title: Immobilization of different biomolecules by atomic force microscopy.
abstract: BACKGROUND
  Micrometer resolution placement and immobilization of probe molecules is an important step in the preparation of biochips and a wide range of lab-on-chip systems. Most known methods for such a deposition of several different substances are costly and only suitable for a limited number of probes. In this article we present a flexible procedure for simultaneous spatially controlled immobilization of functional biomolecules by molecular ink lithography.
  
  
  RESULTS
  For the bottom-up fabrication of surface bound nanostructures a universal method is presented that allows the immobilization of different types of biomolecules with micrometer resolution. A supporting surface is biotinylated and streptavidin molecules are deposited with an AFM (atomic force microscope) tip at distinct positions. Subsequent incubation with a biotinylated molecule species leads to binding only at these positions. After washing streptavidin is deposited a second time with the same AFM tip and then a second biotinylated molecule species is coupled by incubation. This procedure can be repeated several times. Here we show how to immobilize different types of biomolecules in an arbitrary arrangement whereas most common methods can deposit only one type of molecules. The presented method works on transparent as well as on opaque substrates. The spatial resolution is better than 400 nm and is limited only by the AFM's positional accuracy after repeated z-cycles since all steps are performed in situ without moving the supporting surface. The principle is demonstrated by hybridization to different immobilized DNA oligomers and was validated by fluorescence microscopy.
  
  
  CONCLUSIONS
  The immobilization of different types of biomolecules in high-density microarrays is a challenging task for biotechnology. The method presented here not only allows for the deposition of DNA at submicrometer resolution but also for proteins and other molecules of biological relevance that can be coupled to biotin.
authors.affiliation: Fraunhofer Institute for Biomedical Engineering, Department of Nanobiotechnology and Nanomedicine, Am Mühlenberg 13, 14476 Potsdam, Germany. michael.breitenstein@ibmt.fraunhofer.de.
authors.forename: Michael
authors.initials: M
authors.lastname: Breitenstein
authors.forename: Ralph
authors.initials: R
authors.lastname: Hölzel
authors.forename: Frank F
authors.initials: FF
authors.lastname: Bier