Luminescent properties of dye–PMMA composite nanospheres

The luminescent properties of two types of dye-poly(methyl methacrylate) (PMMA) composite nanospheres were discussed and compared. Dye molecules (Ru(bpy)3Cl2) were combined with PMMA nanospheres in two strategies: embedding dye molecules during PMMA nanosphere formation (Em-PMMA NPs) and adsorbing dye molecules onto the surface of the produced PMMA nanospheres (Ad-PMMA NPs). It has been proved that the electrostatic interaction dominated the load of Ru(bpy)32+ on the PMMA matrix. The luminescence intensity of the Em-PMMA NPs was much higher than that of the Ad-PMMA NPs under same dye concentration due to different dye load distribution in two types of dye-PMMA composite nanospheres. Luminescence lifetime measurement of Ru(bpy)32+ in the Em-PMMA NPs (containing 2.20 × 103Ru(bpy)32+ molecules per NP) indicates that ∼60% of dye molecules loaded in inside of the PMMA matrix and ∼40% located close to/on the surface of NPs. For the Ad-PMMA NPs containing same amount of dye as Em-PMMA Nps, most of dye molecules (∼84%) were on the surface of NPs and only ∼16% of them penetrated into the PMMA matrix. The luminescence of the Em-PMMA NPs had nearly seven fold enhancement and the excited-state lifetime had nearly five fold extension relative to a dye aqueous solution. The mechanism of luminescence enhancement was studied. The results indicate that the larger viscosity and weaker polarity of a PMMA matrix led to the luminescence enhancement of Ru(bpy)32+. These luminescent PMMA nanospheres with high stability, long lifetime and high brightness hold great the potential for being a novel biological label.