EMSL: Dehong Hu's Publications

Lei C, D Hu, and EJ Ackerman. 2009. "Clay Nanoparticle-Supported Single-Molecule Fluorescence Spectroelectrochemistry." Nano Letters 9(2):655-658. Abstract We report single-molecule fluorescence spectroelectrochemistry on a clay-modified ITO electrode using cresyl violet as a redox fluorescent probe. Ensemble averaged experiments show that cresyl violet displays well-defined cyclic voltammograms when adsorbed on the clay-modified electrode. By probing the fluorescence intensity of a single cresyl violet molecule absorbed on clay surface, we can trace the redox reaction of individual molecules induced by the cyclic voltammetric potential scanning. Inhomogeneous interfacial electron transfer dynamics of the immobilized single cresyl violet molecules on the clay-modified surface were observed.

Wang D, D Choi, J Li, Z Yang, Z Nie, R Kou, D Hu, CM Wang, LV Saraf, J Zhang, IA Aksay, and J Liu. 2009. "Self-assembled TiO2-Graphene Hybrid Nanostructures for Enhanced Li-ion Insertion ." ACS Nano 3(4):907-914. Abstract We used anionic sulfate surfactants to assist the stabilization of graphene in aqueous solutions and facilitate the self-assembly of in-situ grown nanocrystalline TiO2, rutile and anatase, with graphene. These nanostructured TiO2-graphene hybrid materials were used for investigation of Li-ion insertion properties. The hybrid materials showed significantly enhanced Li-ion insertion/extraction in TiO2. The specific capacity was more than doubled at high charge rates, as compared with the pure TiO2 phase. The improved capacity at high charge-discharge rate may be attributed to increased electrode conductivity in presence of a percolated graphene network embedded into the metal oxide electrodes.

Hu D, Z Tian, W Wu, W Wan, and AD Li. 2008. "Photoswitchable Nanoparticles Enable High-Resolution Cell Imaging: PULSAR Microscopy." Journal of the American Chemical Society 130(46):15279-15281. doi:10.1021/ja805948u Abstract Fluorescence imaging has transformed biological sciences and opened a window to reveal biological mechanisms in real time despite Abbe’s diffraction limit restricts current microscope resolution to 300 nm?.HDH2 Recently, two high-resolution fluorescence microscopic techniques emerged: one uses a special photoactivatable green fluorescent proteinHDH3 and the other employs a pair of cy3/cy5 dyes.HDH4 Both avoid Abbe’s diffraction limit by photoswitching nearby fluorophores off. Thus, photoswitching fluorescence between a bright and a dark state promises to deliver a wealth of information regarding biological phenomena at the nanoscale. The ideal probe is a key-enabling single molecule that can be photoswitched on and off. Such wonderful properties, albeit implausible to imagine at first, were realized in spiropyran derivatives. While being photoswitched, one molecule alternates red-fluorescence on-and-off. Using such photo-actuated unimolecular logical switching attained reconstruction (PULSAR) microscopy, we achieved high-resolution fluorescence imaging down to 80 nm? in nanostructures and cellular organelles.

Lei C, D Hu, and EJ Ackerman. 2008. "Single-molecule Fluorescence Spectroelectrochemistry of Cresyl Violet." Chemical Communications (43):5490-5492. doi:10.1039/b812161c Abstract We coupled scanning fluorescence microscopy with a potentiostat via a three-electrode electrochemical cell to enable single-molecule fluorescence spectroelectrochemistry of cresyl violet in aqueous solution, where the single-molecule fluorescence intensity of cresyl violet is modulated synchronously with the cyclic voltammetric potential scanning.

Li G, D Hu, GG Xia, JM White, and ZC Zhang. 2008. "High Throughput Operando Studies using Fourier Transform Infrared Imaging and Raman Spectroscopy." Review of Scientific Instruments 79:074101. doi:10.1063/1.2949389 Abstract A prototype operando high throughput (OHT) reactor designed and built for catalyst screening and characterization combines Fourier transform infrared (FT-IR) imaging and Raman spectroscopy in operando conditions. Using a focal plane array (FPA) detector (HgCdTe FPA, 128×128 pixels, and 1,610 Hz frame rate) for the FT-IR imaging system, the catalyst activity and selectivity of all parallel reaction channels can be simultaneously followed. Each image dataset possesses16,384 IR spectra with a spectral range of 800 to 4000 cm-1 with an 8 cm-1 resolution. Depending on the signal-to-noise ratio, 2 to 20 seconds are needed to generate a full image of all reaction channels from a dataset. Results on reactant conversion and product selectivity are obtained from FT-IR spectral analysis. Six novel Raman probes, one for each reaction channel, were specially designed and house built at Pacific Northwest National Laboratory (PNNL), to simultaneously collect Raman spectra of the catalysts and possible reaction intermediates on the catalyst surface under operando conditions. As a model system, methanol partial oxidation reaction on silica-supported molybdenum oxide (MoO3/SiO2) catalysts has been studied under different reaction conditions to demonstrate the performance of the OHT reactor.

Orr G, DJ Panther, JL Phillips, BJ Tarasevich, A Dohnalkova, D Hu, JG Teeguarden, and JG Pounds. 2007. "Submicron and Nanoscale Inorganic Particles Exploit the Actin Machinery to be Propelled Along Microvillilike Structures into Alveolar Cells." ACS Nano 1(5):463-475. doi:10.1021/nn700149r Abstract The growing commerce in micro- and nanotechnology is expected to increase our exposure to submicron and nanoscale particles. One of the main targets of this exposure are the cells that line the respiratory tract, among them are the alveolar type II epithelial cells that have microvilli at their exposed apical surface. Here we show a pathway by which positively charged inorganic submicron and nanoscale particles take advantage of the actin turnover machinery within filopodia and microvilli-like structures to guide and advance their way into these cells. Our observations bring a new view of how submicron and nanoscale inorganic matter can be assimilated into the cellular environment and take advantage of its machinery. While the pathway that we describe can be exploited for a targeted drug delivery, it also points to properties of submicron or nanoscale particles that should be avoided in order to reduce particle internalization and possible toxicity.

Pan D, D Hu, R Liu, X Zeng, S Kaplan, and HP Lu. 2007. "Fluctuating Two-State Light Harvesting in a Photosynthetic Membrane." Journal of Physical Chemistry C 111(25):8948-8956. doi:10.1021/jp071493y Abstract How light is converted into chemical energy in a natural photosynthetic system is of great interest in energy sciences. Using single-molecule and single-vesicle fluorescence spectroscopy and imaging, we have observed fluctuating inter-molecular protein energy transfers in the photosynthetic membranes of R. sphaeroides. Our results suggest that there are dynamic coupled and non-coupled states in the light-harvesting protein assembly.

Liu R, D Hu, X Tan, and HP Lu. 2006. "Revealing Two-State Protein-Protein Interaction of Calmodulin by Single-Molecule Spectroscopy." Journal of the American Chemical Society 128(31):10034-10042. Abstract We report a single-molecule fluorescence resonance energy transfer (FRET) and polarization study of conformational dynamics of calmodulin (CaM) interacting with a target peptide, C28W of 28 amino-acid oligomer. The C28W peptide represents the essential binding sequence domain of the Ca-ATPase protein interacting with CaM, which is important in cellular signaling for the regulation of energy in metabolism. However, the mechanism of the CaM-C28W recognition complex formation is still unclear. The amino-terminal (N-terminal) domain of the CaM was labeled with a fluorescein-based arsenical hairpin binder (F1AsH) that enables our unambiguously probing the CaM N-terminal target-binding domain motions at a millisecond timescale without convolution of the probe-dye random motions. By analyzing the distribution of FRET efficiency between F1AsH labeled CaM and Texas Red labeled C28W and the polarization fluctuation dynamics and distributions of the CaM N-terminal domain, we reveal slow (at sub-second time scale) binding-unbinding motions of the N-terminal domain of the CaM in CaM-C28W complexes, which is a strong evidence of a two-state binding interaction of CaM-mediated cell signaling.

Pan D, NA Klymyshyn, D Hu, and HP Lu. 2006. "Tip-Enhanced Near-Field Raman Spectroscopy Probing Single Dye-Sensitized TiO2 Nanoparticles." Applied Physics Letters 88(9):Art. No. 093121. Abstract The correlated metallic tip-enhanced Raman spectroscopy and atomic force microscopy (AFM) technique was used to characterize an interfacial electron transfer system of dye-sensitized titanium oxide (TiO2) nanoparticles. We have obtained the near-field Raman spectra that are associated with the photo-induced charge transfer reaction in Ru(4, 4’-dicarboxy-2,2’-bipyridine)2(NCS)2- sensitized TiO2 single nanoparticles. This method demonstrates that tip-enhanced near-field Raman spectroscopy is an effective approach for probing in homogeneous interfacial electron transfers with nanoscale spatial resolution.

Hu D, and HP Lu. 2005. "Single-Molecule Triplet-State Photon Antibunching at Room Temperature." Journal of Physical Chemistry B 109(20):9861-9864. Abstract We have demonstrated probing single-molecule metal-to-ligand charge transfer (MLCT) dynamics at room temperature. Using photon antibunching measurements under CW laser excitation, non-classical photon statistics, and excitation power dependent measurements, we were able to selectively measure the single-molecule MLTC state lifetime. This work demonstrated the first single-molecule photon antibunching of triplet excited state and presents a step forward in studying single-molecule electron transfer in proteins using MLTC complex as an electron transfer donor or acceptor.