Abstract
The Electric double layer (EDL) gated FET biosensor has been applied to detecting the different biomarkers such as mi-RNA, protein, cell, and heavy metal ion and get successful results. In the past, we made efforts in research on how to develop portable FET biosensors. In this research, the mechanism of antibody-based FET biosensor is deeply investigated. The enhanced EDL is applied to improve the sensitivity of antibody-based FET biosensor and detect protein in high ionic concentration such as physiological salt concentration directly.The sensor response is obtained by directly detecting the different concentrations of C-reactive protein (CRP) in physiological salt concentration. The absolute drain current from our device is analyzed and converted to potential drop in solution by giving different gate voltages during measurement. Furthermore, the total impedance on our sensor chip is also obtained by Agilent B1530/B1500A. Combining with FET sensor electrical signals and total impedance analysis, the sensor performance at different gate bias can be characterized.The result shows sensor response is higher when the higher gate bias is applied to our device. This implies that the high charge density enhances the EDL, causing the higher signal. Furthermore, according to impedance analysis, the total impedance change causing by antibody-antigen interaction is dominated by the imaginary part which proves that our sensor sensing mechanism comes from the capacitive effect. The sensor performance is also analyzed by detecting protein in different salt concentrations. With increasing salt concentration, the total change of potential drop increases. Again, the higher salt concentration enhances the EDL.In conclusion, the mechanism of EDL-modulated FET biosensor is investigated in this study. The unique EDL-modulated FET biosensor not only overcome the charge screening effects in high ionic concentration but also improve the sensitivity by increasing salt concentration. And we can also operate at different gate bias to optimize the drain current signal. Moreover, the impedance analysis shows the dominance of the imaginary part which can prove the sensor response is from the capacitance effect. Figure 1
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