Single-chip based contactless conductivity detection system for multi-channel separations.

In this work, the design and characterization of a multi-cell capacitively coupled contactless conductivity detection system are described. The operation and simultaneous acquisition from 3 detector cells are demonstrated, however, the system is capable of supplying 8 detection cells and can be easily upgraded to maintain 64 capacitively coupled contactless conductivity detection cells. On performing flow-injection analysis, the system recorded as low as 0.01 mM of acetic acid, phosphoric acid, NaH2PO4, and Na2B4O7 solutions in water. The instrument was also capable of recording and distinguishing different mixtures of organic solvents: (a) methanol-acetonitrile, (b) hexane-acetone. The designed detection system is expected to be used coupled with multi-channel separation devices for monitoring simultaneous processes.

Combination of additive and subtractive laser 3D microprocessing in hybrid glass/polymer microsystems for chemical sensing applications.

We present a novel hybrid glass-polymer micromechanical sensor by combining two femtosecond laser direct writing processes: laser illumination followed by chemical etching of glass and two-photon polymerization. This incorporation of techniques demonstrates the capability of combining mechanical deformable devices made of silica with an integrated polymer structure for passive chemical sensing application. We demonstrate that such a sensor could be utilized for investigating the elastic properties of polymeric microstructures fabricated via the two-photon polymerization technique. Moreover, we show that polymeric microstructure stiffness increases when immersed in organic liquids.

Micro-structured polymer scaffolds fabricated by direct laser writing for tissue engineering.

This work presents the latest results on direct laser writing of polymeric materials for tissue engineering applications. A femtosecond Yb:KGW laser (300 fs, 200 kHz, 515 nm) was used as a light source for non-linear lithography. Fabrication was implemented in various photosensitive polymeric materials, such as: hybrid organic-inorganic sol-gel based on silicon-zirconium oxides, commercial ORMOCER® class photoresins. These materials were structured via multi-photon polymerization technique with submicron resolution. Porous three-dimensional scaffolds for artificial tissue engineering were fabricated with constructed system and were up to several millimeters in overall size with 10 to 100 µm internal pores. Biocompatibility of the used materials was tested in primary rabbit muscle-derived stem cell culture in vitro and using laboratory rats in vivo. This interdisciplinary study suggests that proposed technique and materials are suitable for tissue engineering applications.

Closely packed hexagonal conical microlens array fabricated by direct laser photopolymerization.

We apply femtosecond laser direct writing in photopolymers for manufacturing of conical microlenses and closely packed arrays thereof. We demonstrate the fabrication of high optical quality axicons of 15 µm in radius, having 150°, 160°, and 170° cone angles. Their optical properties and performance are modeled using the finite-difference time-domain method and compared with experimentally measured data. Additionally, optimization of the laser direct writing parameters regarding these types of micro-objects is presented. Possible applications of closely packed arrays of axicon microlenses are discussed, having potential attractivity in the fields of modern microscopy, light-based material processing, particle manipulation in microfluidic, and optofluidic applications.

Mechanisms of three-dimensional structuring of photo-polymers by tightly focussed femtosecond laser pulses.

Three-dimensional (3D) micro/nano-structuring of photo-resists is systematically studied at the close-to-dielectric- breakdown irradiance. It is demonstrated that avalanche absorption is playing a major part in free electron generation and chemical bond breaking at these conditions. The steps of photo-initiation and chemical bond breaking in propagation of polymerization are altered as compared with photo-polymerization at low-irradiance and one-photon stereo-lithography. The avalanche dominates radical generation and promotion of polymerization at tight focusing and a high approximately TW/cm(2) irradiance. The rates of electron generation by two-photon absorption and avalanche are calculated for the experimental conditions. Simulation results are corroborated by 3D polymerization in three resists with different photo-initiators at two different wavelengths and pulse durations. The smallest feature sizes of 3D polymerized logpile structures are consistent with spectral dependencies of the two photon nonlinearities. Implications of these findings for achieving sub-100 nm resolution in 3D structuring of photo-polymers are presented.