Jung Hoon Yang

Spontaneous polarization model for surface orientation dependence of diamond hole accumulation layer and its transistor performance

Diamond metal-oxide-semiconductor field-effect transistors (FETs) have been fabricated on IIa-type large-grain diamond substrates with a (110) preferential surface. The drain current and cutoff frequency are −790mA∕mm and 45GHz, respectively, which are higher than those of single-crystal diamond FETs fabricated on (001) homoepitaxial diamond films. The hole carrier density of the hole accumulation layer depends on the orientation of the hydrogen-terminated diamond surface, for which (110) preferentially oriented films show 50%–70% lower sheet resistance than a (001) substrate. We propose that the hole density of the surface accumulation layer is proportional to the C–H bond density on the surface.

Detection of mismatched DNA on partially negatively charged diamond surfaces by optical and potentiometric methods

The effects of surface charge density on DNA hybridization have been investigated on a mixture of hydrogen-, oxygen-, and amine-terminated diamond surfaces. A difference in the hybridization efficiencies of complementary and mismatched DNA was clearly observed by fluorescence and potentiometric observations at a particular coverage of oxygen. In the fluorescence observation, singly mismatched DNA was detected with high contrast after appropriate hybridization on the surface with 10-20% oxygen coverage. The amount of oxygen in the form of C-O(-) (deprotonated C-OH) producing the surface negative-charge density was estimated by X-ray photoelectron spectroscopy. Electrolyte solution gate field-effect transistors (SGFETs) were used for potentiometric observations. The signal difference (change in gate potential) on the SGFET, which was as large as approximately 20 mV, was caused by the difference in the hybridization efficiencies of complementary target DNA (cDNA) and singly mismatched (1MM) target DNA with a common probe DNA immobilized on the same SGFET. The reversible change in gate potential caused by the hybridization and denaturation cycles and discriminating between the complementary and 1MM DNA targets was very stable throughout the cyclical detections. Moreover, the ratio of signals caused by hybridization of the cDNA and 1MM DNA targets with the probe DNA immobilized on the SGFET was determined to be 3:1 when hybridization had occurred (after 15 min on SGFET), as determined by real-time measurements. From the viewpoint of hybridization kinetics, the rate constant for hybridization of singly mismatched DNA was a factor of approximately 3 smaller than that of cDNA on this functionalized (oxidized and aminated) diamond surface.

Characterization of direct immobilized probe DNA on partially functionalized diamond solution-gate field-effect transistors

Amino groups were functionalized directly on the diamond surface after treating 0.5 monolayer of oxidation for detection of DNAs. Also, immobilization of probe DNAs was carried out directly on the partially aminated diamond without linker molecules. Specific hybridization with 21-mer DNA at a concentration of 100 nM could be clearly detected by two methods, fluorescence microscopy and diamond solution-gate field-effect transistors (SGFETs). DNA hybridization was confirmed using Cy-5-labeled target DNA on a micropatterned diamond surface. The changes in gate potential by the negative charge of immobilized or hybridized DNA were measured on SGFETs and hybridization efficiency on the functionalized diamond surface was estimated as about 40%.

Characterization of Hybridization on Diamond Solution-Gate Field-Effect Transistors for Detecting Single Mismatched Oligonucleotides

Using diamond field-effect transistors (FETs) operated in electrolyte solution (solution-gate FETs; SGFETs), a label-free charge detection method between complementary and single mismatched target oligonucleotides is proposed. The probe oligonucleotides immobilized at the activated carboxyl groups of carboxylic aromatic compounds (CACs) on the previously formed amino groups of the diamond surface. The high performance of the diamond surface for oligonucleotides detection was studied with respect to selectivity, sensitivity, and reproducibility of the diamond SGFETs.

Precise detection of singly mismatched DNA with functionalized diamond electrolyte solution gate FET.

The DC operation of diamond electrolyte solution gate FETs (SGFETs) and discrimination of complementary and singly mismatched DNAs in solution were demonstrated. The transconductance (gm), which is the sensitivity for detecting the hybridization of DNA on SGFET, was increased from 60 muS/mm to 9.5 mS/mm by miniaturization of FET. Hybridization of target DNA with probe DNA was detected by the gate potential shift caused by the negative charges on DNA immobilized on the channel surface. The change in gate potential caused by the hybridization of complementary DNA was about 25 mV. The ratio of change in gate potential by hybridization of complementary and single-mismatched DNA was 3:1 on diamond SGFET.

Direct immobilization of DNA on partially functionalized diamond surface

Amino groups were functionalized directly on the diamond surface after treating oxidation and fluorination for detection of DNAs, respectively. For simple process, immobilization of probe DNAs was carried out directly on the partially aminated diamond without linker molecules. After fabricating micropatterned diamond, specific hybridization with Cy-5 labeled target DNA at a concentration of 100 nM could be clearly detected on H-terminated, partially O-terminated, and partially F-terminated diamonds, respectively. The hybridization intensities determined by epifluorescence microscopy were compared and analyzed.