Using fluorescent pH-sensitive nanosensors to report their intracellular location after Tat-mediated delivery.

Nanosensors offer the opportunity to measure intracellular domains with minimal chemical or physical perturbation. Typically only 50 nm in diameter, and synthesised from bio-compatible polymer matrices, they entrap chemical sensing elements and can be surface functionalised allowing for further chemical modification. Upon intracellular localisation the cellular environment can be monitored using conventional techniques such as confocal laser scanning microscopy. Reported here is the use of nanosensors to investigate the mechanisms of intracellular delivery mediated via the cell penetrating peptide, Tat. Information obtained from the nanosensors shows that the post-delivery environment is representative of a lysosome in terms of both pH and morphology. The delivery mechanism of Tat, however, is shown to be dependent upon the cargo being delivered, corresponding to the absence or presence of a body of polymer matrix; thus nanosensors have been used to further the understanding of the cell penetrating mechanisms of Tat peptide.