Accurate detection and profiling of circulating tumor cells (CTCs) is a highly sought after technology to improve cancer management. Such "liquid biopsies" could offer a non-invasive, repeatable window into each patient's tumor, facilitating early cancer diagnosis and treatment monitoring. The rarity of CTCs, approximated at 1 CTC for every billion peripheral blood cells, however, poses significant challenges to sensitive and reliable detection. We have recently developed a new micro-nuclear magnetic resonance (μNMR) platform for biosensing. Through the synergistic integration of microfabrication, nanosensors, and novel chemistries, the μNMR platform offers high detection sensitivity and point-of-care operation, overcoming technical barriers in CTC research. We herein review the μNMR technology with emphasis on its application to CTC detection. Recent advances in the sensing technology will be summarized, followed by the description of the dynamic interplay between our preclinical and clinical CTC studies.