Gold nanoparticles used in cancer cell diagnostics, selective photothermal therapy and catalysis of NADH oxidation reaction

Gold nanoparticles strongly absorb and scatter visible and near infrared light because of the strongly enhanced electric fields at the surface. This provides the potential of designing novel optically active reagents for simultaneous molecular imaging and photothermal cancer therapy. In this thesis, gold nanospheres and nanorods conjugated with anti-epidermal growth factor receptor (anti-EGFR) antibodies that specifically target EGFR on the cell surface are shown to be used for dual diagnostics and therapy. Using micro-absorption spectroscopy and light scattering imaging, cancerous (HOC 313 and HSC 3) and noncancerous cells (HaCat) can be differentiated due to the overexpression of EGFR on the surface of cancer cells. By irradiating the cells with a CW laser, selective photothermal cancer therapy is realized in visible region by using gold nanospheres and in near infrared region by using gold nanorods. The use of nanorods allow for in vivo therapy due to the fact that their absorption is in the near infrared region at which the laser light meets less interference from the tissue absorption. In addition, the catalytic effect of gold nanoparticles on the oxidization of NADH to NAD+ is investigated. The addition of gold nanoparticles is found to quench the NADH fluorescence intensities but has no effect on the fluorescence lifetime. This suggests that the fluorescence quenching is not due to coupling with the excited state, but due to changing the ground state of NADH. The intensity of the 340 nm absorption band of NADH is found to decrease while that of the 260 nm band of NAD+ is found to increase as the concentration of gold nanoparticles increase. This conversion reaction is further supported by nuclear magnetic resonance and mass spectroscopy. The linear relationship between the initial reaction rate of NADH and the concentration of gold nanoparticles strongly supports that NADH is surface catalyzed by the gold nanoparticles. The catalytic property of this important reaction might have important future applications in biological and medical fields.