Wei Sun

University of Washington Seattle, Seattle, WA, United States

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Publications (36)231.95 Total impact

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    ABSTRACT: We report on europium-complex grafted polymer for preparing stable nanoparticle probes with high luminescence brightness, narrow emission bandwidth, and long luminescence lifetimes. Eu complex bearing an amino group was used to react with a functional copolymer poly(styrene-co-maleic anhydride) by the spontaneous amidation reaction, producing the polymer grafted with Eu complexes in the side chains. The Eu-complex grafted polymer was further used to prepare Eu-complex grafted Pdots and Eu-complex blended poly(9-vinylcarbazole) composite Pdots, which showed improved colloidal stability as compared to those directly doped with Eu-complex molecules. Both types of Pdots can be efficiently quenched by a nile blue dye, exhibiting much lower detection limit and higher quenching sensitivity as compared to free Eu-complex molecules. Steady-state spectroscopy and time-resolved decay dynamics suggest the quenching mechanism is via efficient fluorescence resonance energy transfer from the Eu complex inside Pdot to surface dye molecules. The amplified quenching in Eu-complex Pdots, together with efficient cell uptake and specific cell surface labeling observed in mammalian cells, suggests their potential applications in time-resolved bioassays and cellular imaging.
    Langmuir : the ACS journal of surfaces and colloids. 06/2014;
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    ABSTRACT: This communication describes an approach for preparing monovalent semiconducting polymer dots (mPdots) with a size of 5 nm where each mPdot was composed of precisely a single active functional group.
    Chemical Communications 04/2014; · 6.38 Impact Factor
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    ABSTRACT: Bright dots: Semiconducting polymer dots (Pdots) doped with europium complexes possess line-like fluorescence emission, high quantum yield, and long fluorescence lifetime. The Pdots successfully labeled receptors on cells. The long fluorescence lifetime of the Pdots was used to distinguish them from other red fluorescence emitting nanoparticles, and improve the signal-to-noise ratio for time-gated cellular imaging. PVK=poly(9-vinylcarbazole).
    Angewandte Chemie International Edition 09/2013; · 11.34 Impact Factor
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    ABSTRACT: A highly fluorescent fluorinated semiconducting polymer dot (Pdot) with a quantum yield of up to 49% was developed. The fluorinated Pdot was eight times brighter in cell-labeling applications than its non-fluorinated counterpart, and was rod shaped rather than spherical.
    Chemical Communications 08/2013; · 6.38 Impact Factor
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    ABSTRACT: Much work has been done on collapsed chains of conjugated semiconducting polymers and their applications as fluorescent probes or sensors. On surfaces spin-coated with semiconducting polymers, excitation energy transfer along the polymer backbone can be used to quickly and efficiently funnel energy to chromophores with localized energy minima. If each chromophore is immobilized within its matrix, this can result in a large fluorescence anisotropy. Through nanoprecipitation of a matrix polymer blended at low mass ratios with short-chain, hydrophobic, fluorescent semiconducting polymers, we took advantage of this large fluorescence anisotropy to make polarization-sensitive nanoparticles (NPs). These NPs are small (∼7 nm in diameter), exhibit a high quantum yield of 0.75, and are easily functionalized to bind to protein targets. Excitation of the NPs with polarized light on a wide-field fluorescence microscope enabled monitoring of both protein location and changes in protein orientation.
    Journal of the American Chemical Society 07/2013; · 10.68 Impact Factor
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    ABSTRACT: Semiconducting polymer dot (Pdot) bioconjugates are a new class of ultrabright fluorescent probes. Here, we report a procedure for lyophilizing Pdot bioconjugates so that they successfully retain their optical properties, colloidal stability, and cell-targeting capability during storage. We found that, when Pdot bioconjugates were lyophilized in the presence of 10% sucrose, the rehydrated Pdot bioconjugates did not show any signs of aggregation and exhibited the same hydrodynamic diameters as before lyophilization. The brightness of the lyophilized Pdots was at least as good as before lyophilization, but in some cases, the quantum yield of lyophilized Pdots curiously showed an improvement. Finally, using flow cytometry, we demonstrated that lyophilized Pdot bioconjugates retained their biological targeting properties and were able to effectively label cells; in fact, cells labeled with lyophilized Pdot bioconjugates composed of PFBT, which were stored for 6 months at -80 °C, were ∼22% brighter than those labeled with identical but unlyophilized Pdot bioconjugates. These results indicate lyophilization may be a preferred approach for storing and shipping Pdot bioconjugates, which is an important practical consideration for ensuring Pdots are widely adopted in biomedical research.
    Analytical Chemistry 04/2013; · 5.82 Impact Factor
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    ABSTRACT: In stimulated emission depletion (STED)-based or up-conversion depletion-based super-resolution optical microscopy, the donut-shaped depletion beam profile is of critical importance to its resolution. In this study, we investigate the transformation of the donut-shaped depletion beam focused by a high numerical aperture (NA) microscope objective, and model STED point spread function (PSF) as a function of donut beam profile. We show experimentally that the intensity profile of the dark kernel of the donut can be approximated as a parabolic function, whose slope is determined by the donut beam size before the objective back aperture, or the effective NA. Based on this, we derive the mathematical expression for continuous wave (CW) STED PSF as a function of focal plane donut and excitation beam profiles, as well as dye properties. We find that the effective NA and the residual intensity at the center are critical factors for STED imaging quality and the resolution. The effective NA is critical for STED resolution in that it not only determines the donut shape but also the area the depletion laser power is dispersed. An improperly expanded depletion beam will have negligible improvement in resolution. The polarization of the depletion beam also plays an important role as it affects the residual intensity in the center of the donut. Finally, we construct a CW STED microscope operating at 488 nm excitation and 592 nm depletion with a resolution of 70 nm. Our study provides detailed insight to the property of donut beam, and parameters that are important for the optimal performance of STED microscopes. This paper will provide a useful guide for the construction and future development of STED microscopes.
    The Review of scientific instruments 04/2013; 84(4):043701. · 1.52 Impact Factor
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    ABSTRACT: Fluorescent semiconducting polymer dots (Pdots) have attracted great interest because of their superior characteristics as fluorescent probes, such as high fluorescence brightness, fast radiative rates, and excellent photostability. However, currently available Pdots generally exhibit broad emission spectra, which significantly limit their usefulness in many biological applications involving multiplex detections. Here, we describe the design and development of multicolor narrow emissive Pdots based on different boron dipyrromethene (BODIPY) units. BODIPY-containing semiconducting polymers emitting at multiple wavelengths were synthesized and used as precursors for preparing the Pdots, where intraparticle energy transfer led to highly bright, narrow emissions. The emission full width at half-maximum of the resulting Pdots varies from 40 to 55 nm, which is 1.5-2 times narrower than those of conventional semiconducting polymer dots. BODIPY 520 Pdots were about an order of magnitude brighter than commercial Qdot 525 under identical laser excitation conditions. Fluorescence imaging and flow cytometry experiments indicate that the narrow emissions from these bright Pdots are promising for multiplexed biological detections.
    ACS Nano 01/2013; · 12.03 Impact Factor
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    Wei Sun, Lehui Xiao, Ning Fang
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    ABSTRACT: Optical microscopy is a simple yet robust strategy to study live cellular processes. By changing the wavelength of the illumination light, different non-fluorescent nanoparticle probes can be identified and tracked dynamically inside crowded living cells with either differential interference contrast (DIC) microscopy or planar illumination microscopy (PIM). The translational and rotational dynamics of anisotropic nanoparticles can be readily extracted via the modified DIC microscope and the home-built PIM. In this protocol, the optimization procedures for DIC microscopy and PIM imaging are explained, and the sample preparation procedures to image non-fluorescent nanoparticles in living cells are described.
    Methods in molecular biology (Clifton, N.J.) 01/2013; 931:169-86. · 1.29 Impact Factor
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    ABSTRACT: A full understanding of cell mechanics requires knowledge of both translational and rotational dynamics. The single particle orientation and rotational tracking (SPORT) technique is combined here with correlation analysis to identify the fundamental rotational modes: in-plane rotation and out-of-plane tilting, as well as other more complex rotational patterns, from the vast image data captured at a temporal resolution of 5 ms for single gold nanorod probes in live cell imaging experiments. The unique capabilities of visualizing and understanding rotational motions of functional nanoparticles on live cell membranes allow correlation of the rotational and translational dynamics in unprecedented detail and provide new insights into complex membrane processes. Particles with functionalized surfaces, which interact with the membrane in fundamentally different ways, can exhibit distinct rotational modes and are, for the first time, directly visualized, and these show the early events for membrane approach and attachment.
    Small 11/2012; · 7.82 Impact Factor
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    ABSTRACT: This paper describes a method, based on co-precipitation, for generating small semiconducting polymer dot (Pdot) nanocomposites, which contain either gold or iron oxide nanoparticles within the Pdot matrix. We demonstrate the utility of Pdot-Au nanoparticles (Au-NP-Pdots) in dual-modality imaging in which co-localization of fluorescence from Pdot and scattering from Au was used to identify Au-NP-Pdot probes for downstream single-particle tracking and cellular imaging. We also demonstrate the potential of employing Pdot-FeO(x) nanoparticles (FeO(x)-NP-Pdots) for both sample preparation, where cells tagged with FeO(x)-NP-Pdots were isolated using an external magnet, and cellular imaging and detection, owing to the intense fluorescence from Pdots. The method we present here should be generalizable to the formation of other Pdot nanocomposites for creating the next generation of multi-functional Pdot probes.
    Nanoscale 10/2012; · 6.73 Impact Factor
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    ABSTRACT: Semiconducting polymer dots (Pdots) recently have emerged as a new class of ultrabright fluorescent probes with promising applications in biological detection and imaging. We developed photoswitchable Pdots by conjugating photochromic spiropyran molecules onto poly[9,9-dioctylfluorenyl-2,7-diyl)-co-1,4-benzo-{2,1'-3}-thiadiazole)] (PFBT). The modulation of fluorescence was achieved by ultraviolet irradiation, which converted spiropyran into its visible-absorbing merocyanine form. The merocyanine efficiently quenched the fluorescence of PFBT via Förster resonance energy transfer (FRET). We then reversed the quenching by subsequent irradiation with visible light to get back the fluorescence of PFBT. This FRET-based photomodulation of Pdot fluorescence could be repeated multiple times. We next conjugated biomolecules onto the surface of these photoswitchable Pdots and demonstrated their specific cellular and subcellular labeling to different types of cells without any noticeable nonspecific binding. We anticipate these photoswitchable and biocompatible Pdots will be useful in developing bioimaging techniques in the future.
    Analytical Chemistry 10/2012; · 5.82 Impact Factor
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    ABSTRACT: Direct visualization of axonal transport in live neurons is essential for our understanding of the neuronal functions and the working mechanisms of microtubule-based motor proteins. Here we use the high-speed single particle orientation and rotational tracking technique to directly visualize the rotational dynamics of cargos in both active directional transport and pausing stages of axonal transport, with a temporal resolution of 2 ms. Both long and short pauses are imaged, and the correlations between the pause duration, the rotational behaviour of the cargo at the pause, and the moving direction after the pause are established. Furthermore, the rotational dynamics leading to switching tracks are visualized in detail. These first-time observations of cargo's rotational dynamics provide new insights on how kinesin and dynein motors take the cargo through the alternating stages of active directional transport and pause.
    Nature Communications 08/2012; 3:1030. · 10.74 Impact Factor
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    ABSTRACT: A facile cross-linking strategy covalently links functional molecules to semiconducting polymer dots (Pdots) while simultaneously providing functional groups for biomolecular conjugation. In addition to greatly enhanced stability, the formed Pdots are small (<10 nm), which can be difficult to achieve with current methods but is highly desirable for most biological applications. These characteristics are significant for improving labeling efficiency and sensitivity in cellular assays that employ Pdots.
    Advanced Materials 06/2012; 24(26):3498-504. · 14.83 Impact Factor
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    ABSTRACT: Novel non-blinking quantum dots (NBQDs) were utilized in three-dimensional super-localization, high-precision tracking applications under an automated scanning-angle total internal reflection fluorescence microscope (SA-TIRFM). NBQDs were randomly attached to stationary microtubules along the radial axis under gliding assay conditions. By automatically scanning through a wide range of incident angles with different evanescent-field layer thicknesses, the fluorescence intensity decay curves were obtained. Fit with theoretical decay functions, the absolute vertical positions were determined with sub-10-nm localization precision. The emission intensity profile of the NBQDs attached to kinesin-propelled microtubules was used to resolve the self-rotation of gliding microtubules within a small vertical distance of ~50 nm. We demonstrate the applicability of NBQDs in high-precision fluorescence imaging experiments.
    Journal of the American Chemical Society 04/2012; 134(14):6108-11. · 10.68 Impact Factor
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    ABSTRACT: We introduce a precise three-dimensional (3D) localization method of spherical gold nanoparticle probes using model-based correlation coefficient mapping. To accomplish this, a stack of sample images at different z-positions are acquired, and a 3D intensity profile of the probe serving as the model is used to map out the positions of nanoparticles in the sample. By using this model-based correlation imaging method, precise localization can be achieved in imaging techniques with complicated point spread functions (PSF) such as differential interference contrast (DIC) microscopy. We demonstrated the localization precision of 4-7 nm laterally and 16 nm axially for 40-nm gold nanospheres at an imaging rate of 10 frames per second. The 3D superlocalization method was applied to tracking gold nanospheres during live endocytosis events.
    Analytical Chemistry 04/2012; 84(9):4111-7. · 5.82 Impact Factor
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    ABSTRACT: We demonstrate a new compact CN-PPV dot, which emits in the orange wavelength range with high brightness. The small particle size, high brightness, and the ability to highly specifically target subcellular structures make the CN-PPV dots promising probes for biological imaging and bioanalytical applications.
    Chemical Communications 01/2012; 48(12):1778-80. · 6.38 Impact Factor
  • Biophysical Journal 01/2012; 102(3):38-. · 3.67 Impact Factor
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    ABSTRACT: Single-particle rotational tracking is of great importance to monitor orientation changes of biomolecules and to understand their functions and mechanisms in biological systems. Differential interference contrast (DIC) microscopy has been found to be an excellent tool to measure polarization anisotropy for tracking rotational dynamics of gold nanorod (AuNR) probes. DIC polarization anisotropy can be conveniently obtained from the bright and dark intensities of a single DIC image of an AuNR. Here, DIC microscopy-based dual-wavelength detection of rotational motions of AuNRs at both transverse and longitudinal surface plasmon resonance (SPR) wavelengths is demonstrated. The transverse SPR mode was successfully used to track fast rotational dynamics of individual AuNRs on live cell membranes. This is important since the transverse SPR mode is mostly insensitive to the medium refractive index, AuNR aspect ratio, and adsorption of biomolecules. DIC polarization anisotropy was simultaneously obtained from the two SPR wavelengths during the dynamic process. Both wavelengths showed good agreement and provided accurate and reliable measurement of AuNR orientation.
    The Journal of Physical Chemistry C 01/2012; 116:2766-2771. · 4.84 Impact Factor

Publication Stats

217 Citations
231.95 Total Impact Points


  • 2012–2013
    • University of Washington Seattle
      • Department of Chemistry
      Seattle, WA, United States
  • 2008–2013
    • Iowa State University
      • • Ames Laboratory
      • • Department of Chemistry
      Ames, IA, United States
  • 2010–2012
    • U.S. Department of Energy
      • Ames Lab
      Washington, Washington, D.C., United States