Field Effective Transistor DNA Sensor Based On Low Dimensional Materials

As the most important carrier of biological genetic information recording,the type and the order of nucleobases of DNA carry broad range of biological information and genetic instructions,which can bring the diagnosis and treatment of diseases to the molecular level.In recent years,through analyzing the information that abstract from DNA hybridization,the scientific problem such as Alzheimer's disease,Down's three-body syndrome,DNA reaction kinetics and binding energy and the rapid high-precision detection of heavy metal deposition in vivo,have been successively overcome by using field effective transistor based on two-dimensional material.It is the tireless pursuit of researchers to continuously improve the sensitivity of field-effect transistor(FET)biosensor.Based on the existing work,this article focuses on how to eliminate the adverse effects of substrate to sensing materials and find new signal-enhancing sensing mechanisms to further improve the sensitivity of FET biosensor,we researched and manufactured the FET biosensor based on suspended carbon nanotube(CNT)and the FET biosensor with optical field and electric field coupling.The first work of the article is to create a FET biosensor based on suspended carbon nanotube which was fabricated based on the characteristics of infinite mutual solubility of palladium and silver and their highly different melting point.The suspended carbon nanotube based FET overcome the adverse influence of the substrate to sensing material,compared to the traditional FET.The electrical conductivity of the suspended CNT was improved by two orders of magnitude,compared the CNT that directly contacted with the substrate and about 50% of the effective sensing area was released from the substrate.Scanning electron microscopy and Raman spectroscopy was used to characterized that the DNA was successfully bound to the carbon nanotube by using 1-fluorenbutyric acid succinimidyl ester as linker and that the suspended carbon nanotube did not break or sink during the detection process.The sensor shows extremely high detection performance,with DNA concentrations as low as 10 aM being effectivelydetected.Theoretical simulations were used to verify the experimental results and the Slater-Koster tight-binding method was adopted to calculate the geometric optimization and transport properties of carbon nanotube bound with DNA.The simulation results show that as the combination of carbon nanotube with probe DNA and complementary DNA,carbon nanotube's conductivity decreases continuously,and the ability to weaken the conductivity of carbon nanotubes of double-stranded DNA is several times(more than two times)than that of single-stranded DNA.Obtained simulation results are highly consistent with the experimental results.The second work of this paper is to prepare a light driven sensitivity enhanced FET biosensor by electric field coupling light field.The effects of the number of graphene layer and the wavelength of light were considered to investigate the absorbance of graphene to light.Based on the simulation results and the existing experimental conditions,two layers graphene and425 nm light were selected to prepare such a FET biosensor.Similarly,1-pyrene butyric acid succinimide was used to functionalize graphene and perform DNA binding.The results of functionalization and binding were characterized by Raman spectroscopy.Such a sensor shows that the current signal was strongly modulated by the gate voltage and the current is significantly different under different gate voltages.The higher the grid voltage is,the stronger the current signal is.In the range of ?-?v1v5.0,the DNA signals of gradient low concentration can be effectively identified and the signals present good linear relationship.Here,the gating effect produced by the gate voltage and negatively charged DNA is the main mechanism to achieve highly sensitive detection.The graphene band model based that the graphene on the channel is modulated by gating effect and the graphene on the electrode free from the modulation of gating effect was established to analyze the experimental results,which explains the experimental results well.Light field and electric field coupling FET DNA sensors exhibit excellent sensitivity and detection limits as low as 1aM was obtained,which reached the highest level of reported research.A single mismatch,five mismatches,ten mismatches,and a completely mismatched complementary DNA were used to test the specificity of the sensor and the obtained results show that DNA strands with different degrees of mismatch can be effectively identified,which meas that such a sensor can perform good specificity.The third work of this paper proposed a molybdenum disulfide/graphene nanostructure FET biosensor,which was used for DNA hybridization detection.Multilayer molybdenum disulfide with a special charge distribution works as a barrier layer between the electrolyte and graphene to reduce the noise signal caused by water molecule.On the other hand,molybdenum disulfide can shorten the distance between DNA and graphene by polarizing DNA molecules,which makes negative charge of the DNA molecules transfer to graphene and weaken the Debye shielding effect.Similarly,1-pyrene butyric acid succinimide was used to functionalize graphene and perform DNA binding.The results of functionalization and binding were characterized by Raman spectroscopy.Sensing mechanisms dominated by donor or gating effect was discussed.A larger voltage shift of the charge neutral point was obtained due to a strengthened donor effect and a weakened gating effect caused by the introduction of molybdenum disulfide layers.The biosensor achieved an effective response to DNA concentrations in a broad range from 10 aM to100 pM and a limit of detection of 10 aM was obtained,which was one or more orders of magnitude lower than the reported result.