Biomedical Engineering Reference
In-Depth Information
Fig. 7.8
Schematic representation of the autoassembly immunoassay where each square repre-
sents a unique GMR nanosensor in the array. (
a
) After immobilizing unique capture antibodies over
individually addressable sensors, and incubating with the protein of interest, the magnetic nanotags
are added in solution above the sensor. Since there is no chemistry to link the magnetic nanotags
to the captured antigen, no signal is detected by the underlying sensor. (
b
) Once the detection
antibody in solution is added, the detection antibody which is labeled with biotin is capable
of linking the streptavidin-labeled magnetic nanotag to the captured analyte. In the presence of
captured analyte, the magnetic nanotags will congregate over the corresponding GMR sensors in
high enough concentration to be detected.
Insert
: optical microscopy of a section of the array of
nanosensors. Each
square
in the array is one sensor and each
circle
is a nanoliter droplet of capture
antibody uniquely functionalized over the sensor surface [
15
]
sensor (Fig.
7.8
b). Each sensor in the array is monitored in real-time, providing
multiplex protein detection (Fig.
7.9
). Piezoelectric robotic spotter technology is
used to spot 350 picoliter droplets of capture antibody onto individually addressable
GMR nanosensors for high-density protein detection (Fig.
7.8
binsert).
7.4.3
Microfluidic Integration of Magnetic Biosensors for POC
Among the advantages of magnetic nanosensors is that they can be fabricated into
high-density arrays with minimal increase in cost or size of the overall chip. This
allows for highly multiplex protein detection in a single reaction well. While there
are significant advantages to open-well protein detection systems, there are several
limitations as well. An open-well format is limited to running only one sample
per chip. For high-throughput analysis with fewer than 5 biomarkers of interest
