More than a decade ago, to improve cell tracking efficiency, Dr. Seung Koo Lee, in the lab of Dr. Ching Tung, formulated a layer-by-layer nanoplatform. Small interfering RNA (siRNA) had been proposed to treat various diseases by silencing genes, but delivery was problematic. A carefully built assembly approach was generated and used to prepare a protease-assisted nano-delivery system. Protease-degradable poly-L-lysine (PLL) and siRNA were fabricated onto gold nanoparticles (AuNPs) by alternating charged polyelectrolytes. Up to four layers of PLL and three layers of siRNA (sR3P) were coated. Thanks to slow PLL degradation, the siRNAs were slowly emitted, and were thus able to initiate extended gene-silencing effects. The inhibition effect in cells correlated with the number of siRNA layers. This project resulted in the paper titled as seen above in Lee et al., Small: 2010, Dec. 30).