Nanosensors based on the unique electronic properties of nanotubes and nanowires offer high sensitivity and have the potential to revolutionize the field of Point-of-Care (POC) medical diagnosis. The ...direct current (dc) detection of a wide array of organic and inorganic molecules has been demonstrated on these devices. However, sensing mechanism based on measuring changes in dc conductance fails at high background salt concentrations, where the sensitivity of the devices suffers from the ionic screening due to mobile ions present in the solution. Here, we successfully demonstrate that the fundamental ionic screening effect can be mitigated by operating single-walled carbon nanotube field effect transistor as a high-frequency biosensor. The nonlinear mixing between the alternating current excitation field and the molecular dipole field can generate mixing current sensitive to the surface-bound biomolecules. Electrical detection of monolayer streptavidin binding to biotin in 100 mM buffer solution is achieved at a frequency beyond 1 MHz. Theoretical modeling confirms improved sensitivity at high frequency through mitigation of the ionic screening effect. The results should promise a new biosensing platform for POC detection, where biosensors functioning directly in physiologically relevant condition are desired.
The discovery of electric field induced band gap opening in bilayer graphene opens a new door for making semiconducting graphene without aggressive size scaling or using expensive substrates. ...However, bilayer graphene samples have been limited to μm2 size scale thus far, and synthesis of wafer scale bilayer graphene poses a tremendous challenge. Here we report homogeneous bilayer graphene films over at least a 2 in. × 2 in. area, synthesized by chemical vapor deposition on copper foil and subsequently transferred to arbitrary substrates. The bilayer nature of graphene film is verified by Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. Importantly, spatially resolved Raman spectroscopy confirms a bilayer coverage of over 99%. The homogeneity of the film is further supported by electrical transport measurements on dual-gate bilayer graphene transistors, in which a band gap opening is observed in 98% of the devices.
Targeting specificity has been a barrier to applying genome editing systems in functional genomics, precise medicine and plant breeding. In plants, only limited studies have used whole-genome ...sequencing (WGS) to test off-target effects of Cas9. The cause of numerous discovered mutations is still controversial. Furthermore, WGS-based off-target analysis of Cpf1 (Cas12a) has not been reported in any higher organism to date.
We conduct a WGS analysis of 34 plants edited by Cas9 and 15 plants edited by Cpf1 in T0 and T1 generations along with 20 diverse control plants in rice. The sequencing depths range from 45× to 105× with read mapping rates above 96%. Our results clearly show that most mutations in edited plants are created by the tissue culture process, which causes approximately 102 to 148 single nucleotide variations (SNVs) and approximately 32 to 83 insertions/deletions (indels) per plant. Among 12 Cas9 single guide RNAs (sgRNAs) and three Cpf1 CRISPR RNAs (crRNAs) assessed by WGS, only one Cas9 sgRNA resulted in off-target mutations in T0 lines at sites predicted by computer programs. Moreover, we cannot find evidence for bona fide off-target mutations due to continued expression of Cas9 or Cpf1 with guide RNAs in T1 generation.
Our comprehensive and rigorous analysis of WGS data across multiple sample types suggests both Cas9 and Cpf1 nucleases are very specific in generating targeted DNA modifications and off-targeting can be avoided by designing guide RNAs with high specificity.
While metal is the most common conducting constituent element in the fabrication of metamaterials, graphene provides another useful building block, that is, a truly two-dimensional conducting sheet ...whose conductivity can be controlled by doping. Here we report the experimental realization of a multilayer structure of alternating graphene and Al2O3 layers, a structure similar to the metal-dielectric multilayers commonly used in creating visible wavelength hyperbolic metamaterials. Chemical vapour deposited graphene rather than exfoliated or epitaxial graphene is used, because layer transfer methods are easily applied in fabrication. We employ a method of doping to increase the layer conductivity, and our analysis shows that the doped chemical vapour deposited graphene has good optical properties in the mid-infrared range. We therefore design the metamaterial for mid-infrared operation; our characterization with an infrared ellipsometer demonstrates that the metamaterial experiences an optical topological transition from elliptic to hyperbolic dispersion at a wavelength of 4.5 μm.
The core of any optical imaging system is a photodetector. Whether it is film or a semiconductor chip in a camera, or indeed the retina in an eye, conventional photodetectors are designed to absorb ...most of the incident light and record a projected two-dimensional (2D) distribution of light from a scene. The intensity distribution of light from 3D objects, however, can be described by a 4D light field, so optical imaging systems that can acquire higher dimensions of optical information are highly desirable1–3. Here, we report a proof-of-concept light field imaging scheme using transparent graphene photodetector stacks. On a transparent substrate we fabricate a photodetector using graphene as the light-sensing layer, the conducting channel layer, the gate layer and interconnects, enabling sensitive light detection and high transparency at the same time. This technology opens up the possibility of developing sensor arrays that can be stacked along the light path, enabling entirely new configurations of optical imaging devices. We experimentally demonstrate depth ranging using a double stack of transparent detectors and develop a method for computational reconstruction of a 4D light field from a single exposure that can be applied following the successful fabrication of dense 2D transparent sensor arrays.A highly transparent photodetector using graphene as the light-sensing layer, conducting channel layer, gate layer and interconnects enables new approaches for light field photodetection and imaging involving simultaneous detection across multiple focal planes.
Rice (
) responds to various abiotic stresses during growth. Plant-specific NAM, ATAF1/2, and CUC2 (NAC) transcription factors (TFs) play an important role in controlling numerous vital growth and ...developmental processes. To date, 170 NAC TFs have been reported in rice, but their roles remain largely unknown. Herein, we discovered that the TF OsNAC006 is constitutively expressed in rice, and regulated by H
O
, cold, heat, abscisic acid (ABA), indole-3-acetic acid (IAA), gibberellin (GA), NaCl, and polyethylene glycol (PEG) 6000 treatments. Furthermore, knockout of
using the CRISPR-Cas9 system resulted in drought and heat sensitivity. RNA sequencing (RNA-seq) transcriptome analysis revealed that
regulates the expression of genes mainly involved in response to stimuli, oxidoreductase activity, cofactor binding, and membrane-related pathways. Our findings elucidate the important role of
in drought responses, and provide valuable information for genetic manipulation to enhance stress tolerance in future plant breeding programs.
We observed highly efficient generation of electron-hole pairs due to impact excitation in single-walled carbon nanotube p-n junction photodiodes. Optical excitation into the second electronic ...subband E₂₂ leads to striking photocurrent steps in the device$I - V_{SD} $characteristics that occur at voltage intervals of the band-gap energy$E_{GAP} /e$. Spatially and spectrally resolved photocurrent combined with temperature-dependent studies suggest that these steps result from efficient generation of multiple electron-hole pairs from a single hot E₂₂ carrier. This process is both of fundamental interest and relevant for applications in future ultra-efficient photovoltaic devices.
We describe the successful synthesis of modulation-doped silicon nanowires by achieving pure axial elongation without radial overcoating during the growth process. Scanning gate microscopy shows that ...the key properties of the modulated structures--including the number, size, and period of the differentially doped regions--are defined in a controllable manner during synthesis, and moreover, that feature sizes to less than 50 nanometers are possible. Electronic devices fabricated with designed modulation-doped nanowire structures demonstrate their potential for lithography-independent address decoders and tunable, coupled quantum dots in which changes in electronic properties are encoded by synthesis rather than created by conventional lithography-based techniques.
Recent years have seen the rapid growth of new approaches to optical imaging, with an emphasis on extracting three-dimensional (3D) information from what is normally a two-dimensional (2D) image ...capture. Perhaps most importantly, the rise of computational imaging enables both new physical layouts of optical components and new algorithms to be implemented. This paper concerns the convergence of two advances: the development of a transparent focal stack imaging system using graphene photodetector arrays, and the rapid expansion of the capabilities of machine learning including the development of powerful neural networks. This paper demonstrates 3D tracking of point-like objects with multilayer feedforward neural networks and the extension to tracking positions of multi-point objects. Computer simulations further demonstrate how this optical system can track extended objects in 3D, highlighting the promise of combining nanophotonic devices, new optical system designs, and machine learning for new frontiers in 3D imaging.
Nanoelectronic devices based on nanomaterials such as nanowires, carbon nanotubes, graphene, and other 2D nanomaterials offer extremely large surface-to-volume ratios, high carrier mobility, low ...power consumption, and high compatibility for integration with modern electronic technologies. These distinct advantages promise great potential for nanoelectronic devices as next generation chemical and biological sensors. Currently, majority of existing nanoelectronic sensors are direct current (DC) sensors, which rely ubiquitously on detection of conductance change associated with molecular adsorption. However, despite the simplicity of the conventional DC sensing technology, it also has severe limitations such as the Debye screening effect in ionic solutions, and the speed-sensitivity trade-off for the detection of charge-neutral molecules. Hence, the development of nanoelectronic sensors calls for new sensing platform technologies that can truly showcase the advantages of electronic sensors. In this Account, we will summarize recent efforts from our group on the development of a new electronic sensing paradigm, the nanoelectronic heterodyne sensors. Unlike conventional charge-detection based sensors, the heterodyne sensor explores the frequency mixing response between molecular dipoles and a nanoscale transistor. As an example, we first discuss the capability of heterodyne sensing in gas sensing applications by using graphene devices. Rapid (down to 0.1 s) and sensitive (down to 1 ppb) detection of a wide range of vapor analytes is achieved, representing orders of magnitude improvement over state-of-the-art nanoelectronic sensors. Furthermore, the heterodyne sensing technique enables electrical probing and tuning of the noncovalent physisorption of polar molecules on graphene surface for the first time. These results provide insight into small molecule-nanomaterial interaction dynamics and signify the ability to electrically tailor interactions, which can lead to rational designs of complex chemical processes for catalysis and drug discovery. Finally, we discuss the application of heterodyne sensing in solution for chemical and biological sensors by using carbon nanotube devices. The fundamental ionic screening effect can be mitigated by operating carbon nanotube field effect transistor as a heterodyne biosensor. Electrical detection of streptavidin binding to biotin in 100 mM buffer solution can be achieved at a frequency beyond 1 MHz. The results should promise a new biosensing platform for point-of-care detection, where biosensors functioning directly in physiologically relevant condition are desired.
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