Unlike silica nanoparticles, the potential of silica mesoparticles (SMPs) (i.e. particles of submicron size) for biological applications in particular the in vitro (let alone in vivo) cellular delivery of biological cargo has so far not been sufficiently studied. Here we examine the potential of luminescent (namely, octahedral molybdenum cluster doped) SMPs synthesised by a simple one-pot reaction for the labelling of cells and for protein transduction into larynx carcinoma (Hep-2) cells using GFP as a model protein. Our data demonstrates that the SMPs internalise into the cells within half an hour. This results in cells that detectably luminesce via conventional methods. In addition, the particles are non-toxic both in darkness and upon photo-irradiation. The SMPs were modified to allow their functionalisation by a protein, which then delivered the protein (GFP) efficiently into the cells. Thus, the luminescent SMPs offer a cheap and trackable alternative to existing materials for cellular internalisation of proteins, such as the HIV TAT protein and commercial protein delivery agents (e.g. Pierce™).