Table 2.

The comparison of tetrazolium salt assays and RTCA system.

	Cytotoxicity assays
	Tetrazolium salt assays	RTCA system
Kind of cells	Adherent and suspension	Mostly adherent (suspension cell lines after pre-coating of the plate bottom)
Monitoring of cells	Under a microscope at selected time points	Real time and continuous
Obtain results	At one selected time point	At every time point of the experiment
Labeling reagent	Tetrazolium salts	No reagents
Detection principles	Spectrophotometric measuring absorbance of formazan solution produced by living cells with active dehydrogenases	Recording the electrical impedance from the arrayed gold microchips covered the bottom of RTCA plates. Changes in impedance values reflect changes in cellular physiology and proliferation. CI - the basic obtained parameter
Contamination with assay reagent	Yes	No
Use of cells after experiment	No possibility to use	Use of cells for other assays (western blotting, imaging, etc.)
Optimization of cell density prior to experiment	Required	Required
Cost	Low cost	Costly
Use of plates	Disposable and single use	Disposable and single use, but possible regeneration and re-use
Applications	•Cytotoxicity test of natural and synthetic compounds, drugs, plant extracts	•Monitoring of cell adhesion, viability, and proliferation rate •Cytotoxicity test of natural and synthetic compounds, drugs, plant extracts •Assessment of cell migration and invasion •Measuring of cardiomyocyte contractility and viability •Differentiating cytostatic from cytotoxic effect of drugs •RTCA proliferation profiles are useful in study of mechanism action of new drugs by comparison with profiles of well-known drugs
Limitations of application with	•Colored compounds •Compounds that interfere with tetrazolium reagents (e.g. antioxidants)	•Drugs with electroactive additives •Less adherent and suspension cell lines