Gold Nanoflower for Selective Detection of Single Arginine Effect in α-Helix Conformational Change over Lysine in 3-Helix Peptide.

Hydroxylamine-based growth reaction in the presence of natural l-amino acids (9 mM) and gold nanoparticle seed mostly produce aggregated or nonaggregated gold nanostructures except the cases of immediate precipitation with aspartic acid, glutamic acid, cysteine, and tyrosine. Among the other amino acids, arginine shows the control growth reaction to form gold nanoflower from gold nanoparticle seeds, which were preincubated with amine-modified DNA (NH-oln). The absorbance trend with NH-oln in the presence of arginine is similar to the aggregation behavior in the presence of histidine and methionine. The formations of gold nanoflower with arginine and aggregation due to histidine and methionine in the presence of NH-oln were sorted out with lower concentration (50 μM) of these amino acids. This observation was successfully transferred to differentiate 3-helical Ac-(AAAAK)A-NH from α-helical Ac-(AAAAR)A-NH. The concept was further applied for the detection of single arginine modification closest to the carboxy terminus of 3-helical Ac-(AAAAK)A-NH peptide for maximum conformational change toward α-helix.