Fabrication and characterization of CdSe/ZnS quantum dots-doped polystyrene microspheres prepared by self-assembly

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Ching-Shiow Tseng Graduate Institute of Biomedical Engineering, National Central University, Taoyuan 32001, Taiwan, Republic of China; and Department of Mechanical Engineering, National Central University, Taoyuan 32001, Taiwan, Republic of China

Yen-Lin Wei Graduate Institute of Biomedical Engineering, National Central University, Taoyuan 32001, Taiwan, Republic of China (Received 2 May 2012; accepted 16 August 2012)

Semiconductor quantum dots (QDs)-doped polystyrene (PS) microspheres with high luminescence were prepared using a self-assembly approach. Hydrophobic CdSe/ZnS QDs were first carboxylized by ligand exchange using mercaptocarboxylic acid. PS microspheres were separately encapsulated with polyethyleneimine via electrostatic interactions and then adsorbed with the carboxyl QDs to form QDs-doped microspheres. We then characterized the combinations using optical, electrical, and mechanical approaches and obtained the following findings: (i) microspheres can be fully coated by QD nanoparticles with a coverage rate of 1.0 pmole/cm2, in which QDs were evenly distributed on the surfaces; (ii) the anchored QDs exhibited similar optical property as they performed in isolated suspension; and (iii) the fluorescence of QDs-doped microspheres remained intact after stressed by ultrasound-induced cavitation, demonstrating the robustness of interactions between QDs and microspheres. The self-assembly approach developed in this study offered a facile and controllable strategy for preparation of QDs-encoded microparticles with high luminescence and stability.

I. INTRODUCTION

Interest in using quantum dots (QDs)-encoded nano-/ microparticles instead of organic fluorophore counterparts as optical probes is increasing, owing to significant advantages in terms of detection sensitivity, throughput, and photostability.1 Since the QDs-loaded particle was first reported in 2000,2,3 investigations into fabrication methods4–7 and characteristics8–10 of QDs-encoded particles have followed, leading to the development of QDs-tagged particle technology as an intense research subject during the last decade. Microspheres bar-coded by six colors of QDs with 10 intensity levels have been demonstrated as a feasible tool for multiplexed DNA screening.11 QDs-tagged microspheres associated with bioconjugates can be treated as bioprobes for cellular quantification12,13 and/or molecular detection.14,15 Recently, they were further used as a tracer for cancer diagnostics,16–18 exhibiting tremendous potential in a wide spectrum of biomedical applications. So far, there are three major approaches for the fabrication of QDs-encoded polymeric microspheres: (i) diffusion a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.332 J. Mater. Res., Vol. 27, No. 22, Nov 28, 2012

of QDs into swelled/porous microspheres, (ii) incorporation of QDs with microspheres during bead polymerization, and (iii) direct coating of particle surfaces with QDs. The former two approaches have significant advantages such as good size con

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