ORIGINAL PAPER Synthesis of AS1411-Aptamer-Conjugated CdTe Quantum Dots with High Fluorescence Strength for Probe Labeling Tumor Cells Mona Alibolandi & Khalil Abnous & Mohammad Ramezani & Hossein Hosseinkhani & Farzin Hadizadeh Received: 14 May 2014 /Accepted: 11 August 2014 /Published online: 31 August 2014 Abstract In this paper, we report microwave-assisted, one- stage synthesis of high-quality functionalized water-soluble cadmium telluride (CdTe) quantum dots (QDs). By selecting sodium tellurite as the Te source, cadmium chloride as the Cd source, mercaptosuccinic acid (MSA) as the capping agent, and a borate-acetic acid buffer solution with a pH range of 5– 8, CdTe nanocrystals with four colors (blue to orange) were conveniently prepared at 100 °C under microwave irradiation in less than one hour (reaction time: 10–60 min). The influ- ence of parameters such as the pH, Cd:Te molar ratio, and reaction time on the emission range and quantum yield per- centage (QY%) was investigated. The structures and compo- sitions of the prepared CdTe QDs were characterized by transmission electron microscopy, energy-dispersive X-ray spectroscopy, selective area electron diffraction, and X-ray powder diffraction experiments. The formation mechanism of the QDs is discussed in this paper. Furthermore, AS1141- aptamer-conjugated CdTe QDs in the U87MG glioblastoma cell line were assessed with a fluorescence microscope. The obtained results showed that the best conditions for obtaining a high QY of approximately 87 % are a pH of 6, a Cd:Te molar ratio of 5:1, and a 30-min reaction time at 100 °C under microwave irradiation. The results showed that AS1141- aptamer-conjugated CdTe QDs could enter tumor cells effi- ciently. It could be concluded that a facile high-fluorescence- strength QD conjugated with a DNA aptamer, AS1411, which can recognize the extracellular matrix protein nucleolin, can specifically target U87MG human glioblastoma cells. The qualified AS1411-aptamer-conjugated QDs prepared in this study showed excellent capabilities as nanoprobes for cancer targeting and molecular imaging. Keywords CdTe . Microwave-assisted synthesis . Bioimaging . AS1411 . Aptamer targeting . U87MG Introduction Quantum dots (QDs) are semiconductor nanocrystals. QDs systems with small dimensions exhibit quantum mechanical phenomena such as the emission of excitons that are confined in all three spatial dimensions [1–3]. The electronic character- istics of these materials are intermediate between those of bulk semiconductors and discrete molecules [4–6]. Owing to their photostability and narrow emission bandwidth, QD nanocrystals show the promise of having very interesting applications such as sensing, detection, and bioimaging [7–11]. Traditionally, QDs are synthesized in organic media and the resultant QDs has no intrinsic aqueous solubility. During the growing process, they are coated and protected with hydrophobic capping agents such as trioctyl phosphine oxide (TOPO). Then, a cap exchange procedure is required to solu- bilize QDs in water. However, the cap exchange procedure can be adapted to prepare functionalized QDs with reduced colloidal stability and quantum yields (QYs) [12–14]. More- over, water-soluble QDs can be produced through a simple M. Alibolandi : F. Hadizadeh (*) Biotechnology Research Center, School of Pharmacy, Mashhad University of Medical Sciences, P.O.Box 9196773117, Mashhad, Iran e-mail: hadizadehf@mums.ac.ir K. Abnous : M. Ramezani Pharmaceutical Research Center, Mashhad University of Medical Sciences, Mashhad, Iran M. Ramezani Nanotechnology Research Center, Mashhad University of Medical Sciences, Mashhad, Iran H. Hosseinkhani Graduate Institute of Biomedical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan J Fluoresc (2014) 24:1519–1529 DOI 10.1007/s10895-014-1437-5 # Springer Science+Business Media New York 2014