Biomedical Engineering Reference
In-Depth Information
Fig. 7.21.
After functionalization of the air hole surfaces with probe molecules
(
left
), targets are captured by the biosensor (
middle
), which produces a coating on
the air hole walls (
right
)
recognition strongly depends on the surface chemistry, thus, instead of filling
up the pores, the molecules prefer to form a monolayer coating at the pore
(air hole) wall As shown in Fig. 7.21, highly selective probes (e.g., DNA, an-
tibody) can be immobilized on the internal surface of the air holes and form
a monolayer that can capture specific target molecules (e.g., matching DNA,
proteins). Hence, the coating causes a refractive index change only in the
vicinity of the pore wall.
7.4.3 Selected Biosensing Results
Protein Detection
To test the device performance, glutaraldehyde-bovine serum albumin (BSA)
coupling was used as the model system. The air hole is
30 times larger than
the BSA hydrodynamic diameter [38], so that the infiltration proceeds easily,
and both glutaraldehyde and BSA can form a uniform monolayer coated on
the pore walls.
To prepare the surface for capturing biomolecules, the device was first ther-
mally oxidized at 800
◦
C to form a silica-like interface for binding of amino
groups. To functionalize the sensor and capture glutaraldehyde, the microcav-
ity internal surface was silanized. Subsequently, the target, BSA, was immo-
bilized covalently on the sidewall. The experiment protocol is as follows: (1)
clean the sensor surface with DI water and dry it under nitrogen flow. Store
the sensor in moist ambient; (2) drop 5
∼
l of 2% aminopropyltrimethoxysilane
on the sensor for 20 min; (3) rinse the sensor with DI water and dry with
nitrogen flow, and then bake at 100
◦
C for 10 min; (4) drop 5
µ
l of 2.5% glu-
taraldehyde in Hepes buffer on the sensor for 30 min; soak in buffer for 10 min
to dilute the unreacted agents and dry it under nitrogen flow; (5) drop 5
µ
lof
1% BSA on the sensor for 30 min; then soak in buffer for 20 min and dry it
with nitrogen.
µ
