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Dejian Zhou

Publications and source records attributed to Dejian Zhou.

18 recordsLinked to original sources
PubMed2006

Evidence for resonance optical trapping of individual fluorophore-labeled antibodies using single molecule fluorescence spectroscopy.

We report single molecule fluorescence studies of the diffusion of individual multiple fluorophore-labeled antibodies in solution, which show that a trapping potential of about 3.6 k(B)T can be obtained at laser powers below 1 mW with resonant excitation. Individual antibodies can be trapped for up to 140 ms, and bound antibodies can also be used to trap a single virion for up to 1 s. Selective resonance trapping to sort and manipulate fluorophore-labeled biomolecules and complexes may be possible.

Antibodies↗
PubMed2006

A reversible pH-driven DNA nanoswitch array.

An array of surface-immobilized proton-fueled DNA nanomachines is reversibly actuated by cycling of the solution pH between 4.5 and 9, producing a conformational change between a four-stranded and a double-stranded structure, which elongates or shortens the separation distance between the 5' and 3' end of the DNA. By labeling the DNA 3' end with a fluorophore and immobilizing it onto a thin-gold surface through its 5' thiol modification, the nanoscale motion of the DNA produces mechanical work to lift up and bring down the fluorophore from the gold surface by at least 2.5 nm and transduces this motion into an optical "on-and-off" nanoswitch.

DNA↗
PubMed2006

Electrostatic orientation of enzymes on surfaces for ligand screening probed by force spectroscopy.

In this letter, we show that electrostatic immobilization provides a simple but effective approach for the immobilization and orientation of carbonic anhydrase onto charged surfaces. The enzyme is oriented differently on oppositely charged surfaces, with the majority of active sites facing upward on a positively charged surface and downward on a negatively charged surface. An array of negatively charged microscale surface patterns within a positively charged background was prepared by microcontact printing and used as the substrate to immobilize the enzymes. This enabled the probing of the enzyme orientations on the two differently charged surface regions by force spectroscopy with the same atomic force microscopy (AFM) probe modified with a thiolated sulfonamide inhibitor. The unbinding forces between the inhibitor tip and the enzyme immobilized on the two differently charged surfaces were measured. Two control experiments, blocking of the enzyme active site with a competitive inhibitor and removal of the zinc ion from the enzyme catalytic center, were employed to distinguish between specific and nonspecific interactions and to further verify the differences in enzyme orientation. Autocorrelation analysis of the force histograms was carried out to evaluate the specific single enzyme-inhibitor interaction force.

Animals↗
PubMed2006

Macroscopic 2D networks self-assembled from nanometer-sized protein/DNA complexes.

We demonstrate the self-assembly of DNA and DNA binding proteins into two-dimensional networks that are then addressable by sending a second protein to a specific recognition site on the DNA network. These networks cover centimeters in area but can be addressed with nanometer precision. This hierarchical self-assembly of specific DNA protein complexes will be the basis for complex positioning of single molecules in two and three dimensions.

Base Sequence↗
PubMed2006

Nanoscale pipetting for controlled chemistry in small arrayed water droplets using a double-barrel pipet.

We present a new methodology which provides for the miniaturization of one of the most common tools in use in chemistry and biology laboratories today-the micropipet. We have used glass-fabricated double-barrel nanopipets to controllably produce arrayed water droplets with volumes as small as a few attoliters under an organic layer. We have addressed individual droplets and added controlled amounts of either additional volume or reagents from one of the barrels of the pipet. We demonstrate that this method can be used for miniaturized cell-free protein expression.

Chemical Phenomena↗
PubMed2005

The scanned nanopipette: a new tool for high resolution bioimaging and controlled deposition of biomolecules.

The boundary between the physical and biological sciences has been eroded in recent years with new physical methods applied to biology and biological molecules being used for new physical purposes. We have pioneered the application of a form of scanning probe microscopy based on a scanned nanopipette, originally developed by Hansma and co-workers, for reliable non-contact imaging over the surface of a live cell. We have found that the nanopipette can also be used for controlled local voltage-driven application of reagents or biomolecules and this can be used for controlled deposition and the local delivery of probes for mapping of specific species. In this article we review this progress, focussing on the physical principles and new phenomena that we have observed, and then outline the future applications that are now possible.

Aniline Compounds↗
PubMed2004

Influence of the foundation layer on the layer-by-layer assembly of poly-L-lysine and poly(styrenesulfonate) and its usage in the fabrication of 3D microscale features.

The layer-by-layer (LBL) assembly of a polypeptide, poly-L-lysine (PLL), with poly(styrenesulfonate) sodium salt (PSS) on flat template-stripped gold (TSG) surfaces precoated with a self-assembled monolayer of alkanethiols terminated with positive (pyridinium), negative (carboxylic acid), and neutral [hexa(ethylene glycol)] groups is investigated. Both the topography and the rate of film thickness growth are found to be strongly dependent on the initial surface foundation layer. LBL assembly of PLL and PSS on patterned TSG surfaces produced by micro contact printing leads to structurally distinct microscale features, including pillars, ridges, and wells, whose height can be controlled with nanometer precision.

Membranes, Artificial↗
PubMed2004

Molecule by molecule direct and quantitative counting of antibody-protein complexes in solution.

We have used two-color fluorescence coincidence detection to directly count individual protein-antibody complexes of protein G or herpes simplex virus labeled with one or more red- and blue-excited antibodies. This allowed quantitative measurement of the concentration of the protein-antibody complexes over 3 orders of magnitude down to the femtomolar level. Single molecule measurements in diluted serum are also possible. The sample preparation is simple, takes place in solution, and requires no separation. Both the antibody affinity and complex dissociation rate are important in determining the sensitivity of the method. At present, the sensitivity limit of 50 fM is determined by the encounter rate of the labeled analyte with the probe volume. This method can be used to detect and quantitate proteins and to measure the stoichiometry, equilibrium constant, and dissociation rate of protein-protein complexes at low concentrations.

Animals↗
PubMed2004

An addressable antibody nanoarray produced on a nanostructured surface.

The ability to address specific nanoscale features is required to produce diverse biological nanoarrays or perform local assembly using biological building blocks and is an important unsolved problem in nanotechnology. In this work, we describe the use of a novel nanofabricated gold surface, with regions of distinct topography and chemical functionalities, to solve this problem. First, nanoarrays of IgG antibodies were produced by selective immobilization in nanoholes on the surface. The smallest feature size was determined by the hole size (fwhm 90 nm) and not surface diffusion. Using holes of 300 nm diameter, we selectively addressed specific features in the array by nanopipet delivery of a functional antibody, anti-IgG. To our knowledge, this is the first example of addressing specific biologically functional features on a surface at the nanoscale.

3-Mercaptopropionic Acid↗
PubMed2003

Multicomponent submicron features of biomolecules created by voltage controlled deposition from a nanopipet.

We have used a nanopipet as a nanopen to locally and controllably deposit complex biomolecules, including antibodies and DNA, onto a surface to create multicomponent and functional submicron features. Key advantages of this method are that the biomolecules are always in solution and the applied voltage provides fine control of the delivery down to the single molecule level. Two consecutive cycles of deposition, to produce spatially varying features with different biological properties, were demonstrated with fluorescently labeled antibodies or biotin. This approach combines "top-down" fabrication, using the nanopen for local application, and "bottom-up" fabrication, using molecular recognition for self-assembly at defined positions, and opens up new possibilities in nanotechnology.

Animals↗
PubMed2003

Systematic manipulation of surface chemical reaction on the nanoscale: a novel approach for constructing three-dimensional nanostructures.

Nanoscale patches, created by nanografting a maleimide-terminated thiol into a self-assembled monolayer, were elaborated by sequential chemical reactions. Each stage in the nanofabrication was followed by atomic force microscopy (AFM), providing a controlled approach to the fabrication of novel three-dimensional (3D) surface nanostructures.

Journal Article↗
PubMed2002

Writing with DNA and protein using a nanopipet for controlled delivery.

We present a new, general method for the controlled deposition of biological molecules on surfaces, based on a nanopipet operating in ionic solution. The potential applied to the pipet tip controls the flux of biological molecules from the pipet, allowing fine control of the delivery rate. We used the ion current to control the distance of the pipet from the surface of a glass slide and deposited the fluorescently labeled DNA or protein G at a defined location onto the surface. Features of 830 nm size were obtained by depositing the biotinylated DNA onto a streptavidin surface; 1.3 mum size spots were obtained by depositing protein G onto a positively charged glass surface.

DNA, Single-Stranded↗