Highly sensitive smartphone-integrated colorimetric glucose sensor based on MnFe2O4 – graphitic carbon nitride hybrid nanostructure

•MnFe2O4/g-C3N4 was successfully fabricated by a facile hydrothermal synthesis and magnetic separation process.•MnFe2O4/g-C3N4 exhibits excellent peroxidase-like activity.•LOD of MnFe2O4/g-C3N4 toward H2O2 and glucose are at least one and two orders lower values than those of previous reports.•Smartphone integrated colorimetric glucose sensors is demonstrated.