Homogeneous differential magnetic assay.

Assays are widely used for detection of various targets, including pathogens, drugs, toxins etc. Homogeneous assays are promising for the realization of point-of-care diagnostics as they do not require separation, immobilization, or washing steps. For low concentrations of target molecules, the speed and sensitivity of homogeneous assays have hitherto been limited by slow binding kinetics, time-consuming amplification steps, and the presence of a high background signal. Here, we present a homogeneous differential magnetic assay that utilizes differential magnetic readout that eliminates previous limitations of homogeneous assays. The assay uses a gradiometer sensor configuration combined with precise microfluidic sample handling. This enables simultaneous, differential, measurement of a positive test sample containing synthesized Vibrio Cholera target and a negative control sample, which reduces background signal and increases the read-out speed. Very low concentrations of targets down to fM levels are thus detectable without any additional amplification of number of targets. Our homogeneous differential magnetic assay method opens new possibilities for rapid and highly sensitive diagnostics at the point-of-care.