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

•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.