Table 2.

Applications for various imaging techniques to capture Ca²⁺ levels across animal cell types.

Imaging Technique	Representative Targets	Frame Rate	Indicator Types *
Two-photon microscopy	in vitro: cortical; hippocampal; immortal lines (e.g., HeLa); lymphocyte	6–500 Hz	Fluo-4, Rhod-2, OGB-1, Cal-520 [23,37] GCaMP-X, Twitch-1/2B, jRGECO1a [65,66] Nanosensors [67]
	ex vivo: 300 μm brain slice; epithelia	700 Hz	OGB-1, Cal-520 [23] GCaMP3 [68]
	in vivo (up to 600 μm depth): lymph nodes; pancreas; whole brain; whole-mount embryo	<1 Hz–700 Hz	Fura-2, Fluo-4, OGB-1, Cal-590 [34,69] GCaMP5G/6, Twitch-1, Salsa6f, YC-Nano15 [65,70,71,72,73,74]
	in vivo: deep neuronal tissue in awake animal (using microendoscopy)	Commonly 30 Hz, up to 10 kHz [75]	See discussion of method for various dyes [34,69] and GECIs [76,77]
Confocal (single-photon) microscopy	in vitro: adult stem; astrocyte; embryonic; myocyte; hippocampal; cortical; immortal lines (e.g., PC-3); lymphocyte	0.1–20 Hz	CaSiR-1, Fluo-4, Fura-2 [3,29,41,78,79] GCaMP3/6, Salsa6f, YC2.6 [72,80,81] PEBBLE [31]
	ex vivo: aortic rings; brain slices; bone; Drosophila larval wing discs; Xenopus ectoderm (animal cap); pancreatic islet	0.1–10 Hz	Fluo-4, Fluo-8, OGB-1 [82,83,84] GCaMP5G/6, YC-Nano3GS [73,78,85]
	in vivo (up to 370 μm depth): whole brain	6 Hz, up to 70 Hz	GCaMP6 [86]
Non-confocal light microscopy	in vitro: motor neuron	25 Hz	GCaMP6 [87]
Single-lens digital	in vitro: immortal lines (e.g., HEK293); cortical	Up to 30 Hz	Fluo-4 [88]
Plate reader assays	in vitro: myocyte	16–60 Hz	Cal-520, Fluo-4 [79,89] GCaMP6 [79]
Flow cytometry	in vitro: lymphocyte; platelets	N/A	Fluo-4, Fura-2, Indo-1 [41,90,91]

* Citations are not comprehensive, some representative studies are listed.