Green synthesis of reduced graphene oxide-Ag nanoparticles as a dual-responsive colorimetric platform for detection of dopamine and Cu2+

A one pot rapid and green synthesis approach using pine (Pinus densiflora) leaf extracts was developed to prepare AgNPs decorated with graphene nanocomposites (rGO@AgNPs). The rGO@AgNPs was used for an innovative, facile and reliable dual functional assay of dopamine (DA) and copper ions (Cu2+). Synergistic interactions of DA with rGO@AgNPs through π-π interactions and hydrogen bindings could induce aggregation of the rGO@AgNPs and color changing of the solution from yellow to brown. The UV-vis absorption ratio (A515/A405), corresponded to the color changes, was monitored for quantitative determination of DA. The sensor was also utilized to detect Cu2+ through an anti-aggregation mechanism. Cu2+ ions could prevent aggregation of rGO@AgNPs through formation of a complex with DA, and DA acted as a selective chelating agent for Cu2+. In the presence of a certain amount of DA, the aggregation of rGO@AgNPs decreased by increasing the concentration of Cu2+ ions in the solution. It accompanies with a color change from brown to yellow and increasing the absorption ratio of A405/A515. The limit of detection (LOD) for DA and Cu2+ were estimated as 16 and 9.8 nM, respectively. The green synthesized rGO@AgNPs were used for selective detection of DA and Cu2+ in human urine and tomato samples.