Phase contrast tomography at lab on chip scale by digital holography.

High-throughput single-cell analysis is a challenging target for implementing advanced biomedical applications. An excellent candidate for this aim is label-free tomographic phase microscopy (TPM). In this paper, some of the methods used to obtain TPM are reviewed, analyzing advantages and disadvantages of each of them. Moreover, an alternative tomographic technique is described for live cells analysis, and future trends of the method are foreseen. In particular, by exploiting random rolling of cells while they are flowing along a microfluidic channel, it is possible to obtain phase-contrast tomography thus obtaining complete retrieval of both 3D-position and orientation of rotating cells. Thus, a priori knowledge of such information is no longer needed. This approach extremely simplifies the optical system avoiding any mechanical/optical scanning of light source. The proof is given for different classes of biosamples, red-blood-cells (RBCs) and diatom algae. Accurate characterization of each type of cells is reported and compared to that obtained by other tomographic techniques.