Biomedical Engineering Reference
In-Depth Information
Perfusate
pumped into
microdialysis
fibre
Dialysate
containing
analyte of
interest
Epidermis
Semi-permeable
hollow fibre
inserted into
subcutaneous
tissue
Dermis
Subcutaneous
tissue
Molecules of analytes of
interest diffuse from tissue
into fibre under influence of
concentration gradient
Blood
capillaries
11.7
The principle of microdialysis.
catheter. The optical basis for the detection of oxygen is the quenching of
the luminescence of an immobilised chemical substance, such as polycyclic
aromatic hydrocarbons and metal-ligand complexes. Immobilised pH indi-
cators such as phenol red are used for optically detecting pH, and are also
the basis, with the addition of bicarbonate salt, for measuring
p
CO
2
. Hydro-
gel fi lms are used for the immobilisation of these substances, and gas per-
meable fi lms employed in the CO
2
sensor. Catheter-based glucose and
lactate sensors have also been developed.
41
Microdialysis is a technique that has been recently used as a sampling
method in biosensors. It involves the implantation in the subcutaneous
tissue of a dialysis fi bre perfused with isotonic fl uid, into which the target
analyte diffuses, as illustrated in Fig. 11.7. The analyte is then pumped to
the electrode, which is located outside the body. This technology has been
used in combination with amperometric enzyme biosensors for glucose
detection, including the GlucoDay microdialysis device commercialised by
Menarini Diagnostics.
Microdialysis has also been used in cardiac surgery for the monitoring of
myocardial metabolism.
42
A microdialysis probe was implanted in the apical
region of the left ventricles of 30 patients, and used to take samples of
myocardial interstitial fl uid during and after coronary artery bypass surgery.
Subsequent analysis by enzymatic array of glucose, lactate, glycerol and
pyruvate took place to assess the relative effectiveness of two types of
myocardial protection (cold and warm cardioplegia).
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