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The Artificial Pancreas 429

specificity in body fluids is compromised by other optically active com-
pounds in solution (Vashist, 2012).

3.5.10 Electromagnetic Sensing
This method can be used to measure changes in the dielectric characteristics
of blood that vary with glucose concentration. Eddy current or conductivity
measurements using a radiofrequency (RF) probe can be used to obtain this
information (Vashist, 2012).
3.6 The Future of Noninvasive Glucose Monitoring

In 2014 Google through a medical spin-off, Verily Life Sciences and the
Novartis eye care division, Alcon, joined forces to develop and commer-
cialize contact lens-based glucose monitors. This is a hard call as contact
lenses must be compliant to fit the shape of the eye and with a diameter
of only about 14mm and between 0.1 and 0.2mm thick, they must house
the sensor as well as the electronics to control the sensor, handle power
consumption, and provide telemetry toanexternaldevicesuchasasmart
phone.
Batteries are not practical for a number of reasons including their power-
to-weight ratio and the possibility of leaking toxic chemicals into the eye.
This leaves two major alternatives, the first being wireless energy transfer
and the second, the incorporation of a photocell onto the contact lens.
Wireless transfer generally uses near-field inductive coupling using transmit-
ter coils mounted within the frames of eye glasses. Unfortunately, both of
these techniques are only good during the day or while the user is awake
and wearing glasses. Possible alternatives are to embed a piezoelectric ele-
ment into the contact lens to extract energy from eye movement or even
tiny fuel cells that metabolize tears to provide electric power
(Barrettino, 2017).
Contact lenses are designed to be disposable, so the sensors and elec-
tronics need to be low cost and reliable over the life of the device. How-
ever, standard glucose sensing techniques are considered to be too short
lived for this application, so research is focusing on the incorporation of
hundreds or thousands of nanoscale biosensors into the lens. The ultimate
objective of the sensor development is the ability to detect a single mole-
cule of glucose.
There are, of course, problems with monitoring glucose levels in tears.
These include the low concentration, typically only 0.1–0.5mmol/L in tears