This paper reports ex-situ preparation of conductive polymer/single-walled carbon nanotubes (SWNTs) nanocomposites by adding high conductive SWNTs to the polymer matrix. Sonication methods were used to disperse the SWNTs in the polymer. The conductivity of the nanocomposites is tuned by increasing the concentration of SWNTs. Furthermore, we present two-photon polymerization (2PP) method to fabricate structures on the basis of conductive photosensitive composites. The conductive structures were successfully generated by means of 2PP effect induced by a femtosecond laser.
Pumping and mixing of small volumes of liquid samples are basic processes in microfluidic applications. Among the number of different principles for active transportation of the fluids microrotors have been investigated from the beginning. The main challenge in microrotors, however, has been the driving principle. In this work a new approach for a very simple magnetic driving principle has been realized. More precisely, we take advantage of optical grippers to fabricate various microrotors and introduce an optical force method to characterize the fluid flow generated by rotating the structures through magnetic actuation. The microrotors are built of silica and magnetic microspheres which are initially coated with Streptavidin or Biotin molecules. Holographic optical tweezers (HOT) are used to trap, to position, and to assemble the microspheres with the chemical interaction of the biomolecules leading to a stable binding. Using this technique, complex designs of microrotors can be realized. The magnetic response of the magnetic microspheres enables the rotation and control of the structures through an external magnetic field. The generated fluid flow around the microrotor is measured optically by inserting a probe particle next to the rotor. While the probe particle is trapped by optical forces the flow force leads to a displacement of the particle from the trapping position. This displacement is directly related to the flow velocity and can be measured and calibrated. Variations of the microrotor design and rotating speed lead to characteristic flow fields.
New opportunity to improve a sensetivity of a label-free biomolecule detection in sensing systems based on microcavity evanescent wave optical sensors has been recently found and is being under intensive development. Novel technique based on combination of optical resonance on microring structures with plasmon resonance. Recently developed tools based on neural network data processing can realize real-time identification of biological agents. So combining advantages of plasmon enhancing optical microcavity resonance with identification tools can give a new platform for ulta sensitive label-free biomedical sensor. Our developed technique used standard glass and polymer microspheres as sensetive elements. They are fixed in the solution flow by adhesive layer on the surface being in the field of evanescence wave. Sensitive layer have been treated by gold nanoparticel (GN) solution. Another technique used thin film gold layers deposited on the substrate below adhesive. The light from a tuneable diode laser is coupled into the microsphere through a prism and was sharply focussed on the single microsphere. Images were recorded by CMOS camera. Normalized by free spectral range resonance shift of whispering gallery mode (WGM) and a relative efficiency of their excitation were used as input data for biomolecule classification. Both biomolecules and NP injection was obtained caused WGM spectra modification. But after NP treatment spectral shift and intensity of WGM resonances in biomolecule solutions increased. WGM resonances in microspheres fixed on substrate with gold layer with optimized layer thickness in biomolecule solutions also had higher intensity and spectra modification then without gold layer.
Since the early times of Arthur Ashkins groundbreaking experiments on optical tweezers, a great number of theoretical works was dedicated to this subject. Most of them treated the optical trapping of single spherical or elliptical particles. In the last years optical tweezers have become more and more a tool for assembling three dimensional structures using single microspheres as building blocks. Since all structures and particles inside the light beams influence the properties of the traps, we investigated theoretically the influence of additional single particles and particle arrays on the properties of optical traps. For this reason a geometrical optics based model is used with the inherent flexibility to be applied for various shapes and particle numbers.
Due to the increased complexity in terms of materials and geometries for microsystems new assembling techniques are
required. Assembling techniques from the semiconductor industry are often very specific and cannot fulfill all
specifications in more complex microsystems. Therefore, holographic optical tweezers are applied to manipulate
structures in micrometer range with highest flexibility and precision. As is well known non-spherical assemblies can be
trapped and controlled by laser light and assembled with an additional light modulator application, where the incident
laser beam is rearranged into flexible light patterns in order to generate multiple spots. The complementary building
blocks are generated by a two-photon-polymerization process. The possibilities of manufacturing arbitrary
microstructures and the potential of optical tweezers lead to the idea of combining manufacturing techniques with
manipulation processes to “microrobotic” processes. This work presents the manipulation of generated complex
microstructures with optical tools as well as a storage solution for 2PP assemblies. A sample holder has been developed for the manual feeding of 2PP building blocks. Furthermore, a modular assembling platform has been constructed for an ‘all-in-one’ 2PP manufacturing process as a dedicated storage system. The long-term objective is the automation process of feeding and storage of several different 2PP micro-assemblies to realize an automated assembly process.
Integrated hybrid MEMS require new micromanipulation devices in assembly processes. Although absolute forces are restricted optical tweezers are promising tools with unique advantages. Recent developments in beam shaping allow the control of a large number of different particles. Optical manipulation can also be used to assemble tiny structures by a generative process. Any type of particle, primarily coated with high-affinity biomolecules, can be applied as building blocks to form complex structures. By moving the particle into the requested orientation by holographic optical tweezers complex parts become possible. Also, shape-complimentary preforms can be fabricated with 2-photon-polymerization (2PP) and utilized to assemble the desired structure. Finally, microvalves and motors in lab-on-a-chip systems can be optically fabricated and also driven by optical forces.
Holographic optical tweezers have been developed for the manipulation of polymeric microparticles or biological cells
with almost circular shape. As is well known, spherical particles can be trapped and controlled by optical tweezers and
assembled with an additional light modulator application. Complementary building blocks, which are used in the
following experiments, are generated by a two-photon-polymerization process in micrometer range and are not equipped
with spherical trapping points. The possibilities of manufacturing arbitrary building blocks within the 2PP process and
the potential of HOTs lead to the idea of combining manufacturing techniques with manipulation processes in a bottomup
operation. In this work we present an experimental setup with an integrated fiber laser for holographic optical
trapping of non-spherical building blocks. Furthermore experimental requirements which permit trapping will be
illustrated.
Microassembling with holographic optical tweezers (HOT) is a flexible manufacturing technology for the precise
fabrication of complex microstructures. In contrast to classical direct writing techniques, here, microparticles are
transported within a fluid to appropriate positions, where they are finally bound. Therefore, optical forces act against the
inner friction of the fluid. This effect limits the microassembling process in the meaning of process speed. In this work
we investigate these limitations depending on the applied laser power and particle size. Additionally, different to
conventional optical tweezers, HOTs use spatial light modulators (SLM) to control the laser beam and the object's
position. This is performed at discrete step sizes caused by successively imaging respective kinoforms on the SLM at
specific refresh rates. An optimization of the step size and the applied update rate are crucial to reach maximum
velocities in particle movement. Therefore, the performance of dynamic particle manipulation is investigated in
individual experiments. Stable manipulation velocities of up to 114 μm/s have been reported in our work using 6 μm
polystyrene particles and an applied laser power of 445 mW.
This work reports the preparation of polymer/TiO2 nanocomposite by adding TiO2 nanoparticles to the polymer matrices.
TiO2 nanoparticles can be effectively dispersed into the polymer. The refractive index of the nanocomposites can be
tuned by increasing the concentration of TiO2 nanoparticles. The prepared samples exhibit excellent optical transparency
in the Vis-NIR region, i.e. at two-photon polymerization (TPP) processing wavelength, and can be used to write threedimensional
structures by means of TPP. Structures with high refractive index have been produced with the novel ultrahigh
resolution technology based on TPP processing of polymer/TiO2 nanocomposites.
A new method to fabricate microstructures built by polymer microparticles using a bottom-up technique is presented.
The microstructures find broad application in micro-fluidics technology, photonics and tissue-engineering. The handling
of the particles is realized by a holographic optical tweezers setup, ensuring the precise allocation of the particles to the
desired structure. A biochemical technique ensures that the structure remains stable independent of the laser source. We
show that with this method complex two-dimensional durable structures can be assembled and cannot be separated by
optical forces. The structures are extendable during the entire fabrication process and can be linked to further particles
and structures as desired.
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