Research On Hydrogel Modified Silicon Nanowire Field-Effect Biosensors

With the development of technologies such as disease diagnosis,environmental monitoring,and drug development,the detection with high performance for specific lowconcentration biomolecules has become an important challenge in medical diagnostics and life sciences.Current sensing methods such as enzyme-linked immunosorbent assay and immunofluorescence assay still have many limits to meet the requirements of rapid,lowconcentration and low-cost detection.The biosensors on silicon nanowire field-effect transistor(SiNW-FET),can greatly respond to changes in surface charge upon binding of target molecules,enabling rapid,high sensitive,label-free and real-time biodetection.However,the Debye screening effect at the solid-liquid interface between the device and the liquid,interferes the sensing limit and is unable to meet the practical application.At present,the modification of polyethylene glycol and silane molecular spacer on FET can effectively decrease the Debye screening effect.Hydrogels as polymer network structures have been widely used in a range of biointerface applications due to their excellent biocompatibility.In this paper,hydrogels are used as the functional modification layer and gate dielectric of SiNW-FET to overcome the Debye screening effect,and the device sensitivity and stability is investigated.The effects of hydrogel-functionalized SiNW-FETs on the detection of pH and interleukin-6(IL-6)biosensing properties are also investigated.Therefore,based on SiNW-FET,by studying the effect of active small molecules such as traditional Chinese medicine on mesenchymal stem cells(MSCs),new application research of the device is explored.The thesis mainly includes the following three parts:(1)The pH-responsive acrylamide hydrogels are formed by in-situ UV polymerization,and the appropriate synthesis and immobilization process of the hydrogel is studied.Polymerization time and spin-coating parameters are key factors for the synthesis and immobilization of hydrogels.The successfully prepared pH-responsive hydrogels are functionalized on SiNW-FETs for pH sensing performance studies.It is found that the average pH sensitivity of the device is 100 mV/pH with exponential curve relationship between rate of change and pH value.And the device delays the aging of the device and maintaining excellent stability.The swelling of the hydrogel on the gate surface changes the dielectric properties,and its capacitance increases with the increase of pH in the measurement interval 3-13,implying that the hydrogel-modified SiNW-FET exhibits excellent pH sensing performance.(2)The IL-6 aptamer is immobilized in the hydrogel polymer network by chemical bonding.The functionalized sensor is successfully prepared which is specifically responsive to IL-6.It is found that the device responded regularly to different concentrations of IL-6 with a detection limit of 10 pg/L.Comparing conventional modification method of silane molecules with the aptamer hydrogel modification,it is found that the current signal attenuation of novel modified device in 10×PBS solution is relatively smaller than conventional modification.It indicates that the hydrogel modification can effectively decrease the Debye screening effect.(3)It is further carried out using mesenchymal stem cells stimulated by traditional chinese medicine(TCM)based on SiNW-FET.The positive TCM monomers and their effective concentrations are preliminarily screened by the time response curve.The study finds that the ginsenoside Rd,20(R)-ginsenoside Rg3,and ginsenoside F3,has the least influence on the current of the device.Ginsenosides Rb3 and 5,6-dehydroginsenosides Rd have relatively greater effects on the current of the device,indicating that these three monomers have stronger effects on MSCs.