Biomedical Engineering Reference
In-Depth Information
reactions. This is done by attaching a nanoengineered polymeric matrix attached to the
implanted end of the fiber. These authors indicate that the successful management of DM
requires (as is well known) the frequent measurement of glucose measurement (Diabetes
Control and Complications Trials, 1993; UK Prospective Diabetes Study Group, 1998 ).
Liao et al. (2008) emphasize that even though insulin delivery technology is well established,
there are still problems that exist with glucose sensors ( Stell et al., 2004 ). Some of the pro-
perties of an effective biosensor according to them include: low cost to operate (which
includes cost of the sensor itself, of installation, and the frequency at which it would have
to be changed), it should be minimally obstructive, and should permit frequent
measurements. Liao et al. (2008) report that the present method of monitoring blood glucose
levels (MBG) is by self monitoring (e.g., by pricking one's finger followed by subsequent
measurement by a 95-99% accurate meter, the Clark meter ( Clark, 2005 )).
The assay method uses glucose oxidase to consume glucose. However, in the body this
enzyme, glucose oxidase, deteriorates with time, and is also sensitive to pH and temperature
( Usmani and Akmiai, 1994 ; Tamada et al., 2002; Wenholt et al., 2006 ). According to Liao
et al. (2008) there is a further drawback due to limited or uncertain stability. Liao et al.
(2008) are developing a family of disposable, minimally invasive in vivo sensors that could
measure different analytes in diabetic patients over several weeks. Their biosensor measures
glucose concentrations using the fluorescence resonance energy transfer (FRET) assay based
on the selective binding of saccharides by the jack bean lecithin Concanavalin A (con A)
( Meadows and Schultz, 1993 ). Their present biosensor design ( Liao et al., 2008 )isan
improvement on their initial design ( Liao et al., 2005 ), because it permits the sensor to mea-
sure glucose concentrations in the physiological range of 0-500 mg/dL. Liao et al. (2008)
assert that their biosensor is the first step towards the development of a successful sensor.
The next step would be the validation of their results against a gold standard such as intrave-
nous blood glucose, followed by other questions such as degradation of materials (e.g., the
PEG matrix), and speed and accuracy.
Figure 6.10a and b shows the binding of blood glucose to the percutaneous fiber-optic
biosensor used for chronic glucose monitoring ( Liao et al., 2008 ). In both these cases a
dual-fractal analysis is required to adequately describe the binding kinetics. The values of
(a) the binding rate coefficient, k , and the fractal dimension, D f , for a single-fractal analysis,
and (b) the binding rate coefficients, k 1 and k 2 , and the fractal dimensions, D f1 and D f2 , for a
dual-fractal analysis are given in Tables 6.6 and 6.7 .
It is of interest to compare the binding of glucose to the percutaneous fiber-optic biosensor
( Liao et al., 2008 ) with the binding of the glucose in solution to the neodymium
hexacyanoferrate nanoparticles on the glucose oxidase/chitosan-modified GCE ( Sheng
et al., 2008 ). In both these cases, a dual-fractal analysis is required to adequately describe
the binding kinetics. It is seen that as one goes from the percutaneous fiber-optic biosensor
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