An ultrasensitive biosensor for dual-specific DNA based on deposition of polyaniline on a self-assembled multi-functional DNA hexahedral-nanostructure.

Kras and Braf are major oncogenes. The mutation of Kras codon 12 or Braf V600E can lead to ovarian carcinoma. The detection of oncogene-related DNAs and their mutations offers solution for early diagnosis of ovarian cancer. Herein, a size-tunable multi-functional DNA hexahedral-nanostructure (DHN) has been rationally designed and modified on the electrode to response to Kras and Braf DNA. The size of DHN is controlled via polyadenines (polyA). The complete self-assembly of DHN depends on the presence of both target DNAs and two assistant probes. Meanwhile, a HRP-mimicking DNAzyme forms in DHN, which catalyzes the polymerization of aniline. The produced polyaniline is utilized as the output signal through differential pulse voltammetry (DPV). The biosensor shows the linear range from 100 fM to 1 μM, with the detection limit of 48.7 fM for Kras gene; and the linear range from 100 fM to 100 nM, with the detection limit of 44.1 fM for Braf gene, respectively. Since the current response depends on both gene sequences, the high specificity of the biosensor endows it to operate in an "OR"-type logic gate to discriminate the mutation of both genes. When Kras codon 12 or Braf V600E mutation happens, the response decreases significantly due to the incomplete formation of DNAzyme in DHN. The practicability of the biosensor has been verified through challenging human serum samples. Thus, it has great potential for clinical diagnosis of ovarian cancer through simultaneous detection of Kras and Braf genes and their mutations.