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Amino Blue™ pH Sensor

Ursa BioScience offers both an absorption (colorimetric) and fluorescence emission wavelength ratiometric pH Probe, which responds over the pH range 6-8, making it ideal for physiological measurements, such as cellular studies, imaging and microscopy.

Amino Blue™ shows an absorption wavelength ratiometric response to pH in the 325 – 450 nm range and a fluorescence emission wavelength ratiometric response from 400-700 nm. The Quantum yield of Amino Blue™ is ~0.5.

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Figure 1. Absorption spectrum of Amino Blue™ with increasing pH.

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Figure 2. Wavelength ratiometric plots for both Amino Blue™ and Amino Blue C™ based on the A340/A388 nm bands.


Amino Blue C™ – pH Control Fluorophore

Ursa BioScience also offers a Control pH Fluorescent Compound for Amino Blue™. Our Amino Blue C™ has the same chromophore fluorescent backbone, but is only very mildly influenced by pH. For researcher’s and physicians alike undertaking pH analysis, Amino Blue C™ allows for any background interference of the parent fluorophore Amino Blue™ to be corrected for, while not changing any fluorescence instrumentation or filter settings. Subsequently, Amino Blue C™ does not show any ratiometric response to cyanide.  Amino Blue C™ can be readily excited from 375-450 nm, with an emission centered at 560 nm.  


Advantages of Ursa's Amino Blue™ Fluorescence-Wavelength Ratiometric Approach

Fluorescence emission spectra of Amino Blue™

Figure 3. Fluorescence emission spectra of Amino Blue™ with increasing pH.

It is widely accepted that fluorescence ratiometric or lifetime based methods offer intrinsic advantages for both chemical and biomedical fluorescence sensing. Simple Fluorescence intensity measurements are typically unreliable away from the laboratory and can require frequent calibration/s due to a variety of chemical, optical or other instrumental related factors. Unfortunately, while fluorescent probes are known to be useful for many applications such as in fluorescence microscopy, fluorescence sensing and DNA technology, most sensing fluorophores only display changes in intensity in response to analytes and hence relatively few wavelength ratiometric probes are available today. Ursa’s range of sensing probes (Cyanide, pH and Fluoride) offer significant advantages of being both excitation (colorimetric) and emission-wavelength ratiometric, with excitation and emission wavelengths over user friendly ranges.





Methuselah Green 2™ is a strongly Phosphorescent probe. The Fluorescence band of Methuselah Green 2™ can be excited in the region 300-380 nm, with the Phosphorescence, T1, band excited 290-350 nm.


Visual comparison of Phos 1 dissolved at the same concentration in methanol (left cuvette) and in glycerol (right cuvette). The cuvettes are placed on a UV light box and illuminated from below.

Cuvettes with the phosphorescent probe Phos Yellow dissolved in glycerol and in ethanol. The emission from the glycerol sample appears yellow when illuminated with UV light, from the ethanol sampe there is no visible emission.

Phos Yellow™ dissolved at the same concentrations (~5 µM) in air equilibrated glycerol (left cuvette) and in ethanol (right cuvette). The cuvettes are illuminated from below with UV light.