Fabrication Of Large Scale And Small Spacing Gold Nanorods Vertical Array And Application Of MicroRNA Detection

Cancer is one of the current public health challenges facing humanity in the 21 st century that has become a serious threat and second leading cause of death.In comparison with the traditional surgery and chemotherapy,early diagnosis of cancer is a critically necessary and alternative strategy which is capable of reducing disease severity and improving overall survival rates.Recent investigations have demonstrated that the expression non-controllability of mi RNA,which can be used as a probe molecule for the early diagnosis of cancer owing to its specificity,is significantly associated with the pathogenesis and evolution of cancers.However,the current problem concerns the low content that mi RNA in the early stage of the cancer lesion.Therefore,reliable methods for ultra-sensitive detection are greatly needed.Specifically,surface enhanced Raman scattering?SERS?is a promising analytical and sensing technology that utilizes strong local electric fields on the surface of precious metal materials to increase Raman signals,and has drawn great interest due to the potential of strong sensitivity and fast detection speed.Of the various SERS substrates,the gold nanorods?GNRs?arrays with good biocompatibility and close arrangement between GNRs become an ideal candidate for SERS applications.Therefore,the fabrication of self-assembled GNRs arrays with large-area vertical orientation and controllable nanogaps is essential,which can provide homogenous hot spots for sensitivity and reproducibility.Unfortunately,the formation process and mechanism of orientation controllable and large-area GNRs arrays remains unknown and uncertain,thus results in the inhibition of further applications for reproducible and reliable mi RNA detection.Based on the above statements,this paper mainly focuses on the following research:1.The formation process and mechanism of orientation-controlled GNRs arrays: Based on environmentally controlled self-assembly process,our group in the previous work had developed a feasible route for preparing GNRs arrays distributed in millimeter scale.However,the understanding of the assembly process and mechanism is still unclear,which limits the optimization of large-area vertical array structures.To clarify the relationship between the array structure and environmental control,we selected the doublelayer GNRs arrays developed by our research group as a model system and monitors in-situ the self-assembly process of GNRs under different experimental conditions through grazing incidence small-angle X-ray scattering?GISAXS?and grazing incidence wide-angle X-ray?GIWAXS?.We observed that the assembly of GNRs was divided into three stages: volatilization,aggregation,shrinkage.In the initial droplet evaporating stage,GNRs showed a disordered dispersion state and then the concentration of GNRs gradually increased.When the concentration of GNRs reached the critical value,the GNRs arranging side by side gradually form the array structure.After the self-assembly process completed,the remaining solution continued to evaporate and the space between GNRs decreased.Depending on the thermodynamic equilibrium of three forces?electrostatic repulsion,Van der Waals force and depletion force?,a large-area GNRs vertical array were successfully synthesized.Because the substrate hydrophobicity had an important effect on droplet shape,volatilization rates and thickness of liquid film,the substrate with 30° water contact angle was proved the best choice for close-packed GNRs arrays.In summary,we analyzed the role of various weak interaction forces through the structural control factors and assembly critical conditions of GNRs in the self-assembly process,and revealed the behavior characteristics and mechanism of environmentally controlled selfassembly.Thus,our findings optimized the assembly control conditions and methods,which can lay the foundation for the of large-area GNRs vertical arrays with controllable spacing.2.Fabrication of large scale and small spacing GNRs vertical array and application of micro RNA detection: Firstly,the double-layer cetyltrimethylammonium bromide?CTAB?on the surface of GNRs was replaced with a single-layer dodecylmercaptopyridine?Py?.Based on the research in the first chapter,we utilized a silicon wafer with a contact angle of 30° as the substrate,and adjusted the exhaustion force to control the thermodynamic stable state of the three forces in the system by introducing different solutes and concentrations,large scale and small spacing GNRs vertical array was successfully synthesized.The distance between the GNRs before and after modification in the GNRs arrays was reduced from 6.5 nm to 2.1 nm.Meanwhile,malachite green?MG?at a concentration of 10^-15 M could be detected,which initially verified that the GNRs array substrate had high SERS sensitivity.We also applied the Py-GNRs vertical array to the detection of cancer lesion marker mi RNA-141 with a detection limit as low as 10^-12 M concentration.The RSD of these signal intensity at 1616 cm^-1 and 1509 cm^-1 from 43 spots was calculated to be 2.8% and 7.1%,respectively.In addition,the RSD of these SERS intensities of the 28×28 ?m² area for Raman mapping test was around 20%,further indicating that the substrate had good reliability and reproducibility of our selfassembled GNRs array.Finally,it was verified that the self-assembled GNRs array was a SERS sensor and had a excellent specificity for mi RNA-141.Therefore,it is believed that large scale and small spacing GNRs vertical array as a biosensor has extensive application prospects in disease diagnosis.