Wearable electrochemical sensors
Methods, structures, devices and systems are disclosed for fabricating and implementing electrochemical biosensors and chemical sensors. In one aspect, a method of producing an epidermal biosensor includes forming an electrode pattern onto a coated surface of a paper-based substrate to form an electrochemical sensor, the electrode pattern including an electrically conductive material and an electrically insulative material configured in a particular design layout, and attaching an adhesive sheet on a surface of the electrochemical sensor having the electrode pattern, the adhesive sheet capable of adhering to skin or a wearable item, in which the electrochemical sensor, when attached to the skin or the wearable item, is operable to detect chemical analytes within an external environment.
1. An epidermal electrochemical sensor device for detecting lactate in sweat, comprising:
a substrate being a flexible and adhesive sheet including one or more electrically insulative materials that is structured to adhere to skin or a wearable item of a user of the device, the substrate having a first adhesive side and a second adhesive side opposite the first adhesive side;
an electrochemical sensor operable to facilitate a redox reaction to produce an electrical signal, comprising:
a first electrode disposed on the substrate and configured as a working electrode, the first electrode comprising a semi-conductive ink containing carbon microfibers,
a second electrode disposed on the substrate and configured as a counter electrode,
a third electrode disposed on the substrate and configured as a reference electrode, the third electrode comprising a conductive ink,
a sensing layer disposed on an outer surface of the first electrode and comprising an electroactive redox mediator and multi-walled carbon nanotubes, wherein the sensing layer is configured to tether an active site of an enzyme catalyst comprising lactate oxidase, and
a polymer layer disposed on the sensing layer and configured to protect the sensing layer and impede an efflux of constituents of the sensing layer from the first electrode; and
a plurality of electrode interface components each electrically coupled to a respective one of the first electrode, the second electrode, and the third electrode via an electrically conductive conduit,
wherein, when attached to the skin or the wearable item and electrically coupled via the plurality of electrode interface components to one or more electrical circuits, the epidermal electrochemical sensor device is operable to detect lactate in the user's sweat that contacts the device,
wherein the epidermal electrochemical sensor device is able to undergo strain including 120 bends and 80 stretches while maintaining a substantially stable response, and
wherein the first electrode, the second electrode, and the third electrode are disposed on the first adhesive side of the substrate, and wherein the substrate is structured to adhere to the skin or the wearable item of the user on either of the first adhesive side or the second adhesive side of the substrate.
2. The device of claim 1 , wherein the polymer layer includes chitosan and the electroactive redox mediator includes tetrathiafulvalene.
3. The device of claim 1 , wherein the device is configured to attach to the skin or the wearable item by the first adhesive side of the substrate and position the first electrode, the second electrode, and the third electrode to make contact with the skin.
4. The device of claim 1 , wherein the device further comprises:
a paper sheet that is attachable to the second adhesive side of the substrate and configured to be peeled off of the substrate,
wherein the device is configured to attach to the skin or the wearable item by the second adhesive side of the substrate after removal of the paper sheet.
5. The device of claim 1 , wherein the one or more electrically insulative materials of the substrate includes a silicone.
6. The device of claim 1 , wherein the substrate includes one or both of polyvinyl alcohol (PVA) and polydimethylsiloxane (PDMS).
7. The device of claim 1 , wherein the one or more electrical circuits is configured to apply excitation waveforms and transduce the electrical signal produced by the device upon excitation.
8. The device of claim 7 , wherein the one or more electrical circuits includes a potentiostat to obtain amperometric or voltammetric measurements or a galvanostat to obtain potentiometric measurements.
9. The device of claim 1 , wherein the second electrode includes multi-walled carbon nanotubes.
10. The device of claim 1 , wherein the second electrode includes an electrically conductive material that includes an electrically conductive ink, and wherein the electrically conductive ink includes at least one of gold, platinum, nickel, silver, or silver chloride.
11. The device of claim 10 , wherein the second electrode further includes carbon fiber segments dispersed within the conductive ink.
12. The device of claim 1 , wherein the second electrode includes an electrically semi-conductive material.
13. The device of claim 12 , wherein the electrically semi-conductive material includes a semi-conductive ink including at least one of amorphous carbon, carbon black, or graphite.