“Because of their dimensions, nanoparticles can cross biological barriers, including the cell membrane.” That statement, though often repeated in publications and commentary about nanotechnology, is incorrect. Biologists have used nanoparticles to study cell trafficking for six decades [1]. The main result is simple: nanoparticles do not cross the cell membrane. They enter cells by endocytosis and remain confined in vesicular compartments. This entrapment constitutes a severe limitation to applications such as delivery and sensing. Yet, many groups have reported intracellular sensing which raises the question of how (and in what proportion) those probes have escaped the endosomes. A spectacular achievement has been the detection of mRNA in live cells with Nano-Flares,[2] now available commercially under the name SmartFlares. At the time of writing this abstract, we are investigating the mechanisms of entry of SmartFlares. The research, including the raw data, is reported in quasi real-time in an open science notebook (Figure 1A). I will discuss those results and comment on the benefits of data sharing and open science. Contrarily to detection of mRNA, cell tracking using nanoparticles does not require endosomal escape. In the second part of the talk, I will present our efforts to optimize tracking of stem cells with gold nanorods using multispectral optoacoustic tomography (MSOT). For this purpose, the preservation of the optical signature after uptake is critical. Close packing within endosomes induces shifting and broadening of the plasmon band but this can be prevented using a silica shell coating (Figure 1b). [1] J Biophys Biochem Cytol 1957 3 749 [2] J Am Chem Soc 2007 129 15477

Localisation and properties of nanoparticle conjugates after cell entry... and why it matters

250th National Meeting (2015)

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