Page 428 - Handbook of Biomechatronics

The Artificial Pancreas 423

Fig. 8 Cross section showing the SCGM sensor attached to the skin.

0.5mm wide. However, research is underway to develop a sensor that is less
than 1mm long and embedded in the epidermis (Ribet et al., 2017).
The accuracy of subcutaneous devices is generally lower than that pro-
vided by traditional glucose monitors. They also have much more stringent
design specifications to cater for biocompatibility, stability, specificity, lin-
earity, and miniaturization, so they are more expensive to develop and
manufacture.
Microneedle-based arrays can be utilized for a variety of therapeutic and
diagnostic systems. They have a potential for painless sampling in the intra-
dermal space, so as a result there have been attempts to use them as a means of
drawing blood or other fluids for electrochemical glucose sensing. Initial sys-
tems made use of capillary action to draw the analyte out into a separate sen-
sor where analysis could take place. An alternative is to use the needle itself as
the functional electrode array. This is a more elegant and simple design that
uses a platinum-coated stainless steel in-line two-dimensional (2D) micro-
needle array coated with a film of poly(3,4-ethylenedioxythiophene)
PEDOT in which GOx has been immobilized. GOx converts glucose that
contains oxygen into gluconic acid and produces H 2 O 2 . Flavin adenosine
dinucleotide (FAD) cofactor, associated with GOx, undergoes reversible
oxidation and reduction reactions during this process. As the glucose is