| dc.description.abstract | The severe acute respiratory syndrome coronavirus 2 (COVID-19) was discovered in 2019 and spread rapidly around the world, and the WHO declared a pandemic of COVID-19 in March 2020. When the human body is infected with the COVID-19 virus, it will start to activate the body′s immune system[1] If the immune system overreacts, it may release a large number of proinflammatory cytokines, which in turn damages normally functioning tissues or cells. This phenomenon is a so-called cytokine storm. Among many kinds of proinflammatory biomarkers[2], interleukin 6 (IL-6) is highly correlated with the cytokine storm. Therefore, many research groups are devoted to developing high-sensitivity IL-6 detection methods[3].
Currently, the main clinical diagnostic of COVID-19 methods is antigen or antibody rapid test kits. Although the detection time of these kits is short, they can only be qualitatively detected at present. Moreover, the relationship between the changes in the concentration of the target and the course of the disease cannot be clearly and quantitatively observed. More importantly, the probability of false-negative and false-positive test results is very high. In addition, the clinical reports indicate that IL-6 concentrations in COVID-19 patients ranging from 7 pg/mL to 24.3 pg/mL (333 fM to 1.2 pM) will begin to change from asymptomatic to mild, and those above 1.2 pM to severe [4]. To achieve a fast, accurate and diagnostic method that can quantify the target concentration range, this research used the silicon nanowire field-effect transistors (SiNWFETs) with the characteristics of qualitative target concentration, high sensitivity and real-time detection as the detection platform of IL-6.
In this research, three common silanization methods were first investigated: APTES (3-aminopropyl triethoxysilane), APS ((1-(3-Aminopropyl) silatrane), Mixed-SAMs (silane-PEG-NH2: silane-PEG-OH =1: 10 (mM/mM) was modified with GA (Glutaraldehyde) and antibody probe (Anti-IL-6 antibody) on the surface of SiNWFETs for IL-6 calibration curve (1 pM-10 nM) measurement. Whether the surface morphology of different silanization affects the subsequent surface chemical grafting and IL-6 calibration curve detection electrical signal results were analyzed by AFM (Atomic force microscopy).
First, the IL-6 calibration curve was detected by different silanization surfaces of SiNWFETs. The electrical signals on the surface of APTES/GA/Antibody (Anti-IL-6 antibody) showed disordered changes with the change of IL-6 concentration. Although the change of IL-6 concentration on the surface of APS/GA/antibody has a linear trend with the electrical signal generated, its value was regarded as background noise (Noise). The electrical signals generated on the surface of Mixed-SAMs/GA/antibody with the change of IL-6 concentration showed linear changes and were regarded as effective signals. Also, the AFM results revealed that the silanization surface of APTES will probably produce an intermolecular condensation reaction that makes the surface morphology non-uniform. Although the APS has a cage-like symmetric structure to avoid intermolecular condensation reaction, it is more uniform than the APTES silanization surface. Finally, the surface morphology of Mixed-SAMs showed the best uniformity and electrical signal detection of IL-6. To sum up the above results, the silanization surface of the Mixed-SAMs was used for subsequent surface modification experiments of GA/antibody or nucleic acid aptamer probes.
The SiNWFETs results showed that if the immunobiosensor using antibodies as probes was used, the limit of detection (LOD) of IL-6 was 210 pg/mL (10 pM) and the linear range was 10 pM-1 nM. However, the detection of IL-6 by the immunobiosensor can only distinguish patients with severe COVID-19, but cannot distinguish between asymptomatic and mild patients. To address the deficiencies of immunobiosensor for clinical IL-6 detection in COVID-19 patients. Therefore, not only used the antibody probe immunobiosensor but also used the aptamer probes (Anti-IL-6 aptamer) aptabiosensors for IL-6 calibration curve detection in this research. Simultaneously, confirm the correctness of the surface modification of the antibody or aptamer probes through AFM and X-ray photoelectron spectroscopy (XPS). Eventually, the SiNWFETs results showed that the LOD of the aptabiosensor was 2.1 pg/mL (100 fM), and the linear range was 100 fM-1 nM. In conclusion, The aptabiosensor not only has a lower LOD than the immunobiosensor but also increases the linear range of IL-6 detection, meeting the needs of clinical detection the IL-6 of in COVID-19 patients. | en_US |