Microfluidic device for preparing and analyzing a biological sample containing biological species , said device comprising: - a single rigid support (S), - a first unit (U1) comprising a first chamber of nonzero volume delimited by walls of the support, a filter separating said first chamber into a first space and a second space , a first channel made in said support opening at one end onto a surface of said support and at another end into said first space and a second channel made in said support and opening at one end onto a surface of said support and at another end into said second space , characterized in that the device has: - a second unit (U2) comprising a second chamber made in said rigid support (S) and delimited at least partially by a transparent wall of said support (S), a third channel made in said support (S) and opening at one end onto a surface of said support and at another end into said second chamber , - a first fluidic transfer channel between the first chamber and the second chamber , made in said support (S) and opening on the one hand into said second chamber and on the other hand at a first bypass node in said second channel , - first flow switching means arranged for selecting connection of the first chamber: - to the exterior only, via the second channel only, by sealing the mouth of the first transfer channel at the level of the first bypass node, or - to the second chamber only, through the first transfer channel, by opening the connection between the second channel and the second transfer channel at the level of the first bypass node. - a single rigid support (S), - a first unit (U1) comprising a first chamber of nonzero volume delimited by walls of the support, a filter separating said first chamber into a first space and a second space , a first channel made in said support opening at one end onto a surface of said support and at another end into said first space and a second channel made in said support and opening at one end onto a surface of said support and at another end into said second space , - a second unit (U2) comprising a second chamber made in said rigid support (S) and delimited at least partially by a transparent wall of said support (S), a third channel made in said support (S) and opening at one end onto a surface of said support and at another end into said second chamber , - a first fluidic transfer channel between the first chamber and the second chamber , made in said support (S) and opening on the one hand into said second chamber and on the other hand at a first bypass node in said second channel , - first flow switching means arranged for selecting connection of the first chamber: - to the exterior only, via the second channel only, by sealing the mouth of the first transfer channel at the level of the first bypass node, or - to the second chamber only, through the first transfer channel, by opening the connection between the second channel and the second transfer channel at the level of the first bypass node. - to the exterior only, via the second channel only, by sealing the mouth of the first transfer channel at the level of the first bypass node, or - to the second chamber only, through the first transfer channel, by opening the connection between the second channel and the second transfer channel at the level of the first bypass node. <EOS>