Autoantibody biomarker relatively recently gains a lot of research interest for early detection of cancer. Cancer autoantibody is an antibody produced by the host's immune system in response to tumor antigen. It is produced at a much earlier disease stage before other biomarkers can be observed, circulates in the serum for a relatively long period of time, and is present at higher concentrations than antigen biomarkers . In addition to identifying the early antibody biomarker, early detection of cancer needs to be complemented by the availability of ultrasensitive and reliable detection platform. Magneto-Nanosensor is a robust biomolecular diagnostics platform that has been shown to have superior sensitivity and dynamic range compared to the current gold standard ELISA (Enzyme-linked Immunosorbent Assay) . One potential antibody biomarker for the early detection of ovarian cancer is anti-Selenium-Binding Protein 1 (anti-SBP1, also known as anti-SELENBP1). Studies showed that concentration levels of SBP1 are associated with cancer progression . This submission reports highly-sensitive and reliable detection of anti-SBP1 using magnetic immunoassay technique on Magneto-Nanosensor platform. The high sensitivity of our detection platform combined with the early antibody biomarker can serve as a powerful diagnostic tool for enabling early detection of ovarian cancer.