Topological Defects in Smectic Liquid Crystals as a Toolkit for Biosensing Living Microorganisms

Topological defects in liquid crystals (LCs) provide rich theoretical insights and hold substantial promise for practical applications, particularly in biosensing. In this work, we examine the interaction between smectic LCs and bacterial suspensions of Bacillus subtilis and Escherichia coli, focusing on how these microorganisms influence the anchoring properties of the LC interfaces with defined anchoring conditions. By closely observing the resulting textures of the smectic films, we successfully differentiate between bacterial species, leveraging the distinct responses of the LC. We also propose potential mechanisms responsible for these texture changes. Moreover, we introduce the use of focal conic domains (FCDs), a specific type of topological defect in smectic LCs, as a quantitative measure of bacterial concentration at the interface. This study enhances the understanding of bacteria-LC interactions and demonstrates the potential of smectic LCs and their defects as sensitive and versatile tools for biosensing applications.