Optically Active Nanoparticle Coated Polystyrene Spheres
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Optically Active Nanoparticle Coated Polystyrene Spheres Brandy Kinkead, Abdiwali A. Ali, John-C. Boyer, and Byron D. Gates1 1
Department of Chemistry and 4D LABS, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada ABSTRACT Nanoparticles (NPs) with either plasmonic or upconverting properties have been selectively coated onto the surfaces of polystyrene (PS) spheres, imparting their optical properties to the PS colloids. These NP coated PS spheres have many potential applications, such as in medicine as drug-delivery systems or diagnostic tools. To prepare the NP coated PS spheres, gold or core-shell NaYF4Tm0.5Yb30/NaYF4 NPs were synthesized and separately combined with amino-functionalized PS spheres. The mechanism by which the NPs adhered to the PS spheres is attributed to interactions of the NP and a polyvinylpyrrolidone additive with the surfaces of the PS spheres. Two-photon fluorescence microscopy and SERS analysis demonstrate the potential applications of these NP coated PS spheres. INTRODUCTION The unique optical properties of some nanoparticles (NPs) make them useful for an array of applications that include advances in medical, sensing and advanced computing technologies. Nanoparticle-based diagnostics, for example, have the potential to improve specificity and sensitivity for earlier and more accurate detection of pathogens and disease [1, 2]. Nanoparticles may also be used in medical treatment for photothermal therapy of cancer or as drug delivery agents [2, 3]. Other researchers are looking into the use of NPs for optical memory applications, for new sensors and to improve security technologies [4-6]. Upconverting (UC) NPs are of interest for their unique nonlinear optical properties [2, 4, 5, 9-11]. The UC NPs can perform photon upconversion, whereby the NPs absorb low energy radiation (i.e. near IR wavelengths) and emit high energy radiation (i.e. visible wavelengths). The potential of UC NPs in diagnostics has been shown in many studies [2, 5]. In vivo detection of UC NPs has been demonstrated in worms [10] and mice [11] with a good depth of detection owing to the low energy of the excitation wavelengths. Other researchers have used UC NPs for sensor applications [4] and nanoscale thermometry [9]. The applications of these nanomaterials will expand as research continues in this area. Gold NPs are a relatively chemically inert platform whose chemical functionality is often determined by the molecular coatings on their surfaces [12]. Their surface chemistry can be easily modified to suit the needs of particular applications. In addition, their size, shape, and morphology can be fine-tuned to optimize their optical properties [13]. Gold NPs have an established track record as a stable and tunable platform for biological imaging, cancer therapeutics, and optical-based diagnostics [14]. One of the relatively unique applications for Au NPs is as surface enhanced Raman spectroscopy (SERS) substrates [15]. The tunable surface plasmon resonance (SPR) of the Au NPs is used in SERS to e
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