Microstructured optical fibers and live cells: a water-soluble, photochromic zinc sensor

A new biologically compatible Zn(II) sensor was fabricated by embedding a Zn(II) sensing spiropyran within the surface of a liposome derived from Escherichia coli lipids (LSP2). Solution-based experiments with increasing Zn(II) concentrations show improved aqueous solubility and sensitivity compared to the isolated spiropyran molecule (SP2). LSP2 is capable of sensing Zn(II) efflux from dying cells with preliminary data indicating that sensing is localized near the surface membrane of HEK 293 cells. Finally, LSP2 is suitable for development into a nanoliter-scale dip-sensor for Zn(II) using microstructured optical fiber as the sensing platform to detect Zn(II) in the range of 100 ρM with minimal photobleaching. Existing spiropyran based sensing molecules can thus be made biologically compatible, with an ability to operate with improved sensitivity using nanoscale liquid sample volumes. This work represents the first instance where photochromic spiropyran molecules and liposomes are combined to create a new and multifunctional sensing entity for Zn(II).