DNA-ISFETs from Single Crystalline Diamond
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0956-J16-04
DNA-ISFETs from Single Crystalline Diamond Christoph E. Nebel1, Dongchan Shin1, Tomoko Yamamoto1, and Takako Nakamura2 1 AIST, Diamond Research Center, Tsukuba, 305-8568, Japan 2 AIST, Center for Advanced Carbon Material, Tsukuba, 305-8565, Japan ABSTRACT DNA sensitive field-effect transistors (DNA-FET) have been realized using single crystalline diamond grown by plasma-enhanced chemical vapor deposition (CVD). To bond DNA to diamond, amine linker-molecules are covalently attached by photochemical means to H-terminated diamond surfaces. Using hetero-bifunctional cross-linker and thiol-modified single-strand (ss) marker DNA, the gate of diamond FETs is modified to sense hybridization of DNA, forming double-strand (ds) DNA molecules on the gate. The density of DNA bonded to diamond is varied between 1012 and 1013 cm-2 to explore sensitivity enhancements by reduction of the DNA molecule density. DNA-FET characterization in 1M NaCl buffer solution (pH 7.2) reveal gate-potential threshold shifts by hybridization in the range 30 mV to 100 mV with decreasing DNA density. The variation is discussed based on the transfer doping model which predicts with decreasing pH increasing hole-densities in the surface conductive layer of diamond.
1. INTRODUCTION Since the mid-1990s, electronic sensing of biomolecules attracts increasing attention as it is promising with respect to miniaturization and multi-array sensor integration into realtime read-out electronic devices. Electronic detection, however, competes with well established optical techniques based on fluorescence and surface plasmon resonance detection, which are extraordinarily sensitive and which are already realized with arrays containing thousands of unique probe DNA sequences. Their major disadvantage is the sophisticated and expensive instrumentation which is best fitted for laboratory applications. Alternatively, electrochemical detection is well suited for diagnostics, offers high sensitivity but requires direct or catalyzed oxidation, redox reactions of reporter molecules or additional molecular layers like enzymes to generate amperometric signals. A “better” approach may be the use of ion-sensitive field effect transistors (ISFET) with DNA modified gate electrodes, where surface potential changes are transduced into electric signals without expensive instrumentation and reagents. Especially, as DNA molecules are composed out of phosphate groups, which are negatively charged in buffer solution, hybridization with target DNA results in changes of carrier densities in the channel of transistors. Such devices are therefore very interesting for sensing. Up-to-now, most fabricated ISFETs are based on Si which is however not stable in NaCl buffer solutions [1]. Bio-sensor devices based on diamond attract increasing attention as diamond is known to be biocompatibility, chemical inert, shows excellent electrochemical properties and long term chemical stability of bio-molecules bonded to it [1-7]. In the following we introduce recently achieved results with res
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