Fabrication of Silicon Microfluidic Chips for Acoustic Particle Focusing Using Direct Laser Writing

Abstract

We have developed a fast and simple method for fabricating microfluidic channels in silicon using direct laser writing. The laser microfabrication process was optimised to generate microfluidic channels with vertical walls suitable for acoustic particle focusing by bulk acoustic waves. The width of the acoustic resonance channel was designed to be 380 µm, branching into a trifurcation with 127 µm wide side outlet channels. The optimised settings used to make the microfluidic channels were 50% laser radiation power, 10 kHz pulse frequency and 35 passes. With these settings, six chips could be ablated in 5 h. The microfluidic channels were sealed with a glass wafer using adhesive bonding, diced into individual chips, and a piezoelectric transducer was glued to each chip. With acoustic actuation at 2.03 MHz a half wavelength resonance mode was generated in the microfluidic channel, and polystyrene microparticles (10 µm diameter) were focused along the centre-line of the channel. The presented fabrication process is especially interesting for research purposes as it opens up for rapid prototyping of silicon-glass microfluidic chips for acoustofluidic applications.

Node formation mechanisms in acoustofluidic capillary bridges

“…This incident and reflector design is now mostly superseded by systems where the nodes form at right angles to the incident plate, since this is a more convenient viewing angle. Initially hard walls [34][35][36][37] were used, however, today many systems use soft more easily formed walls, made from polydimethylsiloxane (PDMS) [7,38], poly(methyl methacrylate) (PMMA) [39] or SU-8 photoresist [40,41]. These soft walls absorb sound and are poor sound reflectors which quickly led to the realisation that sound reflections from the walls are too weak to form a resonance in the fluid [38,42], although reflections at the polymer-air interfaces may occur in some systems [43].…”

Using 3D printing to fabricate microfluidic chips for biosensing applications

“…Glass has good optical properties which makes it suitable for integration with optical biosensors. Polymers are showing dominance currently because they are affordable and easy to fabricate through laser ablation [7]. Epoxy resin is a type of polymer used in 3D printing to fabricate microfluidic chips.…”

Acoustics-Actuated Microrobots

“…In recent years, acoustics-actuated microrobots have gained considerable attention due to their promising potential use in diverse fields [ 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ]. With the aid of acoustic actuation, many critical tasks can be performed such as targeted drug delivery [ 12 , 13 , 14 ], particle separation [ 15 , 16 , 17 ], mixing [ 18 ], pumping [ 19 , 20 , 21 , 22 ], self-assembly [ 23 , 24 , 25 ], microsurgery [ 26 ], microfluidic operation [ 27 , 28 , 29 ], and chemical analysis [ 30 ].…”