Polyethyleneimine Functionalized ZnO Quantum Dots and their Binding Interaction with Bovine Serum Albumin Protein
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Polyethyleneimine Functionalized ZnO Quantum Dots and their Binding Interaction with Bovine Serum Albumin Protein Prachi Joshi,1,2 $ Soumyananda Chakraborti,3 $ Pinak Chakrabarti,3* Surinder P. Singh,1,4* Z. A. Ansari,2 Virendra Shanker1 1
National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi-110012, India. Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia, New Delhi110025, India. 3 Department of Biochemistry, Bose Institute, P-1/12 CIT Scheme VIIM, Kolkata-700054, India. 4 Engineering Sciences and Materials Department, University of Puerto-Rico, Mayaguez, PR0680, USA. *Address for correspondence: [email protected]; [email protected] $ Both authors have equal contribution 2
ABSTRACT Water stable fluorescent ZnO quantum dots (QDs) have been synthesized by wet chemical route in presence of hydrophilic capping agent polyethyleneimine (PEI) as stabilizing agent. The binding interaction of prepared ZnO QDs is studied with bovine serum albumin (BSA) protein. X-ray diffraction measurement reveals hexagonal wurtzite structure of as synthesized ZnO QDs with an average size 4-6 nm, determined using Scherer’s equation and confirmed by transmission electron microscopy (TEM). The ZnO/PEI QDs exhibit strong yellow-green emission centered at 555 nm (2.23 eV). The interaction between BSA and ZnO/PEI QDs has been studied by using spectroscopic and calorimetric methods. Static mode of tryptophan quenching in BSA by ZnO/PEI QDs indicates that a ground state complex formation is taking place between ZnO/PEI and BSA, where, the week interactions (hydrogen bonding and hydrophobic interaction) are contributing towards the stability of the complex. INTRODUCTION In recent years, the semiconductor QDs have emerged as a potential candidate for biomedical applications such as fluorescent tagging, immunoassay and drug delivery due to their high photostability and sensitivity compare to conventional fluorophores and fluorescent proteins.1 QDs are found to possess broad excitation wavelength, high molar extinction coefficient, high quantum yield and narrow emission wavelength tunable with particle size.2 ZnO is an important QD for bioapplications because of its biocompatibility and high excitonic band gap.3 In Recent studies, nanowires of ZnO found to get soluble in biofluids and the nanoparticles of ZnO have been used for killing of cancer cells and activated human T cells.4,5 But the major drawback associated with ZnO QDs is their poor solubility and stability in water and water-based solvents.6 The highly active surface of ZnO QDs undergoes irreversible agglomeration in water resulting into poor dispersion and loss of their important fluorescence properties. Accordingly, we have synthesized biocompatible ZnO QDs using hydrophilic cationic capping agent polyethyleneimine (PEI) to make them water soluble. PEI is an efficient gene transfer agent and has been successfully used as a nonviral vector for gene delivery both in vitro and in vivo.7 Carrabino et.al. have shown that PEI is more efficient
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