A robust optical sensor for liquid control in fluidic channels is reported. The sensor operates on light intensity
modulation resulting from alteration of total internal reflection into partial reflection. When a liquid guided in a channel
covers an integrated prism, the total internal reflection is changed into a partial reflection, resulting in an intensity
modulation of the reflected light. The set-up comprises a fibre which is built in a coupler unit with integrated LED and
photodiode as well as a prism micro-machined directly into a micro-fluidic polymeric channel by laser ablation. The
Prism is of 45-90-45° type with a dimension of 0.5 mm × 1 mm × 2 mm. In this design the radiation of the LED light
source is transmitted and collected from the prism by a 50:50 fibre coupler by means of total or partial internal reflection.
The sensor was characterised by filling alternately the channel with water and air. The influence of stray light onto the
sensor signal was tested by applying a strong uncollimated illumination of the channel. Only a small increase in the
output signal level in the presence of air but a strong increase in case of the presence of water could be detected.
A robust optical sensor for liquid control in fluidic channels is reported. The sensor operates on light intensity
modulation resulting from alteration of total internal reflection into partial reflection. When a liquid guided in a channel
covers an integrated prism, the total internal reflection is changed into a partial reflection, resulting in an intensity
modulation of the reflected light.
The set-up comprises a fibre which is built in a coupler unit with integrated LED and photodiode as well as a prism
micro-machined directly into a micro-fluidic polymeric channel by laser ablation. The Prism is of 45-90-45° type with a
dimension of 0.5 mm × 1 mm × 2 mm. In this design the radiation of the LED light source is transmitted and collected
from the prism by a 50:50 fibre coupler by means of total or partial internal reflection.
The sensor was characterised by filling alternately the channel with water and air. The signal level for the liquid in
contact with the prism was determined to be 222 mV while the signal level of the air filled channel was 336 mV. The
influence of stray light onto the sensor signal was tested by applying a strong uncollimated illumination of the channel.
Only a small increase in the output signal level in the presence of air but a strong increase in case of the presence of
water could be detected. However, the discrimination between air and liquid was still possible sufficiently (290 mV for
liquid, 340 mV for air). The sensor was also demonstrated to be operated as a micro-refractometer.
The interference of three coherent laser beams of a HeCd-laser with a wavelength of 325 nm was used to create a
periodic intensity distribution into the photo-resist AZ4562. The beam configuration for the laser beam interference was
carefully chosen, so that well defined patterns of two-dimensional periodicity were generated in the photo-resist.
Moulding tools were fabricated from the generated nano-structures via electroforming processes, allowing for a fast
replication of the nano-structured surfaces via hot embossing. Hot embossed polymers were used to increase the
effective surface of micro-fluidic devices like e.g. Polymerase-Chain-Reaction(PCR)-chips. The Nano-structured
surfaces were characterized concerning their contact angles when wetted with de-ionized water. It was found that the
nano-structures influenced the wetting behaviour of micro-fluidic chip surfaces clearly, especially Polypropylene (PP)
surfaces showed a superhydrophobic behaviour.
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