β-Hydroxybutyrate (HB) is one of the main physiological
ketone
bodies that play key roles in human health and wellness. Besides their
important role in diabetes ketoacidosis, ketone bodies are currently
receiving tremendous attention for personal nutrition in connection
to the growing popularity of oral ketone supplements. Accordingly,
there are urgent needs for developing a rapid, simple, and low-cost
device for frequent onsite measurements of β-hydroxybutyrate
(HB), one of the main physiological ketone bodies. However, real-time
profiling of dynamically changing HB concentrations is challenging
and still limited to laboratory settings or to painful and invasive
measurements (e.g., a commercial blood ketone meter). Herein, we address
the critical need for pain-free frequent HB measurements in decentralized
settings and report on a reliable noninvasive, simple, and rapid touch-based
sweat HB testing and on its ability to track dynamic HB changes in
secreted fingertip sweat, following the intake of commercial ketone
supplements. The new touch-based HB detection method relies on an
instantaneous collection of the fingertip sweat at rest on a porous
poly(vinyl alcohol) (PVA) hydrogel that transports the sweat to a
biocatalytic layer, composed of the β-hydroxybutyrate dehydrogenase
(HBD) enzyme and its nicotinamide adenine dinucleotide (NAD+) cofactor, covering the modified screen-printed carbon working electrode.
As a result, the sweat HB can be measured rapidly by the mediated
oxidation reaction of the nicotinamide adenine dinucleotide (NADH)
product. A personalized HB dose–response relationship is demonstrated
within a group of healthy human subjects taking commercial ketone
supplements, along with a correlation between the sweat and capillary
blood HB levels. Furthermore, a dual disposable biosensing device,
consisting of neighboring ketone and glucose enzyme electrodes on
a single-strip substrate, has been developed toward the simultaneous
touch-based detection of dynamically changing sweat HB and glucose
levels, following the intake of ketone and glucose drinks.