Biomedical Engineering Reference
In-Depth Information
Schuler et al. (2008) analyzed and compared the applicability, sensitivity, and specificity of
screen printed electrodes to electrodes produced by standard photolithography. These authors
detected cytomegalovirus (CMV) DNA on their chip. The authors point out that CMV
belongs to the family of human herpes virus. Their results demonstrated screen printing as
a cost efficient and presumably large-scale production technique for microstructure chips.
The electrical DNA detection was based on nanoparticle labeling and subsequent site-specific
silver deposition.
For
their
investigation and analysis Schuler et al.
(2008) used the following DNA-
oligonucleotides (both capture and target probes):
(a) Positive biotin labeled control: (5
0
-NH
2
-C6CAT AGA ATC AAG GAG CAC ATG CTG
AAA AAA-biotin-3
0
)
(b) A complementary capture sequence: (5
0
-NH
2
-C6-TTT TTT CAG CAT GT CTC CTT
GAT TCT ATG-3
0
)
(c) A sequence containing 1 mismatch: (5
0
-NH
2
-C6-TTT TTT CAG CAT G
G
G CTC CTT
GAT TCT ATG-3
0
)
(d) A sequence containing 3 mismatches (5
0
-NH
2
-C6-TTT TTT CAG CAT
TAT
CTC CTT
GAT TCT ATG-3
0
)
(e) A negative control (5
0
-ACT-GAC TGA CTG ACT GAC TGA CTG GGC GGC GAC
CT-NH
2
-C7-3
0
)
(f) Biotin labeled target DNA (5
0
-biotin-CAT AGA ATC AAG GAG CAC ATG CTG AAA
AAA-3
0
) had only a biotin modification
Schuler et al. (2009)
report that the metallic microelectrode structures of the biochips (0.5 in.
square in size) were printed on 50
50 mm glass slides. The screen-printed substrates were
chemically modified by GOPS (3-glycidyloxypropyl-trimethoxysilane) for the binding of
amino-modified ss (single-stranded) capture DNA molecules. Different 30 bp ss capture
sequences were spotted by a noncontact Nanoplotter from Gessellschaft fuer Sclizium-
Mikrosysteme mbH, Grosserkmannscdorf, Germany to detect CMV-DNA on the screen-
printed chips. The concentration of the spotted capture DNA was 10
m
M in the microarray
printing buffer.
The principle of the electrical detection of DNA may be described in the following four steps:
(a) The ss capture molecules are spotted between two microelectrodes.
(b) The biotin-labeled target DNA hybridizes to the specific partner on the chip surface.
(c) The binding between the streptavidin-horseradish peroxidase-polymer occurs due to the
binding molecule, biotin.
(d) A metallic layer between the electrodes is introduced due to a final enzyme-induced sil-
ver deposition. The readout is obtained by an electrical measurement. This occurs due to
the conductivity of the gap filled by the interconnected silver nanoparticles.
