Page 114 - Glucose Monitoring Devices

Glucose transduction technologies 115

FIGURE 6.3
Equilibrium binding of glucose to the fluorescent, abiotic glucose indicating polymer
component of the Senseonics CGM sensors (R 2 denotes connectivity to the polymer
backbone).
When glucose is not present, anthracene fluorescence is quenched by intramolecular
electron transfer from the unpaired electrons on the indicator tertiary amines. When
glucose is bound to the boronic acids, the Lewis acidity of boron is increased, and
weak boronenitrogen bonds are formed. This weak bonding prevents electron trans-
fer from the amines and consequently prevents fluorescence quenching.
As the fluorescent signal emanates from throughout the entire bulk of the fluo-
rescent polymer, not just at the surface as with electrochemical sensors, it is not sub-
ject to the same degree of fouling as sensors that employ enzymatic, electrochemical
transduction methods. Although substances frequently reported to interfere with
enzymatic, electrochemical-based transcutaneous CGM systems, such as acetamin-
ophen and ascorbic acid, have been shown to have no interfering effect, other sub-
stances such as tetracycline (which absorbs light over the spectral operating range of
the sensor) and high concentrations of mannitol (known to occur when used as an
irrigation solution during therapeutic transurethral procedures) have been shown
to interfere with the sensor readings [65]. The fluorescent-based sensor is fully
inserted into the interstitial tissue by a healthcare provider in an office-based proced-
ure. As the sensor does not protrude through the skin, the insertion site is able to
fully close and allow the resolution of the acute inflammatory response that may
limit sensor life.
For this fluorophore, hydrogen peroxide has shown to be the reason for sensors to
lose signal on the first day in CGM systems [70]. The Eversense uses a catalysis
made out of platinum that sputter-coats the sensor core to prevent decomposition
from hydrogen peroxide, which helps make it stable mechanically and chemically
for longer periods of time [69].