A method for detecting the presence of a pathogen in a whole blood sample, the method comprising: (a) providing a whole blood sample from a subject; (b) mixing the whole blood sample with an erythrocyte lysis agent to produce disrupted red blood cells; (c) following step (b), centrifuging the sample to form a supernatant and a pellet, discarding some or all of the supernatant, and resuspending the pellet to form an extract, optionally washing the pellet prior to resuspending the pellet and optionally repeating step (c); (d) lysing cells of the extract to form a lysate; (e) placing the lysate of step (d) in a container and amplifying a target nucleic acid in the lysate to form an amplified lysate solution comprising the target nucleic acid, wherein the target nucleic acid is characteristic of the pathogen to be detected; (f) following step (e), mixing the amplified lysate solution with from 1×10 6 to 1×10 13 magnetic particles per milliliter of the amplified lysate solution to form a liquid sample, wherein the magnetic particles have a mean diameter of from 700 nm to 950 nm, a T 2 relaxivity per particle of from 1×10 9 to 1×10 12 mM -1 s -1, and binding moieties on their surface, the binding moieties operative to alter aggregation of the magnetic particles in the presence of the target nucleic acid or a multivalent binding agent; (g) placing the liquid sample in a device, the device comprising a support defining a well for holding the detection tube comprising the magnetic particles and the target nucleic acid, and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the liquid sample to a bias magnetic field created using one or more magnets and an RF pulse sequence; (h) exposing the sample to a bias magnetic field and an RF pulse sequence; (i) following step (h), measuring the signal from the liquid sample, wherein the liquid sample optionally comprises whole blood proteins and non-target oligonucleotides; and (j) on the basis of the result of step (i), detecting the pathogen, wherein optionally the pathogen is bacteria or fungi, and wherein the method is capable of detecting a pathogen concentration of 10 cells/mL in the whole blood sample, preferably wherein steps (a) through (i) are completed within 3 hours and/or step (i) is carried out without any prior purification of the amplified lysate solution. (a) providing a whole blood sample from a subject; (b) mixing the whole blood sample with an erythrocyte lysis agent to produce disrupted red blood cells; (c) following step (b), centrifuging the sample to form a supernatant and a pellet, discarding some or all of the supernatant, and resuspending the pellet to form an extract, optionally washing the pellet prior to resuspending the pellet and optionally repeating step (c); (d) lysing cells of the extract to form a lysate; (e) placing the lysate of step (d) in a container and amplifying a target nucleic acid in the lysate to form an amplified lysate solution comprising the target nucleic acid, wherein the target nucleic acid is characteristic of the pathogen to be detected; (f) following step (e), mixing the amplified lysate solution with from 1×10 6 to 1×10 13 magnetic particles per milliliter of the amplified lysate solution to form a liquid sample, wherein the magnetic particles have a mean diameter of from 700 nm to 950 nm, a T 2 relaxivity per particle of from 1×10 9 to 1×10 12 mM -1 s -1, and binding moieties on their surface, the binding moieties operative to alter aggregation of the magnetic particles in the presence of the target nucleic acid or a multivalent binding agent; (g) placing the liquid sample in a device, the device comprising a support defining a well for holding the detection tube comprising the magnetic particles and the target nucleic acid, and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the liquid sample to a bias magnetic field created using one or more magnets and an RF pulse sequence; (h) exposing the sample to a bias magnetic field and an RF pulse sequence; (i) following step (h), measuring the signal from the liquid sample, wherein the liquid sample optionally comprises whole blood proteins and non-target oligonucleotides; and (j) on the basis of the result of step (i), detecting the pathogen, wherein optionally the pathogen is bacteria or fungi, and wherein the method is capable of detecting a pathogen concentration of 10 cells/mL in the whole blood sample,