Colorometric sensor for the non-invasive screening of glucose in sweat in pre and type 2 diabetes
Described here are patches and methods for measuring glucose in sweat (and tears and the like). In general, the patches comprise an adhesive layer adapted to bond to skin of an individual, a substrate layer disposed over the adhesive layer and comprising a glucose sensing complex including a chromogen that changes color in the presence of certain concentrations of glucose, and a cover. In typical embodiments, the substrate layer has elements formed to direct and accumulate sweat that migrates from the skin of the individual to the glucose sensing complex. Methods of using the invention can comprise cleaning the skin surface, collecting sweat in a patch comprising this microfluidic constellation of elements, and observing concentrations of glucose collected in the sweat, for example either visually, or by using a smartphone or other computer processing device.
1 . A glucose sensor comprising:
an adhesive layer adapted to bond to skin of an individual, wherein the adhesive layer comprises an opening adapted to allow sweat to migrate from the skin of the individual to a glucose sensing complex within the glucose sensor;
a substrate layer disposed over the adhesive layer and comprising a hydrophilic region, a hydrophobic region and a glucose sensing complex, wherein:
the hydrophilic region and the hydrophobic region of the substrate are adapted to modulate the flow of sweat through the glucose sensor;
the substrate layer comprises at least one channel in operable contact with the glucose sensing complex;
the opening in the adhesive layer is operably connected to the at least one channel; and
the substrate layer accumulates sweat that migrates from the skin of the individual through the opening and into the sensor, and the glucose sensing complex comprises:
an enzyme complex that reacts with glucose and comprises: glucose oxidase, glucose dehydrogenase or a hexokinase/glucose-6-phosphate complex;
a colorimetric indicator that changes color following reaction of glucose with the enzyme complex;
a wetness indicator that indicates when sufficient sweat has accumulated for the glucose sensing reaction;
a spacer layer disposed over the substrate layer, wherein the spacer layer comprises a port that allows visualization of the glucose sensing complex in the substrate layer; and
a cover layer disposed over the spacer layer, wherein the cover layer comprises a port that allows visualization of the glucose sensing complex in substrate layer; wherein:
a region of the substrate layer in which the glucose sensing complex is disposed comprises preloaded buffering compounds adapted to modulate the pH at which the glucose sensing complex senses glucose;
a region of the substrate layer in which the glucose sensing complex is disposed comprises a preloaded concentration of glucose adapted to form a threshold concentration of glucose in an aqueous environment in which the glucose sensing complex is disposed; and
the glucose sensor is adapted to measure glucose in volumes of sweat of at least 5 microliters.
2 . The glucose sensor of claim 1 , wherein the colorimetric indicator in the sensor is adapted to change color when the concentration of glucose in sweat is greater than 1.8 mg/dL.
3 . The glucose sensor of claim 1 , wherein the glucose sensing complex is adapted to measure glucose in volumes of sweat that are between 5 microliters and 25 microliters.
4 . The glucose sensor of claim 1 , further comprising:
a color indicator that indicates the expected color of the colorimetric indicator when concentrations of glucose are greater than 1.8 mg/dL; and/or
a pH indicator that indicates the pH of the glucose sensing reaction.
5 . The glucose sensor of claim 1 , further comprising a transparent layer disposed on the cover layer, wherein the transparent layer comprises an adhesive and further inhibits the evaporation of sweat.
6 . The glucose sensor of claim 1 , wherein the substrate layer and/or the spacer layer are formed from adsorbent material(s) adapted to wick sweat from the skin of the individual through the glucose sensor.
7 . A method of making a glucose sensor for detecting glucose in sweat, the method comprising:
forming an adhesive layer adapted to bond to skin of an individual, wherein the adhesive layer comprises an opening adapted to allow sweat to migrate from the skin of the individual to a glucose sensing complex within the glucose sensor;
forming a substrate layer over the adhesive layer, wherein:
the substrate layer comprises a hydrophilic region and a hydrophobic region;
the hydrophilic region and the hydrophobic region of the substrate are adapted to modulate the flow of sweat through the glucose sensor;
the substrate layer is formed to comprise at least one channel in operable contact with the glucose sensing complex;
the layer of the adhesive comprises an opening adapted to allow sweat to flow from human skin into the substrate layer, wherein the opening is operably connected to the at least one channel; and
the substrate layer is formed to comprise the glucose sensing complex and to be adapted to accumulate sweat that migrates from the skin of the individual into the sensor, and the glucose sensing complex comprises:
an enzyme complex that reacts with glucose and comprises: glucose oxidase, glucose dehydrogenase or a hexokinase/glucose-6-phosphate complex;
a colorimetric indicator that changes color following reaction of glucose with the enzyme complex, wherein the colorimetric indicator in the glucose sensing complex is a first color when the concentration of glucose in the sweat of the individual is less than 1.8 mg/dL, and a second color when the concentration of glucose is greater than 1.8 mg/dL;
forming a wetness indicator that indicates when sufficient sweat has accumulated for the glucose sensing reaction;
forming a spacer layer disposed over the substrate layer, wherein the spacer layer is formed to comprise a port that allows visualization of the glucose sensing complex in the substrate layer; and
forming a cover layer over the spacer layer, wherein the cover layer is formed to comprise a port that allows visualization of the glucose sensing complex in substrate layer; wherein:
a region of the substrate layer in which the glucose sensing complex is formed to comprise preloaded buffering compounds adapted to modulate the pH at which the glucose sensing complex senses glucose;
a region of the substrate layer in which the glucose sensing complex is disposed comprises a preloaded concentration of glucose adapted to form a threshold concentration of glucose in an aqueous environment in which the glucose sensing complex is disposed; and
the glucose sensor is formed to measure glucose in volumes of sweat of at least 5 microliters.
8 . The method of claim 7 , wherein the glucose sensing complex and/or the colorimetric indicator is coupled to the substrate layer.
9 . The method of claim 7 , wherein the method further comprises forming hydrophobic regions on the glucose sensor that are adapted to modulate the flow of sweat through the glucose sensor.
10 . The method of claim 7 , wherein the method further comprises forming on the glucose sensor:
a color indicator that indicates the expected color of the colorimetric indicator when concentrations of glucose are greater than 1.8 mg/dL; and/or
a pH indicator that indicates the pH of the aqueous solution in which glucose is sensed.
11 . The method of claim 7 , wherein the glucose sensor is formed to:
measure glucose in volumes of sweat that are between 5 microliters and 25 microliters.
12 . A method of detecting hyperglycemia in an individual, comprising the steps of:
(1) wiping skin of the individual to remove contaminants at a site at which a sensor will be adhered;
(2) adhering a glucose sensor to the skin of the individual, wherein the glucose sensor is adapted to detect glucose in the sweat of the individual and comprises:
an adhesive layer adapted to bond to skin on an individual, wherein the adhesive layer comprises an opening adapted to allow sweat to migrate from the skin of the individual to a glucose sensing complex within the glucose sensor;
a substrate layer disposed over the adhesive layer and comprising a glucose sensing complex, wherein:
the substrate layer comprises a hydrophilic region and a hydrophobic region;
the hydrophilic region and the hydrophobic region of the substrate are adapted to modulate the flow of sweat through the glucose sensor;
the substrate layer comprises at least one channel in operable contact with the glucose sensing complex;
the opening in the adhesive layer is operably connected to the at least one channel; and the substrate layer accumulates sweat that migrates from the skin of the individual into the sensor, and the glucose sensing complex comprises:
an enzyme complex that reacts with glucose and comprises: glucose oxidase, glucose dehydrogenase or a hexokinase/glucose-6-phosphate complex;
a wetness indicator that indicates when sufficient sweat has accumulated for the glucose sensing reaction;
a colorimetric indicator that changes color when glucose concentrations are when concentrations of glucose in sweat are greater than 1.8 mg/dL;
a spacer layer disposed over the substrate layer, wherein the spacer layer comprises a port that allows visualization of the glucose sensing complex in the substrate layer; and
a cover layer disposed over the spacer layer, wherein the cover layer comprises a port that allows visualization of the glucose sensing complex in substrate layer; wherein:
a region of the substrate layer in which the glucose sensing complex is disposed comprises preloaded buffering compounds adapted to modulate the pH at which the glucose sensing complex senses glucose;
a region of the substrate layer in which the glucose sensing complex is disposed comprises a preloaded concentration of glucose adapted to form a threshold concentration of glucose in an aqueous environment in which the glucose sensing complex is disposed; and
the glucose sensor is adapted to measure glucose in volumes of sweat of at least 5 microliters;
allowing the individual to form sweat in amounts sufficient to measure glucose; and
observing the colorimetric indicator to determine if the concentrations of glucose are greater than 1.8 mg/dL.
13 . The method of claim 12 , wherein the glucose sensor further comprises a:
a color indicator that indicates the expected color of the colorimetric indicator when concentrations of glucose are greater than 1.8 mg/dL; and/or
a pH indicator that indicates the pH of the aqueous solution in which glucose is sensed.
14 . The method of claim 13 , further comprising taking a photograph of the glucose sensing complex and the-color indicator so as to provide a computer readable comparison of the color of the colorimetric indicator with that of the color indicator.
15 . The method of claim 12 , further comprising disposing a transparent layer over the cover layer, wherein the transparent layer:
comprises an adhesive; and
inhibits the evaporation of sweat.