Electrofluidic Positioning of Biofunctionalized Nanowires
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Electrofluidic Positioning of Biofunctionalized Nanowires Thomas J. Morrow1, Jaekyun Kim2, Mingwei Li2, Theresa S. Mayer2, Christine D. Keating1* Departments of Chemistry1 and Electrical Engineering2, The Pennsylvania State University, University Park, PA 16802. *Author to whom correspondence should be addressed at [email protected]
ABSTRACT We functionalized nanowires with three different probe peptide nucleic acid (PNA) sequences, and assembled the three populations onto a lithographically patterned chip. Electrofluidic assembly enabled positioning each set of nanowires to span a different pair of guiding electrodes. Fluorescence imaging was used to probe whether the PNA on the individual nanowires remained able to selectively bind complementary DNA targets following assembly and integration of the positioned nanowires onto the chip surface.
INTRODUCTION Chip-based nanowire sensing methods are promising candidates for ultraportable bioanalysis due to the small size of individual wires, and the potential for ultrasensitive electrical, electrochemical, and mass-based detection of biological target molecules. detection[1- 3]. Such a device would provide critical information in emergency situations, and could aid in the early diagnosis of complex diseases such as cancers or respiratory infections. Consequently there has been intense interest in developing on-chip methods such as nanowire field effect transistors (FETs), micro/nano electromechanical systems (MEMS or NEMS), and electronic noses[4-6]. The incorporation of nanowires functionalizd with probes for a large number of different targets (multiplexing) –while retaining the activity and selectivity of the probe molecules– is an obstacle currently limiting the further development of these sensors. Although some nanowire positioning [7, 8] and probe molecule delivery methods [9-11] have been developed to overcome this obstacle, these methods lack the ability to place nanowires in predetermined locations needed for highly multiplexed systems, have limited types of probe molecules that can be delivered, and cannot ensure optimal attachment chemistries of the probe molecules, possibly leading to cross contamination of adjacent sensing elements. For these reasons, we have developed a versatile electrofluidic positioning method which allows us to position prefunctionalized nanowires to predetermined chip locations, such as between columns of electrodes. Scheme 1 illustrates the concept.
Scheme 1. (A) Selective positioning of pre-functionalized nanowires. Populations of peptide nucleic acid (PNA)/SiO2 Rh nanowires were sequentially injected onto the chip surface while alternating voltages were applied to specific sets of guiding electrodes guiding the nanowires to the gap area. (B) Schematic illustrating the integration procedure of aligned nanowires. Following alignment a second photoresist was applied patterned exposing the ends of the nanowires while protecting the biomolecules functionalized to the middle segment. Ti was evaporated anchoring the
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