Graphene-based Field-Effect Transistor Biosensors For Nucleic Acid Detection

Detection of nucleic acid can provide useful information for research of molecular biology, diagnosis of genetic disease, environment monitoring and so on. Although there have already been many methods developed for nucleic acid detection, it’s still very important to develop ultrasensitive and highly selective methods to detect nucleic acid. With the rapid development of modern electronics and biotechnology, the research of biosensor becomes more and more popular, and this new, interdisciplinary field is believed to play a significant role in life science research and clinical detection.A biosensor is made of a biological recognition component and an appropriate signal transduction component, which is a device for reversible and selective detection of concentration or activity of the biomolecules or chemicals. The biological recognition components, such as nucleic acid, antibody, enzyme and cell, etc, make the biosensors good for detecting targets with high sensitivity and selectivity. Then the signal transduction component converts the biological signal into detectable signal, so the target can be detected by this way.Nanomaterials-based field-effect transistor(FET) biosensors have recenltly been developed to be novel, promising biosensors. A FET biosensor has attracted wide attention for research of life science because of its potential for miniaturization and integration. Furthermore, nanomaterials have been applied to biosensors for their unique physical and chemical propertities, including surface effect, micro-size effect, quantum hall effect, macroscopic quantum tunneling effect and so on. These advantages make the nanomaterials-based FET biosensor suitable for the detection of biomolecules. Compared with the conventional detection methods, the nanomaterials-based FET biosensor has the advantages including ultrasensitivity and high selectivity, rapid analysis, label-free detection, easy operation and low reagent consumption and so on. Therefore, the biosensor will have a significant effect on clinical detection.Graphene, a one-atom-thick 2D carbon material, has the unique properties, such as large detection area, high carrier mobility, excellent thermal conductivity, high mechanical strength and so on. These unique properties can enhance the sensitivity and selectivity of the graphene-based FET biosensor.In this work, graphene-based FET biosensors have been developed by employing reduced graphene oxide(R-GO) as the sensing channel. After specific probe molecule is immobilized on the graphene surface, sensitive and selective detection of target is conducted by the graphene-based FET biosensors through nucleic acid-nucleic acid hybridization and monitoring of electrical signal before and after hybridization. More details are described in the following:I PNA-functionalized graphene FET biosensor for DNA detectionThe fabrication of the FET chip was completed by using the standard conventional macro-nano processing technologies. R-GO was prepared by reduction of graphene oxide(GO) with 98% hydrazine, and the graphene FET biosensor was fabricated by drop-casting the R-GO suspension onto the sensor surface. Peptide nucleic acid(PNA) as the capture probe was immobilized on the graphene surface via the linker molecule(1-pyrenebutanoic acid succinimidyl ester, PASE), and DNA detection was performed through PNA-DNA hybridization by the graphene FET biosensor. Electrical signal was measured before and after the PNA-DNA hybridization. The detection limit was as low as 100 fmol/L, which is one order of magnitude lower than the previously reported graphene FET DNA biosensor based on DNA-DNA hybridization. In addition, the R-GO FET biosensor enabled an accurate distinction of complementary DNA from one-base mismatched DNA and noncomplementary DNA. What’s more, the DNA biosensor was found to have a capability of regeneration. Therefore, the developed R-GO FET DNA biosensor is ultrasensitive and high selective, indicating its potential applications in disease diagnostics as a point-of-care tool.II Gold nanoparticles-decorated graphene FET biosensor for mi RNA detectionThe graphene FET biosensor was fabricated by using the method as described above. Gold nanoparticles(Au NPs) were decorated onto the surface of graphene via HAu Cl4 solution. Then PNA probe was covalently immobilized on the Au NPs surface. After that, mi RNA was introduced to the biosensor to hybridize with PNA probe. Mi RNA detection was conducted by measuring the electrical signal before and after PNA-mi RNA hybridization. The sensitivity of mi RNA detection was found to be 10 fmol/L by the FET biosensor. Furthermore, the graphene FET biosensor was able to distinguish the complementary mi RNA from one-base mismatched mi RNA and noncomplementary mi RNA. Moreover, the graphene FET biosensor with high sensitivity and selectivity was also applied to detect mi RNA in serum samples, making it a novel detection platform for diagnosis of gene-related diseases.