Abstract: A process for preparing a biological sample including biological species, implemented in a preparation system, the preparation system including a device that includes: a housing, a first channel provided in the housing, a second channel provided in the housing, a chamber into which the first channel and the second channel open, a filter separating the chamber into two distinct spaces, the process including the following steps: injection of the biological sample in the form of a fluid via the first channel to concentrate biological species in the first space of the chamber of the device, injection of an immunological buffer fluid via the second channel of the device so as to at least partially elute the biological species with the immunological buffer fluid.