Figure 2. Volume, resazurin and acid phosphatase as methods to determine viability in NSC and UW228-3 spheroids.

A. NSCs spheroids, diameter 200–800 µm. B. UW228-3 tumour spheroids, diameter of 160–700 µm. Both cell types were grown as spheroids for a week and then probed for volume, metabolic and acid phosphatase activity. Spheroids were enzymatically dissociated and normalised assay response plotted against the number of cells per spheroid in order to compare the three assays. Normalised assay responses from three independent experiments were pooled together, plotted and the linearity of each method was examined.