Comment on "trapping single molecules by dielectrophoresis".
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Comment↗
Biomedical subjects
Andreas Bruckbauer
Publications and source records attributed to Andreas Bruckbauer.
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↗
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↗
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↗
Two-component graded deposition of biomolecules with a double-barreled nanopipette.
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Nanostructures↗
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↗
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↗
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↗
Frequency and voltage dependence of the dielectrophoretic trapping of short lengths of DNA and dCTP in a nanopipette.
The study of the properties of DNA under high electric fields is of both fundamental and practical interest. We have exploited the high electric fields produced locally in the tip of a nanopipette to probe the motion of double- and single-stranded 40-mer DNA, a 1-kb single-stranded DNA, and a single-nucleotide triphosphate (dCTP) just inside and outside the pipette tip at different frequencies and amplitudes of applied voltages. We used dual laser excitation and dual color detection to simultaneously follow two fluorophore-labeled DNA sequences with millisecond time resolution, significantly faster than studies to date. A strong trapping effect was observed during the negative half cycle for all DNA samples and also the dCTP. This effect was maximum below 1 Hz and decreased with higher frequency. We assign this trapping to strong dielectrophoresis due to the high electric field and electric field gradient in the pipette tip. Dielectrophoresis in electrodeless tapered nanostructures has potential applications for controlled mixing and manipulation of short lengths of DNA and other biomolecules, opening new possibilities in miniaturized biological analysis.
DNA↗
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↗
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↗
Characterization of a novel light source for simultaneous optical and scanning ion conductance microscopy.
We have developed a novel light source suitable for imaging of biological samples. The method is based on the use of a micropipet filled with fluo-3. A fluorogenic complex is formed when fluo-3 meets calcium in the bath solution. The complex is excited by focusing a laser beam at the pipet tip to produce a submicrometer light source. This source is continually renewed at the tip, eliminating problems with photobleaching, and can be controlled by varying the applied potential. We first characterized the light source using fluorescence correlation measurements in order to optimize its properties. We then recorded an image of a model sample under buffer with submicrometer resolution using ion conductance distance control to demonstrate the feasibility of this approach.
Algorithms↗
Programmable delivery of DNA through a nanopipet.
We report the pulsed delivery of single-stranded DNA molecules through a nanopipet. The conical geometry of the pipet leads to a localized electric field, since all of the potential drop occurs in the tip region. Pulsatile delivery of DNA molecules can be achieved in an experimentally simple way with high precision by controlling the applied voltage. Single-molecule detection and fluorescence correlation spectroscopy in the nanopipet enable us to determine the number of molecules delivered. Anomalous slow diffusion of the DNA molecules in the pipet has also been observed. This nanopumping technique may have potential applications in local drug delivery and nanofabrication of biomolecules on surfaces in aqueous environments.
DNA↗