A simple and sensitive label-free fluorescence sensing of heparin based on Cdte quantum dots B. Rezaei,* M. Shahshahanipour and Ali A. Ensafi ABSTRACT: A rapid, simple and sensitive label-free fluorescence method was developed for the determination of trace amounts of an important drug, heparin. This new method was based on water-soluble glutathione-capped CdTe quantum dots (CdTe QDs) as the luminescent probe. CdTe QDs were prepared according to the published protocol and the sizes of these nanoparticles were verified through transmission electron microscopy (TEM), X-ray diffraction (XRD) and dynamic light scattering (DLS) with an average particle size of about 7 nm. The fluorescence intensity of glutathione-capped CdTe QDs increased with increasing hepa- rin concentration. These changes were followed as the analytical signal. Effective variables such as pH, QD concentration and incubation time were optimized. At the optimum conditions, with this optical method, heparin could be measured within the range 10.0–200.0 ng mL À1 with a low limit of detection, 2.0 ngmL À1 . The constructed fluorescence sensor was also applied successfully for the determination of heparin in human serum. Copyright © 2015 John Wiley & Sons, Ltd. Keywords: heparin; CdTe quantum dot; fluorescence spectroscopy; label-free Introduction Heparin is an important natural biomolecule that is normally extracted and purified from animal tissues, especially from porcine and bovine (1). This drug can be used as an anti-coagulant, anti- thrombotic, anti-lipemic, anti-atherosclerosis, anti-phlogistic and anti-allergic product (2). The use of heparin avoids the formation of clots in blood vessels before or after surgery or during certain medical procedures. Also, it is used to treat certain blood, heart, and lung disorders and helps in the diagnosis and treatment of certain bleeding disorders. It has been widely used in clinical ther- apy for more than 60 years and it is still regarded as the first option to avoid thrombosis and cure urgent vein thrombus (3). High doses of heparin can counteract some undesirable effects (such as internal bleedings, puke, loss of consciousness and headache) (4). Beyond the requirement for simple, accurate and real-time de- terminations of heparin levels in patient serum during surgery and postoperative remedy period, there is also the need for detection methods that can check the heparin levels in infusion solutions to prevent the risk of human errors in dosing. Conventional clinical methods for heparin detection rely on the measurement of activated clotting time or activated partial thromboplastin time (5). Different methods have been developed for heparin measure- ment, including resonance Rayleigh scattering (6), fluorimetry (3,6-8), electrochemical sensor (2,9-11), capillary electrophoresis (12), high performance liquid chromatography (HPLC) (13) and colori- metric methods (4,14,15). These methods are not sufficiently reli- able and exact for clinical settings because of their lack of specificity and possible interference with other factors (16). The main limitations and disadvantages of HPLC are the cost of equip- ment, the use of environmentally dangerous solvents and the co-elution of compounds. The major drawback of capillary electro- phoresis is its complex assay validation. Electrochemical sensors have a number of limitations such as the electroactivity of certain species and as such electrochemically active interference in the sample (17). The main limitation of colorimetric methods is its low sensitivity. In addition, some of these methods are not appro- priate for use outside the laboratory or for field monitoring. Fluo- rescence sensors have many attractive advantages, including high sensitivity, remote control, inexpensiveness, easy recognition, and an especially suitable diagnostic device for analytical concerns. A few techniques have also been reported for determination of heparin applying QDs. Cao and et al. utilized the Ru complex, which quenched CdTe QD fluorescence (18). Heparin addition removed the quencher from the QD surface and led to fluores- cence reclamation by the CdTe QDs. Zhang and coworkers also used MPA (3-mercaptopropionic acid) capped Mn-doped ZnS quantum dots and polybrene (hexadimethrine bromide) for the application of a room temperature phosphorescence (RTP) deter- mination of heparin (19). In their study, the RTP intensity of QDs was strongly enhanced after the addition of polybrene. Heparin could remove polybrene from the surface of QDs, thus the RTP in- tensity of Mn-doped ZnS QDs was decreased with increasing hep- arin concentration. In another study, Liu and coworkers applied L-cysteine-capped CuInS 2 QDs (20). Heparin could aggregate the QDs via electrostatic force and therefore decreased the intensity * Correspondence to: B. Rezaei, Department of Chemistry, Isfahan University of Technology, Isfahan 84156–83111, Iran. E-mail: rezaei@cc.iut.ac.ir Department of Chemistry, Isfahan University of Technology, Isfahan84156- 83111, Iran Abbreviations: DLS, dynamic light scattering; HPLC, high performance liquid chromatography; IUT, Isfahan University of Technology; QY, quantum yields; RTP, room temperature phosphorescence; TEM, transmission electron micros- copy; XRD, X-ray diffraction. Luminescence 2016; 31: 958–964 Copyright © 2015 John Wiley & Sons, Ltd. Research article Received: 12 May 2015, Revised: 9 October 2015, Accepted: 9 October 2015 Published online in Wiley Online Library: 5 November 2015 (wileyonlinelibrary.com) DOI 10.1002/bio.3058 958