Latent fingerprint detection using a scanning Kelvin microprobe

Electrochemical interactions between latent human fingerprints and metal su rfaces in ambient air are investigated using a scanning Kelvin microprobe. Inorganic salts present in sweat deposited at fingerprint ridges locally de passivate the metal surface producing a Volta potential decrease of greater than 200 mV. Volta potential patterns may persist for months and prints ma y be visualized by potential mapping, even when overcoated with a polymer l ayer. Because the Volta potential differences are produced by involatile sa lts they persist when the organic components, of the fingerprint residue ha ve been volatilized by heating to 600 degreesC.