Plasmon-enhanced fluorescence of gold nanoparticle/graphene quantum dots for detection of Cr3+ ions

Graphene quantum dots (GQDs), fascinating semiconductors with stable photoluminescence (PL), have important potential applications in the fields of biology, medicine, and new semiconductor devices. However, it is still challenging to overcome the weak PL intensity. Here, we report a strategy for selective resonance enhancement of GQD fluorescence using gold nanoparticles (AuNPs) as plasmas. Interestingly, the addition of low concentration AuNP makes AuNP/GQDs exhibit significant fluorescence enhancement of 2.67 times in the visible range. The addition of high concentration AuNP leads to the formation of an excitation peak at 421 nm and selectively enhances certain radiation modes. We concluded that the main reason for the selective enhancement of PL intensity in high concentration AuNP is the transfer of generous hot electrons at high energy states from AuNP to GQD and relaxation to the ground state. The electron resonance of low concentration AuNP transfers to GQD and relaxes to lower energy levels, exhibiting an overall enhancement of PL intensity. We apply it for detection of the heavy metal ion Cr3+, and verify that it has a correlation coefficient of 97.36%. We believe AuNP/GQDs can be considered excellent candidates for heavy metal detection and high fluorescence bio-imaging.