A lab-on-chip (LOC) is a device that squeezes onto a single substrate the functionalities of a biological laboratory, by incorporating a network of microfluidic channels, reservoirs, valves, pumps and micro-sensors. Its main advantages are high sensitivity, speed of analysis, low sample and reagent consumption, and the possibility of measurement automation and standardization. The next technological challenge of LOCs is direct on-chip integration of photonic functionalities, by adding optical waveguides. Such integrated approach has many advantages over traditional free-space optical sensing, including compactness and portability, enhanced sensitivity and possibility of parallel excitation at multiple points in the microfluidic channel. Standard fabrication technologies for microchannels and optical waveguides are multistep processes and their integration is rather complicated, strongly limiting its application. Femtosecond-laser inscription of optical waveguides in glass is a powerful technique enabling single-step, three-dimensional fabrication [1], and appears to be particularly suited for their integration into LOCs. In addition, femtosecond-laser irradiation of fused silica followed by chemical etching in HF solution allows the manufacturing of microfluidic channels [2]. This opens the intriguing possibility of using a single laser system for the fabrication of both microfluidic channels and optical waveguides and also gives the capability of a real three-dimensional integration of the two structures.
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