Advanced label-free cellular identification in flow by collaborative coherent imaging techniques

We investigated subclasses of living peripheral blood cells in a microfluidic-based system, with the aim to characterize their morphometric and optical properties, and to track their position in flow in a label-free modality. We employed two coherent imaging techniques: a scattering approach of precisely aligned single cells, and a digital holography approach to achieve optical cell reconstructions in flow. Cells were first 3D-aligned in round shaped capillary and subsequently measured in a following square shaped channel. Results were obtained at two fixed measurement positions, the first one was chosen close to the entrance of the measurement channel to ensure 3D cell alignment for scattering investigations; the second was placed 15 mm after to study additional cell properties by digital holography and to investigate possible variations of axial cell positions. First, the refractive index, ratio of the nucleus over cytoplasm, and cell dimension were investigated from scattering investigations. Further quantitative phase-contrast reconstructions by digital holography were employed to calculate surface area, dry mass, biovolume and positions of cells using the scattering outcomes as input parameters. The precise cell alignment at the first measurement position could be confirmed. At the second measurement position a full label-free characterization of cell classes in distinct vertical positions was realized and supported by applied microfluidic force calculations, which can be used to align, deform and/or separate cells. Our results confirm the possibility to differentiate cell classes in flow, thus avoiding chemical cell staining or labeling, which are nowadays used.