Controllable particles sizes of starch nanoparticles were synthesized via a precipitation in water-in-oil microemulsion approach. Microemulsion method offers the advantages of ultralow interfacial tension, large interfacial area, and being thermodynamically stable and affords monodispersed nanoparticles. The synthesis parameters such as stirring rates, ratios of oil/cosurfactant, oil phases, cosurfactants, and ratios of water/oil were found to affect the mean particle size of starch nanoparticles. Starch nanoparticles with mean particles sizes of 109 nm were synthesized by direct nanoprecipitation method, whereas by using precipitation in microemulsion approach, starch nanoparticles with smaller mean particles sizes of 83 nm were obtained. Materials and Methods2.1. Materials. Native sago (Metroxylon sagu) starch powder, olein palm oil, and sunflower oil (high in monosaturated

Fluorescein 5(6)-isothiocyanate starch maleate (FISM) nanoparticles were prepared by covalently attached fluorescein 5(6)-isothiocyanate (FITC) with starch maleate. FISM nanoparticles with a mean particle size of 87 nm were formed via self-assembly upon precipitation in ethanolic solution. FISM nanoparticles were strongly fluorescent with maximum emission wavelength of 518 nm. The fluorescence of FISM nanoparticles can be quenched by silver (Ag+) and lead (Pb2+) ions in a concentration dependent manner. We have demonstrated the first use of FISM nanoparticles as cheap and effective fluorescent sensing probes for Ag+and Pb2+ions with detection limits as low as 2.55×10−5 M and 3.64×10−5 M, respectively.