Abstract: A method for measuring the concentration of a chemical present in a blood stream of a mammalian subject is disclosed. The method involves contacting the subject's skin with a sensor assembly comprised of an ionically conducting material which contacts the skin, a working electrode which is in contact with the ionically conducting material which electrode has a catalytic surface and a mask having an opening therein. The mask is positioned between the skin and the working electrode. When the electrode is activated, chemical is transported through the skin and the ionically conductive material. The mask is positioned so that it blocks the flow into the catalytic surface except for flow which is substantially axially to the catalytic surface. Electrical signal generated at the working electrode is monitored over a period of time and correlated with a concentration of chemical present in the blood stream of the mammalian subject.

Abstract: A method for sampling of a substance from a subject is provided, which comprises placing one or more sampling chambers on a collection site on a tissue surface on the subject; conducting electric current through the tissue to extract a substance from the subject in a first direction in one or more sampling chambers that functions alternatively as both an anode and cathode during the course of the method; reversing the polarity to cause direct current to flow in second direction opposite the first direction; and analyzing the sampling chamber or chambers for the concentration of a substance or a substance metabolite. There is also provided a device for sampling of a substance from an organism on continuously or intermittently using alternating polarity method based on the application of low intensity electric fields of alternating polarity across the skin (iontophoresis) to enhance the transport of a substance (such as glucose, lactic acid, pyruvic acid, and the like) from body tissues to a sampling chamber.

Abstract: A chemical signal-impermeable mask is positioned in the electrolyte flow such that the mask is between a source of chemical signal and a working electrode which senses the chemical signal transported from the source (e.g., by diffusion). The configuration of the mask is such that the mask prevents substantially all chemical signal transport from the chemical signal source having a radial vector component relative to a plane of the mask and the catalytic face of the working electrode, thus allowing primarily only chemical signal transport that is substantially perpendicular to the place of the mask and the catalytic surface of the working electrode. By reducing or eliminating chemical signal radial transport toward the working electrode, the mask thus significantly reduces or eliminates edge effects. By substantially reducing edge effects created by radial transport of chemical signal, it is possible to obtain a more accurate measurement of the amount (e.g.