Alexander S. Dvornikov

University of California, Irvine, Irvine, California, United States

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Publications (92)118.49 Total impact

  • Viera Crosignani, Sohail Jahid, Alexander S. Dvornikov, Enrico Gratton
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    ABSTRACT: We describe a novel two-photon fluorescence microscopy system capable of producing high-quality second harmonic generation (SHG) images in thick turbid media by using an innovative detection system. This novel detection system is capable of detecting photons from a very large surface area. This system has proven effective in providing images of thick turbid samples, both biological and artificial. Due to its transmission detection geometry, the system is particularly suitable for detecting SHG signals, which are generally forward directed. In this article, we present comparative data acquired simultaneously on the same sample with the forward and epidetection schemes. Microsc. Res. Tech., 2014. © 2014 Wiley Periodicals, Inc.
    Microscopy Research and Technique 03/2014; · 1.59 Impact Factor
  • Viera Crosignani, Alexander Dvornikov, Enrico Gratton
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    ABSTRACT: We constructed an advanced detection system for two-photon fluorescence microscopy that allows us to image in biological tissue and tissue phantoms up to the depth of a few mm with micron resolution. The innovation lies in the detection system which is much more sensitive to low level fluorescence signals than the fluorescence detection configuration used in conventional two-photon fluorescence microscopes. A wide area photocathode photomultiplier tube (PMT) was used to detect fluorescence photons directly from a wide (1 inch diameter) area of the turbid sample, as opposed to the photon collection by the microscope objective which can only collect light from a relatively small area of the sample. The optical path between the sample and the photocathode is refractive index matched to curtail losses at the boundaries due to reflections. The system has been successfully employed in the imaging of tissue phantoms simulating brain optical properties and in biological tissues, such as murine small intestine, colon, tumors, and other samples. The system has in-depth fluorescence lifetime imaging (FLIM) capabilities and is also highly suitable for SHG signal detection, such as collagen fibers and muscles, due to the intrinsically forward-directed propagation of SHG photons.
    Proc SPIE 02/2013;
  • Viera Crosignani, Alexander Dvornikov, Enrico Gratton
    Biophysical Journal 01/2013; 104(2):336-. · 3.67 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: We describe a novel technical approach with enhanced fluorescence detection capabilities in twophoton microscopy that achieves deep tissue imaging, while maintaining micron resolution. Compared to conventional two-photon microscopy, greater imaging depth is achieved by more efficient harvesting of fluorescence photons propagating in multiple-scattering media. The system maintains the conventional two-photon microscopy scheme for excitation. However, for fluorescence collection the detection system harvests fluorescence photons directly from a wide area of the turbid sample. The detection scheme relies on a wide area detector, minimal optical components and an emission path bathed in a refractive-index-matching fluid that minimizes emission photon losses. This detection scheme proved to be very efficient, allowing us to obtain high resolution images at depths up to 3 mm. This technique was applied to in vivo imaging of the murine small intestine (SI) and colon. The challenge is to image normal and diseased tissue in the whole live animal, while maintaining high resolution imaging at millimeter depth. In Lgr5-GFP mice, we have been successful in imaging Lgr5-eGFP positive stem cells, present in SI and colon crypt bases.
    Journal of Biomedical Optics 11/2012; 17(11):116023. · 2.88 Impact Factor
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    ABSTRACT: Recently we described a novel technical approach with enhanced fluorescence detection capabilities in two-photon microscopy that achieves deep tissue imaging, while maintaining micron resolution. This technique was applied to in vivo imaging of murine small intestine and colon. Individuals with Inflammatory Bowel Disease (IBD), commonly presenting as Crohn's disease or Ulcerative Colitis, are at increased risk for developing colorectal cancer. We have developed a Giα2 gene knock out mouse IBD model that develops colitis and colon cancer. The challenge is to study the disease in the whole animal, while maintaining high resolution imaging at millimeter depth. In the Giα2-/- mice, we have been successful in imaging Lgr5-GFP positive stem cell reporters that are found in crypts of niche structures, as well as deeper structures, in the small intestine and colon at depths greater than 1mm. In parallel with these in vivo deep tissue imaging experiments, we have also pursued autofluorescence FLIM imaging of the colon and small intestine-at more shallow depths (roughly 160μm)- on commercial two photon microscopes with excellent structural correlation (in overlapping tissue regions) between the different technologies.
    Proc SPIE 02/2012;
  • Viera Crosignani, Alexander Dvornikov, Enrico Gratton
    Biophysical Journal 01/2012; 102(3):199-. · 3.67 Impact Factor
  • Viera Crosignani, Alexander S Dvornikov, Enrico Gratton
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    ABSTRACT: The depth of two-photon fluorescence imaging in turbid media can be significantly enhanced by the use of the here described fluorescence detection method that allows to efficiently collect scattered fluorescence photons from a wide area of the turbid sample. By using this detector we were able to perform imaging of turbid samples, simulating brain tissue, at depths up to 3 mm, where the two-photon induced fluorescence signal is too weak to be detected by means used in conventional two-photon microscopy.
    Journal of Biophotonics 03/2011; 4(9):592-9. · 3.10 Impact Factor
  • Viera Crosignani, Alexander Dvornikov, Enrico Gratton
    Biophysical Journal 01/2011; 100(3). · 3.67 Impact Factor
  • Yongchao Liang, A. S. Dvornikov, P. M. Rentzepis
    ChemInform 01/2010; 31(8).
  • A. S. DVORNIKOV, J. MALKIN, P. M. RENTZEPIS
    ChemInform 01/2010; 25(48).
  • A S Dvornikov, E P Walker, P M Rentzepis
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    ABSTRACT: We describe the design and construction of ultrahigh capacity three-dimensional, 3D, optical storage devices that operate by two-photon absorption. The molecular systems and their properties that are used as two photon media for writing and one photon for accessing the stored information within the volume of the device are presented in some detail and the nonlinear two-photon absorption mechanism is briefly visited. The optical system and its components, which facilitated writing and reading, are also described and the bit density, bit error rate, store and access speeds, cycle times, and stability of the materials under various experimental conditions are also topics addressed in this review. The first ever storage of terabyte data in a removable storage disk is described in detail.
    The Journal of Physical Chemistry A 10/2009; 113(49):13633-44. · 2.77 Impact Factor
  • Jie Chen, Alexander S Dvornikov, Peter M Rentzepis
    The Journal of Physical Chemistry A 08/2009; 113(30):8818-9; discussion 8820-2. · 2.77 Impact Factor
  • Source
    A.S. Dvornikov, H. Zhang, P.M. Rentzepis
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    ABSTRACT: A new dye precursor (DP) molecule was synthesized and its photochromic, spectroscopic and kinetic properties were determined. This dye precursor yields the strongly fluorescent Rhodamine 700 dye when it is exposed to UV light. The ability to form a highly fluorescent dye was utilized in the fabrication of two-photon volumetric optical memory materials. The spectral characteristics, kinetics and photochemistry were measured and the photoreactions mechanism is proposed.
    Journal of Photochemistry and Photobiology A: Chemistry. 01/2009; 201(1):57-61.
  • Ed Walker, Alexander Dvornikov, Ken Coblentz, Peter Rentzepis
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    ABSTRACT: 1 Tbyte of data has been recorded in 200 layers inside the volume of one of our two-photon 3D disks. Each layer contains 5 Gb of data similar to the capacity of a single layer DVD. The results obtained with our high-performance 1.0 numerical aperture (NA) objective lens show a full disk recording of 1 Tbyte within a standard optical disk form factor 120 mm x 1.2 mm thick utilizing our very stable and efficient materials. Very high sensitivity materials are recorded with bit energies as low as 250 pJ/bit. Materials sensitive at 405 nm are experimentally tested by recording with a 405 nm Nichia laser diode. Results show that bit dimensions are further reduced, which enables future recordings of 5 Tbyte disk capacities by recording 25 Gb/layer, the equivalent of a Blu-ray disk capacity per layer.
    Applied Optics 09/2008; 47(22):4133-9. · 1.69 Impact Factor
  • Ed Walker, Alexander Dvornikov, Ken Coblentz, Peter Rentzepis
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    ABSTRACT: We have recorded 1TeraByte of data in 200 layers in the volume of one DVD-like two-photon 3D disks. Each layer contains 5GBytes of data, equal to single layer DVD capacity. The results obtained with our high-performance 1.0NA objective lens show a full disk recording of 1 TByte within a standard optical disk form factor of 120mm × 1.2mm thick utilizing our very stable and efficient materials. Very high sensitivity materials are used to store information with bit energies as low as 250pJ/bit. Materials sensitive at 405nm are been tested by recording with 405nm Nichia laser diodes. Results show that bit dimensions are further reduced enabling future recordings at 5TByte disk capacities by recording 25GBytes/layer, the equivalent of a Blu-ray disk capacity per layer.
    Proc SPIE 08/2008;
  • Hua Zhang, Jie Chen, Ivan V Tomov, Alexander S Dvornikov, Peter M Rentzepis
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    ABSTRACT: The photochemical redox reaction kinetics of [M(III)(C(2)O(4))(3)](3-) [M = Co, Fe] complexes have been reexamined and studied by time-resolved spectroscopy. The redox mechanisms of the two systems, Co and Fe, were found to be similar to each other, and solvated electrons were observed immediately after 266/267 nm photoexcitation. A reaction mechanism is proposed that involves photoelectron detachment as a primary process. The charge-transfer bands for both complexes, which had been attributed to ligand to metal charge-transfer (LMCT) transitions previously, are reassigned to charge transfer to solvent (CTTS) transitions.
    The Journal of Physical Chemistry A 12/2007; 111(45):11584-8. · 2.77 Impact Factor
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    ABSTRACT: 253GB have been recorded in 300 layers inside the volume of one of our two-photon 3D disks. Each layer contains the equivalent of CD layer bit-densities recorded with a 0.5NA objective lens. A new 1.0NA lens with the desirable first order optical properties of long working distance and small diameter, 1.2mm and 4.5mm, and a self-compensating spherical aberration correction mechanism is designed, manufactured and integrated into our single beam two-photon 3D automated recording system. Experimental data obtained with the 1.0NA lens are presented. The resulting bit densities obtained with our new high-performance liquid immersion singlet (LIS) objective lens indicate that our system is capable of full disk recordings from 0.5 to 1 TB within a standard optical disk form factor of 120mm x 1.2mm thick utilizing our very stable and efficient materials. A compact optical head based on our new objective lens capable of TB storage is described.
    Optics Express 10/2007; 15(19):12264-76. · 3.55 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: 253GB have been recorded in one of our two-photon 3-d disks. Experiments indicate a roadmap of full disk recordings from 0.5 to 1TB utilizing our very stable and efficient materials and new high-performance objective lens.
    Proc SPIE 05/2007;
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    ABSTRACT: An 800-nm 200-fs laser is used to produce DNA damage in rat kangaroo (PtK1) and human cystic fibrosis pancreatic adenoma carcinoma (CFPAC-1) cells. Immunofluorescence staining for DNA repair factors in irradiated cells displays localization of gammaH2AX, Nbs1, and Rad50 to the site of irradiation 3 to 30 min following laser exposure. It is concluded that the 200-fs near-infrared laser is an excellent source for the production and study of spatially defined regions of DNA damage.
    Journal of Biomedical Optics 01/2007; 12(2):020505. · 2.88 Impact Factor
  • Masaharu Akiba, Alexander S. Dvornikov, Peter M. Rentzepis
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    ABSTRACT: The synthesis and photochemical reaction mechanism of N-benzoyl oxazine derivatives have been investigated. The synthesized materials were found to be photosensitive and capable of generating oxazine dye upon light irradiation. The initial reactions were found to include homolytic bond cleavage between the oxazine nitrogen and benzoyl carbon atoms proceeding through the excited singlet state and the formation of oxazine and benzoyl radicals. Subsequent reaction steps include direct electron transfer between two oxazine radicals or disproportionation of the oxazine dimer species formed through the recombination of two oxazine radicals. These reactions lead to the formation of the oxazine dye cation and anion pair.
    Journal of Photochemistry and Photobiology A: Chemistry. 01/2007;