| Summary: | 碩士 === 國立成功大學 === 醫學工程研究所碩博士班 === 92 === By using self assembled monolayer (SAM) with different functional groups to modify a substrate, the surface of the substrate was suitable for specific bio-detection. The aim of this study were two, one was to characterize the physical properties of substrate with SAM modification, the other was that applied a layer of SAM coated with avidin protein on sensing electrode as a bio-probe to quantify the formation of avidin-biotin complex by impedance response in electrical impedance analysis.
There were three types of SAM with carboxyl group to be coated on sensing electrodes by organic solvent which were DTBA, MUA and MHA. For making biotin probe, we use EDC/NHS reagent to activate the SAMs’ COOH to bind the avidins’ NH2 group. Circuit model is established by comparing with impedace response of DTBA, MUA and MHA after modification on the electrodes. In the circuit model, Ret and Cdl element represent density and chain length of SAM respectively. Rs element represents the resistance of supporting solution. Using circuit model to characterize SAM, we have several conclusions. (1) When modified time of SAM is about 60 minutes, SAM arives to saturate. (2) The longest SAM is increase in resistance and decrease in capacitance. (3) The saturated concentration of MUA solution is 10 mM. (4) Using dropping method, SAM becomes denser and modified time for SAM is reduced to 20 minutes as compared to immersion method. (5) Hydrophobic SAM is denser than hydrophilic SAM. For bio-detection, the linear range of biotin is 2-10 μg/ml bu means of △Ret and △Cdl. Correlation factor of Ret element (0.9943) is higher than that of Cdl (0.9624). Sensitivity of Ret and Cdl are 30.27 kΩ/μg/ml and 3.49×10-5 nF-1/μg/ml, respectively. Base on the findings above, we choose Ret element to the quantify concentration of biotin.
In summary, EIS not only is used to characterize SAM modified electrode, but also provids good linear range and reproducibility to detection of avidin-biotin complex. To develop biosensing technique, simulation circuit and impedance analysis could be applied to detection of biotin derivative（such as biotin labled antibody or DNA）and affinity biosample.
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