The poly-
L-lysine-functionalized gold nanoparticle (PLL-GNP) was found to undergo reversible assembly/disassembly in the range of pH from 6.5 to 11.0 at room temperature. At a high pH value, the deprotonatedlysine residues allow the for
mation of
![](/i<font color=)
mages/gifchars/alpha.gif" BORDER=0>-helix and
![](/i<font color=)
mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-sheet structures at the expense of a part of random coiland
![](/i<font color=)
mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-turn structures, thus inducing the assembly of GNPs. With a decrease of pH to 6.5, the assembly ofGNPs is disrupted due to the conversion of the
![](/i<font color=)
mages/gifchars/alpha.gif" BORDER=0>-helix and
![](/i<font color=)
mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-sheet back into the random and
![](/i<font color=)
mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-turn. It isidentified that the for
mation/collapse of an antiparallel
![](/i<font color=)
mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-sheet structure among PLL chains from adjacentGNPs is responsible for reversible pH-dependent assembly/disassembly of GNPs. Since the confor
mation-induced assembly/disassembly process of the PLL-GNP can be well recognized by a shift of the surfaceplasmon resonance band of the GNP and the color change of the solution, this study presents the possibilityof following the confor
mation change of a peptide by monitoring the spectral change of the GNP.