Contents lists available at ScienceDirect Journal of Luminescence journal homepage: www.elsevier.com/locate/jlumin Phosphorescent detection of DNA- drug interaction based on emission quenching of ZnS quantum dots via photoinduced electron transfer Ilkay Ocak, Hayriye Eda Satana Kara ⁎ Gazi University, Faculty of Pharmacy, Department of Analytical Chemistry, 06330 Ankara, Turkey ARTICLE INFO Keywords: Quantum dots Phosphorescence PIET Epirubicin Drug-DNA interaction ABSTRACT A novel room temperature phosphorescence (RTP) sensor consisting of quantum dots (QDs)-drug nanohybrid was used for the investigation of interaction between epirubicin (EPI) and double-stranded deoxyribonucleic acid (ds-DNA). The method based on the quenching effect of EPI on the phosphorescence emission of Mn-doped ZnS QDs via photoinduced electron-transfer (PIET) mechanism. Adsorption of EPI to the QDs surface caused quenching of RTP emission of QDs via photoinduced electron-transfer process. Whereas, with the addition of DNA provided the restoration of emission due to removing of EPI from the surface. The quantum dots were synthesized in an aqueous medium and characterized. The diameter of prepared QDs were about 3.5 nm, spherical, and uniform size. The quenching mechanism of QDs by EPI is not only collisional but also static. The static and dynamic quenching constants were found as 5.36 × 10 5 M -1 and 3.19 × 10 4 M -1 , respectively. In addition to this method, fluorescence and absorption spectrometric methods were used to evaluate DNA/drug interaction and calculate the binding constant (K), which was 3.83 × 10 5 M -1 . Proposed method has advantages such as simplicity and avoids interferences from autofluorescence and scattering light. 1. Introduction Epirubicin (EPI) is an anthracycline antileukemic drug. Similarly to other anthracyclines, EPI interacts with DNA by intercalation which causes inhibition of DNA and RNA synthesis and cell dead. This event is also results of generating of free radicals by EPI. The hydroxyl group at the 4′ carbon of the sugar has a different spatial orientation which brings about faster elimination and less toxicity. The chemical structure of EPI is given in Fig. 1. Phosphorescence is an emission resulting of transition from the excited triplet state (T 1 ) to the singlet ground state (S 0 ). A phosphor- escence technique is more selective and sensitive over the other spec- troscopic techniques. In addition, longer emission lifetime and larger Stokes shift allows avoiding from spectral interferences [1]. In the past decades, room temperature phosphorescence method based on using many different solvent systems such as micelle, cyclodextrins, and heavy atom has been developed as a sensitive and versatile tool in analytical chemistry. Quantum dots (QDs) also known as luminescent nanocrystals are semiconductor nanoparticles that possess remarkable luminescence emission properties. They have some advantages over traditional fluorophores such as size-control emission, broad excitation and sharp emission bands, and high photoluminescence quantum yield [2–6]. QDs are using as luminescent probes to analyze of different type analyte such as ions, biomolecules, pharmaceuticals, and bioimaging [7–11]. The optical, electrical, and magnetic character of QDs can be changed by doping of different dopants. In this study, Mn 2+ was used as a do- pant which gave unique phosphorescence properties to QDs [11]. Quenching of RTP intensities of QDs with the addition of quencher form the basis of method. This mechanism can be explained by PIET system. In here, (i) the quencher is adsorbed onto the surface of QDs, (ii) the photoinduced transfer of electrons from QDs to the quencher cause decreasing of RTP intensities, (iii) the recovery of luminescence in- tensity can be provided by adding a receptor to desorb the quencher from the surface. Decreasing of phosphorescence intensity is depended on the concentration of quencher [12]. DNA is an important macromolecule which has important role such as transcription of the genetic information and the main target for many small molecules, steroids, drugs, and carcinogens. The interaction with anticancer drugs and DNA affects replication and causes chromosome abbreviations. Consequently, the evaluation of DNA-drug interaction is needed for designing DNA-targeted drugs and understanding of the working mechanism of them. Binding of small molecules to DNA occur two modes which are covalent and non-covalent. Non-covalent interactions include electro- static binding, groove binding, and intercalation [13,14]. Most common https://doi.org/10.1016/j.jlumin.2018.01.026 Received 2 August 2017; Received in revised form 9 January 2018; Accepted 17 January 2018 ⁎ Corresponding author. E-mail address: eda@gazi.edu.tr (H.E.S. Kara). Journal of Luminescence 197 (2018) 112–118 0022-2313/ © 2018 Elsevier B.V. All rights reserved. T