Dual-mode melamine detection based on gold nanoparticles aggregation-induced fluorescence “turn-on” and “turn-off” of CdTe quantum dots

Both “turn-on” and “turn-off” fluorescent probe for the determination of melamine have been developed by tuning the inner filter effect (IFE) from CdTe quantum dots (QDs) to gold nanoparticles. Because of the melamine-induced aggregation of gold nanoparticles, the first absorption peak of the transverse surface plasmon resonance (SPR) at 520 nm fades down, whereas the second absorption peak of the longitudinal SPR around 620 nm gets intense. The decrease of the transverse SPR reduces the IFE of the bundled CdTe QDs with an emission band at 525 nm (the corresponding particle size is 1.98 nm), which results in the melamine concentration-dependent fluorescence recovery of CdTe QDs. The increase of the longitudinal SPR enhances the IFE of the bundled CdTe QDs with an emission band at 620 nm (the corresponding particle size is 3.68 nm), which results in the melamine concentration-dependent fluorescence decrease of CdTe QDs. The green mode detection with the fluorescence recovery has a linear response for melamine from 20 to 100 ng/mL with a theoretical detection limit of 8 ng/mL. The red mode detection with the fluorescence decrease has a linear response for melamine from 20 to 100 ng/mL with a theoretical detection limit of 11 ng/mL. Interference studies and real samples detection show that the melamine could be specifically detected using this dual-mode fluorescent probe.