DNA And Two-dimension Nanomaterials-Based Interface Interaction And Its Application In Fluorescent Biosensors

Since discovered in 2004,graphene has attracted a lot of interest,improving the development of two-dimension nanomaterials.Owing to a unique combination of its crystallographic and electronic structure,graphene and its derivatives exhibit several superior and typical properties,and has emerged as an attractive candidate for the fabrication of novel nanobiointerfaces with different kinds of unique applications.As is known,nucleic acids are stable and can easily handle modification,and can recognize a wide range of targets with high selectivity,specificity,and affinity.The integration of nucleic acids with graphene-based materials has been substantially advanced over the past few years,achieving amazing properties and functions,thereby exhibiting attractive potential applications in biosensing,diagnostics,drug screening and biomedicine.While there is still some problem as follows:From the literature,we found a diverse range of sensor performance with the same GO-based signaling method,the difference in the oxidation level of GO might contribute to such inconsistency.Therefore,a comprehensive fundamental understanding is critical to facilitate further rational sensor design;The relationship between the interface reaction of nanomaterials and sensing mechanism is still unclear,unable to effectively regulate the process of signal producing,thus researching on the reaction mechanism of the nanointerface is even more significant.So,in this paper,we used graphene and other nanomaterials as quenching materials,combined them with different sequence of DNA,researching on the functional interface interaction between DNA and two-dimentional materials,and fabricating the biosensors for detecting DNA and Hg2+.The main research results and conclusions as follows:(1)Fluorescently labeled DNA adsorbed on graphene oxide(GO)is a well-established sensing platform for detecting a diverse range of analytes.GO is a loosely defined material and its oxygen content may vary depending on the condition of preparation.Sometimes,a further reduction step is intentionally performed to decrease the oxygen content,and the resulting material is called reduced GO(rGO).In this study,DNA adsorption and desorption from GO and rGo is systematically compared through FRET method.The oxygen content of GO decreased from 40.8%to 18.8%after reduction.Under the same salt concentration,DNA adsorbs slightly faster with a 2.6-fold higher capacity on rGO.At the same time,DNA adsorbed on rGO is more resistant to desorption induced by temperature,pH,urea,and organic solvents.Various lengths and sequences of DNA probes have been tested.When its complementary DNA is added as a model target analyte,the rGO sample has a higher signal-to-background(four-fold)and signal-to-noise ratio(two-fold),whereas the GO sample has a slightly higher absolute signal increase and faster signaling kinetics.DNAs adsorbed on GO or rGO are still susceptible to nonspecific displacement by other DNA and proteins.Overall,although rGO adsorbs DNA more tightly,it allows efficient DNA sensing with an extremely low background fluorescence signal.(2)Interfacing DNA with two-dimensional(2D)materials has been intensely researched for various analytical and biomedical applications.While most of studies were performed on graphene oxide(GO),two metal dichalcogenides,MoS2 and WS2 were also functionalized with DNA.GO,MoS2 and WS2 can all adsorb single-stranded DNA.However,they like use different surface forces for adsorption due to their different chemical structures.In this work,fluorescently labeled DNA oligonucleotides were used and their adsorption capacity and kinetics were studied as a function of ionic strength,DNA length and sequence.Desorption of DNA from these surfaces were also measured.DNA is more easily desorbed from GO by various denaturing agents,while surfactants yield more desorption from MoS2 and WS2.Our results are consistent with that DNA can be adsorbed by GO via ?-? stacking and hydrogen bonding,while for MoS2 and WS2 the van der Waals force is mainly responsible for adsorption.Finally,fluorescent DNA probes were adsorbed by these 2D materials for detecting the complementary DNA.For this assay,GO gave the highest sensitivity,while they all showed a similar detection limit,the detection limit for MoS2,WS2 and GO is 1.48 nM,2.92 nM and 1.61 nM,respectively.This study has enhanced our fundamental understanding of DNA adsorption by two important types of 2D materials and this information is useful for further rational optimization of their analytical and biomedical applications.(3)Attaching DNA to nanomaterials is the basis for DNA-directed assembly,sensing,and drug delivery of such hybrid materials.In addition to covalent conjugation,efforts have been made to search for DNA sequences such as aptamers that can strongly bind to materials surface.In this work,we communicate that poly-C DNA can serve as a general aptamer that strongly bind to four types of commonly used yet very different surfaces including nanocarbons(graphene oxide and single-walled carbon nanotubes),transition metal dichalcogenides(MoS2 and WS2),metal oxides(Fe3O4 and ZnO),and metal nanoparticles(Au and Ag).Compared to other sequences,poly-C DNA has the highest binding affinity,especially for surfaces with an overall weak DNA adsorption affinity.Using diblock DNA containing a poly-C block to attach to surfaces,target DNA was successfully hybridized to the other block,more efficient than those containing a poly-A block.This work has provided a simple solution for attaching functional DNA to most common nanomaterials.(4)Graphene oxide(GO)has attracted extensive research interest as a platform for DNA adsorption and biosensor development.While most researchers use simple physisorption of fluorescently labeled DNA,covalent sensors have the advantage of being less susceptible to non-specific probe displacement and minimizing false positive results.In this work,three thymine-rich DNA probes of different length are modified on their 3'-end with an amino group for covalent conjugation to the GO surface.They also each contain an internally labeled fluorophore so that Hg2+ binding can lead to a large distance increase between the fluorophore and the GO surface for fluorescence signaling.Hg2+-dependent fluorescence signaling from the covalent sensors are compared with that from the non-covalent sensors interms of sensitivity,selectivity,signaling kinetics,and continuous monitoring.The covalent sensors are much more stable and resistant to non-specific probe displacement,while still retaining high sensitivity and similar selectivity.The detection limits are 16.3 and 20.6 nM Hg2+,the sensitivity are 1.58 and 1.93/?M Hg2+ respectively,for the covalent and non-covalent sensors,and detection of spiked Hg2+ in Lake Ontario water is demonstrated.