We want to challenge the perception of bioluminescence and show that it’s applications extend beyond the context of renewable energy. A novel way to exploit bioluminescence is utilising it as a signaling tool that monitors blood glucose levels through sweat. This is achieved by DiaWatch.
Diabetes and Blood Glucose Levels
Monitoring blood glucose levels is crucial for people with diabetes to live a healthy life. It can be achieved by obtaining a small blood sample which is usually done by pricking a finger ideally seven times a day .
As it require pricking a finger, a sensor that can measure glucose levels from sweat and provide immediate notification as glucose levels descend, could greatly improve life quality. It would be a more convenient way of measurement as it could be constantly used and monitored. This would mean that the diabetic population would maintain their health easier than before due to awareness of low blood sugar levels. Since 1 out of every 11 adults have diabetes, the overall impact would be immense .
What DiaWatch offers
Several wearable sensors are under development to measure blood glucose levels from sweat. However, they rely on ionotropic sensors that require sending electric current through the skin to create a voltage gradient . They can cause rashes and burns on the skin, which creates more discomfort then pricking a needle.
Different from others, DiaWatch has a highly sensitive biosensor which uses bioluminescence produced by marine bacterium Vibrio harveyi (non-toxic to humans).
This bacterium also causes the ‘Milky Sea’ phenomenon where large areas on the sea seem to be glowing. The glow is so intense that it is seen from the satellites orbiting the Earth. With this bacterium, a biosensor is designed to illuminate when your blood glucose levels are low; so bright that you (or people around you) simply cannot not-see it.
On the left Milky Sea captured in Maldives and on the right luminous Vibrio harveyi on a petri dish 
How DiaWatch works
Vibrio harveyi’s bioluminescence relies on LuxP receptor recognising a hormone-like substance, AutoInducer-2 (AI-2) . LuxP’s active site is engineered to favor glucose binding over AI-2; making glucose act like a competitive inhibitor. Additionally, LuxP’s active site is designed to be extremely sensitive, allowing it to work even with a residual amount of sweat.
Simplified representation of bioluminescence mechanism of DiaWatch. For the full pathway see the reference 
When normal amount of glucose is present in the sweat, AI-2 binding to the enzyme and luminescence is prevented. As glucose levels decrease lower than the threshold level (exact quantitative correlation between blood glucose and sweat glucose are not yet determined), AI-2 can bind to LuxP and illuminates DiaWatch. When the glucose levels rise again, luminescence disappears within 10 minutes.
DiaWatch illustration. Below the threshold level bioluminescence starts to appear. The intensity of blue luminescence increases as the blood glucose levels and consequently sweat glucose levels decrease.
Bacteria, nutrients and AI-2 are combined in a clear container, which is placed between the dial and the crystal of the watch. The container has a selective filter for the skin interface that lets glucose in, while trapping everything else inside. Bacteria can stay alive in this container up to 2 weeks and it should be replaced regularly.
By combining biology and design, DiaWatch monitors blood glucose levels and fulfills an urgent need.
Written by Elif Gediz Kocaoglan
- Abma, Rebecca K. “Blood Sugar Monitoring: When to Check and Why.” Diabetes Self-Management, 15 Aug. 2017, www.diabetesselfmanagement.com/managing-diabetes/blood-glucose-management/blood-glucose-monitoring-when-to-check-and-why/.
- “Diabetes Prevalence.” How Many People Have Diabetes – Diabetes Prevalence Numbers, 2017, www.diabetes.co.uk/diabetes-prevalence.html.
- Scientific Reports. “Bioengineers create sweat-Based sensor to monitor glucose.” University of Texas, Analytical Chemistry, 13 Oct. 2016, Bioengineers create sweat-based sensor to monitor glucose.
- Reporter, Metro News. “Natural phenomenon turns Maldives sea water brighter than the Milky Way.” Metro, 24 Mar. 2014, metro.co.uk/2012/04/04/natural-phenomenon-turns-maldives-sea-water-brighter-than-the-milky-way-375824/.
- Bassler, Bonnie, and Christopher Waters. “QUORUM SENSING: Cell-Cell Communication in Bacteria.” Annual Review of Cell and Developmental Biology, vol. 21, 10 Nov. 2005, pp. 324–340. Annual Reviews, doi:10.4016/9468.01.