Platinum nanoparticle-graphene quantum dot nanocage as a promising Schottky heterojunction electrocatalyst for electrochemical detection of vanillin in baby milk powder

•We firstly report one strategy for synthesis of Pt-graphene quantum dot nanocomposite.•The composite offers ultrasmall size of Pt nanoparticles and Schottky heterojunction.•Unique structure achieves to high electron conductivity and electrochemical active sites.•The sensor provides better sensitivity, selectivity and reproducibility than other methods.•The composite also can be widely applied in various fuel cells and industrial catalysis.