Label-free SERS-colorimetry dual-mode biosensor based on CRISPR/Cas12a triggered G-quadruplex capped magnetic meso-porous silica microspheres

Stimuli-responsive magnetic mesoporous silica microspheres Fe3O4@mSiO2 have been widely used in biosensors. Here, we developed a CRISPR/Cas 12a system triggered Fe3O4@mSiO2 for label-free detection of cancer marker miRNA-21. A lot of methylene blue (MB) molecules, as surface-enhanced Raman scattering (SERS) signal molecules, were loaded into the mesopores of Fe3O4@mSiO2. G-quadruplex/hemin complexes, as gates, were capped on the surface of Fe3O4@mSiO2. Target miRNA-21 initiated primer exchange reaction (PER), whose product could activate the CRISPR/Cas 12a system. Thus, the activated Cas12a non-specifically cleaved the singlestranded DNA linked between G-quadruplex and Fe3O4@mSiO2, resulting in the removal of the cap and the release of the MB. The supernatant was dropped on the surface of ZnO NRs@AuNPs, and MB was detected through SERS to realize the sensitive detection of target miRNA-21. Meanwhile, the released G4/hemin complex in the supernatant was used to catalyze the oxidation of 2,2 '-azinobis (3-ethylbenzothiazoline-6-sulfonic acid ammonium salt) (ABTS) for colorimetric detection. The limits of detections were 4.7 aM and 0.18 fM for SERS and colorimetry, respectively. In this way, a label-free SERS-colorimetry dual-mode sensing platform was established for highly sensitive analysis of oligonucleotides