Ratiometric fluorescence sensor for the sensitive detection of Bacillus thuringiensis transgenic sequence based on silica coated supermagnetic nanoparticles and quantum dots

[Display omitted] •A ratiometric fluorescence sensor was constructed for the accurate and sensitive detection of target DNA.•rQDs@SiO2 and MS@gQDs probes were obtained based on silica coating method.•MS@gQDs-SA both act as catcher and donor and rQDs@SiO2@GN-H3 as receptor in the sensor.•The excess rQDs@SiO2@GN-H3 could easily be separated from solution for recycling use. Improving the accuracy and sensitivity of fluorescence analysis is of great importance in clinical diagnosis, environmental and food monitoring. Herein, based on fluorescence resonance energy transfer (FRET), a facile and effective ratiometric fluorescence sensor was constructed for the detection of Bacillus thuringiensis (Bt) special gene fragment. In this work, green quantum dots (gQDs) decorated Fe3O4 magnetic beads (MBs) with streptavidin (SA) were acted as donor, and gold nanoparticles (GN) modified red quantum dots (rQDs@SiO2) with hairpin DNA as receptor. When the target sequences exist, the hairpin DNA were unfolded and subsequently captured by MBs@SiO2@gQD-SA via biotin–SA specific interaction. By using the magnetic separation method, the hybridized composites could be easily purified for florescence tests. By this means, rQDs@SiO2@GN could enhance the fluorescence intensity of rQDs (I620) and simultaneously quench the fluorescence response of gQDs (I540) via FRET. Under optimal conditions, the ratio of fluorescence intensity at 620nm and 540nm (I620/I540) showed that Bt transgene fragment detection owning a good linearity from 5.0pM to 10nM with a detection limit of 0.10pM (S/N=3). The high selectivity of the probes was also demonstrated using the single-base and three-base mismatch method.