Diferential near‑infrared imaging of heterocysts using SWCNTs

The internalization of near-infrared (NIR) optical nanoprobes in photosynthetic microbes can be exploited for applications ranging from energy conversion to biomolecule delivery. However, the intrinsic, species-dependent properties of microbial cell walls, including their surface charge density, composition, thickness, and elasticity, can severely impact nanoprobe uptake and afect the cellular response. An examination of the interaction of the optical nanoprobe in various species and its impact on cell viability is, therefore, imperative for the development of new imaging technologies. Herein, we extend the technology recently developed for internalizing fuorescent single-walled carbon nanotubes (SWCNTs) in prokaryotes, specifcally unicellular Synechocystis sp. PCC 6803, to a flamentous cyanobacterial strain, Nostoc punctiforme. Using a combination of NIR fuorescence, scanning electron microscopy (SEM), and Raman spectroscopy, we investigate uptake in vegetative cells as well as diferentiated heterocysts. We demonstrate a strong dependence of long-term cell integrity, activity, and viability on SWCNT surface functionalization. We further show diferential uptake of SWCNTs across a single flament, with positively charged functionalized SWCNTs preferentially localizing within the heterocysts of the flament. This cell dependency of the nanoparticle internalization motivates the use of SWCNTs as a NIR stain for monitoring cell diferentiation.

https://link.springer.com/article/10.1007/s43630-022-00302-3