Biomedical Engineering Reference
In-Depth Information
(a)
(b)
10
7
350
10
6
300
10
5
250
10
4
200
10
3
150
100
10
2
50
10
1
0
10
0
0
20
40
60
0
10
20
30
40
Distance from Ni Surface
[
m
m
]
Figure 3.10
Comparison of simulated results between a
permanent magnet and a Ni microstructure under external
magnetic fi eld: profi les of simulated magnetic fi eld gradient
(a) with a Ni microstructure under external magnetic fi eld and
(b) with a permanent magnet only. Reproduced with
permission from Ref. [20]; © 2007, American
Chemical Society.
Distance from a permanent magnet [mm]
experimental conditions were identical. The height, width, and length of the per-
manent magnet were 10, 25, and 50 mm, respectively, while the height and width
of the Ni microstructure were 50
m, respectively. The distance between
the permanent magnet and the Ni microstructure was 2 mm. The properties of
the permanent magnet were as follows: relative recoil permeability, 1.05; density,
7.4 g cm
− 3
; and specifi c resistivity, 144
μ
m and 50
μ
·cm. Figures 3.10a and b show the simu-
lated results with a Ni microstructure under the external magnetic fi eld and a
permanent magnet only, respectively. The simulated magnetic fi eld gradient of a
permanent magnet was approximately 200 T m
− 1
in the region concerned, which
was approximately 2 mm away from the permanent magnet. By contrast, the Ni
microstructure under the external magnetic fi eld exhibited about a 50-fold
enhanced gradient (
μ
Ω
10
4
T m
− 1
) compared to the permanent magnet, thus confi rm-
ing that the ferromagnetic material had concentrated the magnetic fl ux density.
On the basis of this expectation, the effect of ferromagnetic material in the biosen-
sor was evaluated [53]. When compared with previous results [19], this case
increased the sensitivity about 250-fold, as shown in Figure 3.11. Whereas, the
detection limit of the permanent magnet alone was 244 pg ml
− 1
, that of the ferro-
magnetic material was 1 pg ml
− 1
. It appears, therefore, that the detection sensitivity
of this assay system can be improved to cover femtomolar concentrations.
∼
3.4.3
Disease Diagnosis Using Magnetophoretic Assay Systems
Diagnosis
represents a highly important process in evaluating the condition of
a person and the type of disease(s) that might be present. Often, there is a
