Gelatin-Templated Gold Nanoparticles as Novel Time-Temperature Indicator

Gold nanoparticles (AuNPs) were generated by mixing of gelatin solution and gold precursor (HAuCl4, 1 mM) under isothermal condition (80 degrees C). The effects of gelatin concentration (1% to 6%) and pH (3, 5, and 9) on the color signal of gelatin-templated AuNPs were examined. The ?max of AuNPs shifted from 535 to 552 nm at 1% gelatin, and the color intensity of the AuNPs was a maximum at 2% gelatin. The speed of color development was accelerated at pH 3, and the AuNPs prepared at pH 3 were bigger (45 to 162 nm) and more irregular in shape than those prepared at pH 5 or 9. When the performance of gelatin nanoreactor as timetemperature indicator (2%, pH 5) was evaluated in a simulated frozen storage, clear color signals developed as little as 6 h of exposure at 30 degrees C and the intensity of the color signal was proportional to duration of exposure. Practical Application: Gelatingold precursor mixture acted as a nanoreactor for gold nanoparticle synthesis without need for any additional reactants. When the gelatin-templated AuNPs were exposed to 30 degrees C, color signals developed with intensities that depended on the duration of exposure. The reaction was irreversible and colors were easily discerned by the naked eye.