Nikolaj Agentoft Feidenhans'l

Surface functionalized thiol-ene waveguides for fluorescence biosensing in microfluidic devices

Thiol‐ene polymers possess physical, optical, and chemical characteristics that make them ideal substrates for the fabrication of optofluidic devices. In this work, thiol‐ene polymers are used to simultaneously create microfluidic channels and optical waveguides in one simple moulding step. The reactive functional groups present at the surface of the thiol‐ene polymer are subsequently used for the rapid, one step, site‐specific functionalization of the waveguide with biological recognition molecules. It was found that while the bulk properties and chemical surface properties of thiol‐ene materials vary considerably with variations in stoichiometric composition, their optical properties remain mostly unchanged with an average refractive index value of 1.566 ± 0.008 for thiol‐ene substrates encompassing a range from 150% excess ene to 90% excess thiol. Microfluidic chips featuring thiol‐ene waveguides were fabricated from 40% excess thiol thiol‐ene to ensure the presence of thiol functional groups at the surface of the waveguide. Biotin alkyne was photografted at specific locations using a photomask, directly at the interface between the microfluidic channel and the thiol‐ene waveguide prior to conjugation with fluorescently labeled streptavidin. Fluorescence excitation was achieved by launching light through the thiol‐ene waveguide, revealing bright fluorescent patterns along the channel/waveguide interface.

Industrial characterization of nano-scale roughness on polished surfaces

We report a correlation between the scattering value “Aq” and the ISO standardized roughness parameter Rq. The Aq value is a measure for surface smoothness, and can easily be determined from an optical scattering measurement. The correlation equation extrapolates the Aq value from a narrow measurement range of ±16° from specular to a broader range of ±80°, corresponding to spatial surface wavelengths of 0.8 μm to 25 μm, and converts the Aq value to the Rq value for the surface. Furthermore, we present an investigation of the changes in scattering intensities, when a surface is covered with a thin liquid film. It is shown that the changes in the angular scattering intensities can be compensated for the liquid film, using empirically determined relations. This allows a restoration of the “true” scattering intensities which would be measured from a corresponding clean surface. The compensated scattering intensities provide Aq values within 5.7 % ± 6.1 % compared to the measurements on clean surfaces.

Fabrication of biopolymer cantilevers

With our novel production method biopolymer micro cantilevers can be manufactured cheap and easily, rendering the measurement of degradability a matter of a few days. Our micro cantilevers are made of the PLLA (poly-l-lactide), measure 100 x 500 x 10 µm (width, length, height) but are positioned on a supporting body chip to allow handling with tweezers. As biopolymers are to fragile to process with standard silicon techniques we developed a fabrication method using nanoimprint lithography, where the chip structure is defined by pressing a stamp into the biopolymer layer. This has previously only been done with ordinary plastics. The degradation is then evaluated by placing the chip in a solution and measuring its resonance frequency, which depend on the cantilever mass. As proof of concept this measurement was also performed.