@article {68930, title = {Stimulus edges induce orientation tuning in superior colliculus.}, journal = {Nature Communications}, volume = {14}, year = {2023}, month = {2023 Aug 08}, pages = {4756}, abstract = {

Orientation columns exist in the primary visual cortex (V1) of cat and primates but not mouse. Intriguingly, some recent studies reported the presence of orientation and direction columns in the mouse superficial superior colliculus (sSC), while others reported a lack of columnar organization therein. Using in vivo calcium imaging of sSC in the awake mouse brain, we found that the presence of columns is highly stimulus dependent. Specifically, we observed orientation and direction columns formed by sSC neurons retinotopically mapped to the edge of grating stimuli. For both excitatory and inhibitory neurons in sSC, orientation selectivity can be induced by the edge with their preferred orientation perpendicular to the edge orientation. Furthermore, we found that this edge-induced orientation selectivity is associated with saliency encoding. These findings indicate that the tuning properties of sSC neurons are not fixed by circuit architecture but rather dependent on the spatiotemporal properties of the stimulus.

}, keywords = {Animals, Calcium, Neurons, Photic Stimulation, Superior Colliculi, Visual Cortex}, issn = {2041-1723}, doi = {10.1038/s41467-023-40444-1}, author = {Liang, Yajie and Lu, Rongwen and Borges, Katharine and Ji, Na} } @article {67763, title = {An adaptive optics module for deep tissue multiphoton imaging in vivo.}, journal = {Nature Methods}, volume = {18}, year = {2021}, month = {2021 Oct 01}, pages = {1259-1264}, abstract = {

Understanding complex biological systems requires visualizing structures and processes deep within living organisms. We developed a compact adaptive optics module and incorporated it into two- and three-photon fluorescence microscopes, to measure and correct tissue-induced aberrations. We resolved synaptic structures in deep cortical and subcortical areas of the mouse brain, and demonstrated high-resolution imaging of neuronal structures and somatosensory-evoked calcium responses in the mouse spinal cord at great depths in vivo.

}, issn = {1548-7105}, doi = {10.1038/s41592-021-01279-0}, author = {Rodriguez, Cristina and Chen, Anderson and Rivera, Jos{\'e} A and Mohr, Manuel A and Liang, Yajie and Natan, Ryan G and Sun, Wenzhi and Milkie, Daniel E and Bifano, Thomas G and Chen, Xiaoke and Ji, Na} } @article {67273, title = {A Distinct Population of L6 Neurons in Mouse V1 Mediate Cross-Callosal Communication.}, journal = {Cerebral Cortex}, year = {2021}, month = {2021 May 14}, abstract = {

Through the corpus callosum, interhemispheric communication is mediated by callosal projection (CP) neurons. Using retrograde labeling, we identified a population of layer 6 (L6) excitatory neurons as the main conveyer of transcallosal information in the monocular zone of the mouse primary visual cortex (V1). Distinct from L6 corticothalamic (CT) population, V1 L6 CP neurons contribute to an extensive reciprocal network across multiple sensory cortices over two hemispheres. Receiving both local and long-range cortical inputs, they encode orientation, direction, and receptive field information, while are also highly spontaneous active. The spontaneous activity of L6 CP neurons exhibits complex relationships with brain states and stimulus presentation, distinct from the spontaneous activity patterns of the CT population. The anatomical and functional properties of these L6 CP neurons enable them to broadcast visual and nonvisual information across two hemispheres, and thus may play a role in regulating and coordinating brain-wide activity events.

}, issn = {1460-2199}, doi = {10.1093/cercor/bhab084}, author = {Liang, Yajie and Fan, Jiang Lan and Sun, Wenzhi and Lu, Rongwen and Chen, Ming and Ji, Na} } @article {65322, title = {Kilohertz two-photon fluorescence microscopy imaging of neural activity in vivo.}, journal = {Nature Methods}, volume = {17}, year = {2020}, month = {2020 Mar 02}, pages = {287-290}, abstract = {

Understanding information processing in the brain requires monitoring neuronal activity at high spatiotemporal resolution. Using an ultrafast two-photon fluorescence microscope empowered by all-optical laser scanning, we imaged neuronal activity in vivo at up to 3,000 frames per second and submicrometer spatial resolution. This imaging method enabled monitoring of both supra- and subthreshold electrical activity down to 345 μm below the brain surface in head-fixed awake mice.

}, issn = {1548-7105}, doi = {10.1038/s41592-020-0762-7}, author = {Wu, Jianglai and Liang, Yajie and Chen, Shuo and Hsu, Ching-Lung and Chavarha, Mariya and Evans, Stephen W and Shi, Dongqing and Lin, Michael Z and Tsia, Kevin K and Ji, Na} } @article {65321, title = {Rapid mesoscale volumetric imaging of neural activity with synaptic resolution.}, journal = {Nature Methods}, volume = {17}, year = {2020}, month = {2020 Mar 02}, pages = {291-4}, abstract = {

Imaging neurons and neural circuits over large volumes at high speed and subcellular resolution is a difficult task. Incorporating a Bessel focus module into a two-photon fluorescence mesoscope, we achieved rapid volumetric imaging of neural activity over the mesoscale with synaptic resolution. We applied the technology to calcium imaging of entire dendritic spans of neurons as well as neural ensembles within multiple cortical regions over two hemispheres of the awake mouse brain.

}, issn = {1548-7105}, doi = {10.1038/s41592-020-0760-9}, author = {Lu, Rongwen and Liang, Yajie and Meng, Guanghan and Zhou, Pengcheng and Svoboda, Karel and Paninski, Liam and Ji, Na} } @article {64889, title = {Dynamic super-resolution structured illumination imaging in the living brain.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {116}, year = {2019}, month = {2019 Apr 26}, pages = {9586-91}, abstract = {

Cells in the brain act as components of extended networks. Therefore, to understand neurobiological processes in a physiological context, it is essential to study them in vivo. Super-resolution microscopy has spatial resolution beyond the diffraction limit, thus promising to provide structural and functional insights that are not accessible with conventional microscopy. However, to apply it to in vivo brain imaging, we must address the challenges of 3D imaging in an optically heterogeneous tissue that is constantly in motion. We optimized image acquisition and reconstruction to combat sample motion and applied adaptive optics to correcting sample-induced optical aberrations in super-resolution structured illumination microscopy (SIM) in vivo. We imaged the brains of live zebrafish larvae and mice and observed the dynamics of dendrites and dendritic spines at nanoscale resolution.

}, issn = {1091-6490}, doi = {10.1073/pnas.1819965116}, author = {Turcotte, Raphael and Liang, Yajie and Tanimoto, Masashi and Zhang, Qinrong and Li, Ziwei and Koyama, Minoru and Betzig, Eric and Ji, Na} } @article {49597, title = {High-throughput synapse-resolving two-photon fluorescence microendoscopy for deep-brain volumetric imaging .}, journal = {eLife}, volume = {8}, year = {2019}, month = {2019 Jan 03}, abstract = {

Optical imaging has become a powerful tool for studying brains . The opacity of adult brains makes microendoscopy, with an optical probe such as a gradient index (GRIN) lens embedded into brain tissue to provide optical relay, the method of choice for imaging neurons and neural activity in deeply buried brain structures. Incorporating a Bessel focus scanning module into two-photon fluorescence microendoscopy, we extended the excitation focus axially and improved its lateral resolution. Scanning the Bessel focus in 2D, we imaged volumes of neurons at high-throughput while resolving fine structures such as synaptic terminals. We applied this approach to the volumetric anatomical imaging of dendritic spines and axonal boutons in the mouse hippocampus, and functional imaging of GABAergic neurons in the mouse lateral hypothalamus .

}, issn = {2050-084X}, doi = {10.7554/eLife.40805}, author = {Meng, Guanghan and Liang, Yajie and Sarsfield, Sarah and Jiang, Wan-Chen and Lu, Rongwen and Dudman, Joshua Tate and Aponte, Yeka and Ji, Na} } @article {49031, title = {Adaptive optical microscopy for neurobiology.}, journal = {Current Opinion in Neurobiology}, volume = {50}, year = {2018}, month = {2018 Jun}, pages = {83-91}, abstract = {

Highlights:

With the ability to correct for the aberrations introduced by biological specimens, adaptive optics{\textemdash}a method originally developed for astronomical telescopes{\textemdash}has been applied to optical microscopy to recover diffraction-limited imaging performance deep within living tissue. In particular, this technology has been used to improve image quality and provide a more accurate characterization of both structure and function of neurons in a variety of living organisms. Among its many highlights, adaptive optical microscopy has made it possible to image large volumes with diffraction-limited resolution in zebrafish larval brains, to resolve dendritic spines over 600μm deep in the mouse brain, and to more accurately characterize the orientation tuning properties of thalamic boutons in the primary visual cortex of awake mice.

}, doi = {10.1016/j.conb.2018.01.011}, author = {Rodriguez, Cristina and Ji, Na} } @article {49367, title = {In vivo measurement of afferent activity with axon-specific calcium imaging.}, journal = {Nature Neuroscience}, year = {2018}, month = {2018 Aug 20}, abstract = {

In vivo calcium imaging from axons provides direct interrogation of afferent neural activity, informing the neural representations that a local circuit receives. Unlike in somata and dendrites, axonal recording of neural activity-both electrically and optically-has been difficult to achieve, thus preventing comprehensive understanding of neuronal circuit function. Here we developed an active transportation strategy to enrich GCaMP6, a genetically encoded calcium indicator, uniformly in axons with sufficient brightness, signal-to-noise ratio, and photostability to allow robust, structure-specific imaging of presynaptic activity in awake mice. Axon-targeted GCaMP6 enables frame-to-frame correlation for motion correction in axons and permits subcellular-resolution recording of axonal activity in previously inaccessible deep-brain areas. We used axon-targeted GCaMP6 to record layer-specific local afferents without contamination from somata or from intermingled dendrites in the cortex. We expect that axon-targeted GCaMP6 will facilitate new applications in investigating afferent signals relayed by genetically defined neuronal populations within and across specific brain regions.

}, issn = {1546-1726}, doi = {10.1038/s41593-018-0211-4}, author = {Broussard, Gerard Joey and Liang, Yajie and Fridman, Marina and Unger, Elizabeth K and Meng, Guanghan and Xiao, Xian and Ji, Na and Petreanu, Leopoldo and Tian, Lin} } @article {49381, title = {Optical alignment device for two-photon microscopy.}, journal = {Biomedical Optics Express}, volume = {9}, year = {2018}, month = {2018 Aug 1}, pages = {3624-9}, abstract = {

Two-photon excitation fluorescence microscopy has revolutionized our understanding of brain structure and function through the high resolution and large penetration depth it offers. Investigating neural structures\ in vivo\ requires gaining optical access to the brain, which is typically achieved by replacing a part of the skull with one or several layers of cover glass windows. To compensate for the spherical aberrations caused by the presence of these layers of glass, collar-correction objectives are typically used. However, the efficiency of this correction has been shown to depend significantly on the tilt angle between the glass window surface and the optical axis of the imaging system. Here, we first expand these observations and characterize the effect of the tilt angle on the collected fluorescence signal with thicker windows (double cover slide) and compare these results with an objective devoid of collar-correction. Second, we present a simple optical alignment device designed to rapidly minimize the tilt angle\ in vivo\ and align the optical axis of the microscope perpendicularly to the glass window to an angle below 0.25{\textdegree}, thereby significantly improving the imaging quality. Finally, we describe a tilt-correction procedure for users in an\ in vivo\ setting, enabling the accurate alignment with a resolution of \<0.2{\textdegree} in only few iterations.

}, doi = {10.1364/BOE.9.003624}, author = {Gali{\~n}anes, Gregorio L and Marchand, Paul J and Turcotte, Raphael and Pellat, Sebastien and Ji, Na and Huber, Daniel} } @article {49181, title = {Three-photon fluorescence microscopy with an axially elongated Bessel focus.}, journal = {Optics Letters}, volume = {43}, year = {2018}, month = {2018 Apr 15}, pages = {1914-1917}, abstract = {

Volumetric imaging tools that are simple to adopt, flexible, and robust are in high demand in the field of neuroscience, where the ability to image neurons and their networks with high spatiotemporal resolution is essential. Using an axially elongated focus approximating a Bessel beam, in combination with two-photon fluorescence microscopy, has proven successful at such an endeavor. Here, we demonstrate three-photon fluorescence imaging with an axially extended Bessel focus. We use an axicon-based module that allowed for the generation of Bessel foci of varying numerical apertures and axial lengths, and apply this volumetric imaging tool to image mouse brain slices and for in vivo imaging of the mouse brain.

}, issn = {1539-4794}, doi = {10.1364/OL.43.001914}, author = {Rodriguez, Cristina and Liang, Yajie and Lu, Rongwen and Ji, Na} } @article {48373, title = {Adaptive optical fluorescence microscopy.}, journal = {Nature Methods}, volume = {14}, year = {2017}, month = {2017 Mar 31}, pages = {374-380}, abstract = {

The past quarter century has witnessed rapid developments of fluorescence microscopy techniques that enable structural and functional imaging of biological specimens at unprecedented depth and resolution. The performance of these methods in multicellular organisms, however, is degraded by sample-induced optical aberrations. Here I review recent work on incorporating adaptive optics, a technology originally applied in astronomical telescopes to combat atmospheric aberrations, to improve image quality of fluorescence microscopy for biological imaging.

}, issn = {1548-7105}, doi = {10.1038/nmeth.4218}, author = {Ji, Na} } @article {48891, title = {A general method to fine-tune fluorophores for live-cell and in vivo imaging.}, journal = {Nature Methods}, volume = {14}, year = {2017}, month = {2017 Oct}, pages = {987-994}, abstract = {

Pushing the frontier of fluorescence microscopy requires the design of enhanced fluorophores with finely tuned properties. We recently discovered that incorporation of four-membered azetidine rings into classic fluorophore structures elicits substantial increases in brightness and photostability, resulting in the Janelia Fluor (JF) series of dyes. We refined and extended this strategy, finding that incorporation of 3-substituted azetidine groups allows rational tuning of the spectral and chemical properties of rhodamine dyes with unprecedented precision. This strategy allowed us to establish principles for fine-tuning the properties of fluorophores and to develop a palette of new fluorescent and fluorogenic labels with excitation ranging from blue to the far-red. Our results demonstrate the versatility of these new dyes in cells, tissues and animals.

}, keywords = {Animals, Brain, Cell Line, Coloring Agents, Drosophila, Image Processing, Computer-Assisted, Larva, Mice, Microscopy, Fluorescence, Photochemical Processes, Staining and Labeling}, issn = {1548-7105}, doi = {10.1038/nmeth.4403}, author = {Grimm, Jonathan B and Muthusamy, Anand K and Liang, Yajie and Brown, Timothy A and Lemon, William C and Patel, Ronak and Lu, Rongwen and Macklin, John J and Keller, Philipp J and Ji, Na and Lavis, Luke D} } @article {48417, title = {Near-infrared fluorescent protein iRFP713 as a reporter protein for optogenetic vectors, a transgenic Cre-reporter rat, and other neuronal studies.}, journal = {Journal of Neuroscience Methods}, volume = {284}, year = {2017}, month = {2017 Apr 02}, pages = {1-14}, abstract = {

BACKGROUND: The use of genetically-encoded fluorescent reporters is essential for the identification and observation of cells that express transgenic modulatory proteins. Near-infrared (NIR) fluorescent proteins have superior light penetration through biological tissue, but are not yet widely adopted.

NEW METHOD: Using the near-infrared fluorescent protein, iRFP713, improves the imaging resolution in thick tissue sections or the intact brain due to the reduced light-scattering at the longer, NIR wavelengths used to image the protein. Additionally, iRFP713 can be used to identify transgenic cells without photobleaching other fluorescent reporters or affecting opsin function. We have generated a set of adeno-associated vectors in which iRFP713 has been fused to optogenetic channels, and can be expressed constitutively or Cre-dependently.

RESULTS: iRFP713 is detectable when expressed in neurons both in vitro and in vivo without exogenously supplied chromophore biliverdin. Neuronally-expressed iRFP713 has similar properties to GFP-like fluorescent proteins, including the ability to be translationally fused to channelrhodopsin or halorhodopsin, however, it shows superior photostability compared to EYFP. Furthermore, electrophysiological recordings from iRFP713-labeled cells compared to cells labeled with mCherry suggest that iRFP713 cells are healthier and therefore more stable and reliable in an ex vivo preparation. Lastly, we have generated a transgenic rat that expresses iRFP713 in a Cre-dependent manner.

CONCLUSIONS: Overall, we have demonstrated that iRFP713 can be used as a reporter in neurons without the use of exogenous biliverdin, with minimal impact on viability and function thereby making it feasible to extend the capabilities for imaging genetically-tagged neurons in slices and in vivo.

}, issn = {1872-678X}, doi = {10.1016/j.jneumeth.2017.03.020}, author = {Richie, Christopher T and Whitaker, Leslie R and Whitaker, Keith W and Necarsulmer, Julie and Baldwin, Heather A and Zhang, Yajun and Fortuno, Lowella and Hinkle, Josh J and Koivula, Pyry and Henderson, Mark J and Sun, Wenzhi and Wang, Kai and Smith, Jeffrey C and Pickel, Jim and Ji, Na and Hope, Bruce T and Harvey, Brandon K} } @article {48304, title = {Video-rate volumetric functional imaging of the brain at synaptic resolution.}, journal = {Nature Neuroscience}, volume = {20}, year = {2017}, month = {2017 Feb 27}, pages = {620-8}, abstract = {

Neurons and neural networks often extend hundreds of micrometers in three dimensions. Capturing the calcium transients associated with their activity requires volume imaging methods with subsecond temporal resolution. Such speed is a challenge for conventional two-photon laser-scanning microscopy, because it depends on serial focal scanning in 3D and indicators with limited brightness. Here we present an optical module that is easily integrated into standard two-photon laser-scanning microscopes to generate an axially elongated Bessel focus, which when scanned in 2D turns frame rate into volume rate. We demonstrated the power of this approach in enabling discoveries for neurobiology by imaging the calcium dynamics of volumes of neurons and synapses in fruit flies, zebrafish larvae, mice and ferrets in vivo. Calcium signals in objects as small as dendritic spines could be resolved at video rates, provided that the samples were sparsely labeled to limit overlap in their axially projected images.

}, issn = {1546-1726}, doi = {10.1038/nn.4516}, author = {Lu, Rongwen and Sun, Wenzhi and Liang, Yajie and Kerlin, Aaron and Bierfeld, Jens and Seelig, Johannes D and Wilson, Daniel E and Scholl, Benjamin and Mohar, Boaz and Tanimoto, Masashi and Koyama, Minoru and Fitzpatrick, David and Orger, Michael B and Ji, Na} } @article {47548, title = {in vivo brain imaging with adaptive optical microscope.}, journal = {Conference on Lasers and Electro-Optics (CLEO): Applications and Technology}, year = {2016}, month = {2016 Jun }, pages = {AM40.1}, abstract = {

The diffraction limited resolution of two photon and confocal microscope can be recovered using adaptive optics to explore the detailed neuronal network in the brains of zebrafish and mouse in vivo.

}, doi = {10.1364/CLEO_AT.2016.AM4O.1}, author = {Wang, Kai and Sun, Wenzhi and Ji, Na and Betzig, Eric} } @article {47813, title = {Technologies for imaging neural activity in large volumes.}, journal = {Nature Neuroscience}, volume = {19}, year = {2016}, month = {2016 Aug 26}, pages = {1154-64}, abstract = {

Neural circuitry has evolved to form distributed networks that act dynamically across large volumes. Conventional microscopy collects data from individual planes and cannot sample circuitry across large volumes at the temporal resolution relevant to neural circuit function and behaviors. Here we review emerging technologies for rapid volume imaging of neural circuitry. We focus on two critical challenges: the inertia of optical systems, which limits image speed, and aberrations, which restrict the image volume. Optical sampling time must be long enough to ensure high-fidelity measurements, but optimized sampling strategies and point-spread function engineering can facilitate rapid volume imaging of neural activity within this constraint. We also discuss new computational strategies for processing and analyzing volume imaging data of increasing size and complexity. Together, optical and computational advances are providing a broader view of neural circuit dynamics and helping elucidate how brain regions work in concert to support behavior.

}, issn = {1546-1726}, doi = {10.1038/nn.4358}, author = {Ji, Na and Freeman, Jeremy and Smith, Spencer L} } @article {47265, title = {Thalamus provides layer 4 of primary visual cortex with orientation- and direction-tuned inputs.}, journal = {Nature Neuroscience}, volume = {19}, year = {2016}, month = {2016 Feb}, pages = {308-15}, abstract = {

Understanding the functions of a brain region requires knowing the neural representations of its myriad inputs, local neurons and outputs. Primary visual cortex (V1) has long been thought to compute visual orientation from untuned thalamic inputs, but very few thalamic inputs have been measured in any mammal. We determined the response properties of ~28,000 thalamic boutons and ~4,000 cortical neurons in layers 1{\textendash}5 of awake mouse V1. Using adaptive optics that allows accurate measurement of bouton activity deep in cortex, we found that around half of the boutons in the main thalamorecipient L4 carried orientation-tuned information and that their orientation and direction biases were also dominant in the L4 neuron population, suggesting that these neurons may inherit their selectivity from tuned thalamic inputs. Cortical neurons in all layers exhibited sharper tuning than thalamic boutons and a greater diversity of preferred orientations. Our results provide data-rich constraints for refining mechanistic models of cortical computation.

}, doi = {10.1038/nn.4196}, author = {Sun, Wenzhi and Tan, Zhongchao and Mensh, Brett D and Ji, Na} } @article {46849, title = {Direct wavefront sensing for high-resolution in vivo imaging in scattering tissue.}, journal = {Nature Communications}, volume = {6}, year = {2015}, month = {2015-Jun-15}, pages = {7276}, abstract = {

Adaptive optics by direct imaging of the wavefront distortions of a laser-induced guide star has long been used in astronomy, and more recently in microscopy to compensate for aberrations in transparent specimens. Here we extend this approach to tissues that strongly scatter visible light by exploiting the reduced scattering of near-infrared guide stars. The method enables in vivo two-photon morphological and functional imaging down to 700 μm inside the mouse brain.

}, issn = {2041-1723}, doi = {10.1038/ncomms8276}, author = {Wang, Kai and Sun, Wenzhi and Richie, Christopher T and Harvey, Brandon K and Betzig, Eric and Ji, Na} } @article {46747, title = {Label-free spectroscopic detection of membrane potential using stimulated Raman scattering.}, journal = {Applied Physics Letters}, volume = {106}, year = {2015}, month = {2015 Apr 27}, pages = {173704}, abstract = {

Hyperspectral stimulated Raman scattering microscopy is deployed to measure single-membrane vibrational spectrum as a function of membrane potential. Using erythrocyte ghost as a model, quantitative correlation between transmembrane potential and Raman spectral profile was found. Specifically, the ratio between the area under Raman band at \~{}2930 cm-1 and that at \~{}2850 cm-1 increased by \~{}2.6 times when the potential across the erythrocyte ghost membrane varied from +10 mV to -10 mV. Our results show the feasibility of employing stimulated Raman scattering microscopy to probe the membrane potential without labeling.

}, doi = {10.1063/1.4919104}, author = {Liu, Bin and Lee, Hyeon Jeong and Zhang, Delong and Liao, Chien-Sheng and Ji, Na and Xia, Yuanqin and Cheng, Ji-Xin} } @article {47239, title = {Minimally invasive microendoscopy system for in vivo functional imaging of deep nuclei in the mouse brain.}, journal = {Biomedical Optics Express}, volume = {6}, year = {2015}, month = {2015 Nov 1}, pages = {4546-56}, abstract = {

The ability to image neurons anywhere in the mammalian brain is a major goal of optical microscopy. Here we describe a minimally invasive microendoscopy system for studying the morphology and function of neurons at depth. Utilizing a guide cannula with an ultrathin wall, we demonstrated in vivo two-photon fluorescence imaging of deeply buried nuclei such as the striatum (2.5 mm depth), substantia nigra (4.4 mm depth) and lateral hypothalamus (5.0 mm depth) in mouse brain. We reported, for the first time, the observation of neuronal activity with subcellular resolution in the lateral hypothalamus and substantia nigra of head-fixed awake mice.

}, issn = {2156-7085}, doi = {10.1364/BOE.6.004546}, author = {Bocarsly, Miriam E and Jiang, Wan-Chen and Wang, Chen and Dudman, Joshua T and Ji, Na and Aponte, Yeka} } @article {46972, title = {Neuronal representation of ultraviolet visual stimuli in mouse primary visual cortex.}, journal = {Scientific Reports}, volume = {5}, year = {2015}, month = {2015 Jul 29}, pages = {12597}, abstract = {

The mouse has become an important model for understanding the neural basis of visual perception. Although it has long been known that mouse lens transmits ultraviolet (UV) light and mouse opsins have absorption in the UV band, little is known about how UV visual information is processed in the mouse brain. Using a custom UV stimulation system and in vivo calcium imaging, we characterized the feature selectivity of layer 2/3 neurons in mouse primary visual cortex (V1). In adult mice, a comparable percentage of the neuronal population responds to UV and visible stimuli, with similar pattern selectivity and receptive field properties. In young mice, the orientation selectivity for UV stimuli increased steadily during development, but not direction selectivity. Our results suggest that, by expanding the spectral window through which the mouse can acquire visual information, UV sensitivity provides an important component for mouse vision.

}, issn = {2045-2322}, doi = {10.1038/srep12597}, author = {Tan, Zhongchao and Sun, Wenzhi and Chen, Tsai-Wen and Kim, Douglas and Ji, Na} } @article {6891, title = {Direct phase measurement in zonal wavefront reconstruction using multidither coherent optical adaptive technique.}, journal = {Optics Express}, volume = {22}, year = {2014}, month = {2014 Jan 27}, pages = {1619-28}, abstract = {

In traditional zonal wavefront sensing for adaptive optics, after local wavefront gradients are obtained, the entire wavefront can be calculated by assuming that the wavefront is a continuous surface. Such an approach will lead to sub-optimal performance in reconstructing wavefronts which are either discontinuous or undersampled by the zonal wavefront sensor. Here, we report a new method to reconstruct the wavefront by directly measuring local wavefront phases in parallel using multidither coherent optical adaptive technique. This method determines the relative phases of each pupil segment independently, and thus produces an accurate wavefront for even discontinuous wavefronts. We implemented this method in an adaptive optical two-photon fluorescence microscopy and demonstrated its superior performance in correcting large or discontinuous aberrations.

}, issn = {1094-4087}, doi = {10.1364/OE.22.001619}, author = {Liu, Rui and Milkie, Daniel E and Kerlin, Aaron and Maclennan, Bryan and Ji, Na} } @article {45373, title = {Multiplexed aberration measurement for deep tissue imaging in vivo.}, journal = {Nature Methods}, year = {2014}, month = {2014 Aug 17}, abstract = {

We describe an adaptive optics method that modulates the intensity or phase of light rays at multiple pupil segments in parallel to determine the sample-induced aberration. Applicable to fluorescent protein-labeled structures of arbitrary complexity, it allowed us to obtain diffraction-limited resolution in various samples in vivo. For the strongly scattering mouse brain, a single aberration correction improved structural and functional imaging of fine neuronal processes over a large imaging volume.

}, issn = {1548-7105}, doi = {10.1038/nmeth.3068}, author = {Wang, Chen and Liu, Rui and Milkie, Daniel E and Sun, Wenzhi and Tan, Zhongchao and Kerlin, Aaron and Chen, Tsai-Wen and Kim, Douglas S and Ji, Na} } @article {45374, title = {The practical and fundamental limits of optical imaging in mammalian brains.}, journal = {Neuron}, volume = {83}, year = {2014}, month = {2014 Sep 17}, pages = {1242-1245}, abstract = {

Advances in chemistry and physics have profound effects on neuroimaging. Current and future progress in\ these disciplines will continue to aid in efforts to visualize neural circuitry, particularly in deeper layers of the brain.

}, issn = {1097-4199}, doi = {10.1016/j.neuron.2014.08.009}, author = {Ji, Na} } @article {6675, title = {Characterization and improvement of three-dimensional imaging performance of GRIN-lens-based two-photon fluorescence endomicroscopes with adaptive optics.}, journal = {Optics Express}, volume = {21}, year = {2013}, month = {2013 Nov 4}, pages = {27142-54}, abstract = {

Inherent aberrations of gradient index (GRIN) lenses used in fluorescence endomicroscopes deteriorate imaging performance. Using adaptive optics, we characterized and corrected the on-axis and off-axis aberrations of a GRIN lens with NA 0.8 at multiple focal planes. We demonstrated a rotational-transformation-based correction procedure, which enlarged the imaging area with diffraction-limited resolution with only two aberration measurements. 204.8 {\texttimes} 204.8 {\textmu}m2 images of fluorescent beads and brain slices before and after AO corrections were obtained, with evident improvements in both image sharpness and brightness after AO correction. These results show great promises of applying adaptive optical two-photon fluorescence endomicroscope to three-dimensional (3D) imaging.

}, issn = {1094-4087}, doi = {10.1364/OE.21.027142}, author = {Wang, Chen and Ji, Na} } @article {4446, title = {Characterization and adaptive optical correction of aberrations during in vivo imaging in the mouse cortex.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {109}, year = {2012}, month = {2012 Jan 3}, pages = {22-7}, abstract = {

The signal and resolution during in vivo imaging of the mouse brain is limited by sample-induced optical aberrations. We find that, although the optical aberrations can vary across the sample and increase in magnitude with depth, they remain stable for hours. As a result, two-photon adaptive optics can recover diffraction-limited performance to depths of 450\ μm and improve imaging quality over fields of view of hundreds of microns. Adaptive optical correction yielded fivefold signal enhancement for small neuronal structures and a threefold increase in axial resolution. The corrections allowed us to detect smaller neuronal structures at greater contrast and also improve the signal-to-noise ratio during functional Ca(2+) imaging in single neurons.

}, issn = {1091-6490}, doi = {10.1073/pnas.1109202108}, author = {Ji, Na and Sato, Takashi R and Betzig, Eric} } @article {4900, title = {Pupil-segmentation-based adaptive optical correction of a high-numerical-aperture gradient refractive index lens for two-photon fluorescence endoscopy.}, journal = {Optics Letters}, volume = {37}, year = {2012}, month = {2012 Jun}, pages = {2001-3}, abstract = {

The intrinsic aberrations of high-NA gradient refractive index (GRIN) lenses limit their image quality as well as field of view. Here we used a pupil-segmentation-based adaptive optical approach to correct the inherent aberrations in a two-photon fluorescence endoscope utilizing a 0.8\ NA GRIN lens. By correcting the field-dependent aberrations, we recovered diffraction-limited performance across a large imaging field. The consequent improvements in imaging signal and resolution allowed us to detect fine structures that were otherwise invisible inside mouse brain slices.

}, doi = {10.1364/OL.37.002001}, url = {http://dx.doi.org/10.1364/OL.37.002001}, author = {Wang, Chan and Ji, Na} } @article {4392, title = {Pupil-segmentation-based adaptive optical microscopy with full-pupil illumination.}, journal = {Optics Letters}, volume = {36}, year = {2011}, month = {2011 Nov 1}, pages = {4206-8}, abstract = {

Optical aberrations deteriorate the performance of microscopes. Adaptive optics can be used to improve imaging performance via wavefront shaping. Here, we demonstrate a pupil-segmentation based adaptive optical approach with full-pupil illumination. When implemented in a two-photon fluorescence microscope, it recovers diffraction-limited performance and improves imaging signal and resolution.

}, issn = {1539-4794}, doi = {10.1364/OL.36.004206}, author = {Milkie, Daniel E and Betzig, Eric and Ji, Na} } @article {6309, title = {Pupil-segmentation-based adaptive optics for microscopy.}, journal = {Proceedings of SPIE}, volume = {7931}, year = {2011}, month = {2011}, pages = {79310I}, abstract = {

Inhomogeneous optical properties of biological samples make it difficult to obtain diffraction-limited resolution in depth. Correcting the sample-induced optical aberrations needs adaptive optics (AO). However, the direct wavefront-sensing approach commonly used in astronomy is not suitable for most biological samples due to their strong scattering of light. We developed an image-based AO approach that is insensitive to sample scattering. By comparing images of the sample taken with different segments of the pupil illuminated, local tilt in the wavefront is measured from image shift. The aberrated wavefront is then obtained either by measuring the local phase directly using interference or with phase reconstruction algorithms similar to those used in astronomical AO. We implemented this pupil-segmentation-based approach in a two-photon fluorescence microscope and demonstrated that diffraction-limited resolution can be recovered from nonbiological and biological samples.

}, doi = {10.1117/12.876398}, author = {Ji, Na and Milkie, Daniel E and Betzig, Eric} } @article {2075, title = {Adaptive optics via pupil segmentation for high-resolution imaging in biological tissues. (With commentary)}, journal = {Nature Methods}, volume = {7}, year = {2010}, month = {2010 Feb}, pages = {141-7}, abstract = {

Biological specimens are rife with optical inhomogeneities that seriously degrade imaging performance under all but the most ideal conditions. Measuring and then correcting for these inhomogeneities is the province of adaptive optics. Here we introduce an approach to adaptive optics in microscopy wherein the rear pupil of an objective lens is segmented into subregions, and light is directed individually to each subregion to measure, by image shift, the deflection faced by each group of rays as they emerge from the objective and travel through the specimen toward the focus. Applying our method to two-photon microscopy, we could recover near-diffraction-limited performance from a variety of biological and nonbiological samples exhibiting aberrations large or small and smoothly varying or abruptly changing. In particular, results from fixed mouse cortical slices illustrate our ability to improve signal and resolution to depths of 400 microm.

Commentary: Introduces a new, zonal approach to adaptive optics (AO) in microscopy suitable for highly inhomogeneous and/or scattering samples such as living tissue. The method is unique in its ability to handle large amplitude aberrations (\>20 wavelengths), including spatially complex aberrations involving high order modes beyond the ability of most AO actuators to correct. As befitting a technique designed for in vivo fluorescence imaging, it is also photon efficient.
Although used here in conjunction with two photon microscopy to demonstrate correction deep into scattering tissue, the same principle of pupil segmentation might be profitably adapted to other point-scanning or widefield methods. For example, plane illumination microscopy of multicellular specimens is often beset by substantial aberrations, and all far-field superresolution methods are exquisitely sensitive to aberrations.

}, keywords = {Artifacts, Computer-Aided Design, Equipment Design, Equipment Failure Analysis, Fluorescence, Image Enhancement, Lenses, Lighting, Microscopy, Multiphoton, Reproducibility of Results, Sensitivity and Specificity}, issn = {1548-7105}, doi = {10.1038/nmeth.1411}, url = {http://www.ncbi.nlm.nih.gov/pubmed/20037592}, author = {Ji, Na and Milkie, Daniel E and Betzig, Eric} } @article {4019, title = {Adaptive optics via pupil segmentation for high-resolution imaging in biological tissues.}, journal = {Nature Methods}, volume = {7}, year = {2010}, month = {2010 Feb}, pages = {141-7}, abstract = {

Biological specimens are rife with optical inhomogeneities that seriously degrade imaging performance under all but the most ideal conditions. Measuring and then correcting for these inhomogeneities is the province of adaptive optics. Here we introduce an approach to adaptive optics in microscopy wherein the rear pupil of an objective lens is segmented into subregions, and light is directed individually to each subregion to measure, by image shift, the deflection faced by each group of rays as they emerge from the objective and travel through the specimen toward the focus. Applying our method to two-photon microscopy, we could recover near-diffraction-limited performance from a variety of biological and nonbiological samples exhibiting aberrations large or small and smoothly varying or abruptly changing. In particular, results from fixed mouse cortical slices illustrate our ability to improve signal and resolution to depths of 400 microm.

}, keywords = {Artifacts, Computer-Aided Design, Equipment Design, Equipment Failure Analysis, Fluorescence, Image Enhancement, Lenses, Lighting, Microscopy, Multiphoton, Reproducibility of Results, Sensitivity and Specificity}, issn = {1548-7105}, doi = {10.1038/nmeth.1411}, author = {Ji, Na and Milkie, Daniel E and Betzig, Eric} } @article {4020, title = {Advances in the speed and resolution of light microscopy.}, journal = {Current Opinion in Neurobiology}, volume = {18}, year = {2008}, month = {2008 Dec}, pages = {605-16}, abstract = {

Neurobiological processes occur on spatiotemporal scales spanning many orders of magnitude. Greater understanding of these processes therefore demands improvements in the tools used in their study. Here we review recent efforts to enhance the speed and resolution of one such tool, fluorescence microscopy, with an eye toward its application to neurobiological problems. On the speed front, improvements in beam scanning technology, signal generation rates, and photodamage mediation are bringing us closer to the goal of real-time functional imaging of extended neural networks. With regard to resolution, emerging methods of adaptive optics may lead to diffraction-limited imaging or much deeper imaging in optically inhomogeneous tissues, and super-resolution techniques may prove a powerful adjunct to electron microscopic methods for nanometric neural circuit reconstruction.

}, keywords = {Animals, Electron, Fluorescence, Humans, Microscopy, Nerve Net, Neurology, Photobleaching, Photons}, issn = {1873-6882}, doi = {10.1016/j.conb.2009.03.009}, author = {Ji, Na and Shroff, Hari and Zhong, Haining and Betzig, Eric} } @article {2077, title = {Advances in the speed and resolution of light microscopy. (With commentary)}, journal = {Current Opinion in Neurobiology}, volume = {18}, year = {2008}, month = {2008 Dec}, pages = {605-16}, abstract = {

Neurobiological processes occur on spatiotemporal scales spanning many orders of magnitude. Greater understanding of these processes therefore demands improvements in the tools used in their study. Here we review recent efforts to enhance the speed and resolution of one such tool, fluorescence microscopy, with an eye toward its application to neurobiological problems. On the speed front, improvements in beam scanning technology, signal generation rates, and photodamage mediation are bringing us closer to the goal of real-time functional imaging of extended neural networks. With regard to resolution, emerging methods of adaptive optics may lead to diffraction-limited imaging or much deeper imaging in optically inhomogeneous tissues, and super-resolution techniques may prove a powerful adjunct to electron microscopic methods for nanometric neural circuit reconstruction.

Commentary: A brief review of recent trends in microscopy. The section {\textquotedblleft}Caveats regarding the application of superresolution microscopy{\textquotedblright} was written in an effort to inject a dose of reality and caution into the unquestioning enthusiasm in the academic community for all things superresolution, covering the topics of labeling density and specificity, sample preparation artifacts, speed vs. resolution vs. photodamage, and the implications of signal-to-background for Nyquist vs. Rayleigh definitions of resolution.

}, keywords = {Animals, Electron, Fluorescence, Humans, Microscopy, Nerve Net, Neurology, Photobleaching, Photons}, issn = {1873-6882}, doi = {10.1016/j.conb.2009.03.009}, url = {http://www.ncbi.nlm.nih.gov/pubmed/19375302}, author = {Ji, Na and Shroff, Hari and Zhong, Haining and Betzig, Eric} } @article {2081, title = {High-speed, low-photodamage nonlinear imaging using passive pulse splitters. (With commentary)}, journal = {Nature Methods}, volume = {5}, year = {2008}, month = {2008 Feb}, pages = {197-202}, abstract = {

Pulsed lasers are key elements in nonlinear bioimaging techniques such as two-photon fluorescence excitation (TPE) microscopy. Typically, however, only a percent or less of the laser power available can be delivered to the sample before photoinduced damage becomes excessive. Here we describe a passive pulse splitter that converts each laser pulse into a fixed number of sub-pulses of equal energy. We applied the splitter to TPE imaging of fixed mouse brain slices labeled with GFP and show that, in different power regimes, the splitter can be used either to increase the signal rate more than 100-fold or to reduce the rate of photobleaching by over fourfold. In living specimens, the gains were even greater: a ninefold reduction in photobleaching during in vivo imaging of Caenorhabditis elegans larvae, and a six- to 20-fold decrease in the rate of photodamage during calcium imaging of rat hippocampal brain slices.

Commentary: Na Ji came to me early in her postdoc with an idea to reduce photodamage in nonlinear microscopy by splitting the pulses from an ultrafast laser into multiple subpulses of reduced energy. In six weeks, we constructed a prototype pulse splitter and obtained initial results confirming the validity of her vision. Further experiments with Jeff Magee demonstrated that the splitter could be used to increase imaging speed or reduce photodamage in two photon microscopy by one to two orders of magnitude. This project is a great example of how quickly one can react and exploit new ideas in the Janelia environment.

}, keywords = {Animals, Caenorhabditis elegans, Cell Survival, Cells, Cultured, Equipment Design, Equipment Failure Analysis, Fluorescence, Image Enhancement, Lasers, Light, Lighting, Mice, Microscopy, Nonlinear Dynamics, Rats}, issn = {1548-7105}, doi = {10.1038/nmeth.1175}, url = {http://www.ncbi.nlm.nih.gov/pubmed/18204458}, author = {Ji, Na and Magee, Jeffrey C and Betzig, Eric} } @article {3916, title = {High-speed, low-photodamage nonlinear imaging using passive pulse splitters.}, journal = {Nature Methods}, volume = {5}, year = {2008}, month = {2008 Feb}, pages = {197-202}, abstract = {

Pulsed lasers are key elements in nonlinear bioimaging techniques such as two-photon fluorescence excitation (TPE) microscopy. Typically, however, only a percent or less of the laser power available can be delivered to the sample before photoinduced damage becomes excessive. Here we describe a passive pulse splitter that converts each laser pulse into a fixed number of sub-pulses of equal energy. We applied the splitter to TPE imaging of fixed mouse brain slices labeled with GFP and show that, in different power regimes, the splitter can be used either to increase the signal rate more than 100-fold or to reduce the rate of photobleaching by over fourfold. In living specimens, the gains were even greater: a ninefold reduction in photobleaching during in vivo imaging of Caenorhabditis elegans larvae, and a six- to 20-fold decrease in the rate of photodamage during calcium imaging of rat hippocampal brain slices.

}, keywords = {Animals, Caenorhabditis elegans, Cell Survival, Cells, Cultured, Equipment Design, Equipment Failure Analysis, Fluorescence, Image Enhancement, Lasers, Light, Lighting, Mice, Microscopy, Nonlinear Dynamics, Rats}, issn = {1548-7105}, doi = {10.1038/nmeth.1175}, author = {Ji, Na and Magee, Jeffrey C and Betzig, Eric} } @article {1731, title = {Interfacial structures of acidic and basic aqueous solutions.}, journal = {Journal of the American Chemical Society}, volume = {130}, year = {2008}, month = {2008 Oct 1}, pages = {13033-9}, abstract = {

Phase-sensitive sum-frequency vibrational spectroscopy was used to study water/vapor interfaces of HCl, HI, and NaOH solutions. The measured imaginary part of the surface spectral responses provided direct characterization of OH stretch vibrations and information about net polar orientations of water species contributing to different regions of the spectrum. We found clear evidence that hydronium ions prefer to emerge at interfaces. Their OH stretches contribute to the "ice-like" band in the spectrum. Their charges create a positive surface field that tends to reorient water molecules more loosely bonded to the topmost water layer with oxygen toward the interface, and thus enhances significantly the "liquid-like" band in the spectrum. Iodine ions in solution also like to appear at the interface and alter the positive surface field by forming a narrow double-charge layer with hydronium ions. In NaOH solution, the observed weak change of the "liquid-like" band and disappearance of the "ice-like" band in the spectrum indicates that OH(-) ions must also have excess at the interface. How they are incorporated in the interfacial water structure is, however, not clear.

}, issn = {1520-5126}, doi = {10.1021/ja8021297}, author = {Tian, Chuanshan and Ji, Na and Waychunas, Glenn A and Shen, Y Ron} } @article {1733, title = {Phase-sensitive sum-frequency vibrational spectroscopy and its application to studies of interfacial alkyl chains.}, journal = {Journal of the American Chemical Society}, volume = {129}, year = {2007}, month = {2007 Aug 22}, pages = {10056-7}, abstract = {

The first general phase-sensitive sum-frequency vibrational spectroscopy (SFVS) was described, which recovers the phase information lost in conventional SFVS measurements. Using a self-assembled monolayer, we demonstrated that this novel technique measures the absolute orientation of surface molecular moieties and is very powerful in resolving spectral features.

}, issn = {0002-7863}, doi = {10.1021/ja071989t}, author = {Ji, Na and Ostroverkhov, Victor and Chen, Chao-Yuan and Shen, Yuen-Ron} } @article {1734, title = {Atomic and molecular parity nonconservation and sum frequency generation solutions to the ozma problem.}, journal = {The Journal of Physical Chemistry}, volume = {110}, year = {2006}, month = {2006 Sep 28}, pages = {18744-7}, abstract = {

Two Ozma problems are defined. Parity nonconservation is necessary for their solutions. Both problems may be solved by beta decay or atomic optical activity. Atomic and molecular sum frequency generation is chosen, as it supplies rich methods of effecting "gedanken" solutions to the Ozma problems. A new method of measuring a parameter manifesting molecular parity violations is advanced.

}, issn = {1520-6106}, doi = {10.1021/jp055038i}, author = {Ji, Na and Harris, Robert A} } @article {1736, title = {A novel spectroscopic probe for molecular chirality.}, journal = {Chirality}, volume = {18}, year = {2006}, month = {2006 Feb}, pages = {146-58}, abstract = {

Recent advances in developing sum frequency generation (SFG) as a novel spectroscopic probe for molecular chirality are reviewed. The basic principle underlying the technique is briefly described, in comparison with circular dichroism (CD). The significantly better sensitivity of the technique than CD is pointed out, and the reason is discussed. Bi-naphthol (BN) and amino acids are used as representatives for two different types of chiral molecules; the measured chirality in their electronic transitions can be understood by two different molecular models, respectively, that are extensions of models developed earlier for CD. Optically active or chiral SFG from vibrational transitions are weaker, but with the help of electronic-vibrational double resonance, the vibrational spectrum of a monolayer of BN has been obtained. Generally, optically active SFG is sufficiently sensitive to be employed to probe in-situ chirality of chiral monolayers and thin films.

}, keywords = {Algorithms, Chemistry, Molecular Conformation, Physical, Physicochemical Phenomena, Stereoisomerism}, issn = {0899-0042}, doi = {10.1002/chir.20238}, author = {Ji, Na and Shen, Yuen-Ron} } @article {1735, title = {Three-dimensional chiral imaging by sum-frequency generation.}, journal = {Journal of the American Chemical Society}, volume = {128}, year = {2006}, month = {2006 Mar 22}, pages = {3482-3}, abstract = {

A sum-frequency generation (SFG) microscope that is sensitive toward molecular chirality was demonstrated for the first time. Optically active images of chiral 1,1{\textquoteright}-bi-2-naphthol solutions were obtained with submicron spatial resolution. Three-dimensional sectioning capability of our microscope was also demonstrated. This optically active SFG microscopy can potentially become a powerful imaging technique for biological samples.

}, keywords = {Computer-Assisted, Fluorescence, Image Processing, Microscopy, Naphthols, Stereoisomerism}, issn = {0002-7863}, doi = {10.1021/ja057775y}, author = {Ji, Na and Zhang, Kai and Yang, Haw and Shen, Yuen-Ron} } @article {2729, title = {Toward chiral sum-frequency spectroscopy.}, journal = {Journal of the American Chemical Society}, volume = {128}, year = {2006}, month = {2006 Jul 12}, pages = {8845-8}, abstract = {

Chiral sum-frequency (SF) spectroscopy that measures both the real and the imaginary components of the SF spectral response was demonstrated for the first time. It was based on interference of the SF signal with a dispersionless SF reference. Solutions of 1,1{\textquoteright}-bi-2-naphthol (BN) were used as model systems, and their chiral SF spectra over the first exciton-split transitions were obtained. Chiral spectra are useful for determination of absolute configuration and conformation of chiral molecules.

}, keywords = {Molecular Conformation, Naphthols, Sensitivity and Specificity, Solutions, Spectrum Analysis}, issn = {0002-7863}, doi = {10.1021/ja060888c}, author = {Ji, Na and Ostroverkhov, Victor and Belkin, Mikhail and Shiu, Ying-Jen and Shen, Yuen-Ron} } @article {1737, title = {A dynamic coupling model for sum frequency chiral response from liquids composed of molecules with a chiral side chain and an achiral chromophore.}, journal = {Journal of the American Chemical Society}, volume = {127}, year = {2005}, month = {2005 Sep 21}, pages = {12933-42}, abstract = {

A theoretical formulation for optically active sum frequency generation (OA-SFG) from isotropic chiral solutions was proposed for molecules with a chiral side chain and an intrinsically achiral chromophore. Adapting an electron correlation model first proposed by H{\"o}hn and Weigang for linear optical activity, we presented a dynamic coupling model for OA-SFG near the electronic resonance of the achiral chromophore. As a demonstration, we used this model to explain the observed OA-SFG spectra of a series of amino acids near the electronic resonance of the intrinsically achiral carboxyl group. Our model shows that the nonlinear chiroptical response comes about by the through-space correlative electronic interactions between the chiral side chain and the achiral chromophore, and its magnitude is determined by the position and orientation of the bonds that make up the chiral side chain. Using the bond polarizability values in the literature and the conformations of amino acids obtained from calculation, we were able to reproduce the relative OA-SFG strength from a series of amino acids.

}, keywords = {Amino Acids, Chemical, Infrared, Models, Spectrophotometry, Thermodynamics}, issn = {0002-7863}, doi = {10.1021/ja052715d}, author = {Ji, Na and Shen, Yuen-Ron} } @article {1738, title = {Optically active sum frequency generation from molecules with a chiral center: amino acids as model systems.}, journal = {Journal of the American Chemical Society}, volume = {126}, year = {2004}, month = {2004 Nov 24}, pages = {15008-9}, abstract = {

With amino acids as model systems, optically active sum frequency generation (OA-SFG) was used to probe the chirality of molecules with a chiral center and an intrinsically achiral chromophore in isotropic solution for the first time. Like that of circular dichroism (CD), the OA-SFG{\textquoteright}s near electronic resonance originates from the extrachromophoric chiral perturbation on the carboxyl chromophore. The difference in the relative strengths of OA-SFG and CD among different amino acids can be explained by the difference in the details of perturbations.

}, keywords = {Amino Acids, Chemical, Circular Dichroism, Models, Optics and Photonics, Stereoisomerism}, issn = {0002-7863}, doi = {10.1021/ja045708i}, author = {Ji, Na and Shen, Yuen-Ron} } @article {1739, title = {Sum frequency vibrational spectroscopy of leucine molecules adsorbed at air-water interface.}, journal = {The Journal of Chemical Physics}, volume = {120}, year = {2004}, month = {2004 Apr 15}, pages = {7107-12}, abstract = {

Sum frequency vibrational spectroscopy was used to study adsorption of leucine molecules at air-water interface from solutions with different concentrations and pH values. The surface density and the orientation of the isopropyl head group of the adsorbed leucine molecules could be deduced from the measurements. It was found that the orientation depends on the surface density, but only weakly on bulk pH value at the saturated surface density. The vibrational spectra of the interfacial water molecules appeared to be strongly affected by the charge state of the adsorbed leucine molecules. Enhancement and inversion of polar orientation of interfacial water molecules by surface charges or field controllable by the bulk pH value were observed.

}, keywords = {Adsorption, Air, Chemistry, Hydrogen-Ion Concentration, Leucine, Physical, Spectrophotometry, Spectrum Analysis, Surface Properties, Water}, issn = {0021-9606}, doi = {10.1063/1.1669375}, author = {Ji, Na and Shen, Yuen-Ron} } @article {2730, title = {Sum-frequency vibrational spectroscopic study of surface glass transition of poly(vinyl alcohol).}, journal = {Macromolecules}, volume = {36}, year = {2003}, month = {2003 May}, pages = {3303}, abstract = {

Sum-frequency vibrational spectroscopy was employed to study surface glass transition of

poly(vinyl alcohol) by monitoring the relaxation of rubbing-induced alignment of surface chains with

increase of temperature. The observed chain relaxation is two-dimensional, parallel to the surface. The

surface transition temperature is 58 ( 2 {\textdegree}C, essentially the same as the bulk one.

}, doi = {10.1021/ma025681s}, author = {Ji, Na} } @article {1740, title = {Surface vibrational spectroscopy on shear-aligned poly(tetrafluoroethylene) films.}, journal = {Journal of the American Chemical Society}, volume = {125}, year = {2003}, month = {2003 Nov 26}, pages = {14218-9}, abstract = {

Sum-frequency vibrational spectroscopy was used to obtain the first surface vibrational spectra of shear-deposited highly oriented poly(tetrafluoroethylene) (PTFE, Teflon) thin films. The surface PTFE chains appeared to lie along the shearing direction. Vibrational modes observed at 1142 and 1204 cm-1 were found to have the E1 symmetry, in support of some earlier analysis in the long-lasting controversy over the assignment of these modes.

}, issn = {0002-7863}, doi = {10.1021/ja037964l}, author = {Ji, Na and Ostroverkhov, Victor and Lagugn{\'e}-Labarthet, Fran\c cois and Shen, Yuen-Ron} } @article {2731, title = {Sum-frequency spectroscopy of electronic resonances on a chiral surface monolayer of bi-naphthol.}, journal = {Physical Review B}, volume = {66}, year = {2002}, month = {2002 Oct 25}, pages = {165415}, abstract = {

We study chiral response in optical sum-frequency generation near electronic resonances from a 1,1\ '\ -bi-2\  -naphthol (BN) monolayer adsorbed on water. The polarization dependence of the spectra indicates that the molecules are well oriented at the surface with their symmetry axis along the surface normal. Orientational ordering effectively enhances the chiral response per BN molecule. The results can be quantitatively understood with a simple coupled-oscillator model for BN.

}, doi = {10.1103/PhysRevB.66.165415}, author = {Ji, Na} }