Biomedical Engineering Reference
In-Depth Information
8
without Ni microstructure
with Ni microstructure
n=5
6
4
2
0
10
-1
10
0
10
1
10
2
10
3
10
4
10
5
10
6
10
7
Concentration of rabbit IgG
[
pg mL
-1
]
Figure 3.11
Results of detection for IgG using the microfl uidic
devices with and without the Ni microstructure.
requirement to monitor the infi nitesimally small levels of specifi c proteins in a
patient's serum in order to achieve an early diagnosis of a disease. The need for a
highly sensitive biosensor is a particular diagnostic requirement for the biomarkers
of cancer, and also of the serum levels of immunoglobulin E (IgE) as a criterion of
an allergic response. Based on these needs, a magnetophoretic biosensor for the
diagnosis of allergies was recently developed [20] which incorporated a magneto-
phoretic immunoassay of allergen- specifi c IgEs. This was based on the magneto-
phoretic defl ection velocity of a microbead associated with magnetic nanoparticles
under an enhanced magnetic fi eld gradient in a microfl uidic channel. In this detec-
tion scheme, two types of house dust mite,
Dermatophagoides farinae
and
Derma-
tophagoides pteronyssinus
, were used for the diagnosis of allergy. Polystyrene
microbeads conjugated with each of the mite extracts were incubated with serum
samples, and the resultant mixtures reacted with magnetic nanoparticle-
conjugated anti-human IgE, in order to detect allergen-specifi c IgEs by using
sandwich immunoreactions. Following the creation of a standard curve for the
diagnosis system, unknown samples were subjected to a “ blind ” test and compared
with a conventional test kit (CAP system), the aim being to evaluate the reproduc-
ibility and accuracy of the newly developed magnetophoretic immunoassay system.
To prepare a standard curve for the diagnosis system, pooled serum samples
were used from 44 patients (aged from 2 to 62 years) [20]. It has been reported
that the sera of patients with different allergies demonstrate different IgE reactivity
profi les from those of house mite allergens [57, 58]. In order to minimize the effect
of such differences on IgE reactivity profi les in the standard curve and in sample-
to-sample variation of their protein contents, four or fi ve serum samples from
patients were pooled with the same volume for
D. farinae
and
D. pteronyssinus
,
respectively. Mite allergen- specifi c IgE levels in the pooled serum were then deter-
mined using a commercial diagnostic kit (CAP system).
