Niepelt et al. Nanoscale Research Letters 2011, 6:511 http://www.nanoscalereslett.com/content/6/1/511 N A N O E X P R E S S Open Access Biofunctionalization of zinc oxide nanowires for DNA sensory applications Raphael Niepelt1*†, Ulrich C Schröder1†, Jana Sommerfeld1†, Irma Slowik1, Bettina Rudolph2, Robert Möller2, Barbara Seise2, Andrea Csaki2, Wolfgang Fritzsche2 and Carsten Ronning1* Abstract We report on the biofunctionalization of zinc oxide nanowires for the attachment of DNA target molecules on the nanowire surface. With the organosilane glycidyloxypropyltrimethoxysilane acting as a bifunctional linker, amino- modified capture molecule oligonucleotides have been immobilized on the nanowire surface. The dye-marked DNA molecules were detected via fluorescence microscopy, and our results reveal a successful attachment of DNA capture molecules onto the nanowire surface. The electrical field effect induced by the negatively charged attached DNA molecules should be able to control the electrical properties of the nanowires and gives way to a ZnO nanowire-based biosensing device. Keywords: nanowires, zinc oxide, functionalization, fluorescence microscopy, sensor technology Background Semiconductor nanowires have gained large interest as building blocks for low-cost, highly sensitive biosensors [1,2]. Due to the quasi-one-dimensional geometry of the nanowires and the large surface-to-volume ratio, sur- face-induced effects play a significant role on the electri- cal properties of nanowire-based devices. Even a single molecule attached to the nanowire surface is able to change the electrical properties of the nanowire consid- erably. Therefore, a functionalization of the nanowire surface gives way to highly sensitive sensors that can be arranged in a very dense assembly, owing to their nano- sized dimension. However, both the surface modification and the nanowire device arrangement have to be taken care of in order to prepare a complete nanowire-based DNA sensor. During the last decade, there have been several studies concentrating on the development of Si-based nanowire sensors [1-3]. Si nanowires are complementary metal oxide semiconductor (CMOS) compatible and biocom- patible, and techniques for the functionalization of Si are well understood. Although it is not CMOS * Correspondence: raphael.niepelt@uni-jena.de; carsten.ronning@uni-jena.de † Contributed equally 1Institute of Solid State Physics, Friedrich-Schiller-Universität, Max-Wien-Platz 1, 07743 Jena, Germany Full list of author information is available at the end of the article compatible, ZnO is very stable under ambient condi- tions and compared to silicon especially its surface is stable under oxygen-rich conditions. The stability of ZnO nanostructures under physiological conditions, which is important for biosensing applications, depends on the crystal quality of the nanostructures but can be assumed as sufficient for structures grown by thermal evaporation methods [4-6]. The material is also biocom- patible, non-toxic, and easy available. Nanostructures made of ZnO are easy and reliable to produce in a wide manner of different forms and structures [7,8]. The DNA capture molecule immobilization with organosi- lanes has been successfully shown by Corso and co- workers on planar ZnO surfaces [9], where the biomole- cule layer was used to act as an acoustic wave sensor. With the use of ZnO nanowires instead of planar films, the metal oxide itself can be used to build an electrically working biosensor. Biosensors based on ZnO nanostruc- tures have been reported, using both electrostatic adsorption as well as organosilane modification with subsequent covalent binding for immobilization [10-13]. Various enzymes have been immobilized using electro- static adsorption in order to realize highly selective bioassays [11-13]. Recently, the biofunctionalization of ZnO nanowires with biotin for streptavidin detection has been shown using organosilanes with aldehyde func- tionality that bind the amino group of biotin [10]. The © 2011 Niepelt et al; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.