Biomedical Engineering Reference
In-Depth Information
results. Sensor responses obtained with samples from SLE patients could be dis-
tinguished from those of healthy donors [
133
,
134
]. Furthermore, a QCM biosensor
was modified with dsDNA. Serum samples were diluted to a final protein con-
centration of 0.1 mg/ml. As serum contains 60-80 mg/ml protein [
76
], this equates
to a dilution factor in the range 1:600-1:800. The results regarding antibody content
were reported to be comparable to those from ELISA measurements; however, the
QCM results were more affected by nonspecific binding, i.e., the biosensor signal
response for the healthy donor sample was increased [
135
]. Finally, an SPR bio-
sensor modified with oligodeoxynucleotide allowed serum samples obtained from
SLE patients and serum samples obtained from healthy individuals to be distin-
guished [
136
]. Furthermore, the results were reported to be satisfactory compared
with classic immunoassay methods [
137
].
Celiac Disease
Celiac disease, also referred to as celiac sprue, is an autoimmune disease which is
characterized by a disorder of the small intestine triggered by wheat gluten. Sero-
logical markers include autoantibodies directed against tissue transglutaminase
[
138
]. Screen-printed gold electrodes were coated with transglutaminase and used as
impedimetric immunosensors. Sample signal responses were enhanced by a per-
oxidase-labeled secondary antibody with subsequent biocatalytic oxidation of the
corresponding substrate (sandwich assay). Patient samples could be distinguished
from samples of healthy donors [
139
]. Furthermore, an amperometric immunosensor
was developed for detection of anti-transglutaminase. Transglutaminase was cova-
lently coupled on gold electrodes. Antibodies in serum (dilution factors 1:100 and
1:400) were detected via a peroxidase-labeled secondary antibody (sandwich assay).
Patient samples could also be distinguished from samples of healthy donors [
140
].
Cancer Autoantibodies
Circulating antibodies to cancer-related antigens are considered to be present in
early stages of disease; therefore, autoantibodies are also increasingly being
investigated as cancer biomarkers [
141
]. Autoantibodies against CEA (see
Table
2
), for instance, were detected with an SPR biosensor modified with CEA.
Both direct detection and detection via a secondary antibody (sandwich assay)
allowed patient samples to be distinguished from negative controls which were
obtained from healthy individuals [
142
].
3.5 Detection of Biomarkers for Neurodegenerative Diseases
Neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease,
are mainly characterized by progressive loss of functions of the nervous system.
