**4. Conclusions**

The data presented in this study highlights that the instrument used to assess changes in endothelial cell monolayer properties should be carefully selected, to ensure it is appropriate for the experimental questions being addressed. Although both the ECIS and xCELLigence platforms can facilitate large-scale screening on 96 well plates with similar electrode configurations, the ECIS platform is more sensitive than xCELLigence when detecting impedance changes in response to a stimulus. Furthermore, ECIS can acquire data at multiple frequencies, which can be modelled to identify which of the endothelial barrier components contributing to impedance are being affected, something xCELLigence is unable to do because of its limited frequency acquisition range. The cellZscope instrument also acquires impedance data at multiple frequencies which can be modelled to identify changes in particular endothelial barrier components, however, the reduced sensitivity of this platform relative to ECIS means that subtle changes in endothelial monolayer properties may not be resolved to the same extent as they can be by ECIS technology. The reduced sensitivity of the cellZscope platform could be due to its distinct electrode configuration that allows access to the basolateral compartment, which is essential for certain types of experimental approaches. Ultimately, the choice of platform hinges on: (1) whether access to the basolateral compartment is required, (2) if the researcher wishes to identify which endothelial monolayer properties are being influenced and (3) whether a high degree of sensitivity is required to detect subtle changes.

**Supplementary Materials:** The following is available online at https://www.mdpi.com/article/10.339 0/bios11050159/s1, Supplementary Table S1: ECIS, xCELLigence and cellZscope instrument parameters.

**Author Contributions:** Conceptualization: J.J.W.H., C.E.A. and E.S.G.; methodology: J.J.W.H., A.A., S.J.O., C.E.A., and E.S.G.; software: J.J.W.H.; formal analysis: J.J.W.H., C.P.U., C.E.A., and E.S.G.; resources: S.J.O., C.E.A., and E.S.G.; data curation: J.J.W.H., C.P.U., and E.S.G.; writing—original draft preparation: J.J.W.H., A.A., C.E.A. and E.S.G.; writing—review and editing: J.J.W.H., A.A., S.J.O., C.P.U., C.E.A., and E.S.G.; supervision: C.E.A. and E.S.G.; project administration: J.J.W.H., C.E.A. and E.S.G.; funding acquisition: J.J.W.H., A.A., C.E.A. and E.S.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** J.J.W.H. was supported by an Auckland Medical Research Foundation Doctoral Scholarship, and A.A. was supported by a Neurological Foundation Doctoral Scholarship. The instrument purchase was supported by the New Zealand Lottery Health Fund (E.S.G.; xCELLigence and S.O./E.S.G.; ECIS ZΘ). The cellZscope was purchased with funding from the University of Auckland (E.S.G. and S.O.). The consumables support was provided by the University of Auckland Faculty Research Development Fund (C.E.A.).

**Data Availability Statement:** Not applicable.

**Acknowledgments:** We thank the University of Auckland Statistical Consulting Centre for their input and verification of the statistical analysis conducted in this paper. We also thank Jo Dodd for her generous guidance and technical support.

**Conflicts of Interest:** The authors declare no conflicts of interest. There was no involvement of the funders in any role pertaining to the choice of the research project; the design of the study; in the collection, analyses or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.
