Surface acoustic waves (SAWs) are appealing as a means to manipulate fluids within lab-on-a-chip systems. However, current acoustofluidic devices almost universally rely on elastomeric materials, especially PDMS, that are inherently ill-suited for conveyance of elastic energy due to their strong attenuation properties. Here, we explore the use of a low-viscosity UV epoxy resin for room temperature bonding of lithium niobate (LiNbO 3 ), the most widely used anisotropic piezoelectric substrate used in the generation of SAWs, to standard micromachined superstrates such as Pyrex1 and silicon. The bonding methodology is straightforward and allows for reliable production of submicron bonds that are capable of enduring the high surface strains and accelerations needed for conveyance of SAWs. Devices prepared with this approach display as much as two orders of magnitude, or 20 dB, improvement in SAW transmission compared to those fabricated using the standard PDMS elastomer. This enhancement enables a broad range of applications in acoustofluidics that are consistent with the low power requirements of portable battery-driven circuits and the development of genuinely portable lab-on-a-chip devices. The method is exemplified in the fabrication of a closed-loop bidirectional SAW pumping concept with applications in micro-scale flow control, and represents the first demonstration of closed channel SAW pumping in a bonded glass/LiNbO 3 device.Chip-based fluidic actuators using surface acoustic waves (SAWs) have become popular among microfluidic practitioners, who continue to explore new applications in acoustofluidic integration.

The recent shift among developers of microfluidic technologies toward modularized "plug and play" construction reflects the steadily increasing realization that, for many would-be users of microfluidic tools, traditional clean-room microfabrication is prohibitively complex and/or expensive. In this work, we present an advanced modular microfluidic construction scheme in which pre-fabricated microfluidic assembly blocks (MABs) can be quickly fashioned, without expertise or specialized facilities, into sophisticated microfluidic devices for a wide range of applications. Specifically, we describe three major advances to the MAB concept: (1) rapid production and extraction of MABs using flexible casting trays, (2) use of pre-coated substrates for simultaneous assembly and bonding, and (3) modification of block design to include automatic alignment and sealing structures. Finally, several exemplary applications of these MABs are demonstrated in chemical gradient synthesis, droplet generation, and total internal reflection fluorescence microscopy.

We present a versatile and very low-power traveling SAW microfluidic sorting device able to displace and separate particles of different diameter in aqueous suspension; the travelling wave propagates through the fluid bulk and diffuses via a Schröder diffuser, adapted from its typical use in concert hall acoustics to be the smallest such diffuser to be suitable for microfluidics. The effective operating power range is two to three orders of magnitude less than current SAW devices, uniquely eliminating the need for amplifiers, and by using traveling waves to impart forces directly upon suspended microparticles, they can be separated by size.

Performance and utility of microfluidic systems are often overshadowed by the difficulties and costs associated with operation and control. As a step toward the development of a more efficient platform for microfluidic control, we present a distributed pressure generation scheme whereby independently tunable pressure sources can be simultaneously controlled by using a single acoustic source. We demonstrate how this scheme can be used to perform precise droplet positioning as well as merging, splitting, and sorting within open microfluidic networks. We further show how this scheme can be implemented for control of continuous-flow systems, specifically for generation of acoustically tunable liquid gradients. Device operation hinges on a resonance-decoding and rectification mechanism by which the frequency content in a composite acoustic input is decomposed into multiple independently buffered output pressures.