TLDR
Stretchable sweat sensor with printed battery and real-time display able to measure sodium, pH, glucose, or lactate
Article Source
Nature Electronics
Abbreviations
ECD: Electrochromic display
MCU: Microcontroller unit
Sweat Sensor Components
- Stretchable Ag2O-Zn (Silver Oxide-Zinc) battery
- Electrochemical sensors (sends inputs to MCU)
- Potentiometric type
- Enzymatic type
- Analog-digital-converter
- Low-power microcontroller unit (MCU)
- 10 ECD pixel display
- Silver ink “wires”
- On/Off switch
The Sensor
Figure 1 illustrates the various layers of the sweat sensor. 2 potentiometric sensors are demonstrated for monitoring sodium ions and pH. And 2 enzymatic amperometric sensors are demonstrated for monitoring glucose and lactate.
The printed silver ink that makes up the “wires” are chloride/lactate treated. This makes it so that when the sensor is stretched, as in when your skin stretches, the resistance of the wires is more or less the same. The study’s Supplementary Fig. 2 shows how dramatic the stability changes after treatment.
Researchers developed a rapid room-temperature ‘solvent-welding’ process to bond the rigid chip and soft-printed circuit due to their highly differing elastic moduli (a measure of a material’s resistance to non-permanent deformation). This bonding process also allows the MCU to be connected without having to use conductive adhesives and provided up to 300% strain without any slipping of the MCU metal contact pads with the substrate. With measurements being made every 30 seconds, the sensor was shown to monitor over 14,000 sessions and lasted a total 120 hours (5 days).
Figure 1 – Basic components and stack of the sensor
Opinion
I can imagine that high-paid performance athletes would be eager first customers for a product like this. It’s interesting that the study decided to focus on a real-time on-board display to quantify the measured levels. It would be interesting to see if instead of using the high power battery for the display, if data could be transmitted via bluetooth to a smartphone. Researchers report a 1.6 V battery level at about 5 mAh. Could this be enough to power a sensor for a day or two? From an athlete’s perspective or even your every day person, I think letting your phone monitor sodium levels for example, would be much more convenient than having to look at the display constantly to track your sodium levels.
