The combination of biocompatibility and unique surface properties has led to the extensive study of the biological applications of carbon nanomaterials. We are interested in the application of single walled carbon nanohorns (CNH) for the development of tools for cellular imaging, diagnostics and therapeutics. CNHs are made up of sp2 conical shaped postulates, with diameters of 2–5 nm and lengths of 40–50 nm, assembled into robust bud-like spherical aggregates of between 80 and 100 nm. The key advantage of these materials is their low toxicity, high surface area, and ease of functionalisation.1,2 In this presentation results from our recent work on the use of CNHs for enhanced biosensing of glutamate,3 to study of the cellular interactions of fluorescently labelled CNH systems and their use of CNHs to delivery photodynamic therapy agents to cells will be presented.The poor cellular uptake of many porphyrins is a barrier to their application in phototherapeutic applications,4 biocompatible CNH carriers offer a means to overcome this. A spectroscopic study of the binding interactions of the PtTMPyP4 cationic porphyrin with oxidised carbon nanohorns through non-covalent, electrostatic interactions revealed a high a loading of 200 wgt%. Brightfield microscopy demonstrated the efficacy of sparsely loaded Porphyrin-CNH constructs to be internalised within HeLa cells, which were found to undergo rapid cell death upon visible light excitation.5 The ability to image processes in cells and track the interaction and efficacy of nanomaterial cellular uptake is of great interest. The use of an ON/OFF fluorophore whose emission is triggered upon cellular uptake will be described as a means to monitor time dependent uptake by live-imaging and also to report on the influence of functionalisation on the extent of cellular aggregation.6 Finally, some more recent results on tracking the destination of carbon nanohorns in cells will be reported. 1. Iijima, M. Yudasaka, R. Yamada, S. Bandow, K. Suenaga, F. Kokai, K. Takahashi, Chem. Phys. Lett. 1999, 309, 165−170.S.2. Zhuab, G. Xu, Nanoscale, 2010, 2, 2538–2549.3. R. Ford, S. J. Devereux, S. J. Quinn, R. D. O'Neill, Analyst, 2019, 144, 5299-53074. A. Rajora, J.W.H. Lou and G. Zheng, Chem. Soc. Rev., 2017, 46, 6433 – 6469.5. J. Devereux, M. Massaro, A. Barker, D. T. Hinds, B. Hifni, J. C. Simpson and S. J. Quinn, J. Mater. Chem. B, 2019, 7, 3670–3678.6. S. J. Devereux, S. Cheung, H. C. Daly, D. F. O'Shea and S J. Quinn, Chem. Eur. J., 2018, 24, 14162–14170.