Preparation and characterization of metal (Au)- and bimetallic alloys (AuNi)-gelatin nanocomposites

Hybrid inorganic/organic materials consisting of Au and AuNi nanoparticles and gelatin have been synthesized by soft chemical routes (reduction by N2H4 aqueous solution at 277 and 373 K). The average particle size, obtained by transmission electron microscopy, ranged between 4 and 20 nm. For Au-gelatin sample, at 277 K, the gelatin 3D network was maintained and Au nanoparticles present close-packed linear assemblies along gelatin filaments forming a spider web-like network. Because of inter-particle coupling and gelatin adsorption, Au arrays exhibit dipolar plasmon resonances that shift and broaden by hundreds of nanometers. For the first time, AuNi nanoparticles could also be formed at 373 K. At this temperature gelatin was solubilized but AuNi particles were still stabilized by the protein chains without array formation. AuNi fcc phases were observed by X-ray diffraction. A blue-shift of the plasmon resonance was observed for AuNi-gelatin nanocomposites when compared to Au-gelatin. SQUID magnetometer measurements indicate that AuNi-gelatin samples are ferromagnetic at low temperature. At 2 K hysteresis loops were observed with coercivity (Hc) values between 450 and 650 Oe and squareness values between 0.15 and 0.37. These new nanocomposites therefore appear very promising for the design of nanodevices.