![](bg4.png)
30.0
30.2
30.4
30.6
30.8
31.0
31.2
0 5 10 15 20 25
Time [hour]
Phase shift [deg]
Figure 4: Measurement in fetal bovine serum at 37°C between 2.6 mM and 20 mM.
The sensor sensitivity in FBS dropped to 10% of the
sensitivity in buffer solution. After FBS testing, the
sensor recovered its initial sensitivity in buffer
solution. The loss of sensitivity is therefore
reversible, which leads to the following hypothesis.
Small glycosylated peptides may enter inside the
sensor and competitively interfere with the binding
reaction of ConA to glucose. This hypothesis was
confirmed by conducting similar experiments with
dialysed FBS. A loss of sensitivity of 30% and 40%
were observed in 12 kDa and 3.5 kDa dialysed FBS,
respectively. The pores size should therefore be
significantly reduced to prevent glycosylated
peptides from entering the sensor. We are currently
assessing 2-4 nm AAO nano-membranes, coated
with Al
2
O
3
by atomic layer deposition, to minimize
the pores size.
4 CONCLUSIONS
A viscosity-based affinity sensor was developed for
continuous monitoring in biological fluids. The
sensor was extensively tested in buffer solution,
showing an excellent reproducibility and stability
over 65 hours at 25°C. The sensor sensitivity
matched well within the hypoglycemic and
physiological ranges (2-6 mM) with a resolution of
0.1 mM. The response time of the sensor was higher
for decreasing glucose concentration due to the
conjugated effect of both the reduced mobility of
glucose molecules in the viscous sensitive solution
and the membrane porosity. The sensor showed also
remarkable long term stability (25 days) at 37°C. A
limited loss of sensitivity was nevertheless observed,
which may be explained by ConA leakage through
defects of the AAO porous nano-membrane. In FBS,
the response time did not increase with time,
indicating that biofouling due to protein adsorption
is not an issue. The sensitivity in non-dialysed and
12 kDa dialysed FBS were 10% and 60% of the
sensitivity in buffer solution, respectively.
Glycosylated perptides may enter inside the sensor
and interfere with the ConA-glucose reaction. The
loss of sensitivity in FBS should be solved by
reducing the membrane pores size.
These measurements show good promise for the
sensor to be applied as in vivo monitoring system.
We are currently assessing Al
2
O
3
coated 2-4 nm
AAO nano-membranes for pores size reduction,
which should allow sensitive measurements in FBS.
Sensitive fluids for ionized calcium and pH are also
under development and should allow multi-analyte
sensing in the near future.
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20 mM
2.6 mM
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