Calcium measurement is critical for numerous biological investigations. Fluorescent probes that show spectral responses upon binding Ca2+ have enabled researchers to investigate changes in intracellular free Ca2+ concentrations by using fluorescence microscopy, flow cytometry, fluorescence spectroscopy and fluorescence microplate readers. Rhod-2 is most commonly used among the red fluorescent calcium indicators. However, Rhod-2 AM is only moderately fluorescent in live cells upon esterase hydrolysis, and has very small cellular calcium responses. Quest Rhod-4 has been developed to improve Rhod-2 cell loading and calcium response while maintaining the spectral wavelength of Rhod-2. In CHO and HEK cells Quest Rhod-4 AM has cellular calcium response that is 10 times more sensitive than Rhod-2 AM. AAT Bioquest offers versatile packing sizes of Quest Rhod-4 to meet your special needs, e.g., 1 mg; 10x50 g; 20x50 g; HTS packages with no additional packaging charge.