Enhancing lab-on-a-chip performance via tunable parallel liquid mircolens arrays

Pathogen detection increasingly shows significance not only for hospital laboratories, but also for in-field usage. Nowadays the microfabrication technologies give us the possibility to integrate optical devices for detection and microfluidic channels for fluorescein-labeled pathogen suspension into a single chip (i.e. optofluidics), thus providing simple, sensitive and inexpensive methods of pathogen detection. One interesting optofluidic component is a microlens whose optical axis is parallel to the substrate used. We hereby report an in situ formed tunable liquid microlens array and its applications for dynamic lab-on-a-chip, such as enhancing fluorescence emission in and detection of laminar fluid flows, and characterizing surface reaction. The de-ionized water microlenses are intrinsically formed via liquid-air interfaces of liquid droplets, whose positions are precisely controlled by air/liquid injection and pinned at T-shaped junctions of octadecyltrichlorosilane(OTS) treated polymerized isobornyl acrylate(poly(IBA)) microchannels. By pneumatic manipulation inside the channel, the microlenses can be separately tuned in focal lengths along the microchannels parallel to the substrate. Then via the tunable microlenses, excitation light is dynamically focused onto fluorescent fluidic samples, and thus the fluorescence emission signal for detection is significantly increased compared to the case without the microlenses, as a result of the enhancement of the fluorescence excitation.Meanwhile, in lab-on-a-chip, controlled microfluidic interfaces are also important, and as our microlens array directly faces the cross sections of these interfaces, we have also shown the potential for surface reaction study at such interfaces by the microlens array.