Biosensors Based On DNA Walkers And Ion-Exchange Signal Amplification Strategies For The Detection Of Toxins And Disease Biomarkers

Metal-organic frameworks(MOFs),metal sulfide nanoparticles,and a series of Tb and Ce co-doped Co P nanomaterials with good electrocatalytic activity have attracted great attention.In this paper,based on the stability and excellent biocompatibility of Co-MOF,as well as the large specific surface area and excellent electrical conductivity of MXene,and the ion-exchange properties of Zn S nanoparticles,an electrochemical and fluorescent biosensor was constructed for the detection of ochratoxin.OTA,mi RNA-141 and p53DNA,and the electrocatalytic properties of a series of synthesized Co P nanomaterials co-doped with Tb and Ce were studied.The research of this paper is divided into the following four aspects:(1)Ochratoxin A(OTA)causes serious danger to public health.In this paper,a DNA walker-based dual signal electrochemical ratiometric platform was constructed for the detection of ochratoxin A(OTA).These dual signal ratiometric strategy overcomes the changes of a variety of factors,including basic electrode characteristics and probe loading density.Co-MOFs and toluidine blue were utilized as electrochemical signal tags and internal reference probe,respectively.In the presence of OTA,the released multiple walking strands are allowed for an autonomous walk on the DNA tetrahedral nanostructure(NTH)-based track,resulting in DNA labeled-Co-MOFs far away from the electrode.Thus,the signal of Co-MOFs at-1.18 V was decreased and toluidine blue as internal reference probe at-0.28 V was increased.This ratiometric multiple amplification strategy displayed superior sensitivity.A low detection limit of 0.31 fg/m L was achieved within a wide linear range from 1 fg/m L to 100 ng/m L.The ratiometric sensor was also applied for determining OTA content in red wine samples,and compared with commercial enzyme-linked immunoassay kit with satisfactory results.(2)In this paper,a homogeneous electrochemical sensor based on an enzyme-driven tandem three-dimensional DNA machine was constructed for the detection of mi RNA-141.In a homogeneous solution,using Co-MOF as the signal probe of the electrochemical sensor,two single walkers were constructed by using magnetic beads to immobilize the hairpin-structured substrate chains MB1 and MB2,respectively.In the presence of mi RNA-141,it binds specifically to the blocking pendulum chain and releases the pendulum chain to form an enzyme cleavage site with MB1.The Co-MOF labeled at the 3?end of MB1 is detached from the magnetic beads,and the detached DNA fragment acts as a walking chain to trigger machine 2to realize a nickase-driven cascade DNA machine.After the completion of the reaction in a homogeneous solution,magnetic separation is performed,the magnetic bead part is detected on the electrode.This tandem 3D DNA machine shows excellent sensitivity with a linear range from 1 fmol/L to 10 nmol/L and a detection limit of 0.3 fmol/L(S/N=3).The biosensor can be applied to the detection of mi RNA-141 in real serum samples,which is of great significance in disease diagnosis.(3)In this paper,a fluorescent sensing system based on chain amplification and cation exchange(CX)-triggered multiplex signal amplification catalytic molecular beacons was constructed for the detection of p53DNA.In the presence of p53DNA,DNA self-assembles to form dendritic DNA structures.The streptavidin-modified Zn S nanocrystals were successfully assembled on the DNA dendrimers due to the modification of biotin at the ends of the DNA dendrimers.The exchange of Zn S nanocrystals and Ag⁺replaces a large amount of Zn²⁺,which triggers the catalytic molecular beacon system.A highly sensitive p53DNA fluorescence sensing system was constructed by using DNA self-assembly,ion exchange(CX)reaction and the signal amplification strategy of catalytic molecular beacons.Using the fluorophore carboxyfluorescein(FAM)as the signal,the enhancement of the fluorescence signal is proportional to the concentration of the detected target p53DNA,the linear range is 10 pmol/L?200 nmol/L,and the detection limit is 2.34 pmol/L(S/N=3).The biosensor can be applied to the detection of p53DNA in real serum samples,and has a good application prospect in clinical diagnosis.(4)Ce and Tb co-doped layered cobalt hydroxide(Ce,Tb-Co(OH)₂)were synthesized by one-step hydrothermal method,followed by phosphating at 300°C at low temperature using Na H₂PO₂·H₂O as phosphorus source to obtain Ce and Tb co-doped Co P nanosheets.The effects of Ce,Tb doping content and ratio on oxygen evolution reaction(OER)performance were explored.The results show that the OER performance of the catalyst is optimal when the doping amounts of Ce and Tb are 4%(atomic ratio)of Co,respectively.When the current density is 10 m A/cm~2,the overpotential is 308 m V,the Tafel slope is 59.8 m V/dec,and when the current density is 10 m A/cm~2for 28 h,the voltage decay rate is only 0.25 m V/h,the catalyst durability is excellent.