Ion Indicators and Sensors



The concentration of metal ions such as calcium, sodium, potassium, and zinc in the human body should be kept within an appropriate range to ensure its normal biological function. Various ion concentrations can be obtained by detection of the ion indicator. Sodium and potassium ions are important for maintaining osmotic pressure on both sides of the cell and forming nerve impulses. Calcium ions can inhibit the abnormal excitation of nerves in the brain and keep people calm. The method using the fluorescent probe has the advantages of high sensitivity, good selectivity, easy operation, low cost and the like.

Below is a list of our available Fluorescence probe for ion indicators and sensors (include but not limited to the following):

  • Sodium ion indicator

The sodium ion sensitive material BFI and the potassium ion sensitive material PBFI are selective fluorescent indicators used in the determination of sodium potassium ion concentration. The derivatives of such benzofuran dicarboxylates and their membrane-permeable acetoxymethyl (AM) esters can accurately measure the changes of sodium and potassium ions concentration under certain conditions (including various other monovalent cations). The laser spectrum of such dyes can be selected using a similar filter and detector from Fura-2. These sodium-potassium probe indicators are cyclically linked by a fluorophore and an ether, giving each ligand a site selectivity.

  • Calcium ion indicator

Fluo-3 AM is a fluorescent dye that penetrates cell membranes. Fluo-3 AM has very weak fluorescence. When it enters the cell, it can be cleaved into Fluo-3 by intracellular esterase, which is retained in the cell and binds to free calcium ions in the cell and then strong fluorescence is produced. The degree of cellular damage can be indicated by detecting the intracellular calcium ion concentration. BAPTA and its derivatives are commonly used calcium ion chelators to form stable calcium buffers, which are more selective for calcium ions than EDTA and EGTA. Cell injection or incubation with a chelating agent to control intracellular and extracellular calcium ion concentrations is an important means of studying calcium function.

  • Magnesium ion indicator

Mag-Fura-2 is a UV-susceptible magnesium ion fluorescent indicator with a dissociation constant of 1.9mM. Similar to Fura-2, the Mag-Fura-2 excitation wavelength shifts blue from 369 nm to 330 nm. Mag-Fura-2 also responds to Ca2+, but the dissociation constant is lower than Fura-2. Mag-Fura-2/tetrasodium salt can enter cells by microinjection of cells or scratch marks.

  • Chloride ion indicator

MQAE is the most widely used new type of chloride ion fluorescent probe. Compared to SPQ (a typical chloride indicator, Ksv = 118 M-1), MQAE is more sensitive to chloride ions (Ksv = 200 M-1) and has a higher fluorescence quantum yield. MQAE uses bromide as a paired anion with a maximum excitation wavelength of approximately 350 nm and a maximum emission wavelength of approximately 460 nm. When the chloride ion concentration increases, the fluorescence intensity of MQAE decreases proportionally with the increase of the chloride ion concentration. At chloride ion concentrations below 50 mM, the fluorescence intensity of MQAE is virtually unaffected by pH changes.


We’ve developed a number of Molecular Probes ion indicators to track Sodium and other ion concentrations with intense fluorescent signals and a range of wavelength options. If you have any Ion Indicators and Sensors requirement in mind, please do not hesitate to contact us. We will endeavor to provide highly satisfying products and services!


1. Barykina, N. V., Subach, O. M., Piatkevich, K. D., Jung, E. E., Malyshev, A. Y., & Smirnov, I. V., et al. (2017). Green fluorescent genetically encoded calcium indicator based on calmodulin/m13-peptide from fungi. PLOS ONE, 12(8), e0183757-.

2. Hasan, M. T., Friedrich, R. W., Euler, T., Larkum, M. E., & Denk, W.. (2004). Functional fluorescent ca indicator proteins in transgenic mice under tet control. PLoS Biology, 2(6), e163.