Ultra-stable liquid crystal droplets coated by sustainable plant-based materials for optical sensing of chemical and biological analytes

Herein, we demonstrate for the first time the synthesis of ultra-stable, spherical, nematic LC droplets of narrow size polydispersity coated by sustainable, biodegradable, plant-based materials that trigger a typical bipolar-to-radial configurational transition in dynamic response to chemical and biological analytes. Specifically, a highly soluble polymer, potato protein (PoP) and a physically-crosslinked microgel (PoPM) of ~100 nm in diameter, prepared from the PoP, a byproduct of starch industry, were compared for their ability to coat LC droplets. Although both PoP and PoPM were capable of reducing interfacial tension between water and n-tetradecane < 30 mN/m, PoPM-coated LC droplets showed better stability than the PoP-coated droplets via a Pickering-like mechanism. Strikingly, the Pickering LC droplets outperformed PoP-stabilized droplets in terms of dynamic response with 5× lower detection limit to model chemical analytes (sodium dodecyl sulphate, SDS) due to difference in SDS-binding features between the protein and the microgel. To eliminate the effect of size polydispersity on response, monodisperse Pickering LC droplets of diameter ~ 16 μm were additionally obtained using microfluidics, which mirrored the response to chemical as well as biological analytes i.e. primary bile acid, an important biomarker of liver diseases. We demonstrate that these eco-friendly microgels used for creating monodisperse, ultra-stable, LC complex colloids are powerful templates for fabricating next generation, sustainable optical sensors for early diagnosis in clinical settings and other sensing applications.