Xiaoyuan Chen and colleagues, National Institute of Biomedical Imaging and Bioengineering, USA, have used the ferritin protein as a base for a fluorescence probe which detects the tumor marker, matrix metalloproteinase (MMP). Proteins have not been used as scaffolds for probes before. The lack of chemical groups on the surface makes inclusion of the required functionality difficult, without also disrupting the protein’s function.

Chen et al. used the self-assembly nature of the ferritin protein cages to create ferritin hybrids with different dye/quencher ratios. Under acid conditions, ferritin disassembled and could be functionalized with either a dye or a quencher. The dye- and quencher-containing ferritins could then be mixed and reassembled at neutral pH. This resulted in a protein with dye and quencher in sufficient proximity to display fluorescence activation on sensing MMP.

Images: (c) Wiley-VCH

• Hybrid Ferritin Nanoparticles as Activatable Probes for Tumor Imaging
  X. Lin, J. Xie, L. Zhu, S. Lee, G. Niu, Y. Ma, K. Kim, X. Chen,
  Angew. Chem. Int. Ed. 2011, 50.
  DOI: 10.1002/anie.201006757