A bright and responsive europium probe for determination of pH change within the endoplasmic reticulum of living cells

A ratiometric EuIII complex has been developed that localises selectively within the endoplasmic reticulum of living cells. Careful calibration, using a time-gated spectral imaging microscope, allows the intensity ratio of emission bands and the variation of excited state lifetime to be used for pH determination, with a pKa of 7.15.