A ratiometric fluorophotometer for fluorescence-based viscosity measurement with molecular rotors

Molecular rotors are fluorescent molecules that exhibit viscosity-dependent quantum yield. By using molecular rotors, fluid viscosity can be rapidly determined through spectroscopy. In a clinical setting, rapid viscosity measurements of blood plasma and other biofluids are desirable as a diagnostic tool in several diseases that are accompanied by plasma viscosity changes. In many cases, however, optical properties of the biofluids (absorption and scattering) attenuate the measured emission intensity. When using standard fluorophotometers, resulting viscosity values may be too low. We propose a new instrument that determines biofluid absorption and scattering simultaneously with emission intensity. The additional information gathered with the instrument allows the computation of an emission correction factor. Validation of the prototype showed excellent correlation of emission and absorbance with a standard fluorophotometer and spectrometer (R² > 0.99). We determined the emission of a scattering model composed of microspheres and the molecular rotor 9-(2-Cyano-2-hydroxy carbonyl) vinyl julolidine (CCVJ) in hetastarch solutions as well as mixtures of blood plasma and a high-viscosity plasma expander with CCVJ. The influence of turbidity could widely be eliminated by using additional information provided by the instrument. One additional advantage of the presented device is its ability to use optical fibers for the measurement, thus allowing spectroscopic measurements at remote sites. By correcting emission measurements for fluid optical properties, a major disadvantage of conventional fluorophotometers can be overcome. Therefore, the ratiometric fluorophotometer has a wide range of applications wherever variations in fluid properties must be accounted for in order to accurately determine emission intensity.