Cancer is one of the leading diseases that cause death all around the world. In Turkey, lung cancer is the most common type of cancer type in men and it is the fifth in women. Unfortunately, the percentage of treatment of lung cancer is too low. Gold nanoparticles (AuNPs) are widely used in the biotechnology as imaging, diagnosis, and therapeutic agents because of their unique properties such as plasmon resonance, easy synthesize, biocompatibility, and facile surface modification. In this study, it is aimed to design gold nanoparticles as biosensors for lung cancer cells. For this purpose, different sizes (5-40 nm) of Au nanoparticles were synthesized and their uptake and distribution into the lung cancer cells were investigated. The results of the study revealed that cellular uptake of gold nanoparticles are high for the size of 20 and 40 nm. The optimal visibility into the cells was achieved by using DIC microscopy in which the particles uptaken into the cytoplasm and localized at around nucleus of cells. In the second part of the study, surfaces of 20 and 40 nm particles were conjugated with RGD peptides and their distribution and light scattering properties were investigated in living cells by using dark-field microscopy. Due to the receptor-mediated endocytosis, RGD-AuNPs showed different distribution within the cells. These results indicate that the RGD conjugated Au nanoparticles exhibits much higher light scattering properties than non-conjugated nanoparticles. In addition to this, synthesized Au nanoparticles were conjugated with nucleus-localized peptide (NLS) and directed to the nucleus of cancerous (A549, H358) and healthy (BEAS2B) lung cells. The nucleus targeting properties of the NLS conjugated particles were also investigated to understand if there is any cell line selectivity. The internalizations of peptide conjugated Au nanoparticles into cell lines were visualized in living cells by using DIC microscopy. NLS conjugated AuNPs internalized into nucleus of A549 and H358 cancer cells. Although NLS conjugated AuNPs present inside the cytoplasm of BEAS2B cells, they did not localize into the nucleus of normal cell lines.