Enhanced Luminescence Efficiency from Hydrogel Microbead Encapsulated Quantum Dots
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0959-M02-09
Enhanced Luminescence Efficiency from Hydrogel Microbead Encapsulated Quantum Dots Arup Neogi, Santaneel Ghosh, Jianyou Li, Tong Cai, and Zhibing Hu Department of Physics, University of North Texas, 211 Ave. A, Denton, TX, 76203
ABSTRACT In this paper, a novel quantum dot (QD) based nanomaterial system is presented for efficient FRET analysis. The quantum dots have been embedded in hydrogel microspheres based on poly(N-isopropylacrylamide) (PNIPAM) a thermoresponsive polymer that undergoes a volume phase transition across the low critical solution (LCST). The optical properties of the quantum dots entrapped within the gel microspheres has been modified due to change in refractive index, volume density of the surrounding hydrogel medium. The QDs encapsulated in the PNIPAM microspheres showed 100–200 % enhancement in the PL efficiency as the microgels shrank at the temperature above the LCST temperature of the gel. INTRODUCTION
Fluorescent micro spheres have the potential to provide a new generation of fluorescence markers for biological assays. Compared to molecular-based Förster Resonance Energy Transfer (FRET) systems quantum dot (QD)-based FRET offer several advantages for investigating biological molecules. Since the emission spectra of QDs can be tuned to match practically any energy acceptor molecule by tailoring the size, shape, and composition of the QD, a significant improvement in FRET efficiency for the designed energy donor-acceptor pair can be achieved. Furthermore, QD-based FRET systems can be excited with high efficiency over a broad spectral range making it easy to excite them with simple illumination sources and these FRET process can be effective over larger distances. The FRET efficiency depends significantly on the distance between the donor and the acceptor molecules or quantum dots. However, in colloidal medium, reducing the distance between quantum dots can lead to clustering which results in the increase in the inhomogeneous broadening. In this work, we present a novel QD based nanomaterial system embedded in gel-network for FRET analysis. Cadmium chalcogenide QDs provide the most attractive fluorescence labels in comparison with routine dyes or metal complexes due to their unique photoluminescence behavior, involving size-tunable emission color, a narrow and symmetric emission profile and a broad excitation range [1]. However, the emission of the QDs embedded within the gel spheres remains nearly unchanged in comparison with that of their parent QD’s in aqueous solution [14]. Microbeads on the other hand are the most commonly used carriers of fluorescence labels for fluorescence detection. Due to their aqueous inner environment, biological compatibility, and feasibility for conjugating with biological molecules, hydrogel microspheres have been widely employed as delivery vehicle for drugs, proteins and genes [5]. The integration of fluorescent QDs in hydrogel microbeads therefore provides a new generation of fluorescence markers for biological assays. The incorporation of water
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