3 results
Exploiting Phosphate Dependent DNA Immobilization on HfO2, ZrO2 and AlGaN for Integrated Biosensors
- Nicholas M Fahrenkopf, Vibhu Jindal, Neeraj Tripathi, Serge Oktyabrsky, Fatemeh Shahedipour-Sandvik, Natalya Tokranova, Magnus Bergkvist, Nathaniel C Cady
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- Journal:
- MRS Online Proceedings Library Archive / Volume 1236 / 2009
- Published online by Cambridge University Press:
- 31 January 2011, 1236-SS05-16
- Print publication:
- 2009
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A significant challenge for high throughput nucleic acid analysis and sequencing is to increase both throughput and sensitivity. Electrical detection methods are advantageous since they can be easily scaled to high density arrays, are highly sensitive, and do not require bulky optical equipment for readout. A focus of most nucleic acid based sensors is the detection of sequence-specific hybridization events between complementary strands of DNA or RNA. These hybridization events can be detected electrically, due to the intrinsic negative charge associated with the phosphate-rich nucleic acid backbone. Field effect transistors (FETs) and high electron mobility transistors (HEMTs) are ideal devices for detecting such hybridization events, due to their high sensitivity to changes in electrical field strength. A key concern for the construction of DNA-based FET and HEMT biosensors is the immobilization of probe oligonucleotides on the active region of the sensor. In previous work, our group has shown that single stranded DNA can be directly immobilized onto semiconductor materials without the need for complex surface chemistry or crosslinking strategies. In the present work, we have shown that the immobilization of single stranded DNA onto these materials is influenced by the terminal phosphate group of the DNA molecule, independent of backbone phosphates. This agrees with previous studies in which phosphates and phosphonates exhibited strong attachment to a variety of metal oxides. We have also shown that surface-immobilized DNA is available for hybridization and that hybridization is sequence specific. Phosphate-dependent immobilization was demonstrated for HfO2, AlGaN, and ZrO2 surfaces using optical detection of DNA-DNA hybridization, as well as x-ray photoelectron spectroscopy (XPS) analysis of DNA-modified surfaces.
Phosphate-dependent DNA Immobilization on Hafnium Oxide for Bio-Sensing Applications
- Nicholas M Fahrenkopf, Serge Oktyabrsky, Eric Eisenbraun, Magnus Bergkvist, Hua Shi, Nathaniel C Cady
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- Journal:
- MRS Online Proceedings Library Archive / Volume 1191 / 2009
- Published online by Cambridge University Press:
- 31 January 2011, 1191-OO12-04
- Print publication:
- 2009
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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’ phosphate-terminated 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.
Direct Cell Printing With Microfabricated Quill-Pen Cantilevers
- William F. Hynes, Alison Gracias, Nicholas M. Fahrenkopf, Nurazhani Abdul Raof, Waseem K. Raja, Katherine Lee, Yubing Xie, Magnus Bergkvist, Nathaniel C. Cady
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- Journal:
- MRS Online Proceedings Library Archive / Volume 1235 / 2009
- Published online by Cambridge University Press:
- 31 January 2011, 1235-RR06-02
- Print publication:
- 2009
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A novel direct cell printing technique has been developed to control and manipulate the position of cells on solid surfaces. The method utilizes microfabricated polymeric “quill-pen” cantilevers to transfer living cells onto a wide variety of surfaces. In contrast with existing cell deposition methods, such as ink jet or laser ablation methods, the quill-pen approach imparts minimal thermal and shear stress to cells, preserving cell viability and biological functionality. Deposition of both bacterial and mammalian cells into defined patterns has been demonstrated using this method. The size of printed, cell-containing droplets could be controlled by varying the geometry of the quill-pen stylus and by varying printing conditions such as contact time, relative humidity, and surface hydrophobicity. Initial experiments using 10 μm diameter polymer beads demonstrated that the number of beads per droplet could be controlled by varying spot size and particle concentration in the printing solution. Spots could be printed ranging from 20 μm and 100 μm in diameter with approximate volumes ranging from 1-250 pL. We demonstrated deposition of both cells and beads onto a variety of solid surfaces including agarose gel, polystyrene, polyethylene, and glass. Printed cells have also been immobilized on glass and polymer surfaces using biocompatible hydrogel materials (both alginic acid and hyaluronic acid-based matrices) as well as poly-L-lysine. Similar to polymer beads, the number of cells in printed droplets was shown to be dependent upon the size of the droplet, and could be varied by adjusting the concentration of cells present in the printing fluid. As few as one cell per spot could be achieved by adjusting these parameters. The viability and proliferation of printed cells has been evaluated using live optical imaging to observe cell growth and division. Both bacterial cells (Escherichia coli) and mammalian cells were able to divide and proliferate for at least 96 hr post-printing (experiments were discontinued after 96 hr). Live/dead staining was also used to confirm the viability of printed cells. Rat mammary adenocarcinoma MTLn3 cells and mouse embryonic stem cells were also shown to survive the printing process for at least 24 - 96 hr post-printing. These results demonstrate the feasibility of the printing method and its compatibility with a wide range of cell types. It is especially noteworthy that embryonic stem cells could survive the printing process (and proliferate on the printing substrate). This novel printing method has applications for tissue engineering, cell-to-cell signaling studies, and for directly interfacing cells with nanodevices and biosensors.