There are plenty of choices of dyes of various types that you could use for this (e.g Fura-2, Fluo-4). I used to use CAL-520 am in a microplate format, Abcam have a good general protocol on their product page for it. https://www.abcam.com/products/reagents/cal-520-am-ab171868.html
Really though, you need to give a bit more information so that appropriate recommendations can be made. This review gives a good overview of the various dyes available. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4658286/