Heparin is the most important anticoagulant drug used during surgeries and extracorporeal therapies. Although the blood levels of heparin should be monitored continuously during the procedure to ensure the safety of the patient, there is currently no technique for measuring heparin in real time. This study describes the use of a molecularly imprinted polymer (MIP) as a recognition element in the development of a heparin sensor for real-time monitoring. An indium tin oxide (ITO) electrode grafted with a heparin-specific MIP was used as a working electrode to perform cyclic voltammetry of ferrocyanide. The anodic current was found to be dependent on heparin concentration, probably due to the "gate effect", which is a change in the accessibility of the MIP-modified electrode to ferrocyanide, triggered by specific interaction between MIP and heparin. The kinetics of heparin interaction with the MIP-grafted electrode was evaluated using potentiostatic chronoamperometry of ferrocyanide in an electrochemical flow cell. The response time to stepwise changes in heparin concentration between 0 and 0.04 units per mL was estimated at 20 s, which is remarkably shorter than that achieved using conventional methods for monitoring heparin. The MIP-grafted electrode demonstrated exceptional sensitivity and could detect heparin in whole blood samples (0-6 units per mL) diluted 100-fold with physiological saline containing ferrocyanide. Therefore, the MIP-grafted electrode is suitable for real-time monitoring of heparin in blood. Another advantage is that a very small volume of blood is needed, which is very important, especially when regular measurements are required.
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