Ultrasensitive detection of heparin by exploiting the silver nanoparticle-enhanced fluorescence of graphitic carbon nitride (g-C3N4) quantum dots.

A composite (Ag-g-CNQDs) was prepared from graphitic carbon nitride quantum dots and silver nanoparticles by water phase synthesis. Aided by metal-enhanced fluorescence, the composite exhibits excitation-dependent red emission with a peak at 600 nm with a quantum yield of 21%. If the composite is coated with polyethylenimine (PEI) to form the Ag-g-CNQD/PEI complexe, fluorescence is strongly reduced. Upon addition of heparin, the fluorescence of the system is enhanced because PEI has a higher affinity for heparin than Ag-g-CNQDs. The effect was used to design a fluorometric  assay for heparin. The emission at 600 nm increases linearly in the 0.025 to 2.5 μM heparin concentration range, with a 8.2 nM limit of detection. Graphical abstract Schematic illustration for fabricating a composite consisting of silver nanoparticles and graphitic carbon nitride quantum dots (Ag-g-CNQDs). Its red fluorescence is weak in presence of polyethyleneimine but restored on addition of heparin. This forms the basis for a new method for heparin detection.