The vibration-induced flow (VIF), in which a mean flow is induced by the interaction between the system vibration and micro-structures, has been studied as a fluid/particle micro-manipulation method that does not require an external pump. While the use of VIF with a wide variety of vibrations is expected to realize sophisticated fluid manipulation, numerical tools to predict these unsteady flows remain difficult. In this study, we have performed a numerical simulation of VIF with different vibrations and micropillar cross-sections. A proposed numerical model, which directly solves the continuity and Navier-Stokes equations in the coordinate system moving with the vibrating micropillar, enables us to avoid the introduction of a moving boundary, and therefore has significant advantage in numerical stability and accuracy. The immersed boundary technique allows us to embed arbitrary complex micro-structures in the Cartesian computational domain without requiring boundary-fitted meshes for each geometry. The dependencies of characteristics of flow on vibration parameters, such as vibration frequency, amplitude, direction, and the shape of micro-structures, were investigated and compared with the experimental results obtained by the particle image velocimetry (PIV) measurement. Excellent agreement between the numerical and experimental results validates that the present numerical approach can be a powerful tool to design functional VIF systems, such as mixing, particle/cell transport, trapping, and separation.

The detection of bioactive nanoparticles (NPs) plays an important role in the medical and diagnostic fields. Conventional techniques for the sensitive detection of target NPs must overcome challenges such as long processing time, complex sample preparation, and high cost. Here, we show that vibration-induced flow (VIF), in which a local flow is induced around microscopic objects by applying small periodic vibrations, can facilitate immunoagglutination to realize rapid, facile, sensitive, and low-cost detection of NPs in a minute sample. In the proposed system, the presence of NPs in a sample is detected by the formation of aggregates of affinity microparticles (MPs) stirred by the VIF within a short time (approximately 15 min). The concentration of NPs can be quantified using the average area of aggregates observed in bright-field microscopic images. Finally, we demonstrate the detection of extracellular vesicles (EVs) to validate the applicability of the proposed system in diagnostic applications.

The detection of bioactive nanoparticles (NPs) plays an important role in the medical and diagnostic fields. Conventional techniques for the sensitive detection of target NPs must overcome challenges such as long processing time, complex sample preparation, and high cost. Here, we show that vibration-induced flow (VIF), in which a local flow is induced around microscopic objects by applying small periodic vibrations, can be used to realize rapid, facile, highly sensitive, and low-cost detection of NPs in a minute sample. In the proposed system, the presence of NPs in a sample is detected by the formation of aggregates of affinity capture beads stirred by the VIF within a short time (approximately 15 min). Furthermore, the concentration of NPs can be quantified using the average area of the aggregate observed in bright-field microscopic images without using an expensive image analyzer and fluorescence labeling of targets, which are commonly used in other NP detection protocols. Finally, we demonstrate the detection of extracellular vesicles (EVs) to validate the applicability of the proposed system in diagnostic applications.

No abstract