Starch-based Janus particles: Proof-of-concept heterogeneous design via a spin-coating spray approach

Abstract

The asymmetric nature of Janus particles made from synthetic polymers gives them intriguing properties that have found applications in a wide variety of fields, such as drug delivery, emulsion stabilization, and environmental decontamination. The potential of using natural biopolymers as base materials for Janus particles in the food industry, however, has not yet been fully explored. Here we demonstrate for the first time the design of a starch-only-based Janus particle. Using a spin-coating spray approach, we produced both large (12.2 μm) half-porous, waxy cornstarch Janus granules by alpha-amylase treatment and small (1.2 μm) half-hydrophobic, amaranth starch Janus granules by octenyl succinic anhydride esterification. Optical microscopy, scanning electron microscopy, super resolution-structured illumination spectroscopy, and infrared spectroscopy were used to confirm the binary nature of these particles. A methylene blue adsorption test further showed that the untreated (non-porous), half-porous Janus, and fully porous waxy cornstarch granules had five-hour adsorption rates of 20.5, 72.1, and 100%, respectively, and adsorption capacities of 0.82, 2.88, and 3.96 mg/g. Meanwhile, untreated amaranth starch granules were shown not to interact with each other in water, while >68% of the half-hydrophobic granules self-assembled into wormlike strings and micelles, and >66% of the fully hydrophobic granules aggregated into spherical, complex supermicelles. While the low yield typical of Janus particle formation prevents a more detailed characterization of these starch-based Janus particles, the unique properties they displayed here may open exciting, future applications in the food industry as texturants or surface-active agents, as well as in other fields requiring such uncanny materials.