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ABSTRACT: We report a one-pot, two-step strategy to synthesize fluorescent gold nanodots (AuNDs) co-modified with 1-(10-mercaptodecyl)-5-methylpyrimidine-2,4-dione (TSH) and 11-mercaptoundecanoic acid (MUA) through a ligand exchange reaction and demonstrate their capability of selective sulfide sensing in aqueous media on the basis of fluorescence recovery.
Nanoscale 04/2013; · 5.91 Impact Factor
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ABSTRACT: Hydrogen sulphide (H2S) is a gaseous signalling agent that has important regulatory roles in many biological systems but remains difficult to measure in living biological specimens. Here we introduce a new method for highly sensitive sulphide mapping in live cells via single-particle plasmonic spectral imaging that uses Au-Ag core-shell nanoparticles as probes. This strategy is based on Ag2S formation-induced spectral shifts of the nanoprobes, which is not only highly selective towards sulphide but also shows a linear logarithmic dependence on sulphide concentrations from 0.01 nM to 10 μM. A theoretical model was established that successfully explained the experimental observations, suggesting that the local sulphide concentration as well as its oscillations can be determined indirectly from kinetic measurements of the spectral shifts of the nanoprobes. We demonstrated for the first time the real-time mapping of local variations of sulphide levels in live cells with nM sensitivity.
Nature Communications 04/2013; 4:1708. · 7.40 Impact Factor
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ABSTRACT: With time-resolved high precision single particle tracking methodologies, we explored the adsorption and thermal motion of TAT peptide-modified nanocargo on a model lipid bilayer in the non-electrostatic domain. We found that the lateral and rotational motion of the TAT peptide-modified nanocargo could be effectively suppressed on the surface of neutral lipid membrane, a feature that cannot be explained by existing hypotheses. A semi-quantitative association activation energy analysis revealed that multiple weak bonds were required for the initial adsorption process. As a result, the localized multiple TAT peptides on the surface of the nanocargo can provide a pathway for the creation of a net of peptide-lipid complexes (lipid domain). The dragging forces caused by these complexes effectively confined the thermal motion of the nanocargo on the fluid membrane that cannot be achieved by individual peptides with random spatial and conformational distributions. These interesting findings could provide insightful information for the better understanding of the intracellular internalization mechanism of TAT peptide-modified nanocargo and might shed new light on the development of highly efficient intracellular carriers for site-specific delivery of drugs and genes.
Analytical Chemistry 04/2013; · 5.86 Impact Factor
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ABSTRACT: The enhancement of electromagnetic field on the rough metallic nanostructure has been extensively applied to obtain chemical or biological information about molecules with high sensitivity, and has received much attention due to its potential applications in new types of devices based on nanoelectronics and nanophotonics. The typical size of the field enhancement area, the so-called hotspot, is approximately one order of magnitude smaller than the optical diffraction limit. In the present study, an optical super-resolution microscopic and spectroscopic approach is introduced to explore single-molecule fluorescence within an engineered hotspot where nonhomogeneous spectral modulation is resolved beyond the optical diffraction limit for the first time. Distinct Stokes shifts from individual dyes were directly observed within single hotspots, which were found to be independent of the local electromagnetic field strength. The method reported here provides a robust tool to probe the optical properties of nanoresonantors with high temporal and spatial resolution.
Analytical Chemistry 03/2013; · 5.86 Impact Factor
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ABSTRACT: Core-shell quantum dots suffer from photobleaching by light at wavelengths longer than their emission wavelengths. That is, QD photobleaching can be triggered by photons with low energies that are insufficient to pump electrons into the conduction band. The most probable reason is that electrons are pumped into a surface state and then nonradiatively decayed as in conventional photobleaching.
Physical Chemistry Chemical Physics 01/2013; · 3.57 Impact Factor
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ABSTRACT: A hydrated gel-like pericellular matrix (PCM) covers the surface of all eukaryotic cells and plays a key role in many cellular events, but its effect on nanoparticle internalization has not been studied. Here, using cells with various PCM thicknesses and gold nanoparticles as probes, we demonstrate that, rather than being a barrier to all foreign objects, the PCM can entrap and accumulate NPs, restrict and slow down their diffusion, and enhance their cellular uptake efficiency. Moreover, this newly discovered PCM function consumes energy and seems to be an integral part of the receptor-mediated endocytosis process. These findings are important in understanding the delivery mechanisms of nanocarriers for biomedical applications.
Journal of the American Chemical Society 08/2012; 134(32):13404-9. · 9.91 Impact Factor
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ABSTRACT: We discuss and illustrate recent advances that have been made to image the distribution of metabolites among cells and tissues of plants using different mass spectrometry technologies. These technologies include matrix-assisted laser desorption ionization, desorption electrospray ionization, and secondary ion mass spectrometry. These are relatively new technological applications of mass spectrometry and they are providing highly spatially resolved data concerning the cellular distribution of metabolites. We discuss the advantages and limitations of each of these mass spectrometric methods, and provide a description of the technical barriers that are currently limiting the technology to the level of single-cell resolution. However, we anticipate that advances in the next few years will increase the resolving power of the technology to provide unprecedented data on the distribution of metabolites at the subcellular level, which will increase our ability to decipher new knowledge concerning the spatial organization of metabolic processes in plants.
The Plant Journal 04/2012; 70(1):81-95. · 6.16 Impact Factor
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ABSTRACT: Diffusion of single protein molecules inside gold nanotubes was investigated. 3-dimensional imaging was employed to locate the individual molecules inside the nanotubes as a function of time. As expected, larger proteins and smaller pore sizes resulted in smaller diffusion coefficients. Diffusion within PEG-coated gold nanotubes was found to be two orders of magnitude faster than in previously reported, similar sized untreated polycarbonate membrane pores, showing that adsorption was serious in the latter case. We further demonstrate chromatographic selectivity during transport by modifying the inner surface of the gold nanotubes with self-assembled monolayers of derivatized alkyl thiols. These results should be useful for designing membrane separations.
Journal of chromatography. A 03/2012; 1238:11-4. · 4.19 Impact Factor
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ABSTRACT: Track changes: A robust high-speed and high-precision single nanoparticle translational and rotational tracking method has been developed to directly monitor the interactions between transferrin-modified nanocargos (gold nanorods) and the membrane proteins prior to endocytosis. This approach shows that the translational and rotational diffusions of nanocargos on living cell membranes are unsynchronized in space and in time.
Angewandte Chemie International Edition 03/2012; 51(17):4181-4. · 13.45 Impact Factor
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ABSTRACT: We developed a novel method for counting single gold nanoparticles in free solution with flash-lamp darkfield microscopy and demonstrated that it could be applied to highly sensitive DNA hybridization detection based on target DNA induced AuNP aggregation and counts reduction.
The Analyst 02/2012; 137(13):2930-2. · 4.23 Impact Factor
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ABSTRACT: The key factor of realizing super-resolution optical microscopy at the single-molecule level is to separately position two adjacent molecules. An opportunity to independently localize target molecules is provided by the intermittency (blinking) in fluorescence of a quantum dot (QD) under the condition that the blinking of each emitter can be recorded and identified. Herein we develop a spectral imaging based color nanoscopy which is capable of determining which QD is blinking in the multicolor QD complex through tracking the first-order spectrum, and thus, the distance at tens of nanometers between two QDs is measured. Three complementary oligonucleotides with lengths of 15, 30, and 45 bp are constructed as calibration rulers. QD585 and QD655 are each linked at one end. The measured average distances are in good agreement with the calculated lengths with a precision of 6 nm, and the intracellular dual-color QDs within a diffraction-limited spot are distinguished.
Analytical Chemistry 02/2012; 84(3):1504-9. · 5.86 Impact Factor
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ABSTRACT: We have developed a new methodology for miRNA assay using chemiluminescence imaging by poly(U) polymerase catalyzed miRNA polymerization. This method is very sensitive with a 50 fM limit of detection, which is comparable to or better than current assay methods. Multiplex detection for miRNA can be easily realized by introducing different capture probes onto the biosensor array, which will make it highly versatile for various research purposes.
Analytical and Bioanalytical Chemistry 12/2011; 402(6):2217-20. · 3.78 Impact Factor
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ABSTRACT: The real-time digestion of entrapped single-DNA molecules by λ-exonuclease in nanoporous alumina membranes was observed using an epifluorescence microscope. The alumina membrane provides pL (∼ 10(-12)L) containers for confining single-DNA molecules without immobilization. When one end of the DNA molecule was inserted into a nanopore, it was possible to monitor the digestion process outside, near and inside the pore, where the individual DNA molecules exhibited different characteristic digestion modes. The digestion rates calculated from the decrease in fluorescence intensity showed different values according to the location of the individual molecules. Entrapment rather than immobilization allows the DNA strand to be fully exposed to the enzyme and the reaction buffer. These results confirm that the enzymatic digestion of DNA molecules is affected by their three-dimensional (3D) environment.
Talanta 09/2011; 85(4):2135-41. · 3.79 Impact Factor
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ABSTRACT: We developed a novel strategy to prepare functionalized fluorescent gold nanodots (AuNDs) based on a ligand exchange reaction and demonstrated that glutathione modified AuNDs can be utilized for highly sensitive and selective Pb(2+) sensing in aqueous solution.
Chemical Communications 09/2011; 47(43):11981-3. · 6.17 Impact Factor
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ABSTRACT: Herein, we demonstrated a new optical microscopy method to selectively image small-size gold nanoparticles (GNPs) inside noisy living cells through determination of the difference image between the probe beam (illuminated at the resonance wavelength of GNPs, 532 nm) and the reference beam (illuminated at 473 nm). From computer simulation and single-particle imaging experiments, we demonstrated that GNPs with a diameter of 45 nm could be selectively imaged in the GNPs/cell lysates mixture and inside living cells by dual-wavelength difference (DWD) imaging. The diffusion dynamics of nucleic acids functionalized GNPs on cell membranes and the internalization kinetics of these GNPs by living cells were explored with this method. Our real-time tracking experiments showed that statistically 80% of GNPs were under restricted diffusion on the cell membrane. The cell cytoskeleton fence effect, as observed in the single-particle tracking experiments, may be one of the main factors for the restricted diffusion mode.
Analytical Chemistry 09/2011; 83(19):7340-7. · 5.86 Impact Factor
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ABSTRACT: The experimental conditions necessary for the synthesis of well-defined nanoparticles are often difficult to control. There is thus a compelling need for post-synthesis separation of nanoparticles polydispersed in size and shape. We demonstrate here both theoretically and experimentally that gold nanorods with diverse aspect ratios can be separated using density gradient centrifugation. By analysing the force balance of a Brownian rod falling in a Stokes flow, we derive a rigorous and predictive model that reveals the quantitative dependency of the nanorod sedimentation rates on their mass and shape. The calculations show that while mass dependency is still the dominating factor during centrifugation, the shape factor is not insignificant. Relatively heavier but long and thin rods could sediment slower than certain size of lighter spheres, and some rods and spheres with different masses and shapes may never be separated. This mass and shape dependency is exploited to separate as-prepared gold nanorod colloids by sucrose gradient centrifugation. Two layers of nanorods with narrow aspect-ratio distributions are obtained.
Journal of chromatography. A 06/2011; 1218(25):3823-9. · 4.19 Impact Factor
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ABSTRACT: Here we demonstrated a simple yet powerful method, planar illumination microscopy, to directly track the rotational and translational diffusion dynamics of individual anisotropic nanoparticles in solution and living cells. By illuminating gold nanorods (GNRs) with two orthogonal sheets of light and resolving the polarized scattering signal with a birefringent crystal, we readily achieved three-dimensional angular resolving capability for single GNRs in noisy surroundings. The rotational dynamics of individual GNRs dispersed in glycerol/water mixtures with different chemical modification were tracked, and the measured rotational diffusion coefficient was well fitted to a previously reported theoretical model (Torre, J. G. d. l.; Martinez, M. C. L. Macromolecules 1987, 20, 661-666; Tirado, M. M.; Torre, J. G. d. l. J. Chem. Phys. 1980, 73, 1986-1993). In addition, the translational and rotational movements of individual GNRs transported by kinesin motor protein on microtubules inside living cells were directly imaged. Compared to its motion in free solution, a GNR attached to motor-protein did not rotate significantly while moving forward. Our method can be further generalized to allow determination of three-dimensional orientation of single dipoles using many different illumination modes.
Journal of the American Chemical Society 06/2011; 133(27):10638-45. · 9.91 Impact Factor
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ABSTRACT: Optical detection continues to dominate detection methods in microfluidics due to its noninvasive nature, easy coupling, rapid response, and high sensitivity. In this review, we summarize two aspects of recent developments in optical detection methods on microfluidic chips. The first aspect is free-space (off-chip) detection on the microchip, in which the conventional absorption, fluorescence, chemiluminescence, surface plasmon resonance, and surface enhanced Raman spectroscopies are involved. The second aspect is the optofluidic (inside-chip) detection. Various miniaturized optical components integrated on the microfluidic chip, such as waveguide, microlens, laser, and detectors are outlined.
Topics in current chemistry 04/2011; 304:171-201. · 4.29 Impact Factor
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ABSTRACT: A cold-welding strategy is proposed to rapidly join together Au nanoparticles (AuNPs) into two-dimensional continuous structures for enhancing the electrooxidation of carbon monoxide by injecting a mixture of ethanol and tolulene into the bottom of a AuNP solution.
Chemical Communications 03/2011; 47(15):4481-3. · 6.17 Impact Factor
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Edward S Yeung
Angewandte Chemie International Edition 01/2011; 50(3):583-5. · 13.45 Impact Factor
