Two ways to inactivate the Ki‐67 protein—Fragmentation by nanoparticles,crosslinking with fluorescent dyes

Light can manipulate molecular biological processes with high spatial and temporal precision and optical manipulation has become increasingly popular during the last years. In combination with absorbing dyes or gold nanoparticles light is a valuable tool for cell and protein inactivation with high precision. Here we show distinct differences in the underlying mechanisms whether gold nanoparticles or fluorescent dyes are used for the inactivation of the Ki‐67 protein. The proliferation‐associated protein Ki‐67 was addressed by the antibody MIB‐1. In vitro studies showed a fragmentation of the Ki‐67 protein after laser irradiation of 15 nm gold nanoparticle antibody conjugates with nanosecond pulsed laser, while continuous wave (cw) irradiation of fluorescein isothiocyanate (FITC)‐ and Alexa 488‐labeled antibodies led to specific crosslinking of Ki‐67. The irradiation energy for the gold nanoparticles was above cavitation bubble formation threshold. We observed a fragmentation of the target protein and also of the gold particles. The understanding of the underlying inactivation mechanisms is important for the application and further development of these two techniques, which can harness nanotechnology to introduce molecular selectivity to biological systems.