Niepelt et al. Nanoscale Research Letters 2011, 6:511 http://www.nanoscalereslett.com/content/6/1/511 Page 6 of 7 Figure 4 Reference experiments with untreated nanowires. In (a) and (b), the dark field and fluorescence image of an unmodified nanowire sample are shown. In (c) and (d), the dark field and fluorescence image of a silanized but not biofunctionalized nanowire sample are shown. In both cases, the fluorescence measurement does not show any sign of distracting fluorescence. other control samples show significant less fluorescence, indicating that the strongest binding of the DNA to the nanowire is only achieved with both coupling groups present (epoxy group at GOPS and amino group at DNA) in order to form a covalent binding. In Figure 5d, a comparison of a sample with GOPS and a sample without GOPS is presented. Both samples were biofunctionalized with DNA with amino linker. The samples have been rinsed in Tris-HCl buffer solu- tion for 10 min and then measured. As expected, the Figure 5 Control experiments to confirm a covalent bonding of DNA. In (a), a typical fluorescence image of a silanized and biofunctionalized nanowire is shown. In (b), an image of a nanowire is shown that was treated the same way, but leaving out the silanization step and using DNA without a 5’-amino linker. In (c), the fluorescence intensities of various control samples are compared. In (d), a comparison of a sample with GOPS and a sample without GOPS rinsed in Tris-HCl buffer solution for different periods of time is presented. silanized sample is showing the stronger fluorescence. However, after rinsing both samples for another 12 h, the fluorescence of the sample silanized with GOPS and then functionalized has not dropped, whereas the fluor- escence of the control sample is less present than before. This also indicates a comparatively stable, pre- sumably covalent bond between the DNA and the nano- wire following the reaction scheme in Figure 1. In conclusion, the stable biofunctionalization of ZnO nano- wires has been clearly demonstrated. The bifunctional linker GOPS was used to immobilize a monolayer of DNA capture molecules on the ZnO nanowires. The successful functionalization could be verified with fluor- escence microscopy. Variations of the nanowire thick- ness result in fluorescence variations along the nanowire axes. The functionalized wires may be used as building blocks for electrically driven DNA target molecule detection. Additional material Additional file 1: Supplementary information. Detailed information about the chemicals used in this study, fluorescence images of biofunctionalized bulk crystals, and SEM images of a biofunctionalized nanowire. Acknowledgements We thank Marc Brötzmann, University of Göttingen, for advice and discussion. We thank Christian Leiterer, IPHT Jena, for assistance with both fluorescence microscopy and immobilization protocols. Funding by BMBF (16SV5386K, “NAWION”) and EU (Marie Curie ITN 265073, “Nanowiring”) is acknowledged. Author details 1Institute of Solid State Physics, Friedrich-Schiller-Universität, Max-Wien-Platz 1, 07743 Jena, Germany 2Institute of Photonic Technology (IPHT), PO Box 100239, 07702 Jena, Germany Authors’ contributions US and IS synthesized and characterized the nanowires and conducted the fluorescence microscopy measurements. RN assisted with the nanowire synthesis and drafted the manuscript. JS participated in the fluorescence microscopy measurements and helped to draft the manuscript. BR and BS carried out the biofunctionalization and assisted with the fluorescence microscopy measurements. RM and AC participated in the design of the study and its coordination. CR and WF participated in the design of the study and helped to draft the manuscript. All authors read and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Received: 11 May 2011 Accepted: 25 August 2011 Published: 25 August 2011 References 1. Cui Y, Wei Q, Park H, Lieber CM: Nanowire nanosensors for highly sensitive and selective detection of biological and chemical species. Science 2001, 293:1289-1292. 2. Patolsky F, Timko BP, Zheng G, Lieber CM: Nanowire-based nanoelectronic devices in the life sciences. MRS Bull 2007, 32:142-149.