Integration of red VCSEL in a versatile microchip for encoding and subsequent detection of encoded beads

The integration of discrete optical excitation and detection components in a microfluidic platform is an important pre-requisite for realisation of Lab-on-a-chip devices. This research presents a microfluidic system made of polymer material with integrated miniaturized vertical cavity surface emitting laser (VCSEL) source. The light emitted by the VCSEL is detected by a conventional 5 mm diameter photodiode. The ability to read and detect microbeads encoded with through holes in the silicon substrate verified successful integration of a functional VCSEL in the polymer microchip. The microfluidic system was composed of two processed polymer chips that are bonded together. The substrate contains cavities to accommodate VCSEL components. The second polymer chip (superstrate) contains the microfluidic channel network. The conventional photodiode detector was easily mounted on top of the superstrate. Polymer chip substrates and master templates for hot embossing were fabricated by rapid prototyping technology. Fabricated masters were then moulded into thermoplastic polycarbonate (PC) substrate by hot embossing. Generated polymer sheets with embossed structures were diced into polymer chips and subsequently bonded together using a customised procedure to provide a complementary moulded cavity which accommodates the VCSEL. The optically encoded microbeads are illuminated with a VCSEL which is operated with a power of 0.7 mW. As the bead flows along the channel (illuminated with the VCSEL), the emitted light from the VCSEL device is modulated by the bar code and subsequently detected by the photodiode. Signal measurements confirm that different levels of the VCSEL light can be reproducibly detected by customized Labview software.