SERS detection of microRNA biomarkers for cancer diagnosis using gold-coated paramagnetic nanoparticles to capture SERS-active gold nanoparticles

In this paper, a magnetic-based, surface-enhanced Raman scattering (SERS) assay for detection of a cancer-related microRNA biomarker, miR-141, has been developed. The detection is based on hybridization-dependent recognition, in which the miR-141 target sequences were captured by complementary reporter and capture oligonucleotide probes conjugated to Raman-tagged gold nanoparticles (GNPs) and gold-coated paramagnetic nanoparticles (Au@MNPs) respectively. The resultant hybridization complexes, Raman-tagged GNPs/miR-141/Au@MNPs, are retrieved from solution by magnetic pull-down and concentrated within the focus of laser excitation. A signature spectrum for the Raman tag, 5,5'-dithiobis(succinimidyl-2-nitrobenzoate) (DSNB), was observed in concentrated pellets and specific for the miR-141 sequences. The viability of SERS detection has been demonstrated in a microfluidic platform, in which the hybridizations containing dilutions of the miR-141 sequences yielded a reduction in the DSNB spectrum peaks' intensity. The limit of detection (LOD) is estimated to be 100 fM, which is 100-fold lower than the LOD of 10 pM previously reported in a similar magnetic-capture SERS detection of small oligonucleotides using nonplasmonic MNPs. These results indicate that the addition of Au shells to MNPs facilitates the formation of SERS-active junction regions (hot spots) with nearby Au contents within the magnetic concentrates, which substantially improves the SERS signal and, therefore, detection sensitivity.