Chemical signal-impermeable mask

A sensor assembly for use with a chemical signal monitoring device, comprising;

• a sensor housing having a top portion and a bottom portion, the bottom portion defining a bottom portion opening within the bottom portion;
• a chemical signal impermeable mask positioned between the top portion and the bottom portion, the mask having a surface area greater than or equal to the surface area of the bottom portion opening, and defining a mask opening, the mask being positioned so that the mask opening and the bottom portion opening are aligned;
• and
• a working electrode positioned in the top portion of the sensor housing;
• wherein prior to use a hydrogel is inserted between the sensor housing bottom portion and top portion such that when the sensor assembly is closed, the top portion is positioned directly over the bottom portion such that a first hydrogel face contacts the mask, and the working electrode is in contact with a second hydrogel face opposite the first hydrogel face, the working electrode being positioned directly opposite the bottom portion opening.

A method of measuring the amount of a chemical signal present in the bloodstream of a mammalian subject, the method comprising:

• contacting with a mammalian subject's skin a sensor assembly comprising a) a chemical signal impermeable mask, the mask defining an opening in the mask and having a first face in contact with the skin;
• b) an ionically conductive material having a first face in contact with a second face of the first mask face;
• and c) a working electrode in contact with a second face of the ionically conductive material opposite the first ionically conductive material face, the working electrode positioned on the ionically conductive material directly opposite the mask opening;
• transporting in a direction substantially axial to a catalytic face of the working electrode a chemical signal from the subject's bloodstream, through the subject's skin, into the opening defined by the mask, and through the ionically conductive material;
• and
• monitoring an electrical signal generated at the working electrode by catalytic conversion of the chemical signal into an electric signal at the catalytic face of the working electrode;
• wherein the electrical signal generated at the working electrode is correlated with an amount of chemical signal present in the bloodstream of the mammalian subject.

An assembly for use in monitoring a chemical signal, comprising:

• (a) an ionically conductive material comprised of water, electrolyte and an enzyme;
• (b) a working electrode having a catalytic surface comprised of a material selected from the group consisting of platinum, palladium, nickel, and oxides, dioxides and alloys thereof, the catalytic surface contacting a first face of the ionically conductive material;
• and
• (c) a chemical signal impermeable mask positioned on a second face of the ionically conductive material (a) opposite the first ionically conductive material face and opposite the catalytic surface of the electrode (b), the mask having an outer perimeter which is equal to or extends beyond an outer perimeter of the working electrode (b) and having an opening therein which has a perimeter which is equal to or circumscribed within the outer perimeter of the working electrode.

An assembly for use in a monitoring device for monitoring a chemical signal, comprising:

• a) an ionically conductive material;
• and
• b) a mask characterized by being impermeable to the chemical signal, the mask being positioned between ionically conductive material and a source of chemical signal;
• wherein the mask is concentric to a working electrode which measures chemical signal transported from the source of chemical signal to a catalytic surface of the electrode, and further wherein the chemical signal that passes through a plane of the mask is that chemical signal that is transported from the source to the catalytic surface in a manner which is substantially perpendicular to the catalytic surface.