Biomedical Engineering Reference
In-Depth Information
(dilution 1:40), and the real concentrations were determined by a commercially
available ELISA kit. The microcantilever allowed quantification of final serum
concentrations above 2 ng/ml [
115
]. Both label-free biosensors allowed HER2
detection in the range of clinically relevant concentrations.
Prostate-Specific Antigen
Prostate-specific antigen (PSA), a serine protease produced by the prostate epi-
thelium, is clinically used for the detection and screening of prostate cancer [
116
].
Critical values for PSA are above 4.0 ng/ml total PSA in blood [
7
,
116
]. Actually,
specificity of PSA for prostate cancer is low, resulting in the need for a marker
profile to allow accurate diagnosis [
4
,
116
]. Still, owing to its widespread use as
screening parameter, PSA was commonly used as a model analyte for testing the
performance of biosensors designed for diagnostic applications, which has led to
numerous publications. Biosensors for PSA detection were recently reviewed
[
116
]. The latest developments include mainly methods for enhancing the bio-
sensor signal response to allow determination of low PSA concentrations, pref-
erably in the picogram per milliliter range. This should allow early diagnosis of
prostate cancer recurrence [
116
]. Furthermore, increased levels of PSA (above
1 pg/ml) are considered as a parameter for the detection of breast cancer [
113
].
An amperometric biosensor was used for PSA detection, where signal
enhancement was obtained by labeling the secondary antibody (in addition to the
peroxidase label) with nitrodopamine-functionalized iron oxide nanoparticles.
Serum samples containing 1-10 ng/ml were tested with this biosensor sandwich
assay and with ELISA. The correlation coefficient was 0.992, i.e., the results were
in good agreement. A comparison of the performance of several electrochemical
immunosensors for PSA detection was also given in this work [
117
]. A QCM
biosensor was used for PSA detection in 75% serum. Signal enhancement was
obtained by labeling the secondary antibodies with gold nanoparticles. In this
sandwich assay, a linear range for PSA concentrations between 0.29 and 150 ng/
ml was obtained, corresponding to 0.39-200 ng/ml in 100% serum [
118
]. Finally,
a so-called localized surface plasmon coupled fluorescence fiber-optic biosensor
was used to detect PSA in tenfold diluted normal women's serum. This sandwich
immunoassay combined with the localized surface plasmon technique allowed the
detection of 1.8 pg/ml PSA in diluted serum [
113
].
Carcinoembryonic Antigen
The glycoprotein carcinoembryonic antigen (CEA) has less specificity to a certain
type of tumor than reported for HER2 or PSA (see earlier). Hence, it is associated
with several types of cancer, in particular colorectal cancer, but also pancreatic
cancer, liver cancer, and gastric cancer to name but a few [
3
,
7
]. Critical values for
CEA are above 3.0 ng/ml [
7
].
An SPR biosensor using signal enhancement by a secondary antibody
(sandwich assay) was reported. Samples were spiked with the respective CEA
