Centimeter-long microfluidic channel with an aspect ratio above 1,000 directly fabricated in fused silica by femtosecond laser micromachining

Femtosecond laser micromachining has emerged as a promising technique for creating three dimensional (3D) microstructures. As an essential building block for microfluidics, homogeneous microfluidic channel with high aspectratio is indispensable for lab-on-a-chip (LOC) applications. Fused silica is considered to be an excellent substrate material for LOC applications due to its low thermal expansion coefficient, low autofluorescence, and exceptional transmittance over a wide spectral range. Microfluidic channels can be directly fabricated inside fused silica by femtosecond laser direct writing followed by a subsequent wet chemical etching. However, the fabricated channels usually display a tapered feature and highly elliptical cross-section with limited length (usually <5 mm) and poor inner surface smoothness, which would hamper their applications. Herein, we demonstrate direct fabrication of homogeneous microfluidic channels embedded in fused silica by femtosecond laser direct writing, followed by wet chemical etching and glass drawing. With these procedures, the homogeneity of the fabricated channels has become excellent. Namely, the taper of the microchannels is greatly reduced while their cross-sectional shape becomes circular after the drawing. In addition, an inner surface smoothness of ∼0.2 nm can be realized by this method. Finally, the glass drawing method can lead to centimeters long microfluidic channels with an aspect ratio as high as ∼1,000. We expect that these microfluidic channels will have important applications in optofluidics in the future.