Device for the selective detecting/preconcentrating of charged analytes contained in an electrolyte, comprising: a plurality of observation channels (100a, 100b,...) each extending in a longitudinal direction in a plane, two feed channels (130a, 130b) connected together by the plurality of observation channels and configured to feed the electrolyte into said plurality of observation channels, each observation channel being in particular formed by: a nanochannel comprising a first end and a second end, and having a length, at least one microchannel (120ab 120b) extending from one of the two feed lines (130a, 130b) to one end (110a, 100b) of the nanochannel, the other end of the nanochannel being connected to the other feed line, wherein the nanochannels have a section of area less than the section of the at least one microchannel, wherein, for at least two nanochannels, a dimension among the respective length thereof or the respective section thereof is different, and wherein the section of a channel defines a width, parallel to the plane and orthogonal to the axis longitudinal, and a depth (p), orthogonal to the plane and to the axis longitudinal, wherein the nanochannels have a width comprised between 50 and 500nm, and the microchannels have a width comprised between 1 and 20μm. a plurality of observation channels (100a, 100b,...) each extending in a longitudinal direction in a plane, two feed channels (130a, 130b) connected together by the plurality of observation channels and configured to feed the electrolyte into said plurality of observation channels, each observation channel being in particular formed by: a nanochannel comprising a first end and a second end, and having a length, at least one microchannel (120ab 120b) extending from one of the two feed lines (130a, 130b) to one end (110a, 100b) of the nanochannel, the other end of the nanochannel being connected to the other feed line, wherein the nanochannels have a section of area less than the section of the at least one microchannel, wherein, for at least two nanochannels, a dimension among the respective length thereof or the respective section thereof is different, and wherein the section of a channel defines a width, parallel to the plane and orthogonal to the axis longitudinal, and a depth (p), orthogonal to the plane and to the axis longitudinal, wherein the nanochannels have a width comprised between 50 and 500nm, and the microchannels have a width comprised between 1 and 20μm. a nanochannel comprising a first end and a second end, and having a length, at least one microchannel (120ab 120b) extending from one of the two feed lines (130a, 130b) to one end (110a, 100b) of the nanochannel, the other end of the nanochannel being connected to the other feed line, wherein the nanochannels have a section of area less than the section of the at least one microchannel, wherein, for at least two nanochannels, a dimension among the respective length thereof or the respective section thereof is different, and wherein the section of a channel defines a width, parallel to the plane and orthogonal to the axis longitudinal, and a depth (p), orthogonal to the plane and to the axis longitudinal, wherein the nanochannels have a width comprised between 50 and 500nm, and the microchannels have a width comprised between 1 and 20μm.