A novel surface-enhanced Raman scattering (SERS) strategy for ultrasensitive detection of bacteria based on three-dimensional (3D) DNA walker.

Bacteria seriously endanger human life and health, and the detection of bacteria is vital for the prevention and treatment of related diseases. Surface-enhanced Raman scattering (SERS) is considered as a powerful technique for bacterial detection due to the inherent richness of spectral data. In this work, a novel SERS strategy based on three-dimensional (3D) DNA walker was developed for quantitative analysis of Salmonella typhimurium (S. ty). The complimentary DNA of S.ty-recognizing aptamer (cApt) was replaced from the double-stranded DNA (dsDNA) of Apt@cApt in the presence of S.ty, which can trigger the endonuclease mediated "DNA walker" on the surface of gold modified magnetic nanoparticles (AuMNPs). The DNA residues on the surface of AuMNPs can bind to SERS tag through base complementary pairing, and the complex of "AuMNPs@SERS tag" can be separated from the fluid by an external magnetic field for SERS analysis. It was found that the SERS intensity showed a good linear relationship with both lower (10-104 CFU/mL) and higher (104-106 CFU/mL) S.ty concentration. A superior limit of detection (LOD) as low as 4 CFU/mL was achieved due to the signal amplification effect of "DNA walker", and the preeminent selectivity of the proposed method was determined by the selectivity of the aptamer sequence. This strategy of separating the SERS tag from the biological matrix enables high stability and good repeatability of the SERS spectra, which presents a new method for SERS detection of biomaterials that can benefit various application scenarios.