The ability to rapidly diagnose gram-positive pathogenic bacteria would have far reaching biomedical and technological applications. Here we describe the bioorthogonal modification of small molecule antibiotics (vancomycin and daptomycin), which bind to the cell wall of gram-positive bacteria. The bound antibiotics conjugates can be reacted orthogonally with tetrazine-modified nanoparticles, via an almost instantaneous cycloaddition, which subsequently renders the bacteria detectable by optical or magnetic sensing. We show that this approach is specific, selective, fast and biocompatible. Furthermore, it can be adapted to the detection of intracellular pathogens. Importantly, this strategy enables detection of entire classes of bacteria, a feat that is difficult to achieve using current antibody approaches. Compared to covalent nanoparticle conjugates, our bioorthogonal method demonstrated 1-2 orders of magnitude greater sensitivity. This bioorthogonal labeling method could ultimately be applied to a variety of other small molecules with specificity for infectious pathogens, enabling their detection and diagnosis.

Trehalose is a naturally occurring disaccharide which is associated with extraordinary stress-tolerance capacity in certain species of unicellular and multicellular organisms. In mammalian cells, presence of intra- and extracellular trehalose has been shown to confer improved tolerance against freezing and desiccation. Since mammalian cells do not synthesize nor import trehalose, the development of novel methods for efficient intracellular delivery of trehalose has been an ongoing investigation. Herein, we studied the membrane permeability of engineered lipophilic derivatives of trehalose. Trehalose conjugated with 6 acetyl groups (trehalose hexaacetate or 6-O-Ac-Tre) demonstrated superior permeability in rat hepatocytes compared with regular trehalose, trehalose diacetate (2-O-Ac-Tre) and trehalose tetraacetate (4-O-Ac-Tre). Once in the cell, intracellular esterases hydrolyzed the 6-O-Ac-Tre molecules, releasing free trehalose into the cytoplasm. The total concentration of intracellular trehalose (plus acetylated variants) reached as high as 10 fold the extracellular concentration of 6-O-Ac-Tre, attaining concentrations suitable for applications in biopreservation. To describe this accumulation phenomenon, a diffusion-reaction model was proposed and the permeability and reaction kinetics of 6-O-Ac-Tre were determined by fitting to experimental data. Further studies suggested that the impact of the loading and the presence of intracellular trehalose on cellular viability and function were negligible. Engineering of trehalose chemical structure rather than manipulating the cell, is an innocuous, cell-friendly method for trehalose delivery, with demonstrated potential for trehalose loading in different types of cells and cell lines, and can facilitate the wide-spread application of trehalose as an intracellular protective agent in biopreservation studies.

Small molecule imaging: Aurora kinase A (AKA) was imaged in live cells using an in cellulo bioorthogonal two-step reaction with a small molecule and a fluorescent reporter. The small molecule was localized to spindle poles and microtubules during metaphase, consistent with the localization of both endogenous and GFP-/RFP-tagged AKA. Using this approach, changes in AKA distribution during mitosis were also observed.