A method for assaying target molecules in a sample liquid, the method comprising: providing an impedance monitoring device operably connected to an impedance analyzer; adding a sample liquid suspected of having target molecules to the well thereby permitting binding of target molecules to the capture molecules; monitoring impedance of the well; and determining the presence, amount or concentration of target molecules in the liquid sample from the monitored impedance. The device includes a nonconducting substrate having a well, at least two electrodes fabricated on a bottom of the well and on a same plane, wherein the surfaces of the at least two electrodes are modified with capture molecules configured to bind target molecules in a liquid sample, and at least two connection pads electrically connected to the at least two electrodes.