Real-time and label-free impedimetric analysis of the formation and drug testing of tumor spheroids formed via the liquid overlay technique

To achieve high clinical relevance of drug testing, a spheroid culture model is generally used for a standard assay of early tumors. Currently, the quantification of tumor spheroids is generally based on imaging techniques and conventional bioassays. However, additional processing and sophisticated instrumentation are required, which makes high throughput screening infeasible. In this study, tumor spheroids were formed on a thin layer of non-adherent surface (agarose hydrogel), and their responses were monitored by impedance measurements across the interdigitated electrodes fabricated below the hydrogel. The impedance magnitude change was defined as an index to describe the summation effect of the number and size of tumor spheroids. Real-time and label-free impedimetric analysis of the formation and chemosensitivity of tumor spheroids was demonstrated. The technique has the simplicity of device fabrication and experimental processing. Real-time and quantitative assessment could be realized for a routine tool of a spheroid culture.