Abstract
This report describes methods to fabricate microchannels for an inexpensive Coulter-type haematological analyser. Specifically, laser cutting, 3D printing, and optical fibre pulling were investigated to fabricate the micro channels. Optical microscopy was used to measure the channel dimensions and their quality. An empirical model was developed to describe the channel dimension dependence on fabrication parameters. The fibre pulled channels were the highest quality but required specialist and expensive fabrication equipment. The laser cutting technique produced channels with a rough surface. Fused filament 3D printing also produced rough channels with a substantial amount of debris blocking the channel. However, a simple post-production method was invented to reliably fabricate smooth microchannels as small as 160 µm. Therefore, a combination of fused deposition modelling 3D printing and the novel post-processing technique was selected to fabricate the prototype sensor cell. It was selected because of the ease that this 3D printing process could be integrated into the final cell design and the wide availability of inexpensive printers. Using this technique, an inexpensive palm-sized sensor cell was designed, fabricated and tested to count microparticles that were 98 ± 8 µm in diameter. A sensitive DC electronic counter was designed, tested, and successfully prototyped to produce a voltage spike when a particle passed through the sensor cell. The combined electronics and sensor cell system demonstrated a high signal to noise ratio when counting the 98 ± 8 µm particles, and although not demonstrated here, the bit-depth of the sensing electronics implies that substantially smaller particles could be counted with the same system. The development cost of the entire cell counting device falls below S$25 and will be lower if mass-produced.