Biomedical Engineering Reference
In-Depth Information
samples obtained from healthy individuals . The observed accuracy obtained with
the QCM biosensor was even greater than that obtained by ELISA, i.e., with the
QCM biosensor more rheumatoid arthritis patients with antibodies to the citrul-
linated peptide were identified [
129
]. In another approach, composites of multi-
walled carbon nanotubes and polystyrene were used in an amperometric biosensor
setup. Multiwalled carbon nanotube-polystyrene mixtures were applied on metal
electrodes. The peptide was covalently coupled on these composite-based elec-
trodes. Samples were diluted 1:100 and 1:200, respectively. Peroxidase-labeled
secondary antibodies were used to allow detection (sandwich assay). Only a few
patient samples were tested in preliminary tests, but they could be distinguished
from samples from healthy donors [
128
].
Antiphospholipid Syndrome
Antiphospholipid syndrome is an autoimmune disease which is mainly charac-
terized by recurrent thromboses. According to the name, antibodies against
phospholipids are produced, such as anti-b2-glycoprotein I [
126
]. SPR biosensors
with covalently immobilized b2-glycoprotein I were used to test serum samples
which were diluted 1:100. Distinguishing between antiphospholipid syndrome
patients and healthy individuals was possible [
130
].
Systemic Lupus Erythematosus
SLE is a systemic autoimmune disease which may affect almost any organ as well as
connective tissues and blood vessels. Furthermore, SLE may lead to neurological and
hematological disorders [
126
]. Several autoantibodies are used for diagnosis, mostly
anti-chromatin, antibodies against nuclei, i.e., antinuclear antibodies (ANA), and
anti-dsDNA. In particular, the latter may also be important as a diagnostic parameter
for other autoimmune diseases. An amperometric biosensor was reported to detect
anti-chromatin antibodies. Electrodes were screen-printed on a poly(vinylidene
fluoride) membrane impregnated with chromatin. Serum samples were diluted 1:50
and applied on the sensors, followed by peroxidase-conjugated secondary antibody
(sandwich assay). Serum samples obtained from SLE patients could be distinguished
from serum samples obtained from healthy individuals [
131
]. For the detection of
ANA in serum, a fiber-optic evanescent wave biosensor modified with colloidal gold
has been developed. Extractable nuclear antigens were immobilized on the fiber. The
ANA content detected in samples diluted 1:100 was in good agreement with that
determined by ELISA tests [
132
]. Detection of anti-dsDNA in serum samples has
been performed with potentiometric [
133
,
134
], QCM [
135
], and SPR [
136
,
137
]
biosensors. Potentiometric biosensors were made of glassy carbon electrodes coated
by electropolymerization of aniline [
133
] or phenothiazine dyes (methylene blue and
methylene green) [
134
] and subsequent immobilization of dsDNA. Serum sample
dilution in the range 1:20-1:50 was found to be appropriate to achieve the best
