Comment on "Emissive H-Aggregates of an Ultrafast Molecular Rotor: A Promising Platform for Sensing Heparin".

For heparin sensing, Mudliar and Singh developed fluorescence and absorption spectroscopic approaches by utilizing emissive H-aggregates of thioflavin T (ThT) formed upon heparin binding. It has been proposed that the methods work not only in pure aqueous solution but also in complex biological media such as human serum. However, the optical features used to detect and quantify heparin are very sensitive to the ionic strength of the solution and completely vanish at 1.45 mM NaCl. Curiously, the authors were able to determine the heparin content of 1% serum samples containing the same level of electrolyte. In addition, the experimental conditions employed for heparin detection in serum samples were substantially modified, reducing the optical path length from 1 to 0.1 cm and increasing the dye concentration by an unknown measure. ThT shows a concentration-dependent tendency for aqueous aggregation, which markedly modifies its absorption and fluorescence properties. The authors have failed to verify that spectral characteristics of the ThT-heparin system observed in pure aqueous medium remain unchanged at higher dye concentrations and in the presence of serum components. Taking these issues into consideration, the heparin detection scheme offered for serum samples cannot be reproduced.