Ultrasensitive colorimetric miRNA detection based on magnetic 3D DNA walker and unmodified AuNPs

Gold nanoparticles (AuNPs) based colorimetric assay is a promising platform for simple and low-cost point-ofcare (POC) testing, but tends to have low sensitivity, which limits their clinical applications for trace nucleic acid assays. Herein, a simple colorimetric assay was developed by using unmodified AuNPs and magnetic 3D DNA walker, which could detect as few as 16.7 fM of miRNA-155, thus easily solves the main technical challenge of AuNPs-based colorimetric nucleic acid assays. In this platform, hundreds of substrate sing-stranded DNA (DNA tracks) and dozens of blocked walking strands were attached on an Au-Fe3O4 nanocomposite, applied as a magnetic 3D DNA walker. The target could activate this DNA walker powered by DNAzyme cleavage mechanism, generating a great deal of single-stranded product (displaced ssDNA). After magnetic separation, the generated displaced ssDNA (supernatant) was incubated with AuNPs to protect the unmodified nanoparticles from aggregation in high-salt solutions. Based on this, the concentration of miRNA-155 could be visualized through a color change from grayish black to purple and quantitatively determined by UV-vis spectroscopy. Furthermore, we demonstrated that our approach could be used to detect target miRNA-155 in real human serum samples without complicated sample pretreatment. Thus, the magnetic 3D DNA walker-AuNPs colorimetric method is a facile, sensitive and specific detection platform that shows great potential for development of next-generation POC nucleic acids diagnostics.

Automated summary

A simple colorimetric assay using unmodified AuNPs and magnetic 3D DNA walker was developed to detect miRNA-155 at a sensitivity of 16.7 fM, solving the low sensitivity issue of AuNPs-based colorimetric nucleic acid assays. The platform activated DNA walker through DNAzyme cleavage mechanism, generating displaced ssDNA for visualization and quantification of miRNA-155 concentration by color change and UV-vis spectroscopy. This approach showed potential for POC nucleic acids diagnostics.