A sensor assembly comprising: a first sensor substrate (70, 170) having an upper surface (70a, 170a), a lower surface (70b, 170b) opposite the upper surface (70a, 170a), and a first set of sensors (74, 174) disposed along the lower surface (70b, 170b) of the first sensor substrate (70, 170); a second sensor substrate (80, 180) having an upper surface (80a, 180a), a lower surface (80b, 180b) opposite the upper surface (80a, 180a), and a second set of sensors (84, 184) disposed along the lower surface (80b, 180b) of the second sensor substrate (80, 180); and a base (20, 120) having an upper surface (20a, 120a), a lower surface (20b, 120b) opposite the upper surface (20a, 120a) of the base (20, 120) along a vertical direction, a front end (20c, 120c), a rear end (20d, 120d) opposite the front end (20c, 120c) along a longitudinal direction that is perpendicular to the vertical direction, a first recess (22a, 122a) that extends from the upper surface (20a, 120a) of the base (20, 120) and at least partially holds the first sensor substrate (70, 170), a second recess (22b, 122b) that extends from the upper surface (20a, 120a) of the base (20, 120) and at least partially holds the second sensor substrate (80, 180), a first fluid passage (32, 132) for receiving a fluid, and a second fluid passage (48, 148) in series with and open to the first fluid passage (32, 132), characterized in that the first set of sensors (74, 174) is exposed to the first fluid passage (32, 132), and the second set of sensors (84, 184) is exposed to the second fluid passage (48, 148) and wherein the first and second sensor substrates (70, 80, 170, 180) are spaced apart along a lateral direction that is perpendicular to the longitudinal direction and wherein the first recess (22a, 122a) and the second recess (22b, 122b) are each substantially aligned along the lateral direction, and wherein the sensor assembly further comprises a transfer passage (40, 140, 56, 156) that extends between the first fluid passage (32, 132) to the second fluid passage (48, 148) substantially along the lateral direction, wherein the transfer passage (40, 140, 56, 156) extends from a first outlet passage of the first fluid passage (32, 132) to a second inlet passage of the second fluid passage (48,148), and wherein the base (20, 120) includes an inlet (24, 124) located on the upper or lower surface (20a, 120a or 20b, 120b) for receiving the sample fluid, wherein the inlet is located along the upper or lower surface (20a, 120a or 20b, 120b) at a position that overlies a portion of the first substrate (70, 170) and the first recess (22a,122a). a first sensor substrate (70, 170) having an upper surface (70a, 170a), a lower surface (70b, 170b) opposite the upper surface (70a, 170a), and a first set of sensors (74, 174) disposed along the lower surface (70b, 170b) of the first sensor substrate (70, 170); a second sensor substrate (80, 180) having an upper surface (80a, 180a), a lower surface (80b, 180b) opposite the upper surface (80a, 180a), and a second set of sensors (84, 184) disposed along the lower surface (80b, 180b) of the second sensor substrate (80, 180); and a base (20, 120) having an upper surface (20a, 120a), a lower surface (20b, 120b) opposite the upper surface (20a, 120a) of the base (20, 120) along a vertical direction, a front end (20c, 120c), a rear end (20d, 120d) opposite the front end (20c, 120c) along a longitudinal direction that is perpendicular to the vertical direction, a first recess (22a, 122a) that extends from the upper surface (20a, 120a) of the base (20, 120) and at least partially holds the first sensor substrate (70, 170), a second recess (22b, 122b) that extends from the upper surface (20a, 120a) of the base (20, 120) and at least partially holds the second sensor substrate (80, 180), a first fluid passage (32, 132) for receiving a fluid, and a second fluid passage (48, 148) in series with and open to the first fluid passage (32, 132), characterized in that the first set of sensors (74, 174) is exposed to the first fluid passage (32, 132), and the second set of sensors (84, 184) is exposed to the second fluid passage (48, 148) and wherein the first and second sensor substrates (70, 80, 170, 180) are spaced apart along a lateral direction that is perpendicular to the longitudinal direction and wherein the first recess (22a, 122a) and the second recess (22b, 122b) are each substantially aligned along the lateral direction, and wherein the sensor assembly further comprises a transfer passage (40, 140, 56, 156) that extends between the first fluid passage (32, 132) to the second fluid passage (48, 148) substantially along the lateral direction, wherein the transfer passage (40, 140, 56, 156) extends from a first outlet passage of the first fluid passage (32, 132) to a second inlet passage of the second fluid passage (48,148), and wherein the base (20, 120) includes an inlet (24, 124) located on the upper or lower surface (20a, 120a or 20b, 120b) for receiving the sample fluid, wherein the inlet is located along the upper or lower surface (20a, 120a or 20b, 120b) at a position that overlies a portion of the first substrate (70, 170) and the first recess (22a,122a).