Ultrathin optical-microfluidic layers
The micro-structured PDMS moulds fabricated by mutli-layer micromoulding have favourable optical properties for fluorescence-based detection, due to the fact that it has almost no absorbance and minimal auto-fluorescence in the range of visible wavelengths. Some effort was spent on minimize the thickness of the optical transparent microfluidic layer in order to use high-precision objectives which usually do have very small working-distances around 1 mm. We have reduced the overall thickness the optical-microfluidic layer to a minimum value of 250 µm by pressing a PYREX-glass substrate against the SU8-master during the moulding process. Additionally, it has to be pointed out that the integrated glass slide improves the handling and stability of the elastomeric PDMS mould and prevent the ChµP from external mechanical influence as well as contamination.
Integrated waveguides for PACE
A matter of particular interest ist he technical realization of a photoinitated on-chip programming of microfluidic networks (e.g. open or close microchannels irreversible) by spatial selective irradiation of polymerizable monomer-molecules. The latter could be feasible using a complicated shadow mask based technologie (complex adjustment, limited flexibility) or integrated waveguides.
Further potential advantages are:
- improved signal-to-noise ratio by lateral fluorescence excitation and vertical detection
- improvement in performance of on-chip detection of molecules and liposomes
- simplified experimental setup (e.g. no optical excitation filters required)
- minimize optical loss of power of laserbeams by direct coupling into the chip device
In cooperation with the team of A. Neyers Lab of Micro Structure Technology at the Technical University of Dortmund we developed successfully a procedure based on two variable PDMS prepolymers with different values of refractive indexes (see schematic process flow).