growth = ?

Context:
The Duke researchers synthesized gold, rod-shaped nanoparticles with varying length-to-width ratios. The different-sized particles displayed different optical properties, so by controlling the nanorods' growth the team could "tune" the particles to scatter a specific frequency of light. The researchers next joined the tuned particles to antibodies that bind to growth factor receptor proteins found in unusually high concentrations on the outside of cancer cells. When the antibodies latched on to cancer cells, the gold nanoparticles marked their presence.
More:
http://www.sciencedaily.com/releases/2011/10/111012113559.htm