IP: 37.9.40.17 On: Thu, 28 Feb 2019 10:30:47 Copyright: American Scientific Publishers Delivered by Ingenta Copyright © 2019 American Scientific Publishers All rights reserved Printed in the United States of America Article Journal of Nanoscience and Nanotechnology Vol. 19, 3334–3342, 2019 www.aspbs.com/jnn Comparative Studies on the Aqueous Synthesis and Biocompatibility of L-Cysteine and Mercaptopropionic Acid Capped CdSe/CdS/ZnS Core/Shell/Shell Quantum Dots D. Sukanya 1 , D. Muthu Gnana Theresa Nathan 2 , R. Mahesh 2 , and P. Sagayaraj 2 ∗ 1 PG Department of Physics, Justice Basheer Ahmed Sayeed College for Women, Chennai 600018, India 2 Department of Physics, Loyola College (Autonomous), Chennai 600034, India Quantum dots have now become the most important candidates and widely exploited as promising architectures for use as diagnostic and imaging agents in biomedicine and as semiconductors in the electronics industry. This article emphasizes on the aqueous synthesis of water soluble CdSe/CdS/ZnS core/shell/shell quantum dots with L-cysteine and mercaptopropionic acid as cap- ping agent and their observed properties have been compared. The biocompatibility of the as- synthesized quantum dots have also been analyzed through the cytotoxicity study using MTT assay. The structural, morphological and optical properties of these quantum dots have been examined through X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), UV- Visible absorption spectroscopy (UV-Vis) and Photoluminescence spectroscopy (PL). The capping of L-cysteine and mercaptopropionic acid on the quantum dots has been confirmed from Fourier transform infrared spectroscopy (FTIR). XRD results demonstrated the formation of hexagonal wurtzite structure for L-cysteine and cubic zinc blende structure for mercaptopropionic acid capped CdSe/CdS/ZnS quantum dots. From the optical measurements, it is observed that there is a consid- erable increase in the photoluminescence intensity of L-cysteine capped quantum dots than MPA. The HRTEM images revealed the narrow size distribution and in addition, L-cysteine capped quan- tum dots were found to be more biocompatible than mercaptopropionic acid capped quantum dots which would provide new opportunities for applications in bioimaging and biolabelling. Keywords: L-Cysteine, Mercaptopropionic Acid, CdSe/CdS/ZnS, Quantum Dots, Optical Properties. 1. INTRODUCTION II–VI semiconductor heterostructured nanocrystals, com- monly termed as quantum dots (e.g.,) CdSe–CdS, CdSe– ZnS, CdTe–CdS, CdSe–ZnSe etc. 1 with the radius smaller than the exciton Bohr radius have attracted extensively because of their potential applications in nanoelectron- ics, nanophotonics, biological labels, etc. 2 It is well known that due to quantum confinement, these quan- tum dots possess unique size dependent optical properties such as high photoluminescence quantum yield, photo- bleaching stability, continuous absorption band and size tunable photoluminescence. 3 By changing the chemical ∗ Author to whom correspondence should be addressed. composition, size, shape and structure of these quantum dots, their properties can be tuned across the visible spec- trum. One of the most highlighting applications of quan- tum dots is the new generation fluorescent markers which have wide biological applications in labeling, sensing, imaging, diagnostics etc. 4 5 Since quantum dots exhibit size similarities with the biomolecules, they provide high opportunity to design biosensors and to develop new opti- cal detection methods employing the unique features of quantum dots. Alivisatos et al. 1998 and Nie et al. 1998 did the pioneering work and reported the significant use of these quantum dots in tracking and imaging cells. From the past decade, a great number of synthesis tech- niques have been proposed for the synthesis of quantum 3334 J. Nanosci. Nanotechnol. 2019, Vol. 19, No. 6 1533-4880/2019/19/3334/009 doi:10.1166/jnn.2019.16095