Ultrasensitive biosensing platform based on layered vanadium disulfide-graphene composites coupling with tetrahedron-structured DNA probes and exonuclease III assisted signal amplification

Recently, two-dimensional layered transition metal dichalcogenide materials have been very fascinating in electrochemical fields due to their unique electronic and electrochemical properties. In the present work, a novel VS₂-graphene (VS₂-GR) composite is firstly prepared by a facile one-step hydrothermal method. A sensitive, universal and label-free electrochemical aptamer-based sensor (aptasensor) is then designed to detect the platelet-derived growth factor BB (PDGF-BB) based on VS₂-GR coupled with Exo III-aided autocatalytic signal amplification. In the absence of PDGE-BB, the aptamer hybridized with the complementary DNA (cDNA) and the single-strand signal DNA labeled with biotin at 5' end cannot be cleaved by the Exo III. When the above mixture is applied on the tetrahedron-structured probe (T-DNA) modified AuNP/VS₂-GR electrode, signal DNA hybridizes with the protruding of T-DNA and a large number of avidin-HRP are adsorbed on the modified electrode by the specific binding of avidin-biotin, which leads to a strong current response by the catalysis of HRP to the mixture of hydrogen peroxide and hydroquinone (H₂O₂ + HQ). However, in the presence of PDGF-BB, the aptamer is preferentially associated with PDGF-BB, which facilitates the formation of double-strand DNA between cDNA and signal DNA. The duplex DNA is digested by Exo III from the 3' blunt terminus of signal DNA and the cDNA is released. The liberative cDNA then reacts with the remaining signal DNA in the solution to perform a new cleavage process. Finally, the cyclic hybridization-hydrolysis process leads to a great decrease of biotin on the electrode, thus reducing the quantity of signal molecule HRP and causing an obvious decline of current response. This proposed protocol exhibits high specificity, good sensitivity, and good stability for PDGF-BB detection. Moreover, the aptasensor can be applied as a universal assay for the detection of various targets including proteins, DNAs, and metal ions.