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New flow-cytometric AC impedance procedure for label-free cell differentiation


In flow cytometry, the full blood count is measured applying optical or impedance-based cell-counting instruments. To determine the concentration of white blood cells (the abundance of which is a factor of approx. 1000 – compared to red blood cells), the destruction of red blood cells by hemolysis is required. In the case of certain diseases, e.g. leukemia, however, the hemolysis procedure may lead to a hypersensitivity or even to the destruction of the white blood cells. In blood samples from newborns or from anemic patients, lysis-resistant erythrocytes may be observed which impede the correct differentiation and concentration measurement of leukocytes.

Size comparison between a microfluidic sensor and a one eurocent coin

The flow-cytometric procedure developed at PTB allows blood samples to be analyzed after having been suitably diluted, without modifying the sample by hemolysis or by using dying reagent. This method is based on the observation of the change which occurs in the complex resistance (impedance) when a blood cell passes through the electrode configuration of a microfluidic sensor. In order to identify the cells unequivocally, two alternating voltages are applied with different frequencies and each of the complex AC impedance signals is measured. From these signals, the effective resistance, the reactance and the absolute value of the impedance are determined. By choosing suitable frequencies and measurands, it is possible to differentiate in the micro-flow cytometer between the cells attributed to the full blood count including the 3-part differential white blood count, i.e. red blood cells, platelets, granulocytes, monocytes and the lymphocytes. It follows that investigations of blood samples of certain groups of patients can be carried out much more simply. Perturbing intermediate steps involving staining or labeling are not necessary.