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Jörg Martini

Bio: Jörg Martini is an academic researcher from Bielefeld University. The author has contributed to research in topics: Force spectroscopy & Microscopy. The author has an hindex of 5, co-authored 13 publications receiving 73 citations.

Papers
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Journal ArticleDOI
02 Jan 2007-Small
TL;DR: It was possible to fully control the light-emission state of a single nanocrystal from emitting (blinking) to quenched (dark) by mechanically approaching and retracting the tip, and to measure and quantify the fluorescence emission as a function of distance between the nanocrystals and the tip.
Abstract: In single-molecule-manipulation techniques the physical concepts of optical switching and optomechanics, as well as the local energy transfer (i.e., quenching and fluorescence resonance energy transfer (FRET)) between single nano-objects, open fascinating means of controlling and manipulating matter on the nanometer scale. Single semiconductor nanocrystals (quantum dots) exhibit remarkable resistance to photobleaching, can be derivatized in a biocompatible way, and allow tuning of their spectroscopical properties. Furthermore, these nanosystems are not only isolated position markers but can be regarded as active reporters that interact with their microenvironment and carry information about their local vicinity, for example, in their blinking frequency. 12] In recent years, nanocrystal fluorescence markers for use in biological applications have been designed based on these qualities and new assays based on their energy-transfer properties have been developed. In this context, the external control and switching of singlenanocrystal fluorescence emission is a significant step towards a better control of the functional properties of matter on the single-molecule level. In this Communication, we report on the external but local emission control of a single nano-object by means of a gold-functionalized tip. It was possible to fully control the light-emission state of a single nanocrystal from emitting (blinking) to quenched (dark) by mechanically approaching and retracting the tip. Moreover, we were able to measure and quantify the fluorescence emission as a function of distance between the nanocrystal and the tip. The experimental setup combines total-internal-reflection fluorescence microscopy (TIRFM) with the piezocontrolled nanometer-sensitive movement of an atomic force microscope (AFM) (Figure 1). Previously, the lifetimes of single dyes in the presence of an AFM tip have been investigated with a combination of AFM and confocal microscopy. A similar confocal setup using an AFM tip functionalized with quantum dots has recently been used for a fluorescence-energy-transfer-based microscopy of dye molecules. In contrast to these experiments, our focus is on the effective local switching of a single fluorophore; we use CdSe/ZnS nanocrystals, the emission of which can be recovered after quenching, and an AFM tip covalently functionalized with gold nanoparticles serves as an appropriate and effective quenching agent. The nanocrystals are immobilized in submonolayer coverage on a cover glass so that

29 citations

Proceedings ArticleDOI
TL;DR: In these experiments 2-Photon laser scanning microscopy has been used to acquire 3-dimensional structural information on native unstained biological samples for tissue engineering purposes and imaging depth, fluorescence intensity and surface topology appear promising as key information for discriminating between the non-arthritic and arthritic states.
Abstract: In our experiments 2-Photon laser scanning microscopy (2PLSM) has been used to acquire 3-dimensional structural information on native unstained biological samples for tissue engineering purposes. Using near infrared (NIR) femtosecond laser pulses for 2-photon excitation and second harmonic generation (SHG) it was possible to achieve microscopic images at great depths in strongly (light) scattering collagen membranes (depth up to 300 μm) and cartilage samples (depth up to 460 μm). With the objective of optimizing the process of chondrocyte growth on collagen scaffolding materials for implantation into human knee joints, two types of samples have been investigated. (1) Both arthritic and non-arthritic bovine and human cartilage samples were examined in order to differentiate between these states and to estimate the density of chondrocytes. In particular, imaging depth, fluorescence intensity and surface topology appear promising as key information for discriminating between the non-arthritic and arthritic states. Human chondrocyte densities between 2-10 6 /cm 3 and 20-10 6 /cm 3 , depending on the relative position of the sample under investigation within the cartilage, were measured using an automated procedure. (2) Chondrocytes which had been sown out on different types of I/III-collagen membranes, were discriminated from the scaffolding membranes on the basis of their native fluorescence emission spectra. With respect to the different membranes, either SHG signals from the collagen fibers of the membranes or differences in the emission spectra of the chondrocytes and the scaffolding collagenes were used to identify chondrocytes and membranes.

9 citations

Proceedings ArticleDOI
TL;DR: In this article, a combined AFM and total internal reflection fluorescence (TIRF) microscopy setup is presented that enables ultrasound-induced fluorescence detection of individual fluorophores, control of the AFM probe position in x, y and z-direction with nanometer precision, and simultaneous investigation of optical and mechanical properties at the single molecule level.
Abstract: Single molecules can nowadays be investigated by means of optical, mechanical and electrical methods. Fluorescence imaging and spectroscopy yield valuable and quantitative information about the optical properties and the spatial distribution of single molecules. Force spectroscopy by atomic force microscopy (AFM) or optical tweezers allows addressing, manipulation and quantitative probing of the nanomechanical properties of individual macromolecules. We present a combined AFM and total internal reflection fluorescence (TIRF) microscopy setup that enables ultrasensitive laser induced fluorescence detection of individual fluorophores, control of the AFM probe position in x, y and z-direction with nanometer precision, and simultaneous investigation of optical and mechanical properties at the single molecule level. Here, we present the distance-controlled quenching of semiconductor quantum dot clusters with an AFM tip. In future applications, fluorescence resonant energy transfer between single donor and acceptor molecules will be investigated.

7 citations

01 Jan 2004
TL;DR: In this article, an interactive audio-haptic human-computer interface for controlling an atomic force mi- croscope (AFM) in force spectroscopy experiments on single molecules is presented.
Abstract: This paper presents an interactive audio-haptic human-computer interface for controlling an atomic force mi- croscope (AFM) in force spectroscopy experiments on single molecules. The sensor data used are proportional to the force that is applied to a single molecule. These forces are measured in real-time by using the reflection of a laser beam from a cantilever. We present a system that involves (a) a visual display of the data (b) a force-feedback joystick for navigating the sample and providing a tactile feedback of the forces, and (c) an auditory display to monitor the measured data while interactively moving the sample. The sonification we have developed integrates information at various levels of detail, including audifications of the high-frequency cantilever movement, and an auditory stream that communicates the instantaneous deviation of forces between the approach and retract phase of the sample. The sonification design and offline-computed sonifications will be presented and discussed. We further report on our first experiences with this interactive multi-modal control interface for manipulation of individual DNA molecules.

7 citations

01 Jan 2005
TL;DR: In this paper, a femtosecond, near-infrared (NIR) Ti:Sa laser for 2-photon excitation and a dedicated NIR long distance objective, autofluorescence imaging and measurements of the extracellular matrix (ECM) tissue with incorporated chondrocytes were possible with a penetration depth of up to 460 µm inside the sample.
Abstract: Native hyaline cartilage from a human knee joint was directly investigated with laser scanning microscopy via 2-photon autofluorescence excitation with no additional staining or labelling protocols in a nondestructive and sterile manner. Using a femtosecond, near-infrared (NIR) Ti:Sa laser for 2-photon excitation and a dedicated NIR long distance objective, autofluorescence imaging and measurements of the extracellular matrix (ECM) tissue with incorporated chondrocytes were possible with a penetration depth of up to 460 µm inside the sample. Via spectral autofluorescence separation these experiments allowed the discrimination of chondrocytes from the ECM and therefore an estimate of chondrocytic cell density within the cartilage tissue to approximately 0.2-2·10 7 /cm 3 . Furthermore, a comparison of the relative autofluorescence signals between nonarthritic and arthritic cartilage tissue exhibited distinct differences in tissue morphology. As these morphological findings are in keeping with the macroscopic diagnosis, our measurement has the potential of being used in future diagnostic applications.

5 citations


Cited by
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Book
26 Jan 2011
TL;DR: In this paper, the authors propose a CONCRETE-based approach to solve the problem of concreTE-convexity, i.e., concrete-concrete.
Abstract: CONCRETE

447 citations

Journal ArticleDOI
TL;DR: The principles of near-field optics are outlined, the mechanisms contributing to local field enhancement and how it can be used to enhance optical signals are discussed and several recent examples of Raman and fluorescence microscopy with 10 nm spatial resolution of single molecules are reviewed.
Abstract: Spectroscopic methods with high spatial resolution are essential for understanding the physical and chemical properties of nanoscale materials, including quantum structures and biological surfaces An optical technique is reviewed that relies on the enhanced electric fields in the proximity of a sharp, laser-irradiated metal tip These fields are utilized for spatially confined probing of various optical signals, thus allowing for a detailed sample characterization far below the diffraction limit In addition, tip-enhanced fields also provide the sensitivity crucial for the detection of nanoscale volumes After outlining the principles of near-field optics, the mechanisms contributing to local field enhancement and how it can be used to enhance optical signals are discussed Different experimental methods are presented and several recent examples of Raman and fluorescence microscopy with 10 nm spatial resolution of single molecules are reviewed

262 citations

Journal ArticleDOI
17 Dec 2013-PLOS ONE
TL;DR: Results confirm two hypotheses formulated in a preliminary study: pitch is by far the most used auditory dimension in sonification applications, and spatial auditory dimensions are almost exclusively used to sonify kinematic quantities.
Abstract: The field of sonification has progressed greatly over the past twenty years and currently constitutes an established area of research. This article aims at exploiting and organizing the knowledge accumulated in previous experimental studies to build a foundation for future sonification works. A systematic review of these studies may reveal trends in sonification design, and therefore support the development of design guidelines. To this end, we have reviewed and analyzed 179 scientific publications related to sonification of physical quantities. Using a bottom-up approach, we set up a list of conceptual dimensions belonging to both physical and auditory domains. Mappings used in the reviewed works were identified, forming a database of 495 entries. Frequency of use was analyzed among these conceptual dimensions as well as higher-level categories. Results confirm two hypotheses formulated in a preliminary study: pitch is by far the most used auditory dimension in sonification applications, and spatial auditory dimensions are almost exclusively used to sonify kinematic quantities. To detect successful as well as unsuccessful sonification strategies, assessment of mapping efficiency conducted in the reviewed works was considered. Results show that a proper evaluation of sonification mappings is performed only in a marginal proportion of publications. Additional aspects of the publication database were investigated: historical distribution of sonification works is presented, projects are classified according to their primary function, and the sonic material used in the auditory display is discussed. Finally, a mapping-based approach for characterizing sonification is proposed.

213 citations

Journal ArticleDOI
TL;DR: This review illustrates the physical principle of TENOM that utilizes the antenna function of a sharp probe to efficiently couple light to excitations on nanometer length scales and discusses the antenna-induced enhancement of different optical sample responses including Raman scattering, fluorescence, generation of photocurrent and electroluminescence.
Abstract: Tip-enhanced near-field optical microscopy (TENOM) is a scanning probe technique capable of providing a broad range of spectroscopic information on single objects and structured surfaces at nanometer spatial resolution and with highest detection sensitivity. In this review, we first illustrate the physical principle of TENOM that utilizes the antenna function of a sharp probe to efficiently couple light to excitations on nanometer length scales. We then discuss the antenna-induced enhancement of different optical sample responses including Raman scattering, fluorescence, generation of photocurrent and electroluminescence. Different experimental realizations are presented and several recent examples that demonstrate the capabilities of the technique are reviewed.

152 citations

Journal ArticleDOI
TL;DR: Three-dimensional microfabrication using two-photon polymerization of biocompatible photopolymers is applied for producing scaffolds for tissue engineering of artificial cartilage using methacrylated oligo(lactide-co-caprolactone), urethanes, polyglycerines and biopolymers.
Abstract: Three-dimensional microfabrication using two-photon polymerization of biocompatible photopolymers is applied for producing scaffolds for tissue engineering of artificial cartilage. Different classes of photocrosslinkable polymeric materials including methacrylated oligo(lactide-co-caprolactone), urethanes, polyglycerines and biopolymers like hyaluronan, alginate and dextran were used to fabricate microstructured scaffolds based on CAD models. The biocompatibility of the materials was tested in cell culture experiments using bovine chondrocytes.

112 citations