Page 118 - Glucose Monitoring Devices

Sensor interface and system connectivity 119

have developed such glucose-responsive inks and demonstrated feasibility on an
ex vivo pig skin model; a change in ink color from brown to blue was visible as
the glucose concentration increased [30].
A noninvasive and removable glucose monitoring product that attaches to the ear
(GlucoTrack) is available from Integrity Applications (Ashdod, Israel) but has not
been approved by the FDA for use in the United States. This CGM technology is
reported to measure the physiological effects of glucose in tissue via ultrasonic, elec-
tromagnetic, and thermal measurements, but certain factors such as body mass,
gender, age, and ear piercings may affect measurement results [2].
Lakowicz and coworkers of the University of Maryland School of Medicine
(Baltimore, MD) have reported on development of a contact lens that optically
measures glucose in tear fluid [58]. Phenylboronic acid containing fluorescent
dyes whose intensity changes with glucose concentrations are polymerized into
hydrogels. One potential method for measuring the change in the fluorescent signal
would use a handheld device that flashes light into the eye and measures the fluores-
cence intensity emanating from the contact lens. Similarly, color or fluorescent life-
time changes could be measured in response to glucose binding at the boronic acid
sites using the appropriate dyes [8]. In one proposed type of contact lens, a change of
color is monitored by a user by looking at a mirror and comparing glucose levels by a
color strip [10]. Platform that utilize contact lenses with integrated, on-site
electronics and wireless telemetry have also been developed [59]. These platforms
could use either enzymatic or optical transduction, but the systems would need to
compensate for the differences in the physiological differences between blood and
tear glucose concentrations [60].

Sensor interface and system connectivity
A CGM System is composed of subcomponents and systems that span transduction,
embedded systems, Apps, and PC/Cloud-based systems. An overview of the
functional interaction of these components is shown in Fig. 6.4.
Stepping through this sequence begins with the acquisition of signal through the
glucose transducer; the measurement, either analog or digital at that point, is then
sent to a wearable transmitter using a short-range interface via wired or wireless
connections. The commercial transcutaneous CGM sensors are wired and the subcu-
taneous sensors utilize near-field communication (NFC) wireless communication
with a read range of <2 cm. This signal is then processed in the signal conversion
electronics that is within the wearable transmitter. This wearable transmitter also
enables the conversation of that signal into the glucose value. At this point, the signal
is sent via a mid-range wireless to a unit that is implemented either using a custom
RF protocol, or Bluetooth low energy, or using NFC direct to a hand-held device.
With the measurement information in the handheld device, which is either a custom
receiver or mobile phone, various informatics about the glycemic status and history