Direct measurements of the diffusion length of excitons in air-suspended single-walled carbon nanotubes are reported. Photoluminescence microscopy is used to identify individual nanotubes and to determine their lengths and chiral indices. Exciton diffusion length is obtained by comparing the dependence of photoluminescence intensity on the nanotube length to numerical solutions of diffusion equations. We find that the diffusion length in these clean, as-grown nanotubes is significantly longer than those reported for micelle-encapsulated nanotubes.

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Gate-voltage effects on photoluminescence spectra of suspended single-walled carbon nanotubes are investigated. Photoluminescence microscopy and excitation spectroscopy are used to identify individual nanotubes and to determine their chiralities. Under an application of gate voltage, we observe slight blueshifts in the emission energy and strong quenching of photoluminescence. The blueshifts are similar for different chiralities investigated, suggesting extrinsic mechanisms. In addition, we find that the photoluminescence intensity quenches exponentially with gate voltage. PACS numbers: 78.67.Ch, 85.35.Kt, Understanding of electric-field effects on optical emission from single-walled carbon nanotubes (SWCNTs) is a key to the development of carbon-based nanoscale optoelectronics. 1 It has been shown that electric fields can drive light emission in SWCNTs. 2,3 In comparison, photoluminescence (PL) is quenched by an application of electric fields. Micelle-encapsulated SWCNTs show a reduction of PL intensity by electric fields along the tube axis. 4 Similar quenching occurs in suspended nanotubes within field-effect transistor (FET) structures. 5-7 Such strong quenching of PL has made it difficult to unambiguously resolve shifts in the emission spectra, in contrast to absorption measurements where redshifts due to the Stark effect 8 and doping-induced screening 6 have been observed. Detailed PL spectroscopy on nanotubes with determined chirality would help clarify the role of these effects on optical emission.Here we report on gate-voltage dependence of PL spectra in individual suspended SWCNTs. As-grown nanotubes within FET structures are identified by PL imaging using a laser scanning confocal microscope. Excitation spectroscopy is used to determine their chirality, and PL spectra are collected as a function of gate voltage. Surprisingly, we find that the emission blueshifts when the gate voltages are applied. Furthermore, the PL intensity decreases exponentially with gate voltage, and we find that a model assuming doping-induced exciton relaxation proportional to carrier density 9,10 cannot account for all of the quenching observed.The suspended nanotube FETs [ Fig. 1(a)] are fabricated on p-type Si substrates with 100-nm-thick oxide. We begin by etching 1-µm wide trenches with a depth of ∼ 5 µm. The wafer is then annealed at 900 • C in oxygen for an hour to form an oxide layer inside the trenches. 1-nm Ti and 15-nm Pt are deposited for source and drain contacts, and then catalyst areas are defined on the drain electrodes. Co acetate and fumed silica are dissolved in ethanol, and deposited on the wafer. Finally, carbon nanotubes are grown by chemical vapor deposition using ethanol as a carbon source. 11 Typical device characteristics are shown in Fig. 1(b), and we note that these devices show hysteresis due to water adsorption. 12 PL spectra are collected with a home-built laser scanning confocal microscope. 13 An output of a continuouswave Ti:sapphire laser is focused onto the sample with an objective lens, and a...

Neuropeptide Y (NPY) is thought to have a major role in the physiological control of energy homeostasis. Among five NPY receptors described, the NPY Y5 receptor (Y5R) is a prime candidate to mediate some of the effects of NPY on energy homeostasis, although its role in physiologically relevant rodent obesity models remains poorly defined. We examined the effect of a potent and highly selective Y5R antagonist in rodent obesity and dietary models. The Y5R antagonist selectively ameliorated diet-induced obesity (DIO) in rodents by suppressing body weight gain and adiposity while improving the DIO-associated hyperinsulinemia. The compound did not affect the body weight of lean mice fed a regular diet or genetically obese leptin receptor-deficient mice or rats, despite similarly high brain Y5R receptor occupancy. The Y5R antagonist acts in a mechanism-based manner, as the compound did not affect DIO of Y5R-deficient mice. These results indicate that Y5R is involved in the regulation and development of DIO and suggest utility for Y5R antagonists in the treatment of obesity.antiobesity effect ͉ Y5R-deficient mice ͉ receptor occupancy N europeptide Y (NPY), a 36-aa peptide neurotransmitter, is one of the most potent orexigenic substances when injected into the brain. NPY expression is widely distributed in the CNS, including the hypothalamus, a region involved in energy homeostasis (1). NPY content and mRNA levels in the hypothalamus respond to feeding status, including food deprivation and refeeding (2, 3). Chronic central infusion of NPY in rodents results in a syndrome similar to that in some genetic obesity models, characterized by hyperphagia, insulin resistance, hyperinsulinemia, and reduced thermogenic activity in brown adipose tissue (4). NPY is, therefore, thought to have a major role in the physiological control of energy homeostasis, making it a target for the development of antiobesity agents.Five types of NPY receptors have been characterized (5). Pharmacological data suggest that the NPY Y5 receptor (Y5R) is involved in feeding regulation. For example, functional and binding activities of different peptide agonists at the Y5R in vitro correlated strongly with their efficacy in stimulating food intake (6). Administration of Y5R antagonists suppressed Y5R agonist-induced feeding (7), and mice lacking the Y5R showed a diminished response to exogenously administered Y5R agonists (8). The Y5R is also reported to regulate brown fat thermogenesis and energy expenditure (9). In addition, chronic intracerebroventricular administration of a Y5R-specific agonist, D-Trp-34NPY, produces obesity (10). These findings suggest that the Y5R is involved in the development of obesity. However, the physiological role of the Y5R in obesity models, rather than models that rely on exogenously added Y5R agonists, remains undefined.We reported that orally administered Y5R antagonist [2-(3,3-dimethyl-1-oxo-4H-1H-xanthen-9-yl)-5,5-dimethyl-cyclohexane-1,3-dione] reduced Y5R agonist-induced feeding and Y5R agonist-induced obesity (7, ...

A newly discovered metabotropic glutamate receptor (mGluR) 1 allosteric antagonist, 2-cyclopropyl-5-[1-(2-fluoro-3-pyridinyl)-5-methyl-1H-1,2,3-triazol-4-yl]-2,3-dihydro-1H-isoindol-1-one (CFMTI), was tested both in vitro and in vivo for its pharmacological effects. CFMTI demonstrated potent and selective antagonistic activity on mGluR1 in vitro and in vivo after oral administration. CFMTI inhibited L-glutamate-induced intracellular Ca 2ϩ mobilization in Chinese hamster ovary cells expressing human and rat mGluR1a, with IC 50 values of 2.6 and 2.3 nM, respectively. The selectivity of CFMTI to mGluR1 over mGluR5 was Ͼ2000-fold, and CFMTI at 10 M showed no agonistic or antagonistic activities toward other mGluR subtypes and other receptors. It antagonized face-washing behavior in mice induced by (S)-3,5-dihidroxyphenylglycine at a dose range of 3 to 30 mg/kg, for which receptor occupancy was 73 to 94%. As with the classical neuroleptic haloperidol and an atypical antipsychotic, clozapine, orally administered CFMTI reduced methamphetamine-induced hyperlocomotion and disruption of prepulse inhibition (PPI) at the same dose range as required to antagonize the face-washing behavior. CFMTI and clozapine improved ketamine-induced hyperlocomotion, PPI disruption and (5S,10R)-(ϩ)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801)-induced social withdrawal without any cataleptogenic activities, whereas haloperidol only improved ketamineinduced hyperlocomotion. CFMTI, unlike clozapine, caused neither hypolocomotion nor motor incoordination at therapeutic doses. In c-fos expression studies, CFMTI and clozapine increased the number of fos-positive neurons in the nucleus accumbens and medial prefrontal cortex but not in the dorsolateral striatum. These results suggest that the antipsychotic activities of mGluR1 antagonists are more similar to those of atypical antipsychotics than those of typical antipsychotics.L-Glutamate is a major excitatory neurotransmitter in the mammalian central nervous system (CNS) and acts on both ligand-gated ion channels (ionotropic glutamate receptors; iGluRs) and G protein-coupled metabotropic glutamate receptors (mGluRs). The mGluR family consists of eight recep-A.S. and G.S. contributed equally to this work. Article, publication date, and citation information can be found at