Biomedical Engineering Reference
In-Depth Information
concentrations and diluted 1:10. CEA serum concentrations were determined in
the range 25-800 ng/ml, i.e., only increased CEA levels could be detected [
119
].
Furthermore, two amperometric immunosensors were used for CEA detection via
sandwich assay. The first amperometric biosensor did not use additional means for
signal enhancement. Serum samples from colon cancer patients were tested, i.e.,
the serum CEA concentration was at least 3 ng/ml. The results were in good
agreement with those from ELISA tests performed with the same samples [
120
].
The second biosensor used signal enhancement by labeling the secondary antibody
with a gold nanoparticle carrying several peroxidase molecules. In spiked serum
samples, concentrations in the range 1-40 ng/ml CEA could be determined. This
means that CEA concentrations near and below the threshold value could be
detected. Again, the results were confirmed with ELISA tests [
121
].
Human Chorionic Gonadotropin
The level of the glycoprotein hormone human chorionic gonadotropin (hCG) is
increased in the case of pregnancy, and the threshold value recommended for a
reliable diagnosis is 14.3 mIU/ml in serum [
122
]. In the field of cancer diagnosis,
hCG is used as a biomarker for testicular and ovarian cancers. In this case, the
threshold value is 5.0 mIU/ml, i.e., it is lower than in the case of pregnancy [
7
].
Direct detection of hCG was performed with a label-free capacitive immuno-
sensor. Clinical serum samples were diluted 1:2 and tested both with the immu-
nosensor and with RIA. Serum concentrations were in the range 18-450 mIU/ml
hCG. The results obtained with the immunosensor were in good agreement with
those obtained with RIA tests [
122
].
3.4 Detection of Biomarkers for Autoimmune Disorders
3.4.1 Autoimmune Disease Diagnostics
Autoimmune disorders are pathological conditions in which the immune response
is directed against the patient's own cells and tissues. They can become manifest in
a single organ or tissue (localized or organ-specific autoimmune diseases), such as
type 1 diabetes, or can affect multiple organs and tissues (systemic autoimmune
diseases), such as systemic lupus erythematosus (SLE). More than 80 autoimmune
diseases have been described [
123
,
124
]. All of them have in common that they
are typically chronic, and an early diagnosis of disease type or disease flare-up is
required to enable early treatment and avoid the risk of severe symptoms [
125
].
Autoimmune diseases are mainly characterized by autoantibodies, i.e., antibodies
which are directed against self-proteins. Epitope specificity of autoantibodies as
well as disease-related molecular profiles to identify the disease type and state
have been widely investigated [
123
,
126
].
