Rapid prototyping of all glass microfluidic platforms

Abstract

At present, there exists a great need for the ability to manufacture all glass microfluidic platforms. The advantages to such a device are many: glass platforms are chemically inert, optically transparent (even to the UV range) and can withstand the high laser intensities required of present day nonlinear imaging techniques. The previous microfluidic fabrication techniques (such as chemical etching, lithography, anodic and fusion bonding) fall short. They are time consuming, expensive and require multiple steps to produce a microfluidic device. Laser induced material modification is a promising substitute. It can ablate and bond glass substrates with the same setup. Therefore, laser welding/machining can reduce microfluidic device fabrication to a single step process. Furthermore, an optical technique known as simultaneous spatiotemporal focusing (SSTF), in conjunction with laser welding/machining can improve the quality and efficiency of microfluidic device fabrication. We demonstrate successful bonding of similar (referring to the index of refraction) glass substrates with SSTF ultrafast laser pulses for the first time to our knowledge. The morphology of the bond structures, as determined by means of a third harmonic generation microscope, provides insight to the bonding process at the micron scale of the features produced. To demonstrate the superiority of SSTF for machining applications, single pass channel cuts were made with both SSTF and non-SSTF pulses. The axial profile of the channel cuts were reproduced with third harmonic generation such that the resultant morphology of the two focusing regimes could be compared. A third order interferometeric autocorrelator was constructed and calibrated in order to estimate the temporal pulse width at focus of the SSTF pulses. The THG bond images show that writing direction has a strong influence on the bond morphology: it is recommended to investigate the influence of pulse front tilt. Another critical consideration is to develop an effective means of consistently mounting glass substrates to be bonded is needed. Overall, the work presented demonstrates the feasibility of a single step microfluidic device fabrication: the same laser system can indeed be used to machine and bond similar glass substrates. As well, the comparison of SSTF and non-SSTF channel morphology supports the notion that SSTF can improve laser welding/machining.