Biomedical Engineering Reference
In-Depth Information
The pH variation at the “-cell/gate interface determined on the basis of respiration
activity can be estimated from the electrical signals of the cell-based FET. Basically,
the FET chip utilized in this measurement showed the change of gate voltage
51.4 mV/pH for pH variation. The average change in surface potentials after the
addition of glucose was about 10.3 mV with a standard error of
2:2mV for five-
cell-based FETs. Therefore, the respiration activity triggered by glucose caused the
change of about pH 0.2 at the interface between the pancreatic “-cells and the gate
surface. Strictly, the shift of pH from 7.4 to 7.2 was detected at the “-cell/gate
interface by the cell-based FETs. The amount of eliminated CO
2
was calculated
to be about 1:2
˙
10
8
M on the basis of principle that changes in hydrogen ion
concentration corresponds to pH variation, according to the equilibrium of CO
2
in solutions. In the calculation, O
2
consumption, ATP synthesis, and so on in the
citric acid cycle inside the mitochondrion could be estimated from the amount
of eliminated CO
2
, which was determined from the electrical signals of the cell-
based FET. However, the effect of buffer solution on pH and the diffusion of CO
2
at the “-cell/gate interface has to be considered in order to estimate accurately
the consumption and the generation based on the respiration activity. Also, the
electrical signals of the “-cell-based FET seem to include the effect of ion or
molecular charges in the insulin secretion process other than pH variation based
on respiration activity. The electrical signals of the cell-based FET related to
biochemical information, however, are a significant factor for the convenient and
noninvasive evaluation of cell functions. In a previous work [
45
], the noninvasive
monitoring of transporter function was shown using oocyte-based FETs; the size of
an oocyte was larger than that of a somatic cell, and the amplification of electrical
signals based on transporter function was expected in the case of using oocyte-
based FETs. However, the electrical detection of “-cell activity obtained in this
study has demonstrated the possibility of detection of somatic cell function using
“-cell-based FETs.
6.6
In Vitro Cell Sensing with Semiconductor-Based
Biosensing Technology
Lastly, I would like to summarize in vitro cell sensing with semiconductor, as
follows. In our laboratory, we focus on a direct detection of ions or ionic molecules
through ion channels at cell membrane, because most of cell functions are closely
related to transferring of charged conductors from cell to cell. We have clarified
that a principle of semiconductor devices based on field effect realizes it in a direct,
label-free, real-time, and noninvasive manner for cell functional analysis.
The principle of semiconductor-based biosensing devices is based on the poten-
tiometric detection of charge density changes induced at a gate insulator/solution
interface accompanied by specific biomolecular recognition events. Ionic charges
