Ari Hokkanen

Tunable hydrophilicity on a hydrophobic fluorocarbon polymer coating on silicon

An efficient, economic, reliable, and repeatable patterning procedure of hydrophobic surfaces was developed. A fluorocarbon polymer derived from the C4F8 gas in an inductively coupled plasma etcher was used as the hydrophobic coating. For a subsequent patterning of hydrophilic apertures on the polymer, a short O2 plasma exposure through a silicon shadow mask was utilized. The overall hydrophilicity of the patterned surface can be tuned by the duration of the O2 plasma exposure, and also by the density and the size of the hydrophilic apertures. The laborious photolithography and tricky lift-off procedures are avoided. Optimization of the whole patterning process is explained thoroughly and supported with experimental data. The hydrophilic adhesion of the patterned polymer was evaluated with aqueous droplets, which were studied on matrices of the hydrophilic apertures of different sizes. The deposition parameters of the fluorocarbon polymer, the size of the droplet required to enable rolling on the patterne...

Self-feeding microfluidic structures on silicon and glass

Several microfluidic platforms incorporating cavities and channels have been designed and fabricated in silicon and fused silica. C4F8 and SF6 plasmas are used to etch reproducibly 400 μm features in silicon and 150 μm in fused silica. Hydrophilic surface characteristics allow capillary action without external pumping or electro-osmosis. Filling of poled cavities can be triggered by increasing temperature i.e. by tuning hydrophobicity of a channel. The pole structure can also be used for sieving particles of different size or elasticity. In this work, agarose beads trapped by poles were used for solid phase extraction. By covering the microfluidic features, filling is also achieved by cooling the substrate. Filling velocities of aqueous solutions have been observed to depend strongly on liquid composition, but also final treatment and roughness of silicon or silica surface. Mixing of two aqueous solutions can also be triggered by increasing temperature. Cavities with pre-immobilised substance can be filled simultaneously or, if necessary, sequentially. Various non-leaking 3D channel networks can be constructed by gluing, fusion or anodic bonding of many silicon or glass wafers including via holes. Integrating of electrical circuits for both silicon and silica is possible by standard IC technology.

Active silicon support for DNA diagnostics

Heated liquid cavities have been studied. Microlitre scale liquid cavities were etched to the surface of a silicon wafer. Liquid cavities were sealed with a glass cover. Integration of active components to the silicon support is also possible. A heater and a thermistor element are integrated into the silicon support. A pole structure was used within the wells for thermal optimization and self-feeding. The pole structure increases the surface area between silicon and liquid, which enhances thermal transport between silicon and liquid. The temperature of the water is also more uniform. The pole structure also makes the liquid cavity semiporous, enabling the self-feeding of samples due to capillary force. Active silicon support could be used in diagnostics and in biotechnology. Silicon supports were tested in PCR (Polymerace Chain Reaction). The construction of the temperature controlling setup for the silicon support is described. Temperature controlling setup is an independent measuring setup. Interface to the silicon support is made with a printed board to a microscope glass slide format. It is possible to use the printed board interface in a microarray reader. The contruction of a fluorescence measurement setup based on a microarray reader is described.

Hemispherically ended optical fiber lenses

Fiber lenses were made using a short piece of single mode fiber fusion spliced to the end of a graded index multimode fiber O = 125 μm and the end of the single mode fiber is rounded with fusion splicing. Nearfields, farfields and reflections from flat aluminium plate were measured. The fiber lenses were also modelled.

Microfluidic sampling system for tissue analytics

We have developed a microfluidics based sampling system for tissue analytics. The proof-of-concept of the sampling system was demonstrated by extracting lipid samples from tissue biopsies. The sample collection system consists of a disposable silicon based multiport microneedle integrated with polymer microfluidics. The polymethyl methacrylate polymer microfluidic chip has a 10 μl sample reservoir and actuation membranes for liquid pumping. A special automated robotic system was developed to control the positioning of the needle and the sampling procedure on preselected spots on the tissue. Real breast cancer tissue samples were used to test the feasibility of the sampling system. We successfully measured indicative cancer biomarkers from the tissue surface. Phosphatidylcholine and phosphoethanolamine were extracted from the tissue membrane with methyl tert-butyl ether solvent and detected by mass spectrometry. In the future, this tool could be used in characterization of preoperative biopsies and tumour tissues removed during surgery.

Stimulation of human embryonic stem cell-derived cardiomyocytes on thin-film microelectrodes.

We describe successful long‐term stimulation of human embryonic stem cell‐derived cardiomyocyte clusters on thin‐film microelectrode structures in vitro. Interdigitated electrode structures were constructed using plain titanium on glass as the electrode material. Titanium rapidly oxidizes in atmospheric conditions to produce an insulating TiOχ layer with high relative permittivity. Capacitive coupling to the incubation medium and to the cells adherent to the electrodes was still efficient, and the dielectric layer prevented electrolysis, allowing a wider window of possible stimulation amplitudes to be used, relative to conducting surfaces. A common hypothesis suggests that to achieve proper differentiation of electroactive cells from the stem cells electrical stimuli are also needed. Spontaneously beating cardiomyocyte clusters were seeded on the glass‐electrode surfaces, and we successfully altered and resynchronized a clearly different beat interval. The new pace was reliably maintained for extended periods of several tens of minutes.

Embedded Optical Sensor for Oil Film Pressure Measurements in Journal Bearings

The oil film pressure is one of the essential functional parameters in journal bearings. Until now, the oil film pressure has been estimated by theoretical calculations, since the measurement of oil film pressure has been a demanding or even unfeasible task in journal bearings, especially in bearings carrying dynamic loads. In this study a new approach has been developed for experimental determination of the oil film pressure. The sensor design utilizes the optical fibre technique and the sensor is integrated in the sliding surface of the bearing thus providing the possibility to measure the actual oil film pressure under load. The finite element method (FEM) calculations have been used for optimizing the design of the sensor and for ensuring the appropriate mechanical performance of the sensor design. The optical sensor was integrated in a hydrodynamic journal bearing made of bronze. A versatile bearing test rig was used for testing the journal bearing with integrated optical sensor. The tests were carried out with both static and dynamic loading. The oil film pressure was measured with different loads and speeds and the data was compared with simulated one. The results showed that the optical sensor was capable to measure the oil film pressure in journal bearing at real operating conditions and the sensitivity of the sensor was good enough to verify the speed and load effects on pressure. According to this work, it is possible to increase the knowledge of true operating conditions of journal bearings by using the optical sensor for oil film pressure measurement. The knowledge can be utilized in the development work of safer and more efficient machines and engines with journal bearings carrying high and dynamic loads. The optical sensor can be used also in other applications for smart control of pressure.Copyright

New capillary optical fiber structure for fluorescence sensors

A multilayer capillary fiber was designed for optical sensor applications and its optical properties were evaluated by using a fluorescent layer immobilized on its inner surface. This fiber structure combines a large interaction surface (the inner wall of the capillary fiber) for binding of fluorescent indicators with evanescent wave fluorescence measurement, which may facilitate the design of pseudohomogeneous assays without separation of the bound from nonbound fluorescent indicator. The inner surface of the capillary was derivatized by aminosilanization, followed by biotinylation and addition of streptavidin. This biotin- streptavidin coating facilities subsequent immobilization of any biotinylated species (e.g. antibodies, antigens, etc.) participating in specific molecular recognition. We have evaluated some properties of this capillary fiber design by using fluorescent proteins immobilized on the inner wall of capillary by biotin-avidin-interaction. Fluorescence was excited by a HeNe-laser (fluorescent indicator APC; (lambda) em equals 660 nm) and by a Ar-laser (fluorescent indicator RPE, (lambda) em equals 578 nm), and measured with a spectrum analyzer.

Optimising a grating-coupled evanescent field excitation

Diffraction gratings were designed and fabricated on a SiN/SiO2 planar waveguide to couple light from a low power 488 nm laser beam into the planar waveguide. The light propagating in the waveguide was then used to detect fluoresceine from volume on the planar waveguide surface. The results demonstrate the capability for very simple and fast analytical throughput for quantification of fluorescent samples, essentially without cross-talk. The transmission measurements show about 10% diffraction efficiency with 0.06° FWHM. The diffraction efficiency and the incidence angle for the maximum diffraction efficiency were observed to be highly dependent on the process parameters used to fabricate the gratings. The fluorescence signal was observed to be linear for fluoresceine concentrations between 10-9 and 10-3 M.

Time-resolved UV-excited microarray reader for fluorescence energy transfer (FRET) measurements

Analytical systems based on immunochemistry are largely used in medical diagnostics and in biotechnology. There is a significant pressure to develop the present assay formats to become easier to use, faster, and less reagent consuming. Further developments towards high density array--like multianalyte measurement systems would be valuable. To this aim we have studied the applicability of fluorescence resonance energy transfer and time-resolved fluorescence resonance energy transfer in immunoassays on microspots and in microwells. We have used engineered recombinant antibodies detecting the pentameric protein CRP as a model analyte system, and tested different assay formats. We describe also the construction of a time-resolved scanning epifluorometer with which we could measure the FRET interaction between the slow fluorescence decay from europium chelates and its energy transfer to the rapidly decaying fluorophore Cy5.