Surface-acoustic-wave-enhanced alignment of thiolated carbon nanotubes on gold electrodes.
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Acoustics↗
Biomedical subjects
Achim Wixforth
Publications and source records attributed to Achim Wixforth.
Controlled agitation during hybridization: surface acoustic waves are shaking up microarray technology.
Microarray hybridization experiments are mostly based on quite small sample volumes being confined between the microarray itself and a cover slip or lifter slip on top of the narrow fluid layer. Under such conditions, the system is governed by the rules of microfluidics, i.e., by the regime of small Reynold's numbers. Here, diffusion is the only source for moving sample molecules toward their target spots. However, for a typical macromolecule such as that used in microarray hybridization experiments, the diffusion constant is very small. Hence, because they are driven by diffusion only, traveling over typical distances on a microarray may take them a very long time. Additionally, the slow time constants associated with the diffusion limit lead to pronounced depletion effects, which strongly influence the dynamics of a hybridization assay. In this report, we describe a novel technique to overcome the diffusion limit in microarray hybridization experiments. Surface acoustic waves on a piezoelectric substrate are coupled with the sample fluid on a microarray, where they act as a highly efficient agitation source. We demonstrate that the diffusion limit can be overcome in this fashion, leading to a remarkable increase in signal intensity and homogeneity in fluorescence-labeled microarray assays.
Acoustics↗
Planar chip device for PCR and hybridization with surface acoustic wave pump.
We have developed a microfluidic device operating at a planar surface instead of a closed channel network. The fluid is transported in single droplets using surface acoustic waves (SAW) on a piezoelectric LiNbO(3) substrate. The surface of the piezo is chemically structured to induce high contact angles of the droplets or enclose areas where the liquid can wet the substrate. Combining the SAW technique with thin film resistance heaters, a biological analysis chip with integrated DNA amplification by PCR and hybridization was designed. To prevent evaporation of the PCR reagents at high temperatures the sample is enclosed in droplets of mineral oil. On this chip the SAW resolves dried primers, shifts the oil capped liquid between the two heaters and mixes during hybridization. The chip is able to perform a highly sensitive, fast and specific PCR with a volume as low as 200 nl. During the temperature cycles an online monitoring of the DNA concentration is feasible with an optical unit, providing a sensitivity of 0.1 ng. After PCR the product is moved to the second heater for the hybridization on a spotted DNA array. With our chip we were able to detect a single nucleotide polymorphism (SNP) responsible for the Leiden Factor V syndrome from human blood.
Acoustics↗
Acoustic manipulation of small droplets.
Surface acoustic waves are used to actuate and process smallest amounts of fluids on the planar surface of a piezoelectric chip. Chemical modification of the chip surface is employed to create virtual wells and tubes to confine the liquids. Lithographically modulated wetting properties of the surface define a fluidic network, in analogy to the wiring of an electronic circuit. Acoustic radiation pressure exerted by the surface wave leads to internal streaming in the fluid and eventually to actuation of small droplets along predetermined trajectories. This way, in analogy to microelectronic circuitry, programmable biochips for a variety of assays on a chip have been realized.
Journal Article↗
Nano- and pico-dispensing of fluids on planar substrates using SAW.
The increasing interest in miniaturization of biological and chemical experiments or assays demands precise metering of the smallest amounts of reagents, e.g., on a planar substrate. Very sophisticated spotting systems can nowadays produce arrays of many thousands of different substances on an area of a few square inches. Such micro arrays and the technology behind them have become an important tool in genomic expression assays, proteomic applications, and even in the field of combinatoric chemistry. We present a technique to dispense the smallest amounts of fluids in the form of either simple spots or more complicated microarrays, where we use surface acoustic waves in combination with a predetermined surface chemistry. In addition to a detailed description of the technique, several examples of applications are presented.
Acoustics↗
Enhancing results of microarray hybridizations through microagitation.
Protein and DNA microarrays have become a standard tool in proteomics/genomics research. In order to guarantee fast and reproducible hybridization results, the diffusion limit must be overcome. Surface acoustic wave (SAW) micro-agitation chips efficiently agitate the smallest sample volumes (down to 10 microL and below) without introducing any dead volume. The advantages are reduced reaction time, increased signal-to-noise ratio, improved homogeneity across the microarray, and better slide-to-slide reproducibility. The SAW micromixer chips are the heart of the Advalytix Array-Booster, which is compatible with all microarrays based on the microscope slide format.
Animals↗