Biomedical Engineering Reference
Gold fiber-based gate electrode
of oxide so that it is covered by hydroxyl groups in solutions. The potential of EG-
FET with ITO-gate shows near Nernstian response to pH variation [ 5 ]. However, it
is very important to control making process of ITO surface.
Using the EG-FET, the structure of gate itself can be varied corresponding
to applications. In the field of tissue engineering, the safety and functionality of
artificial organs are required to transplant to living body actually. This is why
3D culture of cells is required for making artificial organs. In order to perform
3D culture on electrode, nano- or microfiber scaffold is able to be developed as
gate electrode of EG-FET. Scaffold architecture affects cell binding and spreading.
Cells binding to scaffolds with microscale architectures flatten and spread as if
cultured on flat surfaces. Scaffolds with nanoscale architectures have larger surface
areas to adsorb proteins, presenting many binding sites to cell membrane receptors.
The adsorbed proteins may also change conformation, exposing additional cryptic
binding sites [ 6 ].
The fiber scaffold gate electrode (FSG) can be prepared by the electrospray
deposition (ESD) method [ 7 ]. The gold micro-FSG is made by sputtering after silica
fiber is prepared using the ESD method, as shown in Fig. 6.6 . The sputtering of gold
is performed for both side of silica fiber membrane. The thickness of silica fiber
membrane is about a few hundred m, and the several sputtered fiber membranes
are piled up for the FSG. The FSG is connected to the gate of MOS-FET, and the
measurement system is composed as shown in Fig. 6.7 . Using the system with the
FSG, the constant potential of interface between fiber surface and solution can be
measured in a phosphate buffer solution of pH 7.41 or a culture medium (Dulbecco's
Modified Eagle's Medium; DMEM). Moreover, HeLa cells, which are a cell type in
an immortal cell line derived from cervical cancer cells taken from Henrietta Lacks,
a patient who eventually died of her cancer, are cultured on the FSG as shown in
Fig. 6.8 . Calcein acetoxymethyl ester (AM) is used as fluorescent dye for live cell
staining. HeLa cells are found even inside the fiber.