A comparison of fluorescence and UV–visible spectrometry techniques for thermal phase transitions of agarose gels

Abstract

In this study, thermoreversible phase transitions of high (HMP) and low (LMP) melting point agarose gels were investigated by using the UV–vis and fluorescence spectroscopy techniques. Pyranine was added to the aqueous solution of agarose as a fluorescence-probe. Transmitted light (I tr) and fluorescence emission (I fl) intensities from the gel samples with different agarose concentrations were monitored during the heating (gel-sol) and cooling (sol–gel) processes. For the both techniques, gel-sol (T gs) and sol–gel (T sg) transition temperatures were determined from the first derivatives of the sigmoidal transition paths. It was observed that the critical transition temperatures obtained from UV–vis and fluorescence data slightly increased depending on the agarose type and concentration, and those values were found to be in accord with each other. Transition activation energies were determined using the Arrhenius type equation and were found to be strongly correlated with the agarose content in the gel system. The produced gel-sol (ΔE gs) and sol–gel (ΔE sg) transition energies from the fluorescence data were found to be lower than that of the UV–vis data, which was attributed to the temperature-dependent fluorescence quenching effect.