A new fluorescence "switch on" assay for heparin detection by using a functional ruthenium polypyridyl complex

In the present study, a new strategy for heparin detection and quantification in biological media, such as fetal bovine serum (FBS), is developed by monitoring the emission change of a functional ruthenium polypyridyl complex ([Ru(phen)(2)dppz-idzo](2+), complex 1) in buffer solution. Polyanionic heparin is found to interact with a positively charged Ru-complex through electrostatic effects and/or hydrogen bonding interactions, which leads to a significant fluorescence enhancement of the Ru-complex. To get insight into this fluorescence "switch on" behavior, the binding model of the Ru-complex to heparin is established by employing molecular docking simulations based on the fluorescence and UV absorption results. The selectivity results of the fluorescence assay reveal that our complex displayed good fluorescence selectivity towards heparin over its analogues, such as chondroitin 4-sulfate (Chs) or hyaluronic acid (Hya), which have lower charge density and/or structural compatibility as compared to that of heparin. Quantification of heparin is also performed and a linear calibration curve is observed in the range of 0.01-4.87 U mL(-1) (the limit of detection is 0.01 U mL(-1)) for heparin detection in diluted FBS solution. This "one-step" fluorescence "switch on" assay for heparin detection is label-free, convenient, sensitive and selective, and has a long emission wavelength and large Stokes shift.