Signal-Amplification Electrochemical Biosensor Based On Transition Metal Selenide Nanosheets

Electrochemical biosensor has the advantages of high sensitivity and good selectivity,and is widely used in clinical medicine,environmental monitoring,food safety and other fields.microRNA（miRNA）and protein molecule play an important role in the normal functioning of human body function,and it is meaningful to accurately and quickly detect them.In order to improve the performance,a new type of electrochemical biosensor were developed based on two-dimensional transition metal selenide nanosheets and bio-amplification technologies.The details are as follows:（1）A sensitive electrochemical biosensor was constructed based on WSe₂ and competitive RNA-RNA for detection of miRNA.First,WSe₂ nanosheets were prepared by hydrothermal method and then are immobilized with gold nanoparticles as electrode substrate materials.A biotinylated miRNA of the self-same sequence with the target miRNA was mixed with the samples,and allowed competition with the target miRNA for a thiolated RNA probe immobilized onto the modified electrode.Combined with streptavidin-horseradish peroxidase catalyzed the H₂O₂ and hydroquinone systems an amplified electrical signal was obtained and therefore established a new method for sensitive detection of target miRNA.This method presented a linear range from 0.1fmol/L to 100 pmol/L with the detection limit of 0.068 fmol/L（S/N=3）.（2）A sandwich-type biosensor was fabricated for the sensitive detection of miRNA based on MoSe₂/N-doped graphene/Au nanoparticles and hemin/G-quadruplexes.AuNPs were first deposited on the surface of a MoSe₂ modified electrode to immobilize the thiol-modified hairpin probe through the strong Au-S bond.When the target miRNA was added,capture DNA hybridized with it and unfolded its stem-and-loop structure.The NG-AuNPs hybrids were used as the signal carrier and were modified by hybridizing with assistance DNA and the terminus of capture DNA,resulting in the formation of the supersandwiched structure.The assistance DNA was embedded into the hemin/G-quadruplex complexes in the presence of hemin and K⁺to generate amplified current signals for sensitive detection of miRNAs.The method displayed a linear range from 10 fmol/L to 1 nmol/L with a detection limit of 0.17 fmol/L（S/N=3）.（3）A sandwich-type biosensor for highly sensitive detection of thrombin was developed based on WSe₂/gold nanoparticles and aptamer.WSe₂ and AuNPs were used as electrode substrate materials,and the AuNPs were linked to aptamer 1 via Au-S bonds.Thrombin was captured by aptamer 1,and then from sandwiched structure through the simultaneous interaction with AuNPs modified aptamer 2 and signal probe.Subsequently,the DNA-linked AuNPs hybrids resulted in the capture of streptavidin-conjugated alkaline phosphatase onto the modified GCE through the specific affinity reaction.The electrode undergone an electrochemical-chemical-chemical reaction,further enhancing the response signal.The method was used for thrombin detection with a linear range from 0.5 pg/mL to 1000 pg/mL and a detection limit of 0.19 fg/mL（S/N=3）.