Rhodamine-Based Fluorescent Nanogel: A Dual Temperature and pH Sensor

We have prepared a pH and thermosensitive, fluorescent nanogel based on sodium alginate and itaconic acid as pH-sensitive moieties, diethylene glycol methyl ether acrylate as thermosensitive monomer and rhodamine B monomer as pH-sensitive fluorescent dye. The nanogel was characterized by Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (1HNMR) spectroscopy. Also, scanning electron microscope (SEM) images were taken and indicated the relative uniform spherical particles with average diameter 250-300 nm. By enhancing the fluorescence emission at 576 nm, we confirmed that the pH sensitive property of the nanogel was more effective than that of the bare rhodamin B. Moreover, the nanogel including the diethylene glycol methyl ether acrylate exhibited changes in fluorescence intensity induced by temperature. By heating the nanogel dispersion to 40 degrees C, at acidic pH the rhodamine emission showed a considerable increase. This result indicated the occurrence of an efficient fluorescence resonance energy transfer (FRET) process between fluorescence dye and polymeric nanogel in collapsed state. Also, the thermo-responsibility of the nanogel was studied by dynamic light scattering (DLS) analysis which indicated the change in hydrodynamic diameter by changing the temperature.