Flexible and wearable sensors have
attracted much attention for
their applications in health monitoring and the human–machine
interaction. The most studied wearable sensors have been demonstrated
for sensing a limited range of metabolites such as ions, glucose,
uric acid, lactate, etc. Both sweat and urine contain numerous other
physiologically relevant metabolites indicative of health and wellness.
This work demonstrates the use of the wearable sensor for the detection
of β-hydroxybutyrate (HB) in sweat. HB is an important biomarker
for diabetic ketoacidosis, a condition caused by the accumulation
of ketone bodies in hyperglycemia or metabolic acidosis patients.
Herein, we fabricated an integrated sensing system coupling an HB
detection chamber with a serpentine electrode for sensing physiological
signals such as pulse beat, vocal cord vibration, etc. The real-time
HB detection was based on a β-hydroxybutyrate dehydrogenase
enzymatic reaction. The stability of the enzyme and the cofactor couple
was achieved by cross-linking networks and a redox mediator, thereby
achieving high selectivity and low detection limits to HB in urine
and sweat. The dual-functional sensor was integrated with a signal
processing circuitry for signal transduction, conditioning, processing,
wireless transmission, and real-time convenient health monitoring
display to a smartphone via home-developed software.