Design And Optimization Of Two Organic Semiconductor Biosensors For DNA Detection

With the advancement of sensing technology and bioinformatics,DNA detection technology attaches increasingly importance to medical diagnosis,drug analysis,environmental monitoring and other fields.Recently,biosensors have achieved vigorous and rapid development due to their high selectivity,high sensitivity,fast analysis speed,low cost,high automation,miniaturization and integration.At present,most of the traditional DNA sensors use fluorescent markers,which are complicated in operation and expensive in monitoring equipment,and this operation is not conducive to rapid one-time detection.In the field of biosensors,the application prospects of organic electronic devices are broad,especially in low-cost,disposable,portable,flexible bending and so on.Therefore,this paper proposes and optimizes two DNA biosensors:an organic field effect transistor(OFET)and an organic heterojunction(OH),and they are optimized and studied separately.The main work completed is:(1)The research and development of current OFET biosensors are summarized,and their characteristics and deficiencies are pointed out accordingly.For the existing OTFT biosensor structure,the device structure and sensor performance are further optimized.Pentacene is used as the active layer,silicon dioxide is the gate insulating layer,heavily doped silicon is the gate,and metallic copper is the source-drain electrode.An OTFT with a bottom-gate top-contact structure is fabricated.The device was developed for adsorption studies using different concentrations(1pmol,10pmol,50pmol,100 pmol)of ssDNA solution,and its molecular structure was 5'-GCGTGCGGGAAATCGAGGTTCAGG-3'.On this basis,OTFT biosensors with different channel thicknesses(7.5,15,22.5,30 nm)were designed and studied with the same ssDNA molecules.The above results show that:1.As the concentration increases,the response current decreases.When the concentration reaches50pmol,the ratio of current change before and after adsorption of ssDNA decreases,indicating that the adsorption of organic semiconductor surface is saturated.2.The 15 nm thickness Pentacene OTFT has the highest detection sensitivity with a sensitivity of 74%.Therefore,by changing the concentration of ssDNA and the channel thickness,the detection sensitivity of the OTFT biosensor can be effectively improved.(2)A new organic heterojunction DNA biosensor structure has been proposed.The sensor has the advantages of simple structure,easy preparation,low price and good biocompatibility.DNA molecules were detected by a planar organic heterostructure composed of perfluorophthalocyanine copper(F₁₆CuPc)/copper phthalocyanine(CuPc).Experiments have shown that the accumulation of electrons and holes at the interface of the heterojunction can form a conductive channel that is very sensitive to external reactions.The results demonstrate that the planar organic heterojunction device has a significant current response to DNA adsorption.In addition,the AFM image shows that the ssDNA molecule has a good fixation on the surface of CuPc,and its negative charge attracts excess holes in the CuPc layer,which improves the electrical conductivity of the device.As the concentration of ssDNA increases,the concentration of the solution gradually appears saturated.And the conductivity of the device increases rapidly during the first few hours and then stabilizes after exposure to air for about two weeks.In addition,F₁₆CuPc/CuPc organic heterojunction devices with different thicknesses were designed.The effect of the thickness of CuPc layer on the current response was studied.The results show that reducing the thickness of CuPc can increase the current response of the device,and the current response of the device with 5 nm CuPc changes the most(109.4%),which means that the ssDNA sensing of the device with 5 nm CuPc is the most sensitive.