Abstract: The present invention describes a method and device for improving the capture and interrogation of a rare cell population in a biological fluid such as in circulating tumor cells (CTC) in blood or Diagnostic Leukapheresis. ReFLECT-CTC is designed to capture CTC in a continuous fashion and interrogate isolated individual CTC. ReFLECT-CTC has the advantage of sampling large volumes of a biological sample which is especially useful in assessing the heterogeneity of a CTC population. The invention has application in cancer diagnostics where assessing tumor cells found in individual cancer patients will determine which drugs are most likely to be effective for an individual.