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Dive into the research topics where Denis Akimov is active.

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Featured researches published by Denis Akimov.


Journal of Biomedical Optics | 2011

Nonlinear microscopy, infrared, and Raman microspectroscopy for brain tumor analysis

Tobias Meyer; Norbert Bergner; Christiane Bielecki; Christoph Krafft; Denis Akimov; Bernd F. M. Romeike; Rupert Reichart; Rolf Kalff; Benjamin Dietzek; J. Popp

Contemporary brain tumor research focuses on two challenges: First, tumor typing and grading by analyzing excised tissue is of utmost importance for choosing a therapy. Second, for prognostication the tumor has to be removed as completely as possible. Nowadays, histopathology of excised tissue using haematoxylin-eosine staining is the gold standard for the definitive diagnosis of surgical pathology specimens. However, it is neither applicable in vivo, nor does it allow for precise tumor typing in those cases when only nonrepresentative specimens are procured. Infrared and Raman spectroscopy allow for very precise cancer analysis due to their molecular specificity, while nonlinear microscopy is a suitable tool for rapid imaging of large tissue sections. Here, unstained samples from the brain of a domestic pig have been investigated by a multimodal nonlinear imaging approach combining coherent anti-Stokes Raman scattering, second harmonic generation, and two photon excited fluorescence microscopy. Furthermore, a brain tumor specimen was additionally analyzed by linear Raman and Fourier transform infrared imaging for a detailed assessment of the tissue types that is required for classification and to validate the multimodal imaging approach. Hence label-free vibrational microspectroscopic imaging is a promising tool for fast and precise in vivo diagnostics of brain tumors.


Journal of Biophotonics | 2009

A comparative Raman and CARS imaging study of colon tissue

Christoph Krafft; Anuradha Ramoji; Christiane Bielecki; Nadine Vogler; Tobias Meyer; Denis Akimov; Petra Rösch; Michael Schmitt; Benjamin Dietzek; Iver Petersen; Andreas Stallmach; Jürgen Popp

An experimental evaluation of the information content of two complimentary techniques, linear Raman and coherent anti-Stokes Raman scattering (CARS) microscopy, is presented. CARS is a nonlinear variant of Raman spectroscopy that enables rapid acquisition of images within seconds in combination with laser scanning microscopes. CARS images were recorded from thin colon tissue sections at 2850, 1660, 1450 and 1000 cm(-1) and compared with Raman images. Raman images were obtained from univariate and multivariate (k-means clustering) methods, whereas all CARS images represent univariate results. Variances within tissue sections could be visualized in chemical maps of CARS and Raman images. However, identification of tissue types and characterization of variances between different tissue sections were only possible by analysis of cluster mean spectra, obtained from k-means cluster analysis. This first comparison establishes the foundation for further development of the CARS technology to assess tissue.


Journal of Biophotonics | 2010

Multimodal imaging to study the morphochemistry of basal cell carcinoma

Nadine Vogler; Tobias Meyer; Denis Akimov; Ines Latka; Christoph Krafft; Niels Bendsoe; Katarina Svanberg; Benjamin Dietzek; Juergen Popp

Basal cell carcinoma is the most abundant malignant neoplasm in humans, the pathology of which is characterized by an abnormal proliferation of basal cells. Basal cell carcinoma can show a variety of different morphologies, which are based on different cellular biology. Furthermore, the carcinoma often grows invisibly to the eye imbedded in the surrounding skin. Therefore, in some cases its clinical detection is challenging. Thus, our work aims at establishing an unsupervised tissue classification method based on multimodal imaging and the application of chemometrics to discriminate basal cell carcinoma from non-diseased tissue. A case study applying multimodal imaging to ex-vivo sections of basal cell carcinoma is presented. In doing so, we apply a combination of various linear and non-linear imaging modalities, i.e. fluorescence, Raman and second-harmonic generation microscopy, to study the morphochemistry of basal cell carcinoma. The joint information content obtained by such multimodal approach in studying various aspects of the malignant tissue alterations associated with basal cell carcinoma is discussed.


Journal of Physical Chemistry B | 2008

Three-dimensional molecular mapping of a multiple emulsion by means of CARS microscopy.

Tobias Meyer; Denis Akimov; Nicolae Tarcea; Susana Chatzipapadopoulos; Gerald Muschiolik; Jens Kobow; Michael Schmitt; Jiirgen Popp

Multiple emulsions consisting of water droplets dispersed in an oil phase containing emulsifier which is emulsified in an outer water phase (W/O/W) are of great interest in pharmacology for developing new drugs, in the nutrition sciences for designing functional food, and in biology as model systems for cell organelles such as liposomes. In the food industry multiple emulsions with high sugar content in the aqueous phase can be used for the production of sweets, because the high sugar content prevents deterioration. However, for these emulsions the refractive indexes of oil and aqueous phase are very similar. This seriously impedes the analysis of these emulsions, e.g., for process monitoring, because microscopic techniques based on transmission or reflection do not provide sufficient contrast. We have characterized the inner dispersed phase of concentrated W/O/W emulsions with the same refractive index of the three phases by micro Raman spectroscopy and investigated the composition and molecular distribution in water-oil-water emulsions by means of three-dimensional laser scanning CARS (coherent anti-Stokes Raman scattering) microscopy. CARS microscopy has been used to study water droplets dispersed in oil droplets at different Raman resonances to visualize different molecular species. Water droplets with a diameter of about 700 nm could clearly be visualized. The advantages of CARS microscopy for studying this particular system are emphasized by comparing this microscopic technique with conventional confocal reflection and transmission microscopies.


ChemPhysChem | 2009

Spectroscopic Investigation of the Ultrafast Photoinduced Dynamics in π‐Conjugated Terpyridines

Ronald Siebert; Denis Akimov; Michael Schmitt; Andreas Winter; Ulrich S. Schubert; Benjamin Dietzek; Jürgen Popp

Ultrafast light-induced processes in a series of pi-conjugated mono-, bis-, tris- and tetrakis(terpyridine) derivatives are investigated by femtosecond time-resolved spectroscopy. Non-exponential excited-state dynamics involving singlet-triplet intersystem crossing are observed which span from picoseconds to nanoseconds (see figure). Time-resolved spectroscopy is applied to investigate the ultrafast relaxation dynamics of several pi-conjugated mono-, bis-, tris- and tetrakis(terpyridine) derivatives. This particular series of structurally closely related systems was prepared applying efficient synthetic strategies and resembles key building blocks for a wide range of photoactive complexes, dendrimers and metallo-polymers with resulting potential applications, for example, in photovoltaics or as organic light-emitting diodes. Aiming for applications of supramolecular assemblies based on these recently presented terpyridine ligands a detailed knowledge of the light-induced processes of the ligands themselves represents a prerequisite. By applying femtosecond time-resolved absorption spectroscopy in concert with time-resolved fluorescence and Raman measurements, we detail the photophysical properties.


Nanotechnology | 2008

Optically controlled thermal management on the nanometer length scale.

F Garwe; U Bauerschäfer; Andrea Csáki; Andrea Steinbrück; K Ritter; Arne Bochmann; J Bergmann; A Weise; Denis Akimov; G Maubach; Karsten König; Gereon Hüttmann; W Paa; Jürgen Popp; Wolfgang Fritzsche

The manipulation of polymers and biological molecules or the control of chemical reactions on a nanometer scale by means of laser pulses shows great promise for applications in modern nanotechnology, biotechnology, molecular medicine or chemistry. A controllable, parallel, highly efficient and very local heat conversion of the incident laser light into metal nanoparticles without ablation or fragmentation provides the means for a tool like a nanoreactor, a nanowelder, a nanocrystallizer or a nanodesorber. In this paper we explain theoretically and show experimentally the interaction of laser radiation with gold nanoparticles on a polymethylmethacrylate (PMMA) layer (one-photon excitation) by means of different laser pulse lengths, wavelengths and pulse repetition rates. To the best of our knowledge this is the first report showing the possibility of highly local (in a 40xa0nm range) regulated heat insertion into the nanoparticle and its surroundings without ablation of the gold nanoparticles. In an earlier paper we showed that near-infrared femtosecond irradiation can cut labeled DNA sequences in metaphase chromosomes below the diffraction-limited spot size. Now, we use gold as well as silver-enhanced gold nanoparticles on DNA (also within chromosomes) as energy coupling objects for femtosecond laser irradiation with single-and two-photon excitation. We show the results of highly localized destruction effects on DNA that occur only nearby the nanoparticles.


Head and Neck-journal for The Sciences and Specialties of The Head and Neck | 2013

Multimodal nonlinear microscopic investigations on head and neck squamous cell carcinoma: toward intraoperative imaging.

Tobias Meyer; Orlando Guntinas-Lichius; Ferdinand von Eggeling; Günther Ernst; Denis Akimov; Michael Schmitt; Benjamin Dietzek; Jürgen Popp

Prognosis and appropriate treatment of head and neck squamous cell carcinoma (HNSCC) depend on the tumor type routinely derived by invasive histopathology. A promising noninvasive alternative is nonlinear optical imaging, which is capable of in vivo tissue visualization for tumor typing and grading.


British Journal of Dermatology | 2013

Multimodal mapping of human skin

Sandro Heuke; Nadine Vogler; Tobias Meyer; Denis Akimov; Franziska Kluschke; H.-J. Röwert-Huber; Jürgen Lademann; Benjamin Dietzek; Jürgen Popp

The combination of coherent anti‐Stokes Raman scattering (CARS), second harmonic generation (SHG) and two‐photon excited fluorescence (TPEF) imaging – referred to as multimodal imaging – provides complementary contrast based on molecular vibrations, the structure of various tissue components and endogenous fluorophores, respectively.


Small | 2009

Quantitative CARS Microscopic Detection of Analytes and Their Isotopomers in a Two‐Channel Microfluidic Chip

Gero Bergner; Susana Chatzipapadopoulos; Denis Akimov; Benjamin Dietzek; Daniéll Malsch; Thomas Henkel; Sebastian Schlücker; Jürgen Popp

Raman microspectroscopy provides label-free vibrational contrast at submicron spatial resolution without the need for sample preparation, and has therefore become an indispensable characterization method in various disciplines, including analytical, life, and materials sciences. The technique is particularly useful for spatially resolved quantification of the concentrations of chemical constituents in a sample, and in situations where labeling of low-molecular-weight compounds by fluorescent labels is not possible or not desired. Coherent anti-Stokes Raman scattering (CARS) microscopy benefits from significantly faster acquisition rates than conventional Raman microspectroscopy. The combination of this nonlinear Raman technique withmicrofluidics for reactionmonitoring and cytometry has been introduced recently. Unfortunately, CARS is not background-free: the signal generation leads to both a coherent excitation of molecular vibrations (nuclear motions) and an intrinsic non-Ramanresonant background (electronic response). This chemically nonspecific background constitutes a severe limitation for CARS detection and the quantification of analytes at low concentrations. Multiplex CARS microspectroscopy with subsequent CARS band-shape analysis allows extraction of


Healthcare | 2013

Detection and Discrimination of Non-Melanoma Skin Cancer by Multimodal Imaging

Sandro Heuke; Nadine Vogler; Tobias Meyer; Denis Akimov; Franziska Kluschke; H.-J. Röwert-Huber; Jürgen Lademann; Benjamin Dietzek; Jürgen Popp

Non-melanoma skin cancer (NMSC) belongs to the most frequent human neoplasms. Its exposed location facilitates a fast ambulant treatment. However, in the clinical practice far more lesions are removed than necessary, due to the lack of an efficient pre-operational examination procedure: Standard imaging methods often do not provide a sufficient spatial resolution. The demand for an efficient in vivo imaging technique might be met in the near future by non-linear microscopy. As a first step towards this goal, the appearance of NMSC in various microspectroscopic modalities has to be defined and approaches have to be derived to distinguish healthy skin from NMSC using non-linear optical microscopy. Therefore, in this contribution the appearance of ex vivo NMSC in a combination of coherent anti-Stokes Raman scattering (CARS), second harmonic generation (SHG) and two photon excited fluorescence (TPEF) imaging—referred as multimodal imaging—is described. Analogous to H&E staining, an overview of the distinct appearances and features of basal cell and squamous cell carcinoma in the complementary modalities is derived, and is expected to boost in vivo studies of this promising technological approach.

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Jürgen Popp

Leibniz Institute of Photonic Technology

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Michael Schmitt

University of Düsseldorf

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Sebastian Schlücker

University of Duisburg-Essen

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Gero Bergner

University of Würzburg

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Rainer Heintzmann

Leibniz Institute of Photonic Technology

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Christoph Krafft

Leibniz Institute of Photonic Technology

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Hartmut Bartelt

Leibniz Institute of Photonic Technology

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