Phosphate-dependent DNA Immobilization on Hafnium Oxide for Bio-Sensing Applications
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Phosphate-dependent DNA Immobilization on Hafnium Oxide for Bio-Sensing Applications Nicholas M. Fahrenkopf1, Serge Oktyabrsky1, Eric Eisenbraun1, Magnus Bergkvist1, Hua Shi2¸ Nathaniel C. Cady1 1 College of Nanoscale Science & Engineering, University at Albany, Albany, NY 12203, USA 2 Department of Biological Sciences, College of Arts and Sciences, University at Albany, Albany, NY 12222, USA ABSTRACT Hafnium(IV) oxide (HfO2) has replaced silicon oxide as a gate dielectric material in leading edge CMOS technology, providing significant improvement in gate performance for field effect transistors (FETs). We are currently exploring this high-k dielectric for its use in nucleic acid-based FET biosensors. Due to its intrinsic negative charge, label-free detection of DNA can be achieved in the gate region of high-sensitivity FET devices. Previous work has shown that phosphates and phosphonates coordinate specifically onto metal oxide substrates including aluminum and titanium oxides. This property can therefore be exploited for direct immobilization of biomolecules such as nucleic acids. Our work demonstrates that 5’ phosphateterminated single stranded DNA (ssDNA) can be directly immobilized onto HfO2 surfaces, without the need for additional chemical modification or crosslinking. Non-phosphorylated ssDNA does not form stable surface interactions with HfO2, indicating that immobilization is dependent upon the 5’ terminal phosphate. Further work has shown that surface immobilized ssDNA can be hybridized to complementary target DNA and that sequence-based hybridization specificity is preserved. These results suggest that the direct DNA-HfO2 immobilization strategy can enable nucleic acid-based biosensing assays on HfO2 terminated surfaces. This work will further enable high sensitivity electrical detection of biological targets utilizing transistor-based technologies. INTRODUCTION Much progress has been made in using field effect transistors (FETs) as transduction elements for biomolecular sensors. Different strategies and architectures have been used, such as extended gate FETs [1], ion-sensitive FETs [2], enzyme FETs [3], high electron mobility transistors (HEMTs) [4], organic thin film transistors [5], dielectric modulating FETs [6], “nanobelt” FETs [7], and nanotube based FETs [8], among others. Deoxyribonucleic acid (DNA) is an attractive biomolecular target for FET-based sensors due to the high specificity of DNA hybridization events, and the intrinsic negative charge associated with the sugar-phosphate backbone. Indeed, research has shown that changes in the concentration of DNA immobilized on the gate region of an FET [9] are electrically detectable, and that the immobilization and hybridization events can both be sensed through current/voltage (I/V) measurements [10]. DNAbased FET biosensors mainly consist of single stranded DNA (ssDNA) “probe” immobilized on the gate region of the FET. Hybridization of this probe with target (complementary) ssDNA increases the amount of charge localized on the gate
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