Frequency tracking in acoustic trapping for improved performance stability and system surveillance

Abstract

This work proposes and demonstrates an acoustic trapping system where the trapping frequency is automatically determined and can be used to analyse changes in the acoustic trap. Critical for the functionality of this system is the use of a kerfed transducer that removes spurious resonances. This makes it possible to determine the optimal trapping frequency by analysing electrical impedance. It is demonstrated that the novel combination of a kerfed transducer and acoustic trapping in glass capillaries creates a high Q-value resonator. This narrows the frequency bandwidth but allows excellent performance, as confirmed by a ten-fold increase in the flow retention speed when compared to previously reported values. Importantly, the use of automatic frequency tracking allows the use of such a narrow bandwidth resonator without compromising system stability. As changes in temperature, buffer-properties, and the amount of captured particles will affect the properties of the acoustic resonator, corresponding changes in resonance frequency will occur. It is shown that such frequency changes can be accurately tracked using the setup. Therefore, monitoring the frequency over time adds a new feature to acoustic trapping, where experimental progress can be monitored and the amount of trapped material can be quantified.

A thin-reflector microfluidic resonator for continuous-flow concentration of microorganisms: a new approach to water quality analysis using acoustofluidics

“…In order to facilitate the translation of the TR device into real-life applications, further developments to the system architecture could be implemented including (i) addition of flow control valves on the outlet lines to achieve passive flow regulation without the need for numerous pumps, and (ii) implementation of temperature regulation 78 or resonance frequency tracking 79 systems for stable operation of the device at higher acoustic powers. These could potentially result in a further increase of bacterial concentration performance.…”

Three-Dimensional Numerical Modeling of Acoustic Trapping in Glass Capillaries

“…In this paper, we study specifically a millimeter-sized glass-capillary system used as a versatile acoustic trap in many experimental studies [8,9,26,27,29] and clinical applications, such as the isolation of cell-secreted membrane vesicles [30] and the capture and enrichment of bacteria from blood samples for rapid sepsis diagnostics [31]. A sketch of a generic capillary system is shown in Fig.…”

“…Examples include cell synchronization [3], the enrichment of prostate cancer cells in blood [4], the manipulation of C. elegans [5], and single-cell patterning [6]. Acoustics can also be used for noncontact microfluidic trapping and particle enrichment [7][8][9], as well as acoustic tweezing [10][11][12][13][14]. Trapping, an important unit operation in sophisticated celland bioparticle-handling systems, can also be obtained using other technologies, such as those in hydrodynamic [15], electro-and dielectrophoretic [16], and opticaltrapping systems [17]; see the review by Nilsson et al [18].…”

Performance Study of Acoustophoretic Microfluidic Silicon-Glass Devices by Characterization of Material- and Geometry-Dependent Frequency Spectra

“…A first step in this direction was taken in experiments on simple glass capillaries by Hammarström et al [14]. A further complication is the influence of thermal heating by the piezoelectric transducer, which directly affects the acoustic response of the device through the temperature dependence of the acoustic-relevant parameters (density, compressibility, and elastic moduli).…”

“…While an experimental knowledge of the system response with respect to an external actuation source plays a central role in the selection of good operative conditions [14], a better comprehension of the phenomena involved in these devices would free the design and implementation steps from the costly and time-consuming methods currently employed.…”