Biomedical Engineering Reference
In-Depth Information
Fig. 6.21
Schematic illustration of cell monitoring. (
a
) Structure of cell-based FET. (
b
) Differen-
tial measurement between reference and cell-based FETs
at 10l. Image analyses were carried out using an optical microscope in parallel
with electrical detection.
Figure
6.21
shows the concept of the cell-based FET. The diagram for the mea-
surement of electrical signals is shown in Fig.
6.21
a. The pancreatic “-cells were cul-
tured on the gate surface of the FET, which is composed of the Ta
2
O
5
=Si
3
N
4
=SiO
2
layers. The Ta
2
O
5
gate surface was not chemically modified with functional
molecules. The potential of a measurement solution is controlled using a Ag/AgCl
reference electrode with saturated KCl solution. Two types of FETs were prepared
in the present study; one is the cell-based FET with pancreatic “-cells cultured
on the gate surface, and the other is the reference FET without cells (Fig.
6.21
b).
Using these FETs, differential measurements were performed in order to eliminate
the common background noises such as temperature changes and changes in ion
concentration.
Figure
6.22
shows the shift of the surface potential of gate sensing area after
introduction of glucose at a concentration of 10 mg/ml using the pancreatic “-cell-
based FET. The “-cells aggregated on the Ta
2
O
5
gate surface in the culture medium,
because it was difficult for “-cells to adhere to the nonmodified gate but easy for
them to aggregate like spheroid. As shown in Fig.
6.22
, the surface potential of the “-
cell-based FET shifted gradually in the positive direction at about 8.5 mV for about
3 h. The average of surface potential changes due to the introduction of glucose
was 10.3 mV for about 3 h using five-cell-based FETs. On the other hand, almost
no surface potential changes of the reference FET were found, although a smaller
shift was detected owing to the background noises such as temperature changes
when glucose was injected to the gate. The electrical signal of the “-cell-based
FET indicates the increase in positive charges or the decrease in negative charges
based on ions or charged molecules through “-cells at the “-cell/gate interface
