained considerable attention over the past decades due to their high sensitivity, short analysis time, low cost, and ease of miniaturization [13,14]. Typically, the electrochemical immunosensors have a sandwich-type structure. Specically, the primary antibody (Ab1) is rst immobilized onto a solid surface. Then, the specic antigen binds to the Ab1 site. Finally,
38.1 Introduction .................................................................................................................................. 657 38.2 Materials ...................................................................................................................................... 659 38.3 Methods ........................................................................................................................................ 659
38.3.1 Preparation of GS ............................................................................................................ 659 38.3.2 Preparation of GS-TH-HRP-Ab2 Label ........................................................................... 659 38.3.3 Preparation of GS-QD-Ab2 Label ................................................................................... 660 38.3.4 Fabrication of the Immunosensor .................................................................................... 660 38.3.5 Electrochemical Measurement Procedures ......................................................................661
