Electrochemical Cytosensor for Cancer Cell Detection and Evaluation of Anticancer Drug

Globally, cancer remains the second leading cause of death and millions of people still suffer from it, and a third of them die every year. Developing new anticancer agents and determining their activities are an essential part of drug discovery, but it takes a long time and needs abundant resources, resulting in the increasing demand for highly effective techniques. To examine the anticancer efficacy of novel drugs, cell staining/counting methods such as Cell Counting Kit-8 (CCK-8), thiazolyl blue tetrazolium bromide (MTT) assay, and trypan blue exclusion have been commonly carried out to detect cell viability. However, those assays have a limitation in assessing the efficiency of colored drugs due to a possibility of signal interference at the specific wavelength. It also requires time-consuming and complicated sampling processes and invasive chemical reagents for measurements of cellular metabolic activities. For these reasons, alternative sensing techniques using optics, electrochemistry, and quartz crystal microbalances have emerged for in vitro toxicological evaluation. Among them, the electrochemical strategy, which features high sensitivity, fast response time, easy miniaturization, real-time monitoring, and cost-effectiveness has been exploited to analyze the anticancer activities with the reduced time and cost in the early stage of drug development. In particular, an electrochemical cell-based biosensor, called a cytosensor, has been regarded as a fast, sensitive, non-invasive, and label-free technique to monitor the various cell types such as pluripotent stem cells and cancer cells. Based on the oxidation/reduction reaction of several biomolecules (e.g., intracellular redox proteins and metalloproteins), distinctive electrochemical redox signals from each cell type were found to be generated and recorded at specific potentials, and these can be applied to investigate the cancer cells’ response to the anticancer drugs.<br/>In this study, we present an electrochemical cytosensor that enables rapid and sensitive assessment of the effects of an anticancer drug, saponin, on the most aggressive form of skin cancer, called human malignant melanoma (SK-MEL28). Electrochemical deposition of gold nanoparticles (AuNPs) onto fluorine-doped tin oxide (FTO) electrodes was conducted to promote their electrocatalytic properties. The AuNPs/FTO platforms were further decorated with biocompatible poly-L-lysine (PLL) to facilitate cell adhesion and growth. By combining the nano and biocompatible materials, direct electron transfer between immobilized cancer cells and the fabricated electrode occurs and both selectivity and sensitivity of the cytosensor were improved. The electrical signal of SK-MEL28 cells was obtained from cyclic voltammetry and differential pulse voltammetry and showed clear linearity (R² = 0.9952) relative to the number of cells, suggesting that the intensity of the cathodic peak current of the cytosensor can be used to detect the number of SK-MEL28 cells. Moreover, the anticancer efficacy of saponin on SK-MEL28 cancer cells was clearly proved to be effective at concentrations higher than 20 μM, which was highly in agreement with the conventional assays. The developed electrochemical cytosensor for assessing anticancer effects of drugs enabled sensitive (Limit of quantification: 2,880 cells/device), rapid (&lt; 2 min), and non-invasive measurements, thus providing a simple and efficient way to do research on the evaluation of novel drug candidates and encourage the development of powerful anticancer reagents.