Magnesium Indicators

Magnesium ions are essential in mediating processes such as enzymatic reaction, muscular contraction, hormonal secretion, and DNA synthesis. The divalent magnesium cation, although in the same group as calcium, is a smaller atom.  It is therefore not surprising that truncated versions of calcium indicators work well for magnesium.  BAPTA-based indicators have a selectivity of about 105, for Ca2+ over Mg2+. Trimming the binding site by roughly half greatly reduces affinity for Ca2+, but still allows binding of the much smaller Mg2+. Thus, APTRA (Figure 7.1), approximately half BAPTA, is a non-fluorescent Mg2+ indicator, and the structural basis for all our other magnesium indicators.  In view of this design, we offer Mg2+ versions of almost all our Ca2+ indicator versions.

These Mg2+ indicators have also gained popularity as very low affinity indicators. The practical problem with their use is one of distinguishing the contribution of Mg2+ in Ca2+ measurements. We therefore offer special low-affinity Ca2+ indicators that are not based on APTRA and that are highly selective for binding Ca2+ over Mg2+ (link to low affinity)

Long wavelength magnesium indicators

TEFLabs offers the long-wavelength FLUO-2 Mg (Figure 7.2), Asante Magnesium RedTM, and Asante Magnesium GreenTM.  Fluo-2 Mg is available as the K+ Salt or the acetoxymethyl (AM) ester.

Long Wavelength magnesium indicatorsTable 7.1- Long Wavelength Magnesium Indicators

UV Magnesium Indicators

TEFLabs offers the UV-excitable Mg2+ indicators that correspond to Fura-2 (Fura-2 Mg, Figure 7.3) and Indo-1 (Indo-1 Mg, Figure. 7.4).   Fura-2 Mg was first invented by Raju et al as “Furaptra”.   

Table 7.2 below illustrates the properties of Fura-2 Mg and Indo-1 Mg.

UV Magnesium IndicatorsTable 7.2 UV Magnesium Indicators


APTRA structure

Figure 7.1 APTRA


Fluo-2 Mg, Fluo-2 MAG, Fluo Magnesium

Figure 7.2 Fluo-2 Mg


Fura-2 Mg

Figure 7.3 Fura-2 Mg


Indo-1 Mg, Magindo

Figure 7.4 Indo-1 Mg