Magnetic-capture-based SERS detection of multiple serum microRNA biomarkers for cancer diagnosis

The selective discrimination of multiple microRNAs (miRNAs) in biological samples holds great potential for the early diagnosis of various cancers. In the present study, we present an extremely sensitive surface-enhanced Raman scattering (SERS) assay for multiplex detection of cancer-related miRNAs-miR-141, miR-429 and miR-200b-derived from the miR-200 family, using three pairs of silica-coated, analyte-embedded Au nanoparticles (SA@GNPs) and Au-coated paramagnetic nanoparticles (Au@MNPs) conjugated with DNA probes specific for each miRNA target. The SA@GNPs with an optimal silica shell (similar to 3 nm) were prepared to provide an effective barrier to prevent the protein-induced disassociation of Raman analytes from the GNPs, therefore allowing more reproducible SERS signaling than uncoated GNPs in serum solution. Moreover, this thin silica shell minimized the interparticle distance between plasmonic nanostructures in dense magnetic concentrates, significantly impacting the formation of hot spots for SERS enhancement. The target miRNA detection was achieved by SERS excitation of magnetically concentrated SA@GNPs/target miRNA/Au@MNP complexes, which are formed by target-specific hybridization reactions. The limit of detection (LOD) of miRNAs in human serum was 120 fM. The discrimination of miR-141, miR-429, and miR-200b in multiplex detection was realized by identifying diagnostic peaks of analytes in mixed Raman spectra. Due to the high-level detection sensitivity and assay reproducibility, the proposed SERS assay offers opportunities for multiplex detection of serum miRNAs and cancer diagnosis in a clinical setting.