In Coulter counters, cells counting and volumetry are achieved by monitoring their electrical print when they flow through a sensing zone. However, the volume measurement may be impaired by the cell dynamics, which may be difficult to control. In this paper, numerical simulations of the dynamics and electrical signature of red blood cells in a Coulter counter are presented, accounting for the deformability of the cells. In particular, a specific numerical pipeline is developed to overcome the challenge of the multi‐scale nature of the problem. It consists in segmenting the whole computation of the cell dynamics and electrical response in a series of dedicated computations, with a saving of one order of magnitude in computational time. This numerical pipeline is used with rigid spheres and deformable red blood cells in an industrial Coulter counter geometry, and compared with experimental measurements. The simulations not only reproduce electrical signatures typical of those measured experimentally, but also allow an analysis of the electrical signature in terms of the heterogeneity of the electrical field and dynamics of the particles in the measurement zone. This study provides a methodology for computing the sizing of rigid or deformable particles by Coulter counters, opening the way to a better understanding of cells signatures in such devices.

The Coulter principle is a widespread technique for sizing red blood cells (RBCs) in hematological analyzers. It is based on the monitoring of the electrical perturbations generated by cells passing through a micro‐orifice, in which a concentrated electrical field is imposed by two electrodes. However, artifacts associated with near‐wall passages in the sensing region are known to skew the statistics for RBCs sizing. This study presents numerical results that emphasize the link between the cell flow‐induced rotation in the detection area and the error in its measured volume. Based on these observations, two methods are developed to identify and reject pulses impaired by cell rotation. In the first strategy, the filtering is allowed by a metric computed directly from the waveform. In the second, a numerical database is employed to train a neural network capable of detecting if the cell has experienced a rotation, given its electrical pulse. Detecting and rejecting rotation‐associated pulses are shown to provide results comparable to hydrodynamical focusing, which enforces cells to flow in the center of the orifice, the gold standard implementation of the Coulter principle.

We present the principle of a fast magnetic field enhanced colloidal agglutination assay, which is based on the acceleration of the recognition rate between ligands and receptors induced by magnetic forces. By applying a homogeneous magnetic field of 20 mT for only 7 s, we detect CRP (C-reactive protein) in human serum at a concentration as low as 1 pM for a total cycle time of about 1 min in a prototype analyzer. Such a short measurement time does not impair the performances of the assay when compared to longer experiments. The concentration range dynamic is shown to cover 3 orders of magnitude. An analytical model of agglutination is also successfully fitting our data obtained with a short magnetic pulse.

Counting and sizing blood cells in hematological analyzers is achieved using the Coulter principle. The cells flow in a micro-aperture in which a strong electrical field is imposed, so that an electrical perturbation, called pulse, is measured each time a cell crosses the orifice. The pulses are expected to contain information on the shape and deformability of Red Blood Cells (RBCs), since recent studies state that RBCs rotate and deform in the micro-orifice. By implementing a dedicated numerical model, the present study sheds light on a variety of cells dynamics, which leads to different associated pulse signatures. Furthermore, simulations provide new insights on how RBCs shapes and mechanical properties affect the measured signals. Those numerical observations are confirmed by experimental assays. Finally, specific features are introduced for assessing the most relevant characteristics from the various pulse signatures and shown to highlight RBCs alterations induced by drugs. In summary, this study paves the way to a characterization of RBC rheology by routine hematological instruments.

The aim of this study is to combine multiple excitation wavelengths in order to improve accuracy of fluorescence characterization of labeled cells. The experimental demonstration is realized with a hematology analyzer based on flow cytometry and a CW laser source emitting two visible wavelengths. A given optical encoding associated to each wavelength allows fluorescence identification coming from specific fluorochromes and avoiding the use of noisy compensation method.