A ratiometric fluorometric heparin assay based on the use of CdTe and polyethyleneimine-coated carbon quantum dots.

CdTe quantum dots (QDs) were integrated with polyethyleneimine-coated carbon dots (PEI-CDs) to form a dually emitting probe for heparin. The red fluorescence of the CdTe QDs is quenched by the PEI-CDs due to electrostatic interactions. In the presence of heparin, the blue fluorescence of PEI-CDs remains unaffected, while its quenching effect on the fluorescence of CdTe QDs is strongly reduced. A ratiometric fluorometric assay was worked out. The ratio of the fluorescences at 595 and 436 nm serves as the analytical signal. Response is linear in the concentration range of 50-600 ng·mL (0.1-1.2 U·mL) of heparin. The limit of detection is 20 ng·mL (0.04 U·mL). This makes the method a valuable tool for heparin monitoring during postoperative and long-term care. This assay is relatively free from the interference by other analogues which commonly co-exist with heparin in samples, and it is more robust than single-wavelength based assays. Graphical abstract In the presence of heparin, the fluorescence of polyethyleneimine-coated carbon dots (PEI-CDs) at 436 nm remains unaffected, while its quenching effect on the fluorescence of CdTe at 595 nm is strongly reduced.