| Execution Methods |
- This project develops a flexible non-invasive sweat sensing device. This system includes a flexible sensor array, signal amplification and processing circuits, and an APP that displays the sensing results.
- The purpose of this project is to detect markers that are important or distinctive to the human body, including glucose, sodium ions, pesticides (insecticides) and temperature.
- Use flexible polyethylene terephthalate (PET) as the substrate, on which the silver/carbon glue layer was coated by the screen printing method as the sensor electrode array. Then the marker sensing film and silver/silver chloride layer were deposited on the working electrode and the reference electrode, respectively.
- The signal amplification and processing circuits were realized by commercially available operational amplifiers, resistors, capacitors, Arduino development boards and Bluetooth modules. A lithium battery and DC/DC converter were used to provide power of all devices.
- Prepare the standard solution of each marker to characterize the sensor and circuit, use the current/voltage measurement instrument to measure the results, and display the sensing results on the smart phone APP.
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| Performance Evaluation |
- Temperature sensor: Silver and carbon based thin film temperature sensor were fabricated and characterized. Their resistance linearly varied with the temperature regardless of Ag or C films and the linearity of 0.9996 and 0.9842 were achieved for Ag and C ones, respectively. The sensitivity of the Ag film-based sensor is 2.15%, which is better than that of the C film (0.45%) at 37.0 °C.
- Na + ion sensor: The sensing characteristics varied with the content of multi-walled carbon nanotubes (MWCNTs) in the sodium ion sensing film. When the sodium ion concentration ranges from 10-3 to 1 M, as the MWCNTs increase from 0 to 0.1 and 0.2wt%, the sensitivity decreased slightly from 110 to 107.5 and 106.1 mV/dec. The sensing voltage value has extremely high linearity (>0.999) to the sodium ion concentration. The response time improved with the increase of MWCNTs. When the MWCNTs increased from 0 to 0.2wt%, the response time decreased from 11.2 to 7.4 s.
- Glucose sensor: The sensing current varied with glucose concentration. For cyclic voltammetry measurement, when the glucose concentration increased from 10-8 to 10-3 M, the sensing oxidation peak current rose from 1.94 to 3.3 uA. When the glucose concentration ranges from 2 to 10 mM, the sensitivity of sensing current is 1.63 mA/M, and the linearity is 0.935.
- Insecticide (cypermethrin) sensor: The sensing current varied with the concentration of cypermethrin. For cyclic voltammetry measurement, when the concentration of cypermethrin increased from 0 to 50 ppm, the sensing oxidation peak current increased from 0.704 to 0.922 mA. When the concentration of cypermethrin ranges from 0 to 10 ppm, the sensitivity of the sensing current is 20.8 uA/ppm, and the linearity is 0.716.
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| Conclusion & Suggestion |
- The proposed sweat sensors consist of flexible sensor plates, signal processing and readout circuits, and could detect sodium ion, glucose, cypermethrin and temperature.
- The sensitivity and linearity of the Ag film-based temperature sensor is better than that of the C film.
- The Na+ ion sensor without MWCNT incorporation exhibited slightly better sensitivity than that with 0.2 wt% MWCNT incorporation. However, the latter had better response time.
- The glucose sensor achieved the sensitivity of 1.63 mA/M and linearity of 0.935.
- The cypermethrin sensor achieved the sensitivity of 20.8 mA/ppm and linearity of 0.716.
- The proposed non-invasive sweat sensor has been developed so far and requires more work to improve certain sensing characteristics and integrate all components for wearable device applications. In the future, we will find manufacturers to cooperate with production-academic projects to push this device to the practical stage.
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| Appendix |
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