Browsing by Author "Chen, Yen-Hao"

Now showing 1 - 6 of 6

Fermi-level shifts in graphene transistors with dual-cut channels scraped by atomic force microscope tips
(2014-01-13)
Lin, Meng-Yu
;
Chen, Yen-Hao
;
Su, Chen-Fung
;
Chang, Shu-Wei
;
Lee, Si-Chen
We investigate the electronic properties of p-type graphene transistors on silicon dioxide with dual-cut channels that were scraped using atomic force microscope tips. In these devices, the current is forced to squeeze into the path between the two cuts rather than flow directly through the graphene sheet. We observe that the gate voltages with minimum current shift toward zero bias as the sizes of the dual-cut regions increase. These phenomena suggest that the Fermi levels in the dual-cut regions are shifted toward the Dirac points after the mechanical scraping process. (C) 2014 AIP Publishing LLC.
Field effect of in-plane gates with different gap sizes on the Fermi level tuning of graphene channels
(2014-05-05)
Lin, Meng-Yu
;
Chen, Yen-Hao
;
Wang, Cheng-Hung
;
Su, Chen-Fung
;
Chang, Shu-Wei
Tuning of the Fermi level is investigated in graphene channels using two in-plane gates with significantly different-sized isolating gaps. While the n-type tuning was achievable in both schemes, the wide-gap device had an enhanced minimum drain current and less prominent current modulation than the narrow-gap device. In addition, further p-type tuning was not observed in the wide-gap device at negative gate biases. These phenomena indicated that both devices had distinct field-strength dependences and Fermi level tuning effects, which may be critical for the practical design of devices. (C) 2014 AIP Publishing LLC.
Nitric Oxide Turn-on Fluorescent Probe Based on Deamination of Aromatic Primary Monoamines
(2012-05-07)
Shiue, Tsun-Wei
;
Chen, Yen-Hao
;
Wu, Chi-Ming
;
Singh, Gyan
;
Chen, Hsing-Yin
The stable, water-soluble, and nonfluorescent FA-OMe can sense nitric oxide (NO) and form the intensely fluorescent product dA-FA-OMe via reductive deamination of the aromatic primary amine. The reaction is accompanied by a notable increase of the fluorescent quantum yield from 1.5 to 88.8%. The deamination mechanism of FA-OMe with NO was proposed in this study. The turn-on fluorescence signals were performed by suppression of photoinduced electron transfer (PeT), which was demonstrated by density functional theory (DFT) calculations of the components forming FA-OMe and dA-FA-OMe. Furthermore, FA-OMe showed water solubility and good stability at physiological pHs. Moreover, the selectivity study indicated that FA-OMe had high specificity for NO over other reactive oxygen/nitrogen species. In an endogenously generated NO detection study, increasing the incubation time of FA-OMe with lipopolysaccharide (LPS) pretreated Raw 264.7 murine macrophages could cause an enhanced fluorescence intensity image. In addition, a diffusion/localization cell imaging study showed that FA-OMe could be trapped in Raw 264.7 cells. These cell imaging results demonstrated that FA-OMe could be used as a turn-on fluorescent sensor for the detection of endogenously generated NO.
Reaction-based epoxide fluorescent probe for in vivo visualization of hydrogen sulfide
(2015-06-15)
Sathyadevi, Palanisamy
;
Chen, Yu-Jen
;
Wu, Shou-Cheng
;
Chen, Yen-Hao
;
Wang, Yun-Ming
Hydrogen sulfide (H2S) has emerged as the most important biosynthetic gasotransmitters along with nitric oxide (NO) and carbon monoxide (CO). In this study, we report the design and the synthesis of a new epoxide fluorescent probe 7-glycidyloxy-9-(2-glycidyloxycarbonylphenyl)-2-xanthone (FEPO) for use in in vivo visualization of hydrogen sulfide. The probe employs a fluorescein as a fluorophore, and is equipped with an operating epoxide unit. FEPO functions via epoxide ring opening upon nucleophilic attack of H2S. This ring opening strategy may open a new avenue for the development of various H2S fluorescent sensors. FEPO showed high selectivity and high sensitivity for H2S. FEPO\'s cytotoxicity was tested using MTT (2-(4,5-dimethyl-2-thiazolyl)-3,5-diphenyl-2H-tetrazolium bromide) assay. Furthermore, the use of confocal imaging of H2S and in vivo imaging in live zebra fish demonstrated FEPO\'s potential biological applications. We anticipate that, owing to their ideal properties, probes of this type will find great uses in exploring the role of H2S in biology. (C) 2015 Elsevier B.V. All rights reserved.
Sensitivity evaluation of NBD-SCN towards cysteine/homocysteine and its bioimaging applications
(2014-06-15)
Chen, Yen-Hao
;
Tsai, Jia-Chun
;
Cheng, Tsan-Hwang
;
Yuan, Shyng-Shiou
;
Wang, Yun-Ming
A push-pull fluorogenic reagent, NBD-SCN, was applied for specific detection of cysteine (Cys) and homocysteine (Hcy). Replacing thiocyanato group with Cys/Hcy increased the push-pull characteristic of the probe and resulted in emission of fluorescence. The fluorescent response of the probe toward Cys/Hcy was significantly higher than toward glutathione and other amino acids. The probe showed a 470-and 745-fold fluorescence enhancement at 550 nm and detection limit of 2.99 and 1.43 nM for Cys and Hcy, respectively. Time-dependent fluorescence assays showed that the fluorescence intensity reached a plateau within 20 s after addition of Cys and within 10 min after addition of Hcy. Furthermore, the fluorescence images of Cys/Hcy in Raw 264.7 cells were obtained after adding this probe to the cells. These results indicate that NBD-SCN not only possesses good selectivity and sensitivity for Cys/Hcy but also can penetrate cells for Cys/Hcy bioimaging. (C) 2014 Elsevier B.V. All rights reserved.
Sensitivity evaluation of rhodamine B hydrazide towards nitric oxide and its application for macrophage cells imaging
(2011-12-05)
Wu, Chi-Ming
;
Chen, Yen-Hao
;
Dayananda, Kasala
;
Shiue, Tsun-Wei
;
Hung, Chen-Hsiung
A colorless and non-fluorescent rhodamine derivative, rhodamine B hydrazide (RH), is applied to detect nitric oxide and form fluorescent rhodamine B (RB). The reaction mechanism of RH with NO is proposed in this study. The probe shows good stability over a broad pH range (pH > 4). Furthermore, fluorescence intensity of RH displays an excellent linearity to the NO concentration and the detection limit is as low as 20 nM. A 1000-fold fluorescence turn-on from a dark background was observed. Moreover, the selectivity study indicated that the fluorescence intensity increasing in the presence of NO was significantly higher than those of other reactive oxygen/nitrogen species. In exogenously generated NO detection study, clear intracellular red fluorescence was observed in the presence of S-nitroso-N-acetyl-D,L-penicillamine (SNAP, a kind of NO releasing agent). In endogenously generated NO detection study, increasing incubation time of RH with lipopolysaccharied (LPS) pre-treated cells could obtain a highly fluorescent cell image. These cell imaging results demonstrated that RH can efficiently penetrate into Raw 264.7 cells and be used for detection of exogenously and endogenously generated nitric oxide. (C) 2011 Elsevier B.V. All rights reserved.