| Summary: | 碩士 === 國立中興大學 === 生醫工程研究所 === 102 === Silicon nanowire field-effect transistors (SiNW FETs) are attractive devices for use as a transducer element in cell-based biosensors (CBBs) because of their ultrasensitivity,real-time response, and label-free detection mechanism. However, SiNW-FET-based CBBs have only been used so far for biomolecular detection and electrophysiological recording. It will be highly advantageous if these biosensors will be able to probe cell condition using more general cellular characteristics, such as cell adhesion. Taking
inspiration from electric cell-substrate impedance sensing (ECIS), this study aims to develop a CBB system based on the impedimetry of SiNW FETs for the sensing of cell adhesion. It was hypothesized that adhesion of cells can induce changes in the impedance of the SiNW FETs because of the surface charges or ion-screening effect of the coupled cells. Single-SiNW and parallel-SiNW FETs (with 1, 5, and 50 parallel-SiNW variants) were fabricated from polysilicon using the top–down approach. The devices were surface-modified with poly-D-lysine via a silane coupling agent to induce attachment of undifferentiated rat adrenal pheochromocytoma (PC12) cells. Impedance measurements were performed using a precision LCR meter which was connected to the
source and drain terminals of SiNW FETs. Time-course impedance sensing of PC12 cells in two-dimensional (2D) and three-dimensional (3D) cultures were performed for
5 days using single-SiNW FET devices. An improvement of the impedance monitoring of 2D PC12 cultures was then attempted using p-type and n-type parallel-SiNW FETs
with a grounded-solution setup. Measurements with the 2D PC12 cultures using single-SiNW FET devices showed a consistent gradual change in the impedance magnitude
(|Z|) and impedance phase (θ) with time which plateaued after 3 days of culture. On the other hand, measurements with the 3D cultures showed an abrupt change in the impedance parameters after cell seeding with almost no further change with time. These results indicate that it is possible to estimate cell adhesion using impedimetry of SiNW FET devices. Moreover, screening of ions in the medium, rather than surface charges in the cell, is the main cause of the time-course impedance changes. Attempts to improve the impedance monitoring of 2D PC12 cultures using p-type parallel-SiNW FETs showed that grounding of the solution results in larger impedance changes with time.
However, no apparent trends consistent with cell adhesion can be observed. It is possible that grounding of the solution via a reference electrode leads to gradual breakdown of the native SiO2 layer of the SiNWs, which in turn, results in measurement artifacts. On the other hand, the use of n-type 5-parallel-SiNW FETs in the impedance monitoring of 2D PC12 cultures revealed time-course changes in |Z| and θ similar to those observed in single-SiNW FETs. The 1-parallel-SiNW FETs only showed the expected time-course changes in θ, while the 50-parallel-SiNW FETs did not exhibit the expected trends. Live observation of cells attached on the n-type parallel-SiNW FETs
supports the correlation between cell adhesion and the observed impedance changes.
With further experimentation and process improvement, the SiNW FET cell-based biosensing technique proposed in this study can provide a simple means for probing
cytotoxicity, with potential application in drug discovery, environmental screening, food safety, and security.
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