Online proceedings - EDA Publishing Association

11-13
May, 2011, Aix-en-Provence, France
y 0.0062x0.932
ln( R(t)/ R(0))
y 0.0069x1.292
y 0.007x1.973
Figure 5. Diffusion induced i-t curves for various AAO membranes
Figure 6 displays the trajectories of the ratio of conductance
difference ( Rt
( ) / R(0)
) with respect to the i-t curves shown in
Figure 5. The conductance difference data were measured using
the Wheatstone bridge circuit shown in Figure 2.
Figure 6. Trajectories of the ratio of conductance difference ( Rt
( ) / R(0)
)
The ( ln( Rt
( ) / R(0))
, t) curves are plotted in Figure 7.
Since the ion diffusion induced currents as shown in Figure 5
almost reached their steady-state conditions in less than 200 sec,
the ( ln( Rt
( ) / R(0))
, t) curves were linearly approximated for
the period from 0 to 180 sec. The approximation equations are
listed adjacent to each curve. The slope of each
( ln( Rt
( ) / R(0))
, t) curve can thus be calculated as depicted in
Table 1. The diffusivity for each sample is calculated using
Equation (11) and shown in Table 1. It can be observed that the
diffusivities are close.
R()
t
ln( )
R(0)
t
D
(m 2 /sec)
Table 1. Diffusivity for various AAO membrane
#1 #2 #3 mean
-0.0070 -0.0062 -0.0069
-0.0067
0.00036
2.5410 -8 2.2510 -8 2.5010 -8 2.430.13
10 -8
Figure 7. ( ln( Rt
( ) / R(0))
, t) curves for different samples
IV. CONCLUSION
Most of the physiological reactions in a cell are owing to
the small changes of the surrounding environment. The in-vivo
detection of the physiological reaction induced molecular
variations can provide a very useful tool for better
understanding of the physiological reaction. The small
variations of the ambient environment are carried out by way of
the diffusion of ions through the ion channels of the cell
membrane. In this study, a simple principle for the detection of
the diffusivity of nanoparticles in a nanochannel based on the
Fick’s first law is proposed. Anodic aluminum oxide (AAO)
membranes are used to replace membranes with single
nanochannel for the measurement of the diffusivity. An
electrochemical bath that can hold an AAO membrane to
separate vessels with different ion concentrations is built. The
across channel ionic concentration difference can be estimated
in terms of the conductance difference that is measured using a
Wheatstone bridge circuit. The diffusivity in the nanochannel
can be estimated by simply plotting the natural logarithmic
value of the electrolyte conductance difference across the
nanochannel versus time and calculating its slope. The average
diffusivity in an AAO membrane with nanopore diameter being
around 80 nm and the thickness being 60 m was measured to
be 2.430.1310 -8 m 2 /sec.
ACKNOWLEDGEMENTS
The authors would like to address their thanks to the
National Science Council of Taiwan for their financial support
of this work under grant NSC-98-2212-E-005-072- MY3.
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