(A) Condensation reaction carried out in living cells. The precursor (22), inside a cell, is converted into the monomer (23), which self-condensates to form the dimer (24) and oligomers (25), which can in turn assemble into nanostructures. (B) Fluorescence images of HeLa cells incubated with 200 μM of monomer based on 21 (R1=SCH2CH3, R2=H, R3=Biotin-Lys). Scale bars: 20 μm. (C) Merged fluorescence and transmitted light images of MDA-MB-468 cells incubated with monomer based on 21 (R1= SC(CH3)3, R2= Ac-Arg-Val-Arg-Arg, R3=Biotin-Lys, 200 μM) for 8 hours. Scale bars: 20 μm. Adapted with permission from ref. 34. Copyright 2010, Nature Publishing Group.