Melanin-mediated synthesis of silver nanoparticle and its use for the preparation of carrageenan-based antibacterial films

Silver nanoparticles (AgNP) were synthesized by a green method using melanin (Mel) as a reducing and capping agent and incorporated to carrageenan (Carr) to prepare antimicrobial nanocomposite films. The optimal reaction condition for the synthesis of AgNP was 1 mM AgNO3 with 10 mg Mel/100 mL 0.1 M KOH at 100 degrees C for 1 h. The formed AgNP was spherical with a diameter of 10-50 nm and exhibited a light absorption peak at 410 nm. X-ray diffraction (XRD) peaks revealed the characteristic of crystalline AgNP. AgNP also showed strong antibacterial activity against food-borne pathogenic bacteria, Escherichia coli and Listeria monocytogenes. The incorporation of AgNP to Carr produced uniform films as observed from a field emission scanning electron microscope (FE-SEM). The addition of AgNP not only affected the color of the film surface but also significantly improved the UV shielding properties of nanocomposite films. The incorporation of AgNP reduced the water contact angle and water vapor barrier properties while increasing the thermal stability, mechanical strength and resilience of the Carr films. The Carr/AgNP nanocomposite films showed strong antibacterial activity against E. coli and L. monocytogenes.