Reduced acoustic resonator dimensions improve focusing efficiency of bacteria and submicron particles

A Microflow Cytometer Enabled by Monolithic Integration of a Microreflector with an Acoustic Resonator

Current microflow cytometers suffer from complicated fluidic integration and low fluorescence collection efficiency, resulting in reduced portability and sensitivity. Herein, we demonstrated a new flow cell design based on an on-chip monolithically integrated microreflector with a bulk acoustic wave resonator (MBAW). It enables simultaneous 3D particle focusing and fluorescence enhancement without using shear flow. Benefited by the on-chip microreflector, the captured fluorescence intensity was 1.8-fold greater than that of the Si substrate and 8.3-fold greater than that of the SiO2 substrate, greatly improving the detection sensitivity. Combined with the contactless acoustic streaming-based focusing, particle sensing with a coefficient of variation as low as 6.1% was achieved. We also demonstrated the difference between live and dead cells and performed a cell cycle assay using the as-developed microflow cytometry. This monolithic integrated MBAW provides a new type of opto-acoustofluidic system and has the potential to be a highly integrated, highly sensitive flow cytometer for applications such as in vitro diagnostics and point of care.

Harnessing the power of Microscale AcoustoFluidics: A perspective based on BAW cancer diagnostics

Cancer directly affects one in every three people, and mortality rates strongly correlate with the stage at which diagnosis occurs. Each of the multitude of methods used in cancer diagnostics has its own set of advantages and disadvantages. Two common drawbacks are a limited information value of image based diagnostic methods and high invasiveness when opting for methods that provide greater insight. Microfluidics offers a promising avenue for isolating circulating tumor cells from blood samples, offering high informational value at predetermined time intervals while being minimally invasive. Microscale AcoustoFluidics, an active method capable of manipulating objects within a fluid, has shown its potential use for the isolation and measurement of circulating tumor cells, but its full potential has yet to be harnessed. Extensive research has focused on isolating single cells, although the significance of clusters should not be overlooked and requires attention within the field. Moreover, there is room for improvement by designing smaller and automated devices to enhance user-friendliness and efficiency as illustrated by the use of bulk acoustic wave devices in cancer diagnostics. This next generation of setups and devices could minimize streaming forces and thereby enable the manipulation of smaller objects, thus aiding in the implementation of personalized oncology for the next generation of cancer treatments.

Square microchannel enables to focus and orient ellipsoidal Euglena gracilis cells by two-dimensional acoustic standing wave

Flow cytometry has become an indispensable tool for counting, analyzing, and sorting large cell populations in biological research and medical practice. Unfortunately, it has limitations in the analysis of non-spherically shaped cells due to the variation of their alignment with respect to the flow direction and, hence, the optical interrogation axis, resulting in unreliable cell analysis. Here, we present a simple on-chip acoustofluidic method to fix the orientation of ellipsoidal cells and focus them into a single, aligned stream. Specifically, by generating acoustic standing waves inside a 100 ⋅ 100 µm square-shaped microchannel, we successfully aligned and focused up to 97.7% of a population of Euglena gracilis (an ellipsoidal shaped microalgal species) cells in the center of the microchannel with high precision at a volume rate of 25 to 200 µL min^-1. Uniform positioning of ellipsoidal cells is essential for making flow cytometry applicable to the investigation of a greater variety of cell populations and is expected to be beneficial for ecological studies and aquaculture.