Biomedical Engineering Reference
In-Depth Information
95
m
m
(a)
(b)
(d)
10 mm
Outlet
10 mm
105
m
m
18 mm
20
m
m
Inlet
(Buffer Solution)
Inlet
(Sample Solution)
100
m
m
200
m
m
(c)
12 mm
Figure 3.7
(a) Layout of the device which has two inlets and
one outlet; (b) At the part of the inlet, sample solution was
hydrodynamically focused; (c) The focused sample solution
fl owed through the 105
μ
m-wide channel before the outlet;
(d) A photograph of the fabricated device. Reproduced with
permission from Ref. [19]; © 2005, The Royal Society
of Chemistry.
through a 10 mm-long microchannel, to the right-hand side of which is located a
permanent magnet.
In these studies, the magnetic force-based microfl uidic immunoassay was
successfully applied to detect rabbit immunoglobulin G (IgG) and mouse IgG
as model analytes. For this, a sandwich immunoassay was performed using the
yellow- green - fl uorescent microbeads immobilized with goat anti mouse IgG, and
red - fl uorescent microbeads immobilized with goat anti rabbit IgG. The concentra-
tion of the red-fl uorescent microbeads was 2.55
×
10
5
microbeads in 70
μ
l of buffer
solution, while the antigen solution (10
l) contained rabbit IgG at different con-
centrations. A control experiment was carried out with 10 ml of 0.1% bovine serum
albumin in phosphate-buffered saline, instead of rabbit IgG. A background veloc-
ity, which was defi ned as the velocity of the microbead without attached SMNPs,
was not observed, except for the oscillation due to the diffusion effect. The back-
ground velocity was
μ
m s
− 1
. In contrast, the mean velocity at a concentration
of 250 ng ml
− 1
rabbit IgG was 2.39
<
0.05
μ
m s
− 1
(Figure 3.8a). As shown in the
fi gure, the velocities of the microbeads were measured over a range of concentra-
tions of rabbit IgG, from 1 ng ml
− 1
to 1
±
0.3
μ
g ml
− 1
. When subsequently, and under the
same experimental conditions, a quantitative analysis of mouse IgG was per-
formed (Figure 3.8b), the velocities of both rabbit and mouse IgGs were almost
saturated at approximately 1
μ
g ml
− 1
, respectively. The reason for this
saturated velocity can be explained by the limited binding capacity of the micro-
bead surface, with the lowest concentrations of rabbit and mouse IgG measured
over the background being 244 pg ml
− 1
and 15.6 ng ml
− 1
, respectively. The velocities
of microbeads conjugated with SMNPs may be demonstrated by magnetic fi eld
gradients in microfl uidic channels.
In this magnetophoretic assay system, the dynamic range was shown to be
controlled by the area on which the reactions between the two proteins were
μ
g ml
− 1
and 2
μ
