## 1 Introduction
In light of the outstanding applications in the biomedical field for cancer diagnostics, different-sized GNPs (10 to 50 nm) were applied against human dendritic cells (DCs), and it was proposed that the effect was much more prominent with the use of GNPs-10, which inhibited lipopolysaccharide-(LPS) induced production of IL-12p70 by DCs [43]. [PERSON] et al. showed the biodistribution and toxicity of AuNPs (5-50 nm) and explored the mechanisms of toxicity in cancer cells [44]. In another study, water-soluble AuNPs ranging from 3 to 45 nm were used for cytotoxic studies involving the cancer cell lines of the human prostate (PC-3) and breast (MCF-7) [45]. Gold nanoparticles are often applied in biological and physicochemical areas as agents in cancer diagnosis and nanomedicine [46; 47]. In yet another article, different-sized gold nanoparticles were used for the study of localization and penetration in cancer cells in in vivo tumor tissue and ex vivo multicellular models of mice [48]. The remarkable size and enhanced surface properties of gold nanoparticles make them ideal vehicles for targeted and selective drug delivery. Several in vitro and in vivo experiments have confirmed that GNPs work as drug delivery agents targeted directly to tumor sites [49]. Due to their biocompatible nature, tested clinically, GNPs have been tagged with radio-sensitizing agents, such as DTX and cisplatin, to a GNP-RT platform to explore radiotherapy in improving the quality of life for all cancer patients [50]. GNPs are also used to encapsulate immunomodators for cancer immunotherapeutic treatment [46; 51; 52]. Although significant research has been carried out in electronic studies and basic biological studies, very few studies are available with respect to the effect of nanostructures' size variations on cancer, especially liver cancer. Accordingly, this study explores the impact of different sizes of gold NPs on liver cancer cells, for cytological analysis. The GNPs were prepared via a colloidal solution process with the citrate method in a very short time, and were well characterized with instruments such as transmission electron microscopy (TEM), which was used for determining morphological and crystalline properties. Hydrodynamic size and zeta potential were analyzed by the dynamic light scattering (DLS) method for different particle sizes of GNPs. In addition, the optical characteristics of GNPs were examined via UV-visible spectroscopy. The morphology of control and treated cancer cells with different-sized NPs was examined via inverted microscopy. The calculation of toxicities was carried out via MTT and NRU assays. In addition, ROS and gene expression were measured in the cancer cells after their exposure to GNPs. Based on the obtained results, further discussion was proposed. The novelty of the current work is that, it describes the synthesizing of small- to large-sized gold nanoparticles with good structural morphology via a cost-effective solution process. These nanoparticles were applied to liver (HepG2) cancer cells. The growth of the cancer cells was significantly affected by very low-sized gold nanoparticles (10-15 nm) in all effective concentrations.