Selective Degradation of Proteins by Laser Irradiation onto Gold Nanoparticles in Solution

Lysozyme and bovine serum albumin (BSA) were selectively degraded in their mixed solution containing gold nanoparticles by an appropriate pH selection of the solution under irradiation of a laser with 532 nm corresponding to the plasma oscillation of the nanoparticles. Lysozyme and BSA were selectively degraded at a pH of 7.0–11.0 and ∼4.0, respectively. The mechanism of the selective degradation is as follows: Lysozyme molecules are considered to aggregate selectively on the gold nanoparticle in a pH range of 7.0–11.0, because they have a sufficiently small net charge of an opposite sign to the ζ-potential of the gold nanoparticle. In this pH range, the lysozyme molecules aggregating on the gold nanoparticle are degraded selectively under the laser irradiation, because the gold nanoparticle creates a high temperature region (chemical species in this region is suffered from degradation) in its close vicinity by the laser irradiation as shown in our previous studies. The same discussion is true to the selective degradation of BSA at a pH of ∼4.0.