AAT Bioquest

What is an AM ester?

Posted December 23, 2021


The acronym 'AM' represents an acetoxymethyl group, and AM esters are primarily used for the modification of negatively charged carboxylate compounds. By their nature, negatively charged compounds are cell-impermeant and require invasive loading techniques. AM ester modification masks the negatively charged carboxylic groups and produces uncharged hydrophobic indicators or chelators. The resulting cell-permeable AM derivatives can be passively loaded into live cells for analysis. Once inside the cell, nonspecific intracellular esterases, hydrolyze (cleave) the AM groups. Removal of the AM groups results in strongly fluorescent indicators or chelators that are well-retained within the cytoplasm.

Uses of AM derivatives include cell proliferation, cell viability and cytotoxicity, measurement of intracellular communication (e.g. calcium signaling), oxidative activity, intracellular pH, and visualization of cellular structures, among others. AM derivatives, after hydrolysis, are fluorescent and should be used with a fluorescence microplate reader, fluorescence microscope, or flow cytometer.

Table 1. Types of AM Derivatives.

AM DerivativeApplicationPlatforms
Calbryte™ 520, AM
Cal-520®, AM
Fluo-8®, AM
Cell permeable fluorescent calcium indicator for fluorescence-based detection of calcium mobilization. Can be used to evaluate GPCR and calcium channel targets, and screen for their respective agonists and antagonists.
  • Fluorescence Microplate Reader
  • Fluorescence Microscope
  • Flow Cytometer
Calcein Ultragreen™, AMCell permeable fluorescent indicator that is primarily used to determine cell viability by measuring the intracellular enzyme activity of viable cells. Calcein Ultragreen™, AM is converted to an intensely green-fluorescent calcein after AM ester hydrolysis by intracellular esterases.
  • Fluorescence Microplate Reader
  • Fluorescence Microscope
  • Flow Cytometer
RatioWorks™ BCFL, AM
Cell permeable dual-excitation ratiometric indicator for measuring changes in the cytosolic pH of cells. Intracellular pH measurements are made by determining the pH-dependent ratio of emission intensity.
  • Fluorescence Microplate Reader
  • Fluorescence Microscope
  • Flow Cytometer
Additional resources

Calbryte™ 520 AM Product Page

List of AM Derivatives

Calcein Ultragreen™, AM

RatioWorks™ BCFL, AM *Superior replacement for BCECF*