Tuning self-organization of phosphonium-functionalized polythiophenes for selective recognition and separation of gram-positive and gram-negative bacteria

Abstract Phosphonium-functionalized polythiophenes have attracted increasing attention as biosensing materials because of their high chemical stability and strong interactions with biological interfaces. In this study, the effect of polymer molecular weight on the optical and biological responses of poly[3-(4-trimethylphosphinobutyl)thiophene bromide] (PTB) with different degrees of polymerization (n = 11, 16, and 26) was systematically investigated. While all PTB samples selectively inhibited the growth of Gram-positive bacteria, independent of chain length, optical measurements revealed that only PTB (n = 11) showed a pronounced absorption shift upon interaction with bacterial cells. Dynamic light scattering and fluorescence microscopy confirmed that PTB (n = 11) formed the largest aggregates with Gram-positive bacteria, whereas longer polymer chains (n = 16 and 26) displayed weaker aggregation and negligible optical responses. Furthermore, this specific aggregation behavior enabled the separation of target bacteria from mixed cultures. Overall, these findings highlight the critical role of polymer molecular weight and identify short polymer chain PTB as a promising candidate for selective bacterial control and separation.