Butterfly-shaped conjugated oligoelectrolyte/graphene oxide integrated assay for light-up visual detection of heparin.

A water-soluble pyrene-based butterfly shaped conjugated oligoelectrolyte (TFP) is synthesized and integrated with graphene oxide (GO) to form a label-free assay for heparin detection. Efficient fluorescence quenching occurs between TFP and GO because of strong electrostatic and π-π interactions, leading to nearly dark emission in the absence of analytes. Addition of heparin into TFP solution significantly minimizes the fluorescence quenching of GO toward TFP, which is less effective for the heparin analogues, such as hyaluronic acid and chondroitin 4-sulfate. As a consequence, the solution emits strong yellow fluorescence only in the presence of heparin, which allows for light-up visual discrimination of heparin from its analogues. Moreover, the linear light-up response of the TFP/GO integrated assay enables heparin quantification in the range of 0-1.76 U/mL with a limit of detection of 0.046 U/mL, which is practical for heparin monitoring during postoperative and long-term care. This study thus demonstrates a new synthetic strategy to develop GO-based chemical and biological sensing without the employment of dye-labeled biomolecules.