The invention discloses methods and devices for rapidly detecting a biological or other residue in a liquid sample. In some embodiments of the instant invention, a single electrode is employed to contact a flowing aqueous solution, with electrical outputs being recorded by an electrical metering device. Injection or flow of sample leads to changes in solution electrostatic behavior; those changes are recorded in the metering device, with absence of predetermined residues or targets yielding the highest signals. General and specific target detection may be performed with various embodiments of the instant invention.