A kit for performing methods of determining the concentration of bacterial target cells in a sample, comprising: - a cartridge (101; 1100; 2100; 3100; 4100) configured to be removably coupled to an instrument configured to rotate the cartridge about a rotation axis and detect a plurality of bacterial target cells within a sample, the cartridge comprising: - an inlet portion defining an inlet reservoir (102; 4122) configured to contain the sample; - a separation portion (2140; 3140; 4140) including a first surface (2141; 3141; 4141) and a second surface (2142; 3142; 4142) defining a separation chamber (104; 2143; 4143), the separation chamber being configured to be fluidically coupled to the inlet reservoir such that at least a portion of the sample can pass from the inlet reservoir to the separation chamber when the cartridge is rotated; and - a detection portion (1160; 2160; 3160; 4160) defining a detection chamber (105; 2163; 3163; 4163), the detection portion including a detection surface (401; 1162; 2161; 3161; 4161) that forms a boundary of the detection chamber, the detection chamber being fluidically coupled to the separation chamber such that at least the plurality of bacterial target cells can pass through the separation chamber and into the detection chamber, the detection surface and the first surface of the separation portion forming a non-zero detection angle, said non-zero detection angle between the detection surface and the first surface of the separation portion being between about 1 degree and about 8 degrees, the detection surface including a surface modification including a coating comprising a charged polymer to enhance adhesion of the plurality of bacterial target cells and thereby being configured to capture the plurality of bacterial target cells; - a density medium formulated to separate bacterial target cells from contaminants having a density of between 1.01 g/cm 3 and 1.13 g/cm 3; and - a staining reagent formulated to bind to and enhance detection of the plurality of bacterial target cells. - a cartridge (101; 1100; 2100; 3100; 4100) configured to be removably coupled to an instrument configured to rotate the cartridge about a rotation axis and detect a plurality of bacterial target cells within a sample, the cartridge comprising: - an inlet portion defining an inlet reservoir (102; 4122) configured to contain the sample; - a separation portion (2140; 3140; 4140) including a first surface (2141; 3141; 4141) and a second surface (2142; 3142; 4142) defining a separation chamber (104; 2143; 4143), the separation chamber being configured to be fluidically coupled to the inlet reservoir such that at least a portion of the sample can pass from the inlet reservoir to the separation chamber when the cartridge is rotated; and - a detection portion (1160; 2160; 3160; 4160) defining a detection chamber (105; 2163; 3163; 4163), the detection portion including a detection surface (401; 1162; 2161; 3161; 4161) that forms a boundary of the detection chamber, the detection chamber being fluidically coupled to the separation chamber such that at least the plurality of bacterial target cells can pass through the separation chamber and into the detection chamber, the detection surface and the first surface of the separation portion forming a non-zero detection angle, said non-zero detection angle between the detection surface and the first surface of the separation portion being between about 1 degree and about 8 degrees, the detection surface including a surface modification including a coating comprising a charged polymer to enhance adhesion of the plurality of bacterial target cells and thereby being configured to capture the plurality of bacterial target cells; - an inlet portion defining an inlet reservoir (102; 4122) configured to contain the sample; - a separation portion (2140; 3140; 4140) including a first surface (2141; 3141; 4141) and a second surface (2142; 3142; 4142) defining a separation chamber (104; 2143; 4143), the separation chamber being configured to be fluidically coupled to the inlet reservoir such that at least a portion of the sample can pass from the inlet reservoir to the separation chamber when the cartridge is rotated; and - a detection portion (1160; 2160; 3160; 4160) defining a detection chamber (105; 2163; 3163; 4163), the detection portion including a detection surface (401; 1162; 2161; 3161; 4161) that forms a boundary of the detection chamber, the detection chamber being fluidically coupled to the separation chamber such that at least the plurality of bacterial target cells can pass through the separation chamber and into the detection chamber, the detection surface and the first surface of the separation portion forming a non-zero detection angle, said non-zero detection angle between the detection surface and the first surface of the separation portion being between about 1 degree and about 8 degrees, the detection surface including a surface modification including a coating comprising a charged polymer to enhance adhesion of the plurality of bacterial target cells and thereby being configured to capture the plurality of bacterial target cells; - a density medium formulated to separate bacterial target cells from contaminants having a density of between 1.01 g/cm 3 and 1.13 g/cm 3; and - a staining reagent formulated to bind to and enhance detection of the plurality of bacterial target cells.