Online proceedings - EDA Publishing Association

dipping method, hydrodynamic transmission of the fluid in a
microenvironment is used to drive the motion of the
biomolecules. Tabeling et al. [10] mentioned that when a fluid
flows through a square-shaped downward concave slot, the
fluid causes a degree of swirling flow in the corner of the slot,
and the side length ratio of the square-shaped slot influences the
flow state of the fluid in the slot. Bruus et al. [11] also observed
that the fluid created a swirling flow in the corner of the
square-shaped slot when the Reynolds number of the
microchannel increased. In this study, we first applied the
special structure present in the microenvironment to cause the
internal fluid to swirl in multiple directions, to increase the
chaos of the fluids in the microenvironment. Next, by the
traction force of the chaotic fluid flow, we drove the motion of
the biomolecules, raised the evenness and the coverage rate of
adhesion of the biomolecules to the sensing field, reducing the
time for adhesion of the biomolecules to the sensing field, and
improving the efficiency and sensibility of the microbial sensor.
Finally, we used the plant virus TYMV to test the effect of the
adhesion of TYMV on the sensing surface of the
microenvironment.
II.
2.1 Sensing Principle
SENSING PRINCIPLE AND SIMULATION
The virus, TYMV, [12] is a tymovirus of the family
Tymoviridae. TYMV are propagated in cabbage leaves and
stored at -20 ℃ . The structure of TYMV is simulated by
RasMol, a computer program written for molecular graphics
(Fig. 1) and 400 amino groups on the TYMV surface is found.
These amino groups can be easily linked with antibodies and
quantum dots. The TYMV we used were obtained from the
Graduate Institute of Biotechnology, National Chung Hsing
University, Taiwan. This TYMV had Alexa Fluor 594 applied
to it to examine the virus distribution under a confocal
microscope. The other type of fluorescent we used was NCD-4
(N-Cyclohexyl-N-4-Dime-thylamino naphthyl carbodiimide).
This can also be linked with TYMV by the thiol groups on the
TYMV. We used the self-assembled monolayers (SAMs) and
the linker to achieve the goal of affixing the virus to the sensing
surface in the microfluidics channel. The kind of SAMs used in
this paper were MUA (11-mercaptoundecanoic acid). At one
end of the chemical structure of MUA are thiol groups which
can be attached on the gold film of the sensing surface. At the
other end of the MUA is a carboxyl functional group. This
functional group can form a connection between the linker and
MUA. The linker layer we used was EDC
(1-Ethyl-3-[3-dimethylaminopropyl]
carbodiimide
Hydrochloride) and NHS (N-hydroxysuccinimide). After EDC
interacts with MUA, TYMVs will be captured by designed
SAMs. The compound NHS is used to prevent EDC layer
hydrolysis. Therefore, we can achieve a connection between the
virus and the sensing surface. After the virus with quantum dots
was anchored to the sensing surface of the microfluidics
channel, a confocal microscope was used to monitor the surface
of the silicon membrane. A laser beam with a wavelength of
615 nm was passed through an aperture and was focused by an
objective lens onto a small focal volume on the sensor surface.
A mixture of emitted fluorescent lights (594 nm) and reflected
11-13
May, 2011, Aix-en-Provence, France
laser lights from the quantum dots were then reobtained by the
objective lens. A photodetection device was used to transforme
the reflected light signal. The results of the confocal
microscopy measurement are shown in Fig. 10(a). Only a few
TYMV with quantum dots were observed on the silicon
membrane and the coverage rate of TYMV was poor. Also,
some large molecules or particles were stuck on the surface
which might result from the aggregation of MUA, EDC, or
NHS by the dipping method. This result is unfavorable if
researchers want to detect viruses at extremely low
concentrations in the solution.
(a)
(b)
Fig. 1 (a) Structure of TYMV (b) amine functional groups of TYMV
2.2 Microfluidics Theory
When TYMV is in a microenvironment, because it cannot
infect any cells and parasitize on them, the virus does not exist
in a living state but in a form of chemical compound. We
therefore regard it as a small particle without life. When the
liquid in the microenvironment is static, the virus particles can
only move by diffusion of Brownian motion caused by the
continuous collision of the media molecules in the
microenvironment. The coefficient of diffusion signifies the
movement capability of the virus by diffusion. Through the
coefficient of diffusion we can understand the movement speed
of the virus in static liquid. Table 1 [13] shows the coefficients
of diffusion of the different viruses in various sizes in water
under room temperature.
Table 1 Different virus diffusion coefficient
Diameter of
Virus
virus (nm)
Diffusion
coefficients (m 2 /s)
Poliovirus [13] 25 1.72×10 –11
Turnip Yellow Mosaic Virus [12] 31.8 1.35×10 –11
Hepatitis B virus [13] 42 1.02×10 –11
Adenovirus [13] 75 5.72×10 –12
Human Immunodeficiency Virus [13] 120 3.58×10 –12
When the virus is in a microenvironment where the medium
is water, assuming the average displacement from the starting
point to the terminal point is 5 mm, and the temperature is 293
K, the time required for adhesion of each virus is shown in Fig.
2. From the figure, we see that 230 hours is required for the
movement of the virus by diffusion. Therefore, if we apply the
diffusion effect as the mechanism of TYMV for adhering to the
sensing surface, the action time is extremely long and the
adhesion efficiency is poor. To solve the aforementioned
obstacles, our study utilizes a microenvironment to drive the
movement of the TYMV, and thus raise the adhesion efficiency
of the TYMV.
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