Journal of Photochemistry and Photobiology A: Chemistry 215 (2010) 118–122 Contents lists available at ScienceDirect Journal of Photochemistry and Photobiology A: Chemistry journal homepage: www.elsevier.com/locate/jphotochem Study of the interaction between CdSe/ZnS core-shell quantum dots and bovine serum albumin by spectroscopic techniques Milohum Mikesokpo Dzagli a,b , Valentin Canpean a , Monica Iosin a,∗ , Messanh Agbeko Mohou b , Simion Astilean a,∗ a Babes-Bolyai University, Faculty of Physics and Institute for Interdisciplinary Experimental Research in Bionanoscience, Nanobiophotonics Center, Treboniu Laurian 42, 400271, Cluj-Napoca, Romania b Laboratoire de Physique des composants à semi-conducteurs, Université de Lomé, BP 1515 Lomé, Togo article info Article history: Received 13 May 2010 Received in revised form 2 August 2010 Accepted 4 August 2010 Available online 11 August 2010 Keywords: Quantum dots Bovine serum albumin Quenching Fluorescence Biosensing abstract In this work we studied the interaction between CdSe/ZnS core-shell quantum dots (QDs) and bovine serum albumin (BSA) protein, and the temperature effects on the structural and spectroscopic properties of both, individual QDs and protein and their bioconjugates (QDs@BSA), by fluorescence and UV–vis spec- troscopy. The recorded UV–vis data and the calculated rate of BSA fluorescence quenching by the QDs demonstrated that the interaction between them leads to the formation of QDs@BSA complex. Moreover we show that, compared to the monotonically decrease of the non-conjugated QDs fluorescence inten- sity, the temperature dependence of the QDs@BSA emission has a much more complex behavior, highly sensitive to the conformational changes of the protein. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Determination of trace of biomolecular concentrations is of foremost importance for the discovery and development of biomolecular mechanisms and medical diagnosis. Most common detection methods are based on the design of sensors that can selectively recognize and signal the presence of a specific analyte. Classical staining agents like organic dyes, fluorescent proteins or lanthanide chelates, have several limitations, such as broad spec- trum profile, low photobleaching threshold or poor photochemical stability [1]. Quantum dots (QDs) represent a new class of fluo- rescent labels that have attracted much interest for biosensing and bioimaging due to their unique optical properties [2–4]. In compar- ison to classical staining agents, the fluorescence emission spectra of QDs can be continuously tuned by changing the particle size, and a single wavelength can be used for simultaneous excitation of different-sized QDs. Also, surface-passivated QDs are highly sta- ble against photobleaching and have narrow, symmetric emission peaks about 25–30 nm full width at half maximum. However, due to the increasing extension of nanotechnology in biological sciences, it is imperative to develop a detailed under- ∗ Corresponding authors. Tel.: +40 264 454554/119; fax: +40 264 591906. E-mail addresses: monica.iosin@phys.ubbcluj.ro (M. Iosin), simion.astilean@phys.ubbcluj.ro (S. Astilean). standing of how biological entities, and at the most basic level, proteins, may interact with nanoscale particles. In addition, rel- atively little is known about the effects of temperature on the QDs–biological system interfaces. Since QDs are intensely used as a fluorescent marker in biological applications, such effect can play a major role in their use. For instance, the interesting phenomenon of QDs blinking, i.e., intermittent fluorescence under excitation, is known to depend on several experimental parameters, including the biological environment or temperature. As result, the blinking behavior could represent a critical issue for the development of bio- logical applications based on monitoring the photoluminescence of QDs as a function of time. A number of previous studies have been devoted to better understanding the influence of luminiscence blinking in fluorescence spectroscopy of bioconjugated core/shell QDs [5,6]. In this work we demonstrate the applicability of CdSe/ZnS core- shell QDs as probes to monitor the thermal behavior of bovine serum albumin (BSA) protein. BSA is one of the most extensively studied proteins, particularly because of its structural homology with human serum albumin [7,8]. Compared to non-conjugated QDs, which exhibit a linear dependence of the fluorescence inten- sity as a function of temperature, the bioconjugated QDs exhibit a more complex behavior, highly sensitive to the structural changes of the protein. Increasing the temperature up to 51 ◦ C, the fluores- cence intensity of bioconjugated QDs exhibits a decrease, due to the generation on the surface of the particles of alternative non- 1010-6030/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jphotochem.2010.08.008