Gelatin-templated gold nanoparticles as novel time-temperature indicator

Gold nanoparticles (AuNPs) were generated by mixing of gelatin solution and gold precursor (HAuCl(4,) 1 mM) under isothermal condition (80 °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 λ(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 time-temperature indicator (2%, pH 5) was evaluated in a simulated frozen storage, clear color signals developed as little as 6 h of exposure at 30 °C and the intensity of the color signal was proportional to duration of exposure. Practical Application: Gelatin-gold 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 °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.