| dc.description.abstract | Recently, silicon nanowire field-effect transistors (SiNWFETs) have attracted the most because they have many indispensable advantages, such as, high sensitivity, label-free detection, real-time detection and mass-production because of relating to the semiconductor industry. Therefore, it has been not only widely used to detect liquid biopsy but also regarded as a detection platform with great development potential.
The common SiNWFETs detection mechanism is based on the charge of the target and then analyzes the change of the electrical conductance before and after the hybridization, for example in the n-type FET, the charged carriers would accumulate on the surface of the channel and increase the drain current if positively charged target molecules were detected. On the other hand, when the receptors captured negatively charged target molecules, the charged carriers would decrease and hence reduce the electrical conductance.
Although most researches agree with this concept, the actual interfacial phenomena would become extremely complicated during the hybridization. Counterions in the electrolyte solution would be attracted and move to the interface because RNA targets were charged. The counterions which were appealed not only screened the charges of the RNA targets but also exerted the electric field which was opposite to it exerted by the RNA/DNA duplexes. Thus, it is difficult to analyze the results based on the common detection mechanism.
In order to verify our concept, we fabricated the biosensor by modifying the SiNWFETs with Mixed-SAMs of PEG including silane-PEG-NH2 and silane-PEG-OH at the ratio of 1:3 before treating with glutaraldehyde to immobilize the DNA probes which were complementary with miR-21 sequence. After that, X-ray photoelectron spectroscopy and atomic force microscope were used to confirm that Mixed-SAMs surface modification was successful. On the other hand, we confirmed the influence caused by counterion effects on the SiNWFETs electrical signal by using the chip on board system. Also, we verified the change of the zeta potential before and after the hybridization.
According to chip on board results, we could realize that the SiNWFETs electrical signals would be dominated by counterions under higher ionic strength environment (50 mM BTP). On the other hand, the SiNWFETs electrical signals would be dominated by miR-21 under lower ionic strength environment (DI water). Furthermore, zeta potential results implied that counterions would be dominant. After hybridization, the counterions are also attracted simultaneously even though the negatively charged complementary strands were recognized and hybridized by the miR-21 probe. Thus, zeta potential didn’t become more negative but more relatively positive.
Based on our results, we could realize that the common SiNWFETs detection mechanism won′t be able to elucidate the detection results. Therefore, we would like to integrate the counterion effects with the common SiNWFETs detection mechanism and provides a more precise mechanism perspective to describe the relationship between electrical signal changes of SiNWFETs and the ion redistribution caused by hybridization during the miRNA detection under ultra-low concentration. | en_US |