Leukocytes, or white blood cells (WBCs), can provide access to a veritable treasure-trove of information on the health status of each individual. For example, leukocytes can serve as indicators of pathogen infection1, especially for leukocyte-specific pathogens such as the human immunodeficiency virus (HIV). Additionally, during T-cell adoptive therapy isolated leukocytes can be expanded ex-vivo for re-targeting and re-infusion into an individual2. An important prerequisite for many leukocyte assays is the depletion of contaminating erythrocytes, or red blood cells (RBCs), as well as the isolation of specific phenotypes. Established methods are typically based on centrifugation, fluorescence-activated3, 4, and magnetic-activated cell sorting5–7. These methods are often costly, require relatively large samples, and expose leukocytes to harsh chemical and physical treatment, which may cause cell lysis, contribute to undesirable phenotypic changes8, and corrupt the information obtained from these cells9.