This paper reports an enhancement in fluorescence detection via the formation of fluidic microlens in micro-optical fluidic system (MOFS). The fluidic microlens is formed by three laminar flows in the expansion chamber. By changing the flow rate of each flow, the shape and focal length of the fluidic lens will be changed. There- fore, the fluidic microlens provides a wide range of tunability to enhance the detec- tion of fluorescence signal in MOFS chip. With such tunability, the designed MOFS can be used to suit different detection methods and applications especially in low- concentration bio-molecules.