Here, a method for label-free, real-time interrogation, monitoring, detection, and sorting of biological rare cells in magnetically suspended heterogeneous samples is developed. To achieve this, heterogeneous populations of cells are levitated and confined in a microcapillary channel. This strategy enables spatiotemporal differential magnetic levitation of rare fragile dead cells equilibrating at different heights based on the balance between magnetic and corrected gravitational forces. In addition, the sorting of fragile rare dead cell populations is monitored in real-time. This technique provides a broadly applicable label-free tool for high resolution, real-time research, as well as forensic evidence processing of rape kits. This method is validated with forensic mock samples dating back to 2003, isolating sperm from epithelial cells (E. cells) with >90% efficiency and >97% purity. Overall, this method reduces the processing time by over 20-fold down to 20 min, eliminating centrifugation and labels, and providing an inexpensive and high-yield alternative to the current centrifuge-based differential extraction techniques. It can potentially facilitate the forensic downstream genomic analyses, accelerating the identification of suspects, and advancing public safety.
Keywords: forensics; label-free detection; magnetic levitation; microfluidics; sperm.
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